ZXLD1374EST20TC [DIODES]
60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST LED DRIVER CONVERTER; 60V高精度1.5A降压/升压/降压 - 升压LED驱动器转换器
| 型号： | ZXLD1374EST20TC |
| 厂家： | 
DIODES INCORPORATED |
| 描述： | 60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST LED DRIVER CONVERTER |
| 文件： | 总35页 (文件大小：725K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
A Product Line of
Diodes Incorporated
ZXLD1374
60V HIGH ACCURACY 1.5A BUCK/BOOST/BUCK-BOOST LED DRIVER CONVERTER
Description
Pin Assignments
The ZXLD1374 is an LED driver converter IC with integrated
1.5A low side switch to drive high current LEDs. It is a multi-
topology converter enabling it to efficiently control the
current through series connected LEDs. The multi-topology
enables it to operate in Buck, Boost and Buck-boost
configurations.
The 60V capability coupled with its multi-topology capability
enables it to be used in a wide range of applications and
drive in excess of 16 LEDs in series.
The ZXLD1374 is a modified hysteretic converter using a
patent pending control scheme providing high output current
accuracy in all three topologies. High accuracy dimming is
achieved through DC control and high frequency PWM
control.
The ZXLD1374 uses two pins for fault diagnosis. A flag
output highlights a fault, while the multi-level status pin gives
further information on the exact fault.
TSSOP-20EP
ADJ
REF
1
2
20 GI
19 PWM
18 FLAG
3
TADJ
SHP
4
17
16
15
14
13
12
11
ISM
VIN
VAUX
LX
5
STATUS
SGND
PGND
PGND
N/C
Thermal
Pad
6
7
8
LX
9
N/C
N/C
ZXLD1374
10
N/C
Features
•
•
•
•
0.5% typical output current accuracy
6.3 to 60V operating voltage range
1.5A integrated low side switch
LED driver supports Buck, Boost and Buck-boost
topologies
•
Wide dynamic range dimming
o
o
20:1 DC dimming
1000:1 dimming range at 500Hz
•
•
•
Up to 1MHz switching
High temperature control of LED current using TADJ
Green mold compound (No Br, Sb) and RoHS
compatible
Typical Application Circuit
Curve showing LED current vs. TLED
Page 1 of 35
www.diodes.com
October 2010
© Diodes Incorporated
ZXLD1374
Document number: DS35032 Rev. 1 - 2
A Product Line of
Diodes Incorporated
ZXLD1374
Pin Descriptions
Pin
Pin
Type
(Note 1)
Description
Adjust input (for dc output current control)
Name
Connect to REF to set 100% output current.
Drive with dc voltage (125mV<VADJ< 2.5V) to adjust output current from 10% to 200% of
set value. The ADJ pin has an internal clamp that limits the internal node to less than
3V. This prevents the LED and power switch from delivering too much current should
ADJ get overdriven.
ADJ
1
I
REF
TADJ
2
3
O
I
Internal 1.25V reference voltage output
Temperature Adjust input for LED thermal current control
Connect thermistor/resistor network to this pin to reduce output current above a preset
temperature threshold.
Connect to REF to disable thermal compensation function (See section on thermal
control).
Shaping capacitor for feedback control loop
Connect 100pF ±20% capacitor from this pin to ground to provide loop compensation
SHP
4
5
I/O
O
Operation status output (analog output)
Pin is at 4.5V (nominal) during normal operation.
Pin switches to a lower voltage to indicate specific operation warnings or fault
conditions (See section on STATUS output).
Status pin voltage is low during shutdown mode.
Signal ground
Connect to 0V and pins 7 and 8.
Power ground
Connect to 0V and pin 6 to maximize copper area.
STATUS
SGND
PGND
6
P
P
7,8
9, 10,
11, 12
Not Connected internally
To maximize PCB copper for thermal dissipation connect to pins 7 and 8.
N/C
LX
-
13, 14
15
O
Low-side power-switch output
Auxiliary positive supply to internal switch gate driver
Connect to VIN, or auxiliary supply from 6V to 15V supply to reduce internal power
dissipation (Refer to application section for more details).
VAUX
P
Decouple to ground with capacitor close to device (refer to Applications section).
Input supply to device (6.3V to 60V)
Decouple to ground with capacitor close to device (refer to Applications section).
VIN
16
17
P
I
Current monitor input
ISM
Connect current sense resistor between this pin and VIN.
The nominal voltage across the resistor is 225mV.
Flag open drain output
FLAG
PWM
18
19
O
I
Pin is high impedance during normal operation.
Pin switches low to indicate a fault, or warning condition.
Digital PWM output current control
Pin driven either by open Drain or push-pull 3.3V or 5V logic levels.
Drive with frequency higher than 100Hz to gate output ‘on’ and ‘off’ during dimming
control.
The device enters standby mode when PWM pin is driven with logic low level for more
than 15ms nominal (Refer to application section for more details).
Gain setting input
Used to set the LED current in Boost and Buck-boost modes.
Connect to ADJ in Buck mode operation.
GI
20
I
For Boost and Buck-boost modes, connect to resistive divider from ADJ to SGND. This
defines the ratio of switch current to LED current (see application section). The GI pin
has an internal clamp that limits the internal node to less than 3V. This provides some
failsafe should the GI pin get overdriven.
Exposed paddle.
Connect to 0V plane for electrical and thermal management.
EP
PAD
P
Notes: 1. Type refers to whether or not pin is an Input, Output, Input/Output or Power supply pin.
Page 2 of 35
www.diodes.com
October 2010
© Diodes Incorporated
ZXLD1374
Document number: DS35032 Rev. 1 - 2
A Product Line of
Diodes Incorporated
ZXLD1374
Absolute Maximum Ratings (Voltages to GND Unless Otherwise Stated)
Symbol
VIN
Parameter
Rating
Unit
V
Input supply voltage relative to GND‡
Auxiliary supply voltage relative to GND‡
Current monitor input relative to GND‡
-0.3 to 65
-0.3 to 65
-0.3 to 65
-0.3 to 5
-0.3 to 65
1.8
VAUX
VISM
V
V
VSENSE
VLX
Current monitor sense voltage (VIN-VISM
)
V
Low side switch output voltage to GND‡
Low side switch continuous output current
Status pin output current
V
ILX
A
ISTATUS
VFLAG
±1
mA
V
Flag output voltage to GND‡
-0.3 to 40
VPWM, VADJ
VTADJ, VGI
,
Other input pins to GND‡
-0.3 to 5.5
V
TJ
Maximum junction temperature
Storage temperature
150
°C
°C
TST
-55 to 150
These are stress ratings only. Operation outside the absolute maximum ratings may cause device failure.
Operation at the absolute maximum rating for extended periods may reduce device reliability.
Semiconductor devices are ESD sensitive and may be damaged by exposure to ESD events. Suitable ESD precautions should be taken when handling and
transporting these devices.
Notes: ‡ For correct operation SGND and PGND should always be connected together.
