SMD1210 [DIODES]
60V HIGH ACCURACY BUCK/BOOST/BUCK-BOOST LED DRIVER CONTROLLER; 60V高精度降压/升压/降压 - 升压型LED驱动器控制器
| 型号： | SMD1210 |
| 厂家： | 
DIODES INCORPORATED |
| 描述： | 60V HIGH ACCURACY BUCK/BOOST/BUCK-BOOST LED DRIVER CONTROLLER |
| 文件： | 总33页 (文件大小：849K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
A Product Line of
Diodes Incorporated
ZXLD1370
60V HIGH ACCURACY BUCK/BOOST/BUCK-BOOST LED DRIVER CONTROLLER
Description
Pin Assignments
The ZXLD1370 is an LED driver controller IC for driving
external MOSFETs to drive high current LEDs. It is a multi-
topology controller 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 15 LEDs in series.
TSSOP-16 EP
The ZXLD1370 is a modified hysteretic controller using a
patent pending control scheme providing high output current
accuracy in all three modes of operation. High accuracy
dimming is achieved through DC control and high frequency
PWM control.
The ZXLD1370 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.
Features
•
•
•
•
•
0.5% typical output current accuracy
6 to 60V operating voltage range
LED driver supports Buck, Boost and Buck-boost
configurations
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
Typical Application Circuit
Buck-boost diagram utilizing thermistor and Tadj
Curve showing LED current vs. TLED
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ZXLD1370
Document number: DS32165 Rev. 2 - 2
A Product Line of
Diodes Incorporated
ZXLD1370
Pin Descriptions
Pin Name
Pin
Type‡
Description
Adjust input (for dc output current control)
Connect to REF to set 100% output current.
ADJ
REF
1
2
3
I
O
I
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 provides some failsafe should they get overdriven
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.
TADJ
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
Status pin voltage is low during shutdown mode
SGND
PGND
6
7
P
P
Signal ground (Connect to 0V)
Power ground - Connect to 0V and pin 8 to maximize copper area
Not Connected internally – recommend connection to pin 7, (PGND), to maximize PCB
copper for thermal dissipation
N/C
8
-
Not Connected internally – recommend connection pin 10 (GATE) to permit wide copper
trace to gate of MOSFET
N/C
9
GATE
10
O
P
Gate drive output to external NMOS transistor – connect to pin 9
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)
11
VAUX
Decouple to ground with capacitor close to device (refer to Applications section)
Input supply to device (6V to 60V)
Decouple to ground with capacitor close to device (refer to Applications section)
12
13
P
I
VIN
Current monitor input. Connect current sense resistor between this pin and VIN
The nominal voltage across the resistor is 225mV
ISM
Flag open drain output
FLAG
14
O
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
PWM
15
I
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 device in Buck mode or Boost, Buck-boost modes
Connect to ADJ in Buck mode operation
GI
16
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 they get overdriven
EP
PAD
P
Exposed paddle. Connect to 0V plane for electrical and thermal management
‡
Notes:
. Type refers to whether or not pin is an Input, Output, Input/Output or Power supply pin.
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© Diodes Incorporated
ZXLD1370
Document number: DS32165 Rev. 2 - 2
A Product Line of
Diodes Incorporated
ZXLD1370
Absolute Maximum Ratings (Voltages to GND Unless Otherwise Stated)
Symbol
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 20
18
VIN
V
VAUX
V
VISM
V
VSENSE
VGATE
IGATE
Current monitor sense voltage (VIN-VISM
)
Gate driver output voltage
V
Gate driver continuous output current
Flag output voltage
mA
V
-0.3 to 40
VFLAG
VPWM, VADJ
VTADJ, VGI,
VPWM
TJ
,
Other input pins
-0.3 to 5.5
V
Maximum junction temperature
Storage temperature
150
°C
°C
-55 to 150
TST
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.
Recommended Operating Conditions
Symbol
Parameter
Performance/Comment
Normal operation
Functional (Note 1)
Normal operation
Functional
Min
8
6.3
8
Max
Unit
Input supply voltage range
60
V
VIN
Auxiliary supply voltage range (Note 2)
60
V
VAUX
6.3
Current sense monitor input range
Differential input voltage
External dc control voltage applied to ADJ
pin to adjust output current
Reference external load current
Recommended switching frequency range
(Note 3)
6.3
0
60
V
VISM
450
mV
VSENSE
VVIN-VISM, with 0 ≤ VADJ ≤ 2.5
DC brightness control mode
from 10% to 200%
0.125
2.5
1
V
VADJ
IREF
fmax
REF sourcing current
mA
kHz
300
0
1000
Temperature adjustment (TADJ) input voltage
range
Recommended PWM dimming frequency range
(Note 4)
PWM pulse width in dimming mode
PWM pin high level input voltage
V
VTADJ
fPWM
VREF
To achieve 1000:1 resolution
To achieve 500:1 resolution
PWM input high or low
100
100
0.002
500
1000
10
Hz
Hz
ms
tPWMH/L
VPWMH
VPWML
TJ
2
0
5.5
0.4
V
V
PWM pin low level input voltage
Operating Junction Temperature Range
Gain setting ratio for boost and buck-boost modes
-40
0.20
125
0.50
°C
GI
Ratio= VGI/VADJ
Notes:
1. The functional range of V is the voltage range over which the device will function. Output current and device parameters may deviate from their
IN
normal values for V and V
voltages between 6V and 8V, depending upon load and conditions.