Package Thermal Data
Thermal Resistance
Package
Unit
Junction-to-Case, θJC
TSSOP-20EP
4
°C/W
Recommended Operating Conditions
Symbol
Parameter
Performance/Comment
Min
8
6.3
8
6.3
0
Max
Unit
Normal operation
Functional (Note 2)
Normal operation
Functional
VIN
Input supply voltage range
60
V
VAUX
Auxiliary supply voltage range (Note 3)
60
V
VSENSE Differential input voltage
VLX
ILX
VVIN-VISM, with 0 ≤ VADJ ≤ 2.5
450
60
1.5
mV
V
A
Low side switch output voltage
Low side switch continuous output current
External dc control voltage applied to ADJ
pin to adjust output current
DC brightness control mode
from 10% to 200%
VADJ
0.125
2.5
V
ISTATUS Status pin output current
100
1
µA
mA
kHz
V
Hz
Hz
ms
V
IREF
fSW
Reference external load current
Recommended switching frequency range (Note 4)
REF sourcing current
300
0
100
100
0.005
2
1000
VREF
500
1000
10
VTADJ Temperature adjustment (TADJ) input voltage range
To maintain 1000:1 resolution
To maintain 200:1 resolution
PWM input high or low
fPWM Recommended PWM dimming frequency range
tPWMH/L PWM pulse width in dimming mode
VPWMH PWM pin high level input voltage
VPWML PWM pin low level input voltage
5.5
0.4
0
V
TJ
GI
Operating Junction Temperature Range
Gain setting ratio for Boost and Buck-boost modes Ratio= VGI/VADJ
-40
0.20
125
0.50
°C
Notes: 2. The functional range of VIN is the voltage range over which the device will function. Output current and device parameters may
deviate from their normal values for VIN and VAUX voltages between 6.3V and 8V, depending upon load and conditions.
3. VAUX can be driven from a voltage higher than VIN to provide higher efficiency at low VIN voltages, but to avoid false operation; a
voltage should not be applied to VAUX in the absence of a voltage at VIN.
4. The device contains circuitry to control the switching frequency to approximately 400kHz. The maximum and minimum
operating frequency is not tested in production.
Page 3 of 35
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October 2010
© Diodes Incorporated
ZXLD1374
Document number: DS35032 Rev. 1 - 2
A Product Line of
Diodes Incorporated
ZXLD1374
Electrical Characteristics (Test conditions: V = V
= 12V, T = 25°C, unless otherwise specified.)
IN
AUX
A
Symbol
Supply and reference parameters
Under-Voltage detection threshold
Parameter
Conditions
IN or VAUX falling
Min
Typ Max Units
V
V
VUV-
5.2
5.5
5.6
6
6.3
6.5
Normal operation to switch disabled
Under-Voltage detection threshold
Switch disabled to normal operation
VIN or VAUX rising
V
VUV+
IQ-IN
IQ-AUX
ISB-IN
Quiescent current into VIN
Quiescent current into VAUX
Standby current into VIN.
PWM pin floating.
Output not switching
1.5
150
90
3
mA
µA
µA
µA
V
300
150
10
PWM pin grounded
for more than 15ms
ISB-AUX
VREF
Standby current into VAUX
.
0.7
Internal reference voltage
No load
1.237 1.25 1.263
Change in reference voltage with output Sourcing 1mA
-5
mV
ΔVREF
current
Sinking 25µA
5
VREF_LINE Reference voltage line regulation
VREF-TC Reference temperature coefficient
DC-DC converter parameters
VIN = VAUX , 6.5V<VIN = <60V
-60
-90
dB
+/-50
ppm/°C
DC brightness control mode
10% to 200%
External dc control voltage applied to ADJ
VADJ
0.125 1.25
2.5
V
pin to adjust output current (Note 5)
V
ADJ ≤ 2.5V
100
5
nA
µA
IADJ
VGI
ADJ input current (Note 5)
VADJ = 5.0V
GI Voltage threshold for Boost and Buck-
boost modes selection (Note 5)
VADJ = 1.25V
0.8
V
V
GI ≤ 2.5V
100
5
nA
µA
IGI
GI input current (Note 5)
VGI = 5.0V
IPWM
PWM input current
VPWM = 5.5V
36
100
µA
PWM pulse width
(to enter shutdown state)
tPWMoff
PWM input low
10
15
25
ms
Thermal shutdown upper threshold
(LX output inhibited)
TSDH
TSDL
Temperature rising.
Temperature falling.
150
125
ºC
ºC
Thermal shutdown lower threshold
(LX output re-enabled)
High-Side Current Monitor (Pin ISM)
IISM
Input Current
Measured into ISM pin and VISM = VIN
VADJ = 1.25V
11
20
µA
%
Accuracy of nominal VSENSE threshold
voltage
VSENSE_acc
±0.25 ±2
350 375
VSENSE-OC Over-current sense threshold voltage
300
mV
Notes:
5. The ADJ and GI pins have an internal clamp that limits the internal node to less than 3V. This limits the switch current should
those pins get overdriven.
Page 4 of 35
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October 2010
© Diodes Incorporated
ZXLD1374
Document number: DS35032 Rev. 1 - 2
A Product Line of
Diodes Incorporated
ZXLD1374
Electrical Characteristics (Test conditions: V = V
= 12V, T = 25°C, unless otherwise specified.)
IN
AUX
A
Symbol
Parameter
Conditions
Min
Typ
Max
Units
Output Parameters
VFLAGL FLAG pin low level output voltage
IFLAGOFF FLAG pin open-drain leakage current
Output sinking 1mA
VFLAG=40V
0.5
1
V
µA
Normal operation
4.2
3.3
4.5
3.6
4.8
Out of regulation (VSHP out of range)
(Note 7)
3.9
VIN under-voltage (VIN < 5.6V)
Switch stalled (tON or tOFF> 100µs)
LX over-voltage state (VLX >60V)
Over-temperature (TJ > 125°C)
3.3
3.3
2.4
1.5
3.6
3.6
2.7
1.8
3.9
3.9
3.0
2.1
STATUS Flag no-load output voltage
VSTATUS
(Note 6)
V
Excess sense resistor current
(VSENSE > 0.375V)
0.6
0.6
0.9
1.2
1.2
Excessive switch current (ISW>1.5A)
Normal operation
0.9
10
RSTATUS Output impedance of STATUS output
kΩ
Low side switch output (LX pins tied together)
ILX-LG
Low side switch leakage current
Output stage off, VLX = 60V (Note 8)
ILX = 1.5A (tON < 100µs)
60
0.5
86
µA
Ω
RDS(ON) LX pin MOSFET on resistance
0.8
tPDHL
tPDLH
tLXR
Propagation delay high-low
Propagation delay low-high
LX output rise time
ns
ns
ns
ns
131
208
12
VSENSE = 225mV ± 30%, CL = 680pF,
RL = 120Ω
tLXF
LX output fall time
Time to assert ‘STALL’ flag and
tSTALL warning on STATUS output
(Note 9)
LX low or high
100
170
690
µs
LED Thermal control circuit (TADJ) parameters
Onset of output current reduction
(VTADJ falling)
VTADJH
Upper threshold voltage
560
380
625
440
mV
Output current reduced to <10% of
set value (VTADJ falling)
VTADJL
ITADJ
Lower threshold voltage
TADJ pin Input current
500
1
mV
µA
VTADJ = 1.25V
Notes: 6. In the event of more than one fault/warning condition occurring, the higher priority condition will take precedence. E.g.
‘Excessive coil current’ and ‘Out of regulation’ occurring together will produce an output of 0.9V on the STATUS pin. The
voltage levels on the STATUS output assume the Internal regulator to be in regulation and VADJ<=VREF. A reduction of the
voltage on the STATUS pin will occur when the voltage on VIN is near the minimum value of 6V.
7. Flag is asserted if VSHP<2.5V or VSHP>3.5V
8. With the device still in switching mode the LX pin has an over-voltage detection circuit connected to it with a resistance of
approximately 1MΩ.
9. If tON exceeds tSTALL, LX turns off and then an initiate a restart cycle occurs. During this phase, ADJ is grounded internally and
the SHP pin is switched to its nominal operating voltage, before operation is allowed to resume. Restart cycles will be repeated
automatically until the operating conditions are such that normal operation can be sustained. If tOFF exceeds tSTALL, the switch
will remain off until normal operation is possible.
Page 5 of 35
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October 2010
© Diodes Incorporated
ZXLD1374
Document number: DS35032 Rev. 1 - 2
A Product Line of
Diodes Incorporated
ZXLD1374
Typical Characteristics
3
900
750
1500
1250
1000
2.5
2
600
450
I
LED
1.5
1
750
500
Switching
Frequency
300
T
= 25C
A
V
= V = 12V
AUX
IN
250
0
0.5
0
2LEDs
L = 33µH
150
0
R
= 300mΩ
S
6
12 18
24
30 36 42
48 54 60
0
0.5
1
1.5
2
2.5
ADJ Voltage (V)
Supply Voltage (V)
Figure 2. Buck LED Current, Switching Frequency vs. VADJ
Figure 1. Supply Current vs. Supply Voltage
1400
1200
700
700
650
600
700
650
600
550
600
550
500
450
400
350
300
500
400
500
450
400
350
300
250
200
150
100
1000
800
I
LED
I
LED
Switching
Frequency
Switching
Frequency
300
200
100
0
600
250
200
150
100
400
200
0
T
= 25C
A
T
= 25°C
A
V
= V = 12V
IN
AUX
12 LEDs
L = 33µH
V
= V = 24V
AUX
8LEDs
L = 33µH
GI = 0.23
IN
R
= 300mΩ
S
50
0
50
0
R
= 300mΩ
S
0
0.25 0.5 0.75
1
1.25 1.5 1.75
2 2.25 2.5
0
0.5
1
1.5
2
2.5
ADJ Voltage
ADJ Voltage
Figure 4. Boost LED Current, Switching Frequency vs. VADJ
Figure 3. Buck-Boost LED Current, Switching Frequency vs. VADJ
1500
V
T
= 24V
IN
= 25°C
A
1250
1000
750
500
250
0
I
= 100Hz
PWM
I
LED
0
10 20 30 40 50 60 70 80 90 100
PWM Duty Cycle (%)
Figure 5. ILED vs. PWM Duty Cycle
Figure 6. ILED vs time - PWM pin transient response
Page 6 of 35
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October 2010
© Diodes Incorporated
ZXLD1374
Document number: DS35032 Rev. 1 - 2
A Product Line of
Diodes Incorporated
ZXLD1374
Typical Characteristics
100%
1.252
1.2515
80%
60%
40%
1.251
1.2505
1.25
1.2495
1.249
20%
0%
1.2485
1.248
0
250
500
750
1000
1250
-40 -25 -10
5
20 35 50 65 80 95 110 125
Junction Temperature (°C)
Figure 8. VREF vs. Temperature
TADJ Pin Voltage (mV)
Figure 7. LED Current vs. TADJ Voltage
0.9
0.8
0.7
0.6
0.5
0.4
100%
90%
T
= 25°C
A
L = 33µH
= 150mΩ
R
S
80%
70%
60%
50%
40%
30%
20%
Buck Mode
2 LEDS
0.3
0.2
V
I
= 12V
IN
= 1.3A
0.1
0
10%
0%
LX
-40 -25 -10
5
20 35 50 65 80 95 110 125
Junction Temperature (°C)
Figure 9. RDS(ON) vs. Temperature
6
12
18 24
30
36 42 48 54 60
Input Voltage (V)
Figure 10. Duty Cycle vs. Input Voltage
Page 7 of 35
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October 2010
© Diodes Incorporated
ZXLD1374
Document number: DS35032 Rev. 1 - 2
A Product Line of
Diodes Incorporated
ZXLD1374
Typical Characteristics – Buck Mode – RS = 146mΩ – L = 33µH - ILED = 1.5A
1.65
T
= 25°C
= V
A
V
AUX
IN
L = 33µH
= 146mΩ
1.60
R
S
9 LEDs
11 LED s
13 LEDs
15 LEDs
1.55
1.50
1.45
1.40
1.35
7 LEDs
3 LEDs
5 LEDs
1 LED
6
12
18
24
30
36
42
48
54
60
Input Voltage (V)
Figure 11. Load Current vs. Input Voltage and Number of LED
1200
T
= 25°C
= V
A
V
AUX
IN
L = 33µH
= 146mΩ
1000
800
R
S
600
400
200
0
3 LEDs
7 LEDs
13 LEDs
1 LED
5 LEDs
9 LEDs
11 LED s
15 LEDs
6
12
18
24
30
36
42
48
54
60
Input Voltage (V)
Figure 12. Frequency vs. Input Voltage and Number of LED
100%
95%
15 LEDs
5 LEDs
90%
85%
80%
75%
70%
3 LEDs
1 LED
13 LEDs
7 LEDs
9 LEDs
11 LED s
T
= 25°C
A
V
= V
IN
AUX
L = 33µH
65%
60%
R
= 146mΩ
S
6
12
18
24
30
36
42
48
54
60
Input Voltage (V)
Figure 13. Efficiency vs. Input Voltage and Number of LED
Page 8 of 35
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October 2010
© Diodes Incorporated
ZXLD1374
Document number: DS35032 Rev. 1 - 2
A Product Line of
Diodes Incorporated
ZXLD1374
Typical Characteristics – Buck Mode – RS = 291mΩ - L = 33µH - ILED = 750mA
0.825
0.800
0.775
0.750
0.725
0.700
0.675
T
= 25°C
= V
A
V
AUX
IN
L = 33µH
R
= 291mΩ
S
3 LEDs
7 LEDs
11 LED s
15 LEDs
9 LEDs
13 LEDs
5 LEDs
1 LED
6
12
18
24
30
36
42
48
54
60
Input Voltage (V)
Figure 14. ILED vs. Input Voltage and Number of LED
1000
900
800
700
T
= 25°C
= V
A
11 LED s
V
AUX
IN
L = 33µH
= 291mΩ
9 LEDs
R
S
7 LEDs
5 LEDs
600
500
400
15 LEDs
3 LEDs
13 LEDs
300
200
1 LED
100
0
6
12
18
24
30
36
42
48
54
60
Input Voltage (V)
Figure 15. Frequency ZXLD1374 - Buck Mode = L = 47μH
100%
95%
90%
5 LEDs
7 LEDs
9 LEDs
11 LED s
13 LEDs
15 LEDs
3 LEDs
85%
80%
75%
70%
65%
1 LED
T
= 25°C
A
V
= V
IN
AUX
L = 33µH
= 291mΩ
R
S
60%
6
12
18
24
30
36
42
48
54
60
Input Voltage (V)
Figure 16. Efficiency vs. Input Voltage and Number of LED
Page 9 of 35
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October 2010
© Diodes Incorporated
ZXLD1374
Document number: DS35032 Rev. 1 - 2
A Product Line of
Diodes Incorporated
ZXLD1374
Typical Characteristics – Boost mode – RS = 150mꢀ - L = 33µH – ILED = 325mA – GIRATIO = 0.21
0.358
T
= 25°C
A
L = 33µH
R
R
R
= 150mΩ
S
0.347
0.336
= 33kΩ
GI1
GI2
= 120kΩ
0.325
0.314
6 LEDs
8 LEDs
10 LEDs
0.303
0.292
16 LEDs
12 LEDs
14 LEDs
12
17
22
27
32
37
42
47
Input Voltage (V)
Figure 17. ILED vs. Input and Number of LED
700
650
600
T
= 25°C
A
L = 33µH
R
R
R
= 150mΩ
S
= 33kΩ
GI1
GI2
= 120kΩ
550
500
450
400
350
300
12 LEDs
14 LEDs
16 LEDs
6 LEDs
250
200
8 LEDs
10 LEDs
12
17
22
27
Input Voltage (V)
Figure 18. Frequency vs. Input Voltage and Number LED
32
37
42
47
100%
95%
6 LEDs
8 LEDs
10 LEDs
12 LEDs
14 LEDs
16 LEDs
90%
85%
T
= 25°C
A
L = 33µH
80%
75%
R
R
R
= 150mΩ
S
= 33kΩ
GI1
GI2
= 120kΩ
12
17
22
27
32
37
42
47
Input Voltage (V)
Figure 19. Efficiency vs. Input Voltage and Number of LED
Page 10 of 35
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October 2010
© Diodes Incorporated
ZXLD1374
Document number: DS35032 Rev. 1 - 2
A Product Line of
Diodes Incorporated
ZXLD1374
Typical Characteristics – Boost mode – RS = 150mꢀ - L = 33µH – ILED = 350mA – GIRATIO = 0.23 – with bootstrap
0.385
0.368
15 LEDs
13 LEDs
11 LE Ds
0.350
7 LEDs
9 LEDs
5 LEDs
0.333
0.315
TA = 25°C
L = 33µH
RS = 150mΩ
RGI1 = 36mΩ
RGI2 = 120mΩ
6.5
8
9.5
11
12.5
14
15.5
17
Input Voltage (V)
Figure 20. Load Current vs. Input Voltage and Number of LED
700
600
15 LEDs
13 LEDs
500
400
300
200
11 LED s
9 LEDs
7 LEDs
5 LEDs
T
= 25°C
A
L = 33µH
R
R
R
= 150mΩ
S
100
0
= 36mΩ
GI1
GI2
= 120mΩ
6.5
8
9.5
11
12.5
14
15.5
17
Input Voltage (V)
Figure 21. Frequency vs. Input Voltage and Number of LED
100%
95%
90%
7 LEDs
5 LEDs
15 LEDs
85%
80%
13 LEDs
9 LEDs
11 LEDs
75%
70%
T = 25°C
A
L = 33µH
= 150mΩ
R
S
6.5
8
9.5
11
12.5
14
15.5
17
Input Voltage (V)
Figure 22. Efficiency vs. Input Voltage and Number of LED
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Typical Characteristics – Buck-boost mode – RS = 150mꢀ - L = 33µH – ILED = 350mA – GIRATIO = 0.23 – with bootstrap
0.385
0.375
0.365
8 LEDs
7 LEDs
6 LEDs
0.355
0.345
0.335
4 LEDs
5 LEDs
T
3 LEDs
= 25°C