IN
AUX
2. V
can be driven from a voltage higher than V to provide higher efficiency at low V voltages, but to avoid false operation; a voltage should not
AUX
IN
IN
be applied to V
in the absence of a voltage at V .
IN
AUX
3. The device contains circuitry to control the switching frequency to approximately 400kHz. The maximum and minimum operating frequency are not
tested in production.
4. This gives maximum resolution at the expense of accuracy. To ensure accuracy the following equation should be used: 2*Resolution *f
< f
SWH
PWM
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© Diodes Incorporated
ZXLD1370
Document number: DS32165 Rev. 2 - 2
A Product Line of
Diodes Incorporated
ZXLD1370
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
5.2
5.5
5.6
6
6.3
6.5
VUV-
Normal operation to switch disabled
Under-Voltage detection threshold
Switch disabled to normal operation
V
VIN or VAUX rising
VUV+
PWM pin floating.
Output not switching
mA
µA
µA
µA
V
1.5
150
90
3
IQ-IN
Quiescent current into VIN
Quiescent current into VAUX
Standby current into VIN.
300
150
10
IQ-AUX
ISB-IN
ISB-AUX
VREF
PWM pin grounded
for more than 15ms
0.7
Standby current into VAUX
.
No load
Internal reference voltage
1.237 1.25 1.263
Change in reference voltage with output Sourcing 1mA
-5
mV
ΔVREF
current
Sinking 100 µA
5
Reference voltage line regulation
Reference temperature coefficient
dB
-60
-90
VREF_LINE
VREF-TC
VIN = VAUX , 6.5V<VIN = <60V
ppm/°C
+/-50
DC-DC converter parameters
External dc control voltage applied to ADJ DC brightness control mode
‡
0.125 1.25
2.5
V
VADJ
pin to adjust output current
10% to 200%
VADJ ≤ 2.5V
VADJ = 5.0V†
100
5
nA
µA
ADJ input current
IADJ
GI Voltage threshold for boost and buck-
boost modes selection
‡
0.8
V
VGI
VADJ = 1.25V
V
GI ≤ 2.5V
100
5
nA
µA
GI input current
IGI
VGI = 5.0V†
PWM input current
PWM pulse width
(to enter shutdown state)
Thermal shutdown upper threshold
(GATE output forced low)
Thermal shutdown lower threshold
(GATE output re-enabled)
36
100
25
µA
ms
IPWM
VPWM = 5.5V
PWM input low
10
15
tPWMoff
Temperature rising.
Temperature falling.
150
125
ºC
ºC
TSDH
TSDL
High-Side Current Monitor (Pin ISM)
Measured into ISM pin and
Input Current
11
20
µA
IISM
VISM = 12V
Accuracy of nominal VSENSE threshold
voltage
Over-current sense threshold voltage
±0.25 ±2
350 375
%
VSENSE_acc
VADJ = 1.25V
300
mV
VSENSE-OC
Notes:
† The ADJ and GI pins have an internal clamp that limits the internal node to less than 3V. This provides some failsafe should those
pins get overdriven.
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© Diodes Incorporated
ZXLD1370
Document number: DS32165 Rev. 2 - 2
A Product Line of
Diodes Incorporated
ZXLD1370
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
FLAG pin low level output voltage
Output sinking 1mA
0.5
1
V
VFLAGL
FLAG pin open-drain leakage current
µA
IFLAGOFF
VFLAG=40V
Normal operation
4.2
3.3
4.5
3.6
4.8
Out of regulation (VSHP out of range)
(Note 6)
3.9
3.3
3.3
1.5
3.6
3.6
1.8
3.9
3.9
2.1
VIN under-voltage (VIN < 5.6V)
STATUS Flag no-load output voltage
(Note 5)
V
VSTATUS
Switch stalled (tON or tOFF> 100µs)
Over-temperature (TJ > 125°C)
Excess sense resistor current
(VSENSE > 0.32V)
0.6
0.9
10
1.2
Output impedance of STATUS output
Normal operation
kΩ
RSTATUS
Driver output (PIN GATE)
No load Sourcing 1mA
(Note 7)
High level output voltage
10
11
V
V
VGATEH
Low level output voltage
Sinking 1mA, (Note 8)
0.5
15
VGATEL
VGATECL
VIN = VAU X= VISM = 18V
High level GATE CLAMP voltage
12.8
V
IGATE = 1mA
Charging or discharging gate of
external switch with QG = 10nC and
400kHz
Dynamic peak current available during
rise or fall of output voltage
±300
mA
IGATE
Time to assert ‘STALL’ flag and
warning on STATUS output
(Note 9)
GATE low or high
100
170
µs
tSTALL
LED Thermal control circuit (TADJ) parameters
Upper threshold voltage
Lower threshold voltage
TADJ pin Input current
Onset of output current reduction
(VTADJ falling)
Output current reduced to <10% of
set value (VTADJ falling)
560
380
625
440
690
500
1
mV
mV
µA
VTADJH
VTADJL
ITADJ
VTADJ = 1.25V
Notes:
5. 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.