A
L = 33µH
R
R
R
= 150mΩ
S
0.325
0.315
= 36mΩ
GI1
GI2
= 120mΩ
6.5
8.0
9.5
11.0
12.5
14.0
15.5
17.0
Input Voltage (V)
Figure 23. LED Current vs. Input Voltage and Number of LED
600
500
6 LEDs
7 LEDs
8 LEDs
400
300
200
5 LEDs
4 LEDs
3 LEDs
T
= 25°C
A
L = 33µH
100
0
R
R
R
= 150mΩ
S
= 36kΩ
GI1
GI2
= 120kΩ
8.0
9.5
11.0
Input Voltage (V)
Figure 24. Switching Frequency vs. Input Voltage and Number of LED
12.5
14.0
15.5
17.0
6.5
100%
95%
T
= 25°C
A
L = 33µH
R
R
R
= 150mΩ
S
= 36KΩ
GI1
GI2
= 120kΩ
90%
85%
80%
75%
70%
8 LEDs
7 LEDs
6 LEDs
4 LEDs
3 LEDs
5 LEDs
6.5
8.0
9.5
11.0
Input Voltage (V)
12.5
14.0
15.5
17.0
Figure 25. Efficiency vs. Input Voltage and Number of LED
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Applications Information
The ZXLD1374 is a high accuracy hysteretic inductive Buck/Boost/Buck-boost converter with an internal NMOS switch
designed to be used for current-driving single or multiple series-connected LEDs. The device can be configured to operate
in Buck, Boost, or Buck-boost modes by suitable configuration of the external components as shown in the schematics
shown in the device operation description.
Device Operation
a) Buck mode
The most simple Buck circuit is shown in Figure 26
LED current control in Buck mode is achieved by sensing the
VIN
Rs
coil current in the sense resistor Rs, connected between the
LED1
two inputs of a current monitor within the control loop block.
D1
An output from the control loop drives the input of a
comparator which drives the gate of the internal NMOS switch
transistor.
When the switch is on, current flows from VIN, via Rs, LED,
coil and switch to ground. This current ramps up until an
upper threshold value is reached. At this point the switch is
turned off and the current flows via Rs, LED, coil and D1 back
to VIN. When the coil current has ramped down to a lower
threshold value the switch is turned on again and the cycle of
events repeats, resulting in continuous oscillation.
VAUX VIN
ISM
LEDn
PWM
GI
L1
LX
LX
ADJ
REF
TADJ
C2
FLAG
NC x4
PGND
SHP STATUS SGND
C1
GND
The average current in the LED and coil is equal to the
average of the maximum and minimum threshold currents.
The ripple current (hysteresis) is equal to the difference
between the thresholds.
Figure 26. Buck Configuration
The control loop maintains the average LED current at the set
level by adjusting the thresholds continuously to force the
average current in the coil to the value demanded by the
voltage on the ADJ pin. This minimizes variation in output
current with changes in operating conditions.
The control loop also attempts to minimize changes in
switching frequency by varying the level of hysteresis. The
hysteresis has a defined minimum (typ 5%) and a maximum
(typ 20%), the frequency may deviate from nominal in
extreme conditions. Loop compensation is achieved by a
single external capacitor C1, connected between SHP and
SGND.
Figure 27. Operating Waveforms (Buck Mode)
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Applications Information (Continued)
b) Boost and Buck-boost modes
A basic ZXLD1374 application circuit for Buck-boost and Boost modes is shown in Figure 28.
Control in Boost and Buck-boost mode is achieved by
sensing the coil current in the series resistor Rs,
connected between the two inputs of a current monitor
within the control loop block.
An output from the control loop drives the input of a
comparator which drives the gate of the internal NMOS
switch transistor. In Boost and Buck-boost modes, when
the switch is on, current flows from VIN, via Rs, coil and
switch to ground. This current ramps up until an upper
threshold value is reached. At this point the switch is
turned off and the current flows via Rs, coil, D1 and LED
back to VIN (Buck-boost mode), or GND (Boost mode).
When the coil current has ramped down to a lower
threshold value the switch is turned on again and the
cycle of events repeats, resulting in continuous oscillation.
The average current in the coil is equal to the average of
the maximum and minimum threshold currents and the
ripple current (hysteresis) is equal to the difference
between the thresholds.
Figure 28. Boost and Buck-boost Configuration
The average current in the LED is always less than the
average current in the coil and the ratio between these
currents is set by the values of external resistors RGI1 and
RGI2
.
The peak LED current is equal to the peak coil
current. The control loop maintains the average LED
current at the set level by adjusting the thresholds and the
hysteresis continuously to force the average current in the
coil to the value demanded by the voltage on the ADJ and
GI pins. This minimizes variation in output current with
changes in operating conditions. Loop compensation is
achieved by a single external capacitor C2, connected
between SHP and SGND.
For more detailed descriptions of device operation and for
choosing external components, please refer to the
application circuits and descriptions in the later sections of
this specification.
Figure 29. Operating Waveforms
(Boost and Buck-boost Modes)
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Applications Information (Continued)
Component Selection
External component selection is driven by the characteristics of the load and the input supply, since this will determine the
kind of topology being used for the system.
Component selection starts with the current setting procedure and the inductor/frequency setting. Finally after selecting the
freewheeling diode and the output capacitor (if needed), the application section will cover the PWM dimming and thermal
feedback.
Setting the output current
The first choice when defining the output current is whether the device is operating with the load in series with the sense
resistor (Buck mode) or whether the load is not in series with the sense resistor (Boost and Buck-boost modes).
The output current setting depends on the choice of the sense resistor RS, the voltage on the ADJ pin and the voltage on the
GI pin, according to the device working mode. The sense resistor RS sets the coil current IRS
.
The ADJ pin may be connected directly to the internal 1.25V reference (VREF) to define the nominal 100% LED current. The
ADJ pin can also be overdriven with an external dc voltage between 125mV and 2.5V to adjust the LED current proportionally
between 10% and 200% of the nominal value.
ADJ and GI are high impedance inputs within their normal operating voltage ranges. An internal 2.6V clamp protects the
device against excessive input voltage and limits the maximum output current to approximately 4% above the maximum
current set by VADJ if the maximum input voltage is exceeded.
Below are provided the details of the LED current calculation both when the load in series with the sense resistor (Buck
mode) and when the load is not in series with the sense resistor (Boost and Buck-boost modes).
RS
In Buck mode, GI is connected to ADJ which results in the average LED
current (ILED) equal to the average sense resistor/coil current (IRS). A loop
VIN
ISM
gain compensation factor, K, compensates for GI being connected to ADJ.
This gives the following equation for ILED
:
REF
225mV VADJ 218mV VADJ
ILED
=
IRs = K
=
where K = 0.97
RS VREF
RS VREF
ADJ
GI
If ADJ (and GI pin) is directly connected to VREF, this becomes:
218mV
ILED
=
IRs =
RS
Therefore:
Rs =
SGND
218mV
ILED
Figure 30: Buck configuration
In Boost and Buck-boost mode GI is connected to ADJ through a voltage divider.
RS
With VADJ equal to VREF, the ratio defined by the resistor divider at the GI pin
determines the ratio of average LED current (ILED) to average sense
resistor/coil current.
VIN
ISM
REF
ILED
ILEDxRS
ICOIL
=
⇒
VRS = ICOILxRS =
1−D
1−D
ADJ
GI
Where
ILED
RGI2
VGI VADJ
0.225
=
=
VADJ VREF RS
RGI1
RGI1
VADJ 0.225
SGND
=
(RGI1 + RGI2) VREF RS
Therefore:
Figure 31: Boost and Buck-boost
connection
RGI1
(RGI1 + RGI2
225mV VADJ
ILED VREF
Rs =
)
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Applications Information (Continued)
When the ADJ pin is directly connected to the REF pin, this becomes:
RGI1
225mV
) ILED
Rs =
(RGI1 + RGI2
Note that the average LED current for a Boost or Buck-boost converter is always less than the average sense resistor
current. For the ZXLD1374, the recommended potential divider ratio is given by:
RGI1
0.2 ≤
≤ 0.50
(RGI1 + RGI2
)
It is possible to use a different combination of GI pin voltages and sense resistor values to set the LED current.
In general the design procedure to follow is:
-
-
-
Define input conditions in terms of VIN and IIN
Set output conditions in terms of LED current and the number of LEDs
Define controller topology – Buck, Boost or Buck-boost
Calculate the maximum duty-cycle as:
Buck mode
VLEDs
VINMIN
DMAX
=
Boost mode
VLEDS − V
INMIN
DMAX
=
=
VLEDS
Buck-boost mode
VLEDS
DMAX
VLEDS + V
IN MIN
Set the appropriate GIRATIO according to the circuit duty and the max switch current admissible limitations
VGI
RGI1
GIRATIO
=
=
≤ 1−DMAX
VADJ
(RGI1 +RGI2)
-
-
Set RGI1 as:
10kΩ ≤ RGI1 ≤ 200kΩ
Calculate RGI2 as:
DMAX
RGI2
≈
x RGI1
1−DMAX
-
Calculate the sense resistor as:
RGI1
225mV
) ILED
Rs =
(RGI1 + RGI2
If the potential divider ratio is greater than 0.64, the device detects that Buck-mode operation is desired and the output
current will deviate from the desired value.
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Applications Information (Continued)
For example, as in the typical application circuit, in order to get ILED= 350mA with IRS=1.5A the ratio has to be set as:
ILED
VGI
RGI1
=
=
≈ 0.23
IRS
VADJ
(RGI1 +RGI2)
Setting RGI1= 33kꢀ it results
VADJ
VGI
RGI2 = RGI1
(
−1) =110kΩ
This will result in:
RGI1
225mV
Rs =
= 150mΩ
(RGI1 + RGI2
) ILED
Table 1 shows typical resistor values used to determine GIRATIO with E24 series resistors:
Table 1
GIRATIO
0.2
RGI1
30kΩ
33kΩ
39kΩ
30kΩ
100kΩ
51kΩ
30kΩ
RGI2
120kΩ
100kΩ
91kΩ
56kΩ
150kΩ
62kΩ
0.25
0.3
0.35
0.4
0.45
0.5
30kΩ
The values shown have been chosen so that they do not load REF too much or create offset errors due to the GI pin input
current. A ZXLD1374 calculator is available from http://www.diodes.com/destools/calculators.html that will help with
component selection.
INDUCTOR/FREQUENCY SELECTION
Recommended inductor values for the ZXLD1374 are in the range 22 µH to 100 µH. The chosen coil should have a
saturation current higher than the peak sensed current and a continuous current rating above the required mean sensed
current by at least 50%.
The inductor value should be chosen to maintain operating duty cycle and switch 'on'/'off' times within the recommended
limits over the supply voltage and load current range.
The frequency compensation mechanism inside the chip tends to keep the frequency within the range 300kHz ~ 400kHz in
most of the operating conditions. Nonetheless, the controller allows for higher frequencies when either the number of LEDs
or the input voltage increases.
The graphs below can be used to select a recommended inductor to maintain the ZXLD1374 switching frequency within a
predetermined range when used in different topologies.
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Applications Information (Continued)
INDUCTOR/FREQUENCY SELECTION
15
13
11
9
L=47uH
7
5
L=33uH
3
L=22uH
L=10uH
1
0
10
20
30
Supply Voltage (V)
Figure 32: 1.5A Buck mode inductor selection for target frequency of 400 kHz
40
50
60
15
13
11
9
L=47uH
7
5
L=33uH
L=22uH
L=10uH
3
1
0
10
20
30
40
50
60
Supply Voltage (V)
Figure 33: 1.5A Buck mode inductor selection for target frequency > 500kHz
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Applications Information (Continued)
For example, in a Buck configuration (VIN =24V and 6 LEDs), with a load current of 1.5A; if the target frequency is around
400 kHz, the Ideal inductor size is L= 33µH.
The same kind of graphs can be used to select the right inductor for a Buck configuration and a LED current of 750mA, as
shown in figures 34 and 35.
15
13
11
9
7
L=100uH
5
L=68uH
L=47uH
3
1
L=33uH
0
10
20
30
40
50
60
Supply Voltage (V)
Figure 34: 750mA Buck mode inductor selection for target frequency 400kHz
15
13
11
9
L=47uH
7
5
L=33uH
L=22uH
L=10uH
3
1
0
10
20
30
40
50
60
Supply Voltage (V)
Figure 35: 750mA Buck mode inductor selection for target frequency > 500kHz
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Applications Information (Continued)
In the case of the Buck-boost topology, the following graphs guide the designer to select the inductor for a target frequency
of 400kHz (figure 36) or higher than 500kHz (figure 37).
15
13
11
9
L=47uH
7
5
3
1
L=33uH
L=22uH
0
10
20
30
Supply Voltage (V)
Figure 36: 350mA Buck-boost mode inductor selection for target frequency 400kHz
40
50
60
15
13
11
9
L=47uH
7
5
L=33uH
3
L=22uH
10
1
0
20
30
40
50
60
Supply Voltage (V)
Figure 37: 350mA Buck-boost mode inductor selection for target frequency > 500kHz
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Applications Information (Continued)
For example, in a Buck-boost configuration (VIN =10-18V and 4 LEDs), with a load current of 350mA; if the target frequency
is around 400kHz, the Ideal inductor size is L= 33uH. The same size of inductor can be used if the target frequency is higher
than 500kHz driving 6LEDs with a current of 350mA from a VIN =12-24V.
In the case of the Boost topology, the following graphs guide the designer to select the inductor for a target frequency of
400kHz (figure 38) or higher than 500kHz (figure 39).