6. Flag is asserted if VSHP<2.5V or VSHP>3.5V
7. GATE is switched to the supply voltage VAUX for low values of VAUX (i.e. between 6V and approximately 12V). For VAUX>12V, GATE is clamped
internally to prevent it exceeding 15V.
8. GATE is switched to PGND by an NMOS transistor
9. If tON exceeds tSTALL, the device will force GATE low to turn off the external switch and then initiate a restart cycle. 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.
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© Diodes Incorporated
ZXLD1370
Document number: DS32165 Rev. 2 - 2
A Product Line of
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ZXLD1370
Typical Characteristics – Buck Mode – RS = 150mΩ – L = 33µH - ILED = 1.5A
1.500
7 LEDs
9 LEDs
5 LEDs
11 LEDs
13 LEDs
1 LED
3 LEDs
15 LEDs
1.490
1.480
1.470
1.460
1.450
1.440
1.430
6.5
11
15.5
20
24.5
29
33.5
38
42.5
47
51.5
56
60.5
Input Voltage (V)
Figure 1: Load Current vs. Input Voltage & Number of LED
1000
1 LED
3 LEDs
5 LEDs
7 LEDs
9 LEDs
11 LEDs
13 LEDs
15 LEDs
900
800
TA = 25°C
VAUX = VIN
700
600
500
400
300
200
100
0
6.5
11
15.5
20
24.5
29
33.5
38
42.5
47
51.5
56
60.5
Input Voltage (V)
Figure 2: Frequency vs. Input Voltage & Number of LED
100%
95%
90%
85%
80%
75%
70%
65%
60%
6.5
11
15.5
20
24.5
29
33.5
38
42.5
47
51.5
56
60.5
Input Voltage (V)
Figure 3: Efficiency vs. Input & Number of LED
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© Diodes Incorporated
ZXLD1370
Document number: DS32165 Rev. 2 - 2
A Product Line of
Diodes Incorporated
ZXLD1370
Typical Characteristics – Buck Mode – Rs = 300mꢀ - L = 47µH - ILED = 750mA
0.740
0.735
T
= 25°C
= V
A
V
AUX
IN
0.730
0.725
0.720
0.715
2 LEDs
3 LEDs
5 LEDs
7 LEDs
9 LEDs
11 LEDs
13 LEDs
15 LEDs
6.5
11
15.5
20
24.5
29
33.5
38
42.5
47
51.5
56
60.5
60.5
60.5
Input Voltage (V)
Figure 4: ILED vs. Input & Number of LED
1000
900
800
700
600
500
400
300
200
2 LEDs
3 LEDs
5 LEDs 7 LEDs 9 LEDs
11 LEDs
13 LEDs
15 LEDs
TA = 25°C
VAUX = VIN
100
0
6.5
11
15.5
20
24.5
29
33.5
38
42.5
47
51.5
56
Input Voltage (V)
Figure 5: Frequency ZXLD1370 - Buck Mode - L47μH
100%
95%
90%
85%
80%
TA = 25°C
VAUX = VIN
75%
70%
65%
60%
2 LEDs
3 LEDs
5 LEDs
7 LEDs
9 LEDs
11 LEDs
13 LEDs
15 LEDs
6.5
11
15.5
20
24.5
29
33.5
38
42.5
47
51.5
56
Input Voltage (V)
Figure 6: Efficiency vs. Input Voltage & Number of LED
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ZXLD1370
Document number: DS32165 Rev. 2 - 2
A Product Line of
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ZXLD1370
Typical Characteristics – Boost mode – ILED = 350mA – RS = 150mꢀ – GIRATIO = 0.23
0.400
0.350
TA = 25°C
VAUX = VIN
0.300
0.250
0.200
0.150
0.100
0.050
3 LEDs
10
4 LEDs
13.5 17
6 LEDs
8 LEDs
10 LEDs
27.5 31
12 LEDs
14 LEDs
38 41.5
16 LEDs
0.000
6.5
20.5
24
34.5
45
48.5
Input Voltage (V)
Figure 7: ILED vs. Input Voltage & Number of LED
500
450
3 LEDs
4 LEDs
6 LEDs
8 LEDs
10 LEDs
12 LEDs
14 LEDs
16 LEDs
TA = 25°C
VAUX = VIN
400
350
300
250
200
150
100
50
Boosted voltage across
LEDs approaching VIN
6.5
10
13.5
20.5
24
Input Voltage (V)
Figure 8: Frequency vs. Input Voltage & Number of LED
27.5
31
34.5
38
41.5
45
48.5
17
100%
95%
6 LEDs
8 LEDs
10 LEDs
4 LEDs
12 LEDs
14 LEDs
16 LEDs
3 LEDs
90%
85%
80%
TA = 25°C
VAUX = VIN
75%
70%
65%
60%
20.5
6.5
10
13.5
17
24
27.5
31
34.5
38
41.5
45
48.5
Input Voltage (V)
Figure 9: Efficiency vs. Input Voltage & Number of LED
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ZXLD1370
Document number: DS32165 Rev. 2 - 2
A Product Line of
Diodes Incorporated
ZXLD1370
Typical Characteristics – Buck-Boost mode – RS=150mꢀ - ILED = 350mA - GIRATIO = 0.23
0.370
3 LEDs
4 LEDs
5 LEDs
6 LEDs
7 LEDs
8 LEDs
0.365
0.360
0.355
0.350
0.345
0.340
0.335
0.330
6.5
8
9.5
11
12.5
14
15.5
17
Input Voltage (V)
Figure 10: LED Current vs. Input Voltage & Number of LED
800
700
3 LEDs
4 LEDs
5 LEDs
6 LEDs
7 LEDs
8 LEDs
600
500
400
300
200
100
0
6.5
8
9.5
11
12.5
14
15.5
17
Input Voltage (V)
Figure 11: Switching Frequency vs. Input Voltage & Number of LED
100%
95%
90%
3 LEDs
4 LEDs
5 LEDs
6 LEDs
7 LEDs
8 LEDs
85%
80%
75%
70%
65%
60%
6.5
8
9.5
11
12.5
14
15.5