L=47uH
15
13
11
9
L=33uH
7
L=22uH
5
3
1
0
10
20
30
Supply Voltage (V)
40
50
60
Figure 38: 350mA Boost mode inductor selection for target frequency 400kHz
L=47uH
15
13
11
9
L=33uH
7
L=22uH
5
3
1
0
10
20
30
40
50
60
Supply Voltage (V)
Figure 39: 350mA Boost mode inductor selection for target frequency > 500kHz
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Applications Information (Continued)
Suitable coils for use with the ZXLD1374 may be selected from the MSS range manufactured by Coilcraft, or the NPIS
range manufactured by NIC components.
The following websites may be useful in finding suitable components
www.coilcraft.com
www.niccomp.com
www.wuerth-elektronik.de
DIODE SELECTION
For maximum efficiency and performance, the rectifier (D1) should be a fast low capacitance Schottky diode* with low
reverse leakage at the maximum operating voltage and temperature. The Schottky diode also provides better efficiency
than silicon PN diodes, due to a combination of lower forward voltage and reduced recovery time.
It is important to select parts with a peak current rating above the peak coil current and a continuous current rating higher
than the maximum output load current. In particular, it is recommended to have a voltage rating at least 15% higher than the
maximum LX voltage to ensure safe operation during the ringing of the switch node and a current rating at least 10% higher
than the average diode current. The power rating is verified by calculating the power loss through the diode.
The higher forward voltage and overshoot due to reverse recovery time in silicon diodes will increase the peak voltage on
the LX pin. If a silicon diode is used, care should be taken to ensure that the total voltage appearing on the LX pin, including
supply ripple, does not exceed the specified maximum value.
*A suitable Schottky diode would be PDS3100 (Diodes Inc).
OUTPUT CAPACITOR
An output capacitor may be required to limit interference or for specific EMC purposes. For Boost and Buck-boost
regulators, the output capacitor provides energy to the load when the freewheeling diode is reverse biased during the first
switching subinterval. An output capacitor in a Buck topology will simply reduce the LED current ripple below the inductor
current ripple. In other words, this capacitor changes the current waveform through the LED(s) from a triangular ramp to a
more sinusoidal version without altering the mean current value.
In all cases, the output capacitor is chosen to provide a desired current ripple of the LED current (usually recommended to
be less than 40% of the average LED current).
Buck:
ΔIL−PP
COUTPUT
=
8xfSW xrLED xΔILED−PP
Boost and Buck-boost
DxILED
COUTPUT
=
fSW xrLED xΔILED−PP
where:
•
•
•
•
ΔIL is the ripple of the inductor current, usually ± 20% of the average sensed current
ΔILED is the ripple of the LED current, it should be <40% of the LEDs average current
f
sw is the switching frequency (from graphs and calculator)
rLED is the dynamic resistance of the LEDs string (n times the dynamic resistance of the single LED from the
datasheet of the LED manufacturer).
The output capacitor should be chosen to account for derating due to temperature and operating voltage. It must also have
the necessary RMS current rating. The minimum RMS current for the output capacitor is calculated as follows:
Buck
ILED−PP
ICOUTPUT−
=
RMS
12
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Applications Information (Continued)
Boost and Buck-boost
DMAX
ICOUTPUT−RMS = ILED
1−DMAX
Ceramic capacitors with X7R dielectric are the best choice due to their high ripple current rating, long lifetime, and
performance over the voltage and temperature ranges.
BOOTSTRAP CIRCUIT
In Boost and Buck-boost modes with input voltages below 12V to fully enhance the internal power switch it is required to use a
bootstrap network as shown in figure 40.
Figure 40: Bootstrap circuit for low voltage operations
The bootstrap circuit is realized by adding a reservoir capacitor, C8, current limiting resistor R13 (=100ꢀ) and a blocking
diode D2 (DFSL160). During the power switch turn-on C8 needs to be able to supply approximately 10mA current.
A capacitor of 1uF (C8) provides a reasonable trade-off between VAUX supply needs and LED current accuracy. At start-up
the VAUX pin requires only a few mA of current from the LED current. In normal operation the current taken from the LED
current to supply VAUX will be negligible.
INPUT CAPACITOR
The input capacitor and minimum RMS current for the output capacitor can be calculated knowing the input voltage ripple
ΔVIN-PP as follows:
Input capacitor
Minimum RMS current
Buck
Dx(1−D)xILED
fSW xΔVIN−PP
ICIN−RMS = ILED x Dx(1− D)
CIN =
use D=0.5 as worst case
use D=0.5 as worst case
Boost
ΔICOIL−PP
IL−PP
CIN =
ICIN−
=
RMS
8xfSW xΔV
12
IN−PP
Buck-boost
DxILED
D
CIN =
ICIN−RMS = ILED
x
fSW xΔV
(1−D)
IN−PP
Use D = DMAX as worst case
Use D = DMAX as worst case
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Applications Information (Continued)
PWM OUTPUT CURRENT CONTROL & DIMMING
The ZXLD1374 has a dedicated PWM dimming input that allows a wide dimming frequency range from 100Hz to 1kHz with
1000:1 resolution; however higher dimming frequencies can be used – at the expense of dimming dynamic range and
accuracy.
Typically, for a PWM frequency of 1kHz, the error on the current linearity is lower than 5%; in particular the accuracy is
better than 1% for PWM from 5% to 100%. This is shown in the graph below:
15.0%
12.5%
10.0%
7.5%
1500
1250
1000
750
500
250
0
VIN = 24V
TA = 25°C
fPWM = 1kHz
ILED
5.0%
2.5%
Normalized LED
Current Error
0.0%
0%
10%
20%
30%
40%
50%
60%
70%
80%
90% 100%
PWM duty cycle
Figure 41. LED current linearity and accuracy with PWM dimming at 1kHz
For a PWM frequency of 100Hz, the error on the current linearity is lower than 2.5%; it becomes negligible for PWM greater
than 5%. This is shown in the graph below:
15.0%
12.5%
10.0%
7.5%
1500
1250
1000
750
500
250
0
VIN = 24V
TA = 25°C
ILED
f
PWM = 100Hz
5.0%
2.5%
Normalized LED
Current Error
0.0%
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
PWM duty cycle
Figure 42. LED current linearity and accuracy with PWM dimming at 100Hz
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Applications Information (Continued)
The PWM pin is designed to be driven by both 3.3V and 5V logic levels. It can be driven also by an open drain/collector
transistor. In this case the designer can either use the internal pull-up network or an external pull-up network in order to
speed-up PWM transitions, as shown in the Boost/ Buck-boost section.
Figure 43. PWM Dimming from Open Collector Switch
Figure 44. PWM Dimming from MCU
LED current can be adjusted digitally, by applying a low frequency PWM logic signal to the PWM pin to turn the controller on
and off. This will produce an average output current proportional to the duty cycle of the control signal. During PWM
operation, the device remains powered up and only the output switch is gated by the control signal.
The PWM signal can achieve very high LED current resolution. In fact, dimming down from 100% to 0, a minimum pulse
width of 5us can be achieved resulting in very high accuracy. While the maximum recommended pulse is for the PWM
signal is10ms.
Figure 45. PWM Dimming Minimum and Maximum Pulse
Page 25 of 35
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Applications Information (Continued)
The device can be put in standby by taking the PWM pin to ground, or pulling it to a voltage below 0.4V with a suitable open
collector NPN or open drain NMOS transistor, for a time exceeding 15ms (nominal). In the shutdown state, most of the
circuitry inside the device is switched off and residual quiescent current will be typically 90µA. In particular, the Status pin
will go down to GND while the FLAG and REF pins will stay at their nominal values.