17
Input Voltage (V)
Figure 12: Efficiency vs. Input Voltage & Number of LED
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ZXLD1370
Document number: DS32165 Rev. 2 - 2
A Product Line of
Diodes Incorporated
ZXLD1370
Applications Information
The ZXLD1370 is a high accuracy hysteretic inductive buck/boost/buck-boost controller designed to be used with an
external NMOS switch 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 13
LED current control in buck mode is achieved by sensing
the coil current in the sense 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
external NMOS switch transistor M1 via the internal Gate
Driver. 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
GATE goes low, 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, GATE
goes high, the switch is turned on again and the cycle of
events repeats, resulting in continuous oscillation.
Figure 13: Buck configuration
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. 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 30%), the frequency may deviate from nominal in extreme conditions. Loop compensation is
achieved by a single external capacitor C2, connected between SHP and SGND.
Gate Voltage
~15V
0V
V
VIN
V
-225mV
VIN
ISM Voltage
Coil/LED current
225mV/Rs
0A
t
t
ON
OFF
Figure 14: Operating waveforms (Buck mode)
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ZXLD1370
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ZXLD1370
b) Boost and Buck-Boost modes
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
external NMOS switch transistor M1 via the internal Gate
Driver. 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 GATE goes low, 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, GATE goes high, 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 15: 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 minimises variation in
output current with changes in operating conditions. Loop compensation is achieved by a single external capacitor C2,
connected between SHP and SGND.
Gate Voltage
~15V
0V
V
VIN
VVIN -225mV
ISM Voltage
Coil current
225mV/Rs
0A
LED current
225mV/Rs
Average
LED current
0A
tOFF
t
ON
Figure 16 - Operating waveforms (Boost and Buck-boost modes)
Note: In Boost and Buck-boost modes, average ILED= average ICOIL x RGI1/(RGI1+RGI2
)
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.
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ZXLD1370
Document number: DS32165 Rev. 2 - 2
A Product Line of
Diodes Incorporated
ZXLD1370
Application Information
A basic ZXLD1370 application circuit is shown in Figure 13 and 15.
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, the inductor/frequency setting and the MOSFET selection.
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 giving the ratio of
average LED current (ILED) to average sense resistor/coil
VIN
ISM
current (IRS).
ILED
REF
VADJ
225mV
=
IRs =
RS VREF
ADJ
GI
If the ADJ and GI pins are connected to VREF directly, this
becomes:
225mV
ILED
=
IRs =
RS
SGND
Therefore:
Rs =
225mV
ILED
Figure 17: Buck configuration
In Boost and Buck-boost mode GI is connected to ADJ
RS
through a voltage divider.
VIN
ISM
With VADJ equal to VREF, the ratio defined by the resistor
divider at the GI pin determines the ratio of average LED
REF
current (ILED) to average sense resistor/coil current (IRS).
VGI
RGI1
ADJ
GI
ILED
=
IRs
=
IRs
VADJ
(RGI1 + RGI2)
RGI2
225mV VADJ
RS VREF
Where
IRs =
RGI1
SGND
When the ADJ pin is connected to VREF directly, this
becomes:
225mV
IRs
=
Figure 18: Boost and Buck-boost connection
RS
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Therefore:
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 ZXLD1370, 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
DMAX
=
VINMIN
Boost mode
VLEDS − V
INMIN
DMAX
=
VLEDS
Buck-boost mode
VLEDS
VLEDS + V
DMAX
=
IN MIN
Set the appropriate GI ratio according to the circuit duty and the max switch current admissible cycle limitations
VGI
RGI1
=
≤ 1−DMAX
VADJ
(RGI1 + RGI2)
- Set RGI1 as:
- Calculate RGI2as:
10kΩ ≤ RGI1 ≤ 200kΩ
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.
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:
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ILED
VGI
RGI1
=
=
≈0.23
IRS
VADJ
(RGI1 +RGI2)
Setting RGI1= 33kꢀ it results
VADJ
RGI2 = RGI1
(
−1) =110kΩ
VGI
This will result in:
RGI1
225mV
) ILED
Rs =
= 150mΩ
(RGI1 + RGI2
Table 1 shows typical resistor values used to determine GIRATIO with E24 series resistors
Table 1
GI ratio
0.2
RGI1
30kΩ
33kΩ
39kΩ
30kΩ
100kΩ
51kΩ
30kΩ
RG2
120kΩ
100kΩ
91kΩ
56kΩ
150kΩ
62kΩ
30kΩ
0.25
0.3
0.35
0.4
0.45
0.5
INDUCTOR/FREQUENCY SELECTION
Recommended inductor values for the ZXLD1370 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 ZXLD1370 switching frequency within a
predetermined range when used in different topologies.
Buck inductor selection:
ZXLD1370 Buck Mode 1.5A Minimum Recommended Inductor
Target Switching frequency - 400kHz
15
13
11
9
L=47uH
7
5
L=33uH
3
L=22uH
L=10uH
1
0
10
20
30
40
50
60
Supply Voltage (V)
Figure 19: 1.5A Buck mode inductor selection for target frequency of 400 kHz
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ZXLD1370 Buck Mode 1.5A Minimum Recommended Inductor
Target Switching frequency > 500kHz
15
13
11
9
L=47uH
7
5
L=33uH
L=22uH
3
L=10uH
1
0
10
20
30
Supply Voltage (V)
40
50
60
Figure 20: 1.5A Buck mode inductor selection for target frequency > 500kHz
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 21 and 22.
ZXLD1370 Buck Mode 750mA Minimum Recommended Inductor
Target Switching frequency 400kHz
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 21: 750mA Buck mode inductor selection for target frequency 400kHz
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ZXLD1370 Buck Mode 750mA Minimum Recommended Inductor
Target Switching frequency > 500kHz
15
13
11
9
L=100uH
7
5
L=68uH
L=47uH
3
L=33uH
1
0
10
20
30
40
50
60
Supply Voltage (V)
Figure 22: 750mA Buck mode inductor selection for target frequency > 500kHz
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 23) or higher than 500kHz (figure 24).
ZXLD1370 Buck-Boost Mode 350mA Minimum Recommended Inductor
Target Switching frequency - 400kHz
15
13
11
9
L=47uH
7
5
3
1
L=33uH
L=22uH
0
10
20
30
Supply Voltage (V)
40
50
60
Figure 23: 350mA Buck-Boost mode inductor selection for target frequency 400kHz
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ZXLD1370 Buck-Boost Mode 350mA Minimum Recommended Inductor
Target Switching frequency > 500kHz
15
13
11
9
L=47uH
7
5
L=33uH
3
L=22uH
1
0
10
20
30
40
50
60
Supply Voltage (V)
Figure 24: 350mA Buck-Boost mode inductor selection for target frequency > 500kHz
For example, in a Buck-bust 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 25) or higher than 500kHz (figure 26).
ZXLD1370 Boost Mode 350mA Minimum Recommended Inductor
Target Switching frequency - 400kHz
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 25: 350mA Boost mode inductor selection for target frequency 400kHz
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ZXLD1370 Boost Mode 350mA Minimum Recommended Inductor
Target Switching frequency > 500kHz
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 26: 350mA Buck-Boost mode inductor selection for target frequency > 500kHz
Suitable coils for use with the ZXLD1370 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
MOSFET Selection
The ZXLD130 requires an external NMOS FET as the main power switch with a voltage rating at least 15% higher than the
maximum transistor voltage to ensure safe operation during the ringing of the switch node. The current rating is
recommended to be at least 10% higher than the average transistor current. The power rating is then verified by calculating
the resistive and switching power losses.
P =Presistive +Pswitching
Resistive power losses
The resistive power losses are calculated using the RMS transistor current and the MOSFET on-resistance.
Calculate the current for the different topologies as follows:
Buck mode
IMOSFET−MAX = DMAX x ILED
Boost / Buck-boost mode
DMAX
IMOSFET−MAX
=
x ILED
1− DMAX
The approximate RMS current in the MOSFET will be:
Buck mode
IMOSFET−RMS =ILED
D
Boost / Buck-boost mode
D
IMOSFET −RMS
=
x ILED
1− D
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The resistive power dissipation of the MOSFET is:
P
=IMOSFET−RMS2 xRDS−ON
resistive
Switching power losses
Calculating the switching MOSFET's switching loss depends on many factors that influence both turn-on and turn-off. Using
a first order rough approximation, the switching power dissipation of the MOSFET is:
CRSS x V2 x fsw x ILOAD
IN
Pswitching
where
=
IGATE
C
RSS is the MOSFET's reverse-transfer capacitance (a data sheet parameter),
fSW is the switching frequency,
GATE is the MOSFET gate-driver's sink/source current at the MOSFET's turn-on threshold.