Fig 46. Stand-by state from PWM signal
TADJ pin - Thermal control of LED current
The ‘Thermal control’ circuit monitors the voltage on the TADJ pin and reduces output current if the voltage on this pin falls
below 625mV. An external NTC thermistor and resistor can therefore be connected as shown below to set the voltage on
the TADJ pin to 625mV at the required temperature threshold. This will give 100% LED current below the threshold
temperature and a falling current above it as shown in the graph. The temperature threshold can be altered by adjusting the
value of Rth and/or the thermistor to suit the requirements of the chosen LED.
The Thermal Control feature can be disabled by connecting TADJ to REF.
Here is a simple procedure to design the thermal feedback circuit:
1. Select the temperature threshold TTHRESHOLD at which the current must start to decrease
2. Select the Thermistor TH1 (both resistive value at 25˚C and beta)
3. Select the value of the resistor RTH as RTH = TH1 at TTHRESHOLD
Figure 47. Thermal feedback network
For example,
1) Temperature threshold TTHRESHOLD = 70˚C
2) TH1 = 10kꢀ at 25˚C and beta= 3500
3) TH = TH1 at TTHRESHOLD = 3.3kꢀ
Æ
TH1 = 3.3kꢀ at 70˚C
R
Page 26 of 35
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A Product Line of
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ZXLD1374
Applications Information (Continued)
Over-Temperature Shutdown
The ZXLD1374 incorporates an over-temperature shutdown circuit to protect against damage caused by excessive die
temperature. A warning signal is generated on the STATUS output when die temperature exceeds 125°C nominal and the
output is disabled when die temperature exceeds 150°C nominal. Normal operation resumes when the device cools back
down to 125°C.
FLAG/STATUS Outputs
The FLAG/STATUS outputs provide a warning of extreme operating or fault conditions. FLAG is an open-drain logic output,
which is normally high resistance, but switches low resistance to indicate that a warning, or fault condition exists. STATUS is
a DAC output, which is normally high (4.5V), but switches to a lower voltage to indicate the nature of the warning/fault.
Conditions monitored, the method of detection and the nominal STATUS output voltage are given in the following table:
Table 2
Severity
(Note 10)
Monitored
parameters
Warning/Fault condition
FLAG
Nominal STATUS voltage
Normal operation
H
L
L
4.5
4.5
3.6
1
2
VAUX<5.6V
VIN<5.6V
Supply under-voltage
Output current out of regulation
(Note 11)
VSHP outside normal
voltage range
2
L
3.6
Driver stalled with switch ‘on’, or
‘off’ (Note 12)
2
3
L
L
3.6
2.7
tON, or tOFF>100µs
LX voltage > 60V
Switch over-voltage
Device temperature above
maximum recommended
operating value
4
L
1.8
TJ>125°C
Sense resistor current IRS above
specified maximum
5
5
L
L
0.9
0.9
VSENSE>0.375V
ILX > 1.5A
Average switch current greater
than 1.5A
Notes:
10. Severity 1 denotes lowest severity.
11. This warning will be indicated if the output power demand is higher than the available input power; the loop may not be able
to maintain regulation.
12. This warning will be indicated if the LX pin stays at the same level for greater than 100us (e.g. the internal transistor cannot
pass enough current to reach the upper switching threshold).
Page 27 of 35
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Applications Information (Continued)
VREF
0V
4.5V
Normal
Operations
VAUX
UVLO
3.6V
2.7V
1.8V
0.9V
- VIN UVLO
- STALL
- OUT of REG
ZXLD1374
Switch OV
Over
Temperature
Over
Current
0A
5
0
1
2
3
4
SEVERITY
Fig 48. Status levels
In the event of more than one fault/warning condition occurring, the higher severity condition will take precedence. E.g.
‘Excessive coil current’ and ‘Out of regulation’ occurring together will produce an output of 0.9V on the STATUS pin.
If VADJ>1.7V, VSENSE may be greater than the excess coil current threshold in normal operation and an error will be
reported. Hence, STATUS and FLAG are only guaranteed for VADJ<=VREF
.
Diagnostic signals should be ignored during the device start – up for 100μs. The device start up sequence will be initiated
both during the first power on of the device or after the PWM signal is kept low for more than 15ms, initiating the standby
state of the device.
In particular, during the first 100μs the diagnostic is signaling an over-current then an out-of-regulation status. These two
events are due to the charging of the inductor and are not true fault conditions.
VREF
Out of
regulation
Over-
current
1.4
1.2
1
0.8
0.6
0.4
0.2
0
0
20
40
60
80
100
120
140
160
180
200
time (µs)
Figure 49. Diagnostic during Start-Up
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Applications Information (Continued)
Over-voltage Protection
The ZXLD1374 is inherently protected against open-circuit load when used in Buck configuration. However care has to be
taken with open-circuit load conditions in Buck-boost or Boost configurations. This is because in these configurations there
is only an over-voltage FLAG but no internal open-circuit protection mechanism for the internal MOSFET. In this case an
Over-Voltage-Protection (OVP) network should be provided to the MOSFET to avoid damage due to open circuit conditions.
This is shown in Figure 37 below, highlighted in the dotted blue box.
Figure 50. OVP Circuit
The zener voltage is determined according to: Vz = VLEDMAX +10%. The LX pin voltage exceeds Vz then the gate of
MOSFET Q2 will start to turn on causing the PWM pin to be brought low. This will disable to LX output until the voltage on
the LX falls below Vz. If the fault exists for longer than 20ms then the ZXLD1374 will enter into a shutdown state.
Take care of the max voltage drop on the Q2 MOSFET gate.
Alternatively, to perform the OVP function, it can be used the diagnostic section of the ZXLD1374. In particular a
microcontroller can read the FLAG and the status pins, and if they signal an over-voltage, the microcontroller can switch the
device off by pulling the PWM signal low.
Page 29 of 35
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A Product Line of
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ZXLD1374
Applications Information (Continued)
PCB Layout considerations
PCB layout is a fundamental activity to get the most of the device in all configurations. In the following section it is possible
to find some important insight to design with the ZXLD1374 both in Buck and Buck-boost/Boost configurations.
Figure 51. Circuit Layout
Here are some considerations useful for the PCB layout:
-
-
-
In order to avoid ringing due to stray inductances, the inductor L1, the anode of D1 and the LX pin should be placed
as close together as possible.
The shaping capacitor C1 is fundamental for the stability of the control loop. To this end it should be placed no more
than 5mm from the SHP pin.
Input voltage pins, VIN and VAUX, need to be decoupled. It is recommended to use two ceramic capacitors of 2.2uF,
X7R, 100V (C3 and C4). In addition to these capacitors, it is suggested to add two ceramic capacitors of 1uF, X7R,
100V each (C2, C8), as well as a further decoupling capacitor of 100nF close to the VIN/VAUX pins (C9) the device
is used in Buck mode, or can be driven from a separate supply.
Page 30 of 35
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© Diodes Incorporated
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Document number: DS35032 Rev. 1 - 2
A Product Line of
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ZXLD1374
Applications Examples
1.5A Buck LED driver
In this application example, ZXLD1374 is
connected as a Buck LED driver with
schematic and parts list shown below.
The LED driver is able to deliver 1.5A of
LED current to single or multiple LEDs in
series with input voltage ranged from
10V to 50V. In order to achieve high
efficiency under high LED current, Super
Barrier Rectifier (SBR) with low forward
voltage is used as free wheeling rectifier.
With only a few extra components, the
ZXLD1374 LED driver is able to deliver
LED power of greater than 60W. This is
suitable for applications which require
high LED power likes high power down
lighting, wall washer, automotive LED
lighting etc.
Figure 52. Application circuit of 1.5A Buck LED driver
Bill of Material
Ref No.
U1
Value
60V 1.5A LED driver
100V 3A SBR
33uH 4.2A
Part No.