I
Matching the MOSFET with the controller is primarily based on the rise and fall time of the gate voltage. The best rise/fall
time in the application is based on many requirements, such as EMI (conducted and radiated), switching losses, lead/circuit
inductance, switching frequency, etc. How fast a MOSFET can be turned on and off is related to how fast the gate
capacitance of the MOSFET can be charged and discharged. The relationship between C (and the relative total gate
charge Qg), turn-on/turn-off time and the MOSFET driver current rating can be written as:
dV ⋅C Qg
dt =
=
I
I
where
dt = turn-on/turn-off time
dV = gate voltage
C = gate capacitance = Qg/V
I = drive current – constant current source (for the given voltage value)
Here the constant current source” I ” usually is approximated with the peak drive current at a given driver input voltage.
Example 1)
Using the DMN6068 MOSFET (VDS(MAX) = 60V, ID(MAX) = 8.5A):
Æ QG = 10.3nC at VGS = 10V
ZXLD1370 IPEAK = I GATE = 300mA
Qg
10.3nC
dt =
=
= 35ns
IPEAK 300mA
Assuming that cumulatively the rise time and fall time can account for a maximum of 10% of the period, the maximum
frequency allowed in this condition is:
tPERIOD = 20*dt
Æ
f = 1/ tPERIOD = 1.43MHz
This frequency is well above the max frequency the device can handle, therefore the DNM6068 can be used with the
ZXLD1370 in the whole spectrum of frequencies recommended for the device (from 300kHz to 1MHz).
Example 2)
Using the ZXMN6A09K (VDS(MAX) = 60V, ID(MAX) = 12.2A):
Æ QG = 29nC at VGS = 10V
ZXLD1370 IPEAK = 300mA
Qg
29nC
dt =
=
= 97ns
IPEAK 300mA
Assuming that cumulatively the rise time and fall time can account for a maximum of 10% of the period, the maximum
frequency allowed in this condition is:
t
PERIOD = 20*dt
Æ
f = 1/ tPERIOD = 515kHz
This frequency is within the recommended frequency range the device can handle, therefore the ZXMN6A09K is
recommended to be used with the ZXLD1370 for frequencies from 300kHz to 500kHz).
The recommended total gate charge for the MOSFET used in conjunction with the ZXLD1370 is less than 30nC.
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Junction temperature estimation
Finally, the ZXLD1370 junction temperature can be estimated using the following equations:
Total supply current of ZXLD1370:
I
QTOT ≈ IQ + f • QG
Where IQ = total quiescent current IQ-IN + IQ-AUX
Power consumed by ZXLD1370
PIC = VIN • (IQ + f • Qg)
Or in case of separate voltage supply, with VAUX < 15V
PIC = VIN • IQ-IN + Vaux • (IQ-AUX + f • Qg)
TJ =
TA + PIC • RTH(JA)
=
TA + PIC • (RTH(JC)+ RTH(CA))
Where the total quiescent current IQTOT consists of the static supply current (IQ) and the current required to charge and
discharge the gate of the power MOSFET. Moreover the part of thermal resistance between case and ambient depends on
the PCB characteristics.
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 transistor 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 Drain of the external MOSFET. If a silicon diode is used, care should be taken to ensure that the total voltage appearing
on the Drain of the external MOSFET, 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−PP
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
fsw is the switching frequency (From graphs and calculator)
r
LED 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:
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Buck
ILED−PP
12
ICOUTPUT−
=
RMS
Boost and Buck-boost
ICOUTPUT−RMS = ILED
DMAX
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.
INPUT CAPACITOR
The input capacitor can be calculated knowing the input voltage ripple ΔVIN-PP as follows:
Buck
Dx(1−D)xILED
fSW xΔVIN−PP
CIN =
Use D = 0.5 as worst case
Boost
ΔIL−PP
8x fSW xΔVIN−PP
CIN
Buck-boost
CIN
=
DxILED
=
Use D = DMAX as worst case
fSW xΔVIN−PP
The minimum RMS current for the output capacitor is calculated as follows:
Buck
ICIN−RMS = ILEDx Dx(1−D)
use D=0.5 as worst case
Boost
IL−PP
ICIN−
=
RMS
12
Buck-boost
D
ICIN−RMS = ILED
x
Use D=DMAX as worst case
(1−D)
PWM OUTPUT CURRENT CONTROL & DIMMING
The ZXLD1370 has a dedicated PWM dimming input that allows a wide dimming frequency range from 100Hz to 1kHz with
up to 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:
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Buck mode - L=33uH - Rs = 150mꢀ - PWM @ 1kHz
1500.00
1250.00
1000.00
750.00
500.00
250.00
0.00
10%
9%
8%
7%
6%
5%
4%
3%
2%
1%
0%
0
10
20
30
40
50
60
70
80
90
100
PWM
PWM @ 1kHz
Error
Figure 27: 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:
Buck mode - L=33uH - Rs = 150mꢀ - PWM @ 100Hz
1500.00
1250.00
1000.00
750.00
500.00
250.00
0.00
10%
9%
8%
7%
6%
5%
4%
3%
2%
1%
0%
0
10
20
30
40
50
60
70
80
90
100
PWM
PWM @ 100Hz
Error
Figure 28: LED current linearity and accuracy with PWM dimming at 100Hz
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 30: PWM dimming from MCU
Figure 29: PWM dimming from open collector switch
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2µs
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.