ZXLD1374
SBR3U100
744770933
SMD 0805/0603
SMD1206
Manufacturer
Diodes Inc
Diodes Inc
Wurth Electronik
Generic
D1
L1
C1
100pF 50V
C2
1uF 100V X7R
2.2uF 100V X7R
300mꢀ 1%
Generic
C3 C4 C5
R1 R2
R3
SMD1210
Generic
SMD1206
Generic
4.7ꢀ
SMD1206
Generic
Typical Performance
LED Current vs Input Voltage
Efficiency vs Input Voltage
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
1600
1200
800
400
0
1 LED VF=3.4V
1 LED VF=3.4V
3 LED VF=9.8V
5 LED VF=16V
3 LED VF=9.8V
5 LED VF=16V
10
15
20
25
30
35
40
45
50
10
15
20
25
30
35
40
45
50
Input Voltage (V)
Input Voltage (V)
Figure 53. Efficiency
Figure 54. Line regulation
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Document number: DS35032 Rev. 1 - 2
A Product Line of
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ZXLD1374
Applications Examples
350mA Boost LED diver
In this application example,
ZXLD1374 is connected as a
Boost LED driver with schematic
and parts list shown below. The
LED driver is able to deliver
350mA of LED current into 12
high brightness LED with input
voltage ranged from 16V to 28V.
Overall high efficiency of 92%+
make it ideal for applications
likes solar LED street lighting
and general LED illuminations.
Figure 55. Application circuit of 350mA Boost LED driver
Bill of Material
Ref No.
Value
Part No.
ZXLD1374
Manufacturer
Diodes Inc
Diodes Inc
Diodes Inc
Diodes Inc
Wurth Electronik
Generic
U1
60V LED driver
60V MOSFET
100V 3A Schottky
51V 410mW Zener
47uH 2.6A
Q1
2N7002A
D1
PDS3100-13
BZT52C51
Z1
L1
744771147
C1
100pF 50V
SMD 0805/0603
SMD1210
C3 C4
4.7uF 100V X7R
1uF 50V X7R
300mꢀ 1%
Generic
C2
SMD1206
Generic
R1 R2
SMD1206
Generic
R3
120kꢀ 1%
SMD 0805/0603
SMD 0805/0603
SMD 0805/0603
R4
R5
36kꢀ 1%
2.7kꢀ
Generic
Generic
Typical Performance
Efficiency vs Input Voltage
LED Current vs Input Voltage
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
400
350
300
250
200
150
100
50
12 LED VF=37V
15 LED VF=47V
12 LED VF=37V
15 LED VF=47V
0
16
18
20
22
24
26
28
30
16
18
20
22
24
26
28
30
Input Voltage
Input Voltage
Figure 57. Line regulation
Figure 56. Efficiency
Page 32 of 35
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© Diodes Incorporated
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Document number: DS35032 Rev. 1 - 2
A Product Line of
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ZXLD1374
Applications Examples
350mA Buck-boost LED driver
In
this
application
example,
ZXLD1374 is connected as a Buck-
boost LED driver with schematic and
parts list shown below. The LED
driver is able to deliver 350mA of
LED current into 4/5 high brightness
LED with input voltage ranged from
7V to 20V. In order to increase the
driving voltage level for the internal
MOSFET during low voltage input,
bootstrap circuit formed by R6 D2
and C6 are used to supply higher
voltage to the VAUX pin.
Since the Buck-boost LED driver can
handle an input voltage range below
and above the LED voltage, this
versatile input voltage range makes
it ideal for automotive lighting
applications.
Figure 58. Application circuit of 350mA Buck-boost LED driver
Bill of Material
Ref No.
U1
Q1
Value
60V LED driver
60V MOSFET
Part No.
ZXLD1374
2N7002A
Manufacturer
Diodes Inc
Diodes Inc
D1
100V 3A Schottky
100V 1A Schottky
47V 410mW Zener
47uH 2.6A
PDS3100-13
B1100
Diodes Inc
Diodes Inc
Diodes Inc
Wurth Electronik
Generic
D2
Z1
BZT52C47
L1
744771147
C1
100pF 50V
SMD 0805/0603
SMD1210
C3 C4 C5
4.7uF 50V X7R
1uF 50V X7R
300mꢀ 1%
120kꢀ 1%
Generic
C2 C6
SMD1206
Generic
R1 R2
SMD1206
Generic
R3
SMD 0805/0603
SMD 0805/0603
SMD 0805/0603
SMD 1206
Generic
R4
36kꢀ 1%
Generic
R5
2.7kꢀ
Generic
R6
1kꢀ
Generic
Typical Performance
Efficiency vs Input Voltage
LED Current vs Input Voltage
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
400
350
300
250
200
150
100
50
4 LED VF=12.5V
5 LED VF=15.6V
4 LED VF=12.5V
5 LED VF=15.6V
0
7
8
9
10
11
12
13
14
15
16
17
18
19
20
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Input Voltage
Input Voltage
Figure 59. Efficiency
Figure 60. Line regulation
Page 33 of 35
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Document number: DS35032 Rev. 1 - 2
A Product Line of
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ZXLD1374
Ordering Information
Part
Marking
ZXLD1374
Reel
Quantity
Device
Packaging
Status
Tape Width
16mm
Reel Size
ZXLD1374EST20TC TSSOP-20EP
Active
2500
13”
Package Mechanical Data
TSSOP-20 EP
θ1
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© Diodes Incorporated
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Document number: DS35032 Rev. 1 - 2
A Product Line of
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ZXLD1374
IMPORTANT NOTICE
DIODES INCORPORATED MAKES NO WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, WITH REGARDS TO THIS DOCUMENT,
INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
PURPOSE (AND THEIR EQUIVALENTS UNDER THE LAWS OF ANY JURISDICTION).
Diodes Incorporated and its subsidiaries reserve the right to make modifications, enhancements, improvements, corrections or other changes
without further notice to this document and any product described herein. Diodes Incorporated does not assume any liability arising out of the
application or use of this document or any product described herein; neither does Diodes Incorporated convey any license under its patent or
trademark rights, nor the rights of others. Any Customer or user of this document or products described herein in such applications shall
assume all risks of such use and will agree to hold Diodes Incorporated and all the companies whose products are represented on Diodes
Incorporated website, harmless against all damages.
Diodes Incorporated does not warrant or accept any liability whatsoever in respect of any products purchased through unauthorized sales
channel.
Should Customers purchase or use Diodes Incorporated products for any unintended or unauthorized application, Customers shall indemnify
and hold Diodes Incorporated and its representatives harmless against all claims, damages, expenses, and attorney fees arising out of,
directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized application.
Products described herein may be covered by one or more United States, international or foreign patents pending. Product names and
markings noted herein may also be covered by one or more United States, international or foreign trademarks.
LIFE SUPPORT
Diodes Incorporated products are specifically not authorized for use as critical components in life support devices or systems without the
express written approval of the Chief Executive Officer of Diodes Incorporated. As used herein:
A. Life support devices or systems are devices or systems which:
1. are intended to implant into the body, or
2. support or sustain life and whose failure to perform when properly used in accordance with instructions for use provided in the
labeling can be reasonably expected to result in significant injury to the user.
B. A critical component is any component in a life support device or system whose failure to perform can be reasonably expected to cause
the failure of the life support device or to affect its safety or effectiveness.
Customers represent that they have all necessary expertise in the safety and regulatory ramifications of their life support devices or systems,
and acknowledge and agree that they are solely responsible for all legal, regulatory and safety-related requirements concerning their products
and any use of Diodes Incorporated products in such safety-critical, life support devices or systems, notwithstanding any devices- or systems-
related information or support that may be provided by Diodes Incorporated. Further, Customers must fully indemnify Diodes Incorporated and
its representatives against any damages arising out of the use of Diodes Incorporated products in such safety-critical, life support devices or
systems.
Copyright © 2010, Diodes Incorporated
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