< 10ms
Gate
0V
The PWM signal can achieve very high LED current
resolution. In fact, dimming down from 100% to 0, a
minimum pulse width of 2µs can be achieved
resulting in very high accuracy. While the maximum
recommended pulse is for the PWM signal is10ms.
PWM
< 10 ms
0V
2µs
Figure 31:PWM dimming minimum and maximum pulse
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 32: Stand-by state from PWM signal
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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 = TH at Tthreshold
Figure 33: Thermal feedback network
For example,
1) Temperature threshold Tthreshold = 70˚C
2) TH1 = 10kꢀ at 25˚C and beta= 3500 Æ TH = 3.3kꢀ @ 70˚C
3) Rth = TH at Tthreshold = 3.3kꢀ
Over-Temperature Shutdown
The ZXLD1370 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.
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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 off, but switches low 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 9)
Monitored
parameters
Warning/Fault condition
FLAG
Nominal STATUS voltage
Normal operation
H
L
L
4.5
4.5
3.6
1
2
V
AUX<5.6V
Supply under-voltage
VIN<5.6V
Output current out of regulation
V
SHP outside normal
voltage range
2
2
L
L
3.6
3.6
(Note 10)
Driver stalled with switch ‘on’, or
t
ON, or tOFF>100µs
‘off’ (Note 11)
Device temperature above
maximum recommended
operating value
3
4
L
L
1.8
0.9
TJ>125°C
Sense resistor current IRS above
specified maximum
VSENSE>0.32V
Notes:
9. Severity 1 denotes lowest severity.
10. 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.
11. This warning will be indicated if the gate pin stays at the same level for greater than 100us (e.g. the output transistor cannot pass enough current
to reach the upper switching threshold).
VREF
0V
4.5V
Normal
Operations
VAUX
UVLO
3.6V
2.7V
1.8V
- VIN UVLO
- STALL
- OUT of REG
Over
Temperature
0.9V
Over
Current
0A
3
4
2
1
0
SEVERITY
Fig 34: 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
.
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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.
V
R E F
0 V
O
r e
u
u
t
o
f
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.
g
la tio
n
O
v e r
C
u r r e n t
2 2 5 m
V /R 1
0 A
1 0 0 u s
Fig 35: Diagnostic during Start-up
Boosting VAUX supply voltage in Boost and Buck-Boost mode
When the input voltage is lower than 8V, the gate voltage will also be lower 8V. This means that depending on the
characteristics of the external MOSFET, the gate voltage may not be enough to fully enhance the power MOSFET. This
boosting technique is particularly important when the output MOSFET is operating at full current, since the boost circuit
allows the gate voltage to be higher than 12V. This guarantees that the MOSFET is fully enhanced reducing both the power
dissipation and the risk of thermal runaway of the MOSFET itself. An extra diode D2 and decoupling capacitor C3 can be
used, as shown below in figure 36, to generate a boosted voltage at VAUX when the input supply voltage at VIN is below 8V.
This enables the device to operate with full output current when VIN is at the minimum value of 6V. In the case of a low
voltage threshold MOSFET, the bootstrap circuit is generally not required.
Fig 36: Bootstrap circuit for Boost and Buck-boost low voltage operations
The resistor R2 can be used to limit the current in the bootstrap circuit in order to reduce the impact of the circuit itself on the
LED accuracy. The impact on the LED current is usually a decrease of maximum 5% compared to the nominal current
value set by the sense resistor.
The Zener diode D3 is used to limit the voltage on the VAUX pin to less than 60V.
Due to the increased number of components and the loss of current accuracy, the bootstrap circuit is recommended only
when the system has to operate continuously in conditions of low input voltage (between 6 and 8V) and high load current.
Other circumstances such as low input voltage at low load current, or transient low input voltage at high current should be
evaluated keeping account of the external MOSFET power dissipation.
Over-voltage Protection
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The ZXLD1370 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 no internal open-circuit protection mechanism for the external MOSFET. In this case an Over-Voltage-Protection (OVP)
network should be provided externally to the MOSFET to avoid damage due to open circuit conditions. This is shown in
Figure 33 below, highlighted in the dotted blue box.
Fig 37: OVP circuit
The zener voltage is determined according to: Vz = VLEDMAX +10%
Take care of the max voltage drop on the Q2 MOSFET gate.
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 ZXLD1370 both in Buck and Buck-Boost/Boost configurations.
SHP pin
Inductor, Switch
and
Freewheeling
diode
VIN / VAUX
decoupling
Figure 38: 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 drain of Q1 should be
placed as close together as possible.
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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).
VIN and VAUX pins can be short-circuited when the device is used in buck mode, or can be driven from a separate
supply.
APPLICATION EXAMPLES
Example 1:
2.8A Buck LED driver
In this application example, the ZXLD1370 is connected as a buck LED driver. The schematic and parts list are shown
below. The LED driver is able to deliver 2.8A of LED current with an input voltage range of 8V to 24V. In order to achieve
high efficiency at high LED current, a Super Barrier Rectifier (SBR) with a low forward voltage is used as the free wheeling
rectifier.
This LED driver is suitable for applications which require high LED current such as LED projector, automatic LED lighting
etc.
Figure 39: Application circuit: 2.8A Buck LED driver
Table 3: Bill of Material
Ref No.
Value
Part No.
ZXLD1370
Manufacturer
Diodes Inc
U1
Q1
D1
L1
60V LED driver
60V MOSFET
45V 10A SBR
33uH 4.2A
ZXMN6A09K
SBR10U45SP5
744770933
Diodes Inc
Diodes Inc
Wurth Electronik
Generic
C1
C2
100pF 50V
1uF 50V X7R
4.7uF 50V X7R
300mꢀ 1%
400mꢀ 1%
0ꢀ
SMD 0805/0603
SMD1206
Generic
Generic
Generic
Generic
Generic
C3 C4 C5
R1 R2 R3
R4
SMD1210
SMD1206
SMD1206
R5
SMD 0805/0603
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Typical Performance
Efficiency vs Input Voltage
LED Current vs Input Voltage
3000
2500
2000
1500
1000
500
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
1 LED
2 LED
0
10
12
14
16
18
20
22
24
10
12
14
16
18
20
22
24
Input Voltage (V)
Input Voltage (V)
Figure 41: Line regulation
Figure 40: Efficiency
Example 2:
400mA Boost LED driver
In this application example, the ZXLD1370 is connected as a boost LED driver. The schematic and parts list are shown
below. The LED driver is able to deliver 400mA of LED current into 12 high-brightness LEDs with an input voltage range of
16V to 32V.
The overall high efficiency of 92%+ makes it ideal for applications such as solar LED street lighting and general LED
illuminations.
Figure 42: Application circuit - 400mA Boost LED driver
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Table 4: Bill of Material
Ref No.
U1
Value
Part No.
Manufacturer
60V LED driver
60V MOSFET
60V MOSFET
100V 3A Schottky
47V 410mW Zener
68uH 2.1A
ZXLD1370
Diodes Inc
Diodes Inc
Diodes Inc
Diodes Inc
Diodes Inc
Wurth Electronik
Q1
ZXMN6A25G
2N7002A
Q2
D1
PDS3100-13
BZT52C47
Z1
L1
744771168
SMD 0805/0603
SMD1210
C1
100pF 50V
Generic
Generic
C3 C9
C2
4.7uF 50V X7R
1uF 50V X7R
560mꢀ 1%
33Kꢀ 1%
Generic
Generic
Generic
Generic
Generic
SMD1206
R1 R2
R9 R10
R12
R15
SMD1206
SMD 0805/0603
SMD 0805/0603
SMD 0805/0603
0ꢀ
2.7Kꢀ
Typical Performance
Efficiency vs Input Voltage
LED Current vs Input Voltage
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
450
400
350
300
250
200
150
100
50
0
16
18
20
22
24
26
28
30
32
16
18
20
22
24
26
28
30
32
Input Voltage
Input Voltage
Figure 43: Efficiency
Figure 44: Line regulation
Example 3:
700mA Buck-Boost LED driver
In this application example, the ZXLD1370 is connected as a buck-boost LED driver. The schematic and parts list are
shown below. The LED driver is able to deliver 700mA of LED current into 4 high-brightness LEDs with an input voltage
range of 7V to 20V.
Since the Buck-boost LED driver handles an input voltage range from below and above the total LED voltage, the versatile
input voltage range make it ideal for automotive lighting applications.
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Figure 45: Application circuit - 700mA Buck-Boost LED driver
Table 5: Bill of Material
Ref No.
U1
Value
Part No.
Manufacturer
60V LED driver
60V MOSFET
60V MOSFET
100V 5A Schottky
47V 410mW Zener
22uH 2.1A
ZXLD1370
Diodes Inc
Diodes Inc
Diodes Inc
Diodes Inc
Diodes Inc
Q1
ZXMN6A25G
2N7002A
Q2
D1
PDS5100-13
BZT52C47
Z1
L1
744771122
Wurth Electronik
Generic
C1
100pF 50V
SMD 0805/0603
SMD1210
Generic
Generic
Generic
Generic
Generic
Generic
Generic
C3 C9
C2
4.7uF 50V X7R
1uF 50V X7R
300mꢀ 1%
33Kꢀ 1%
SMD1206
R1 R2 R3
R9
SMD1206
SMD 0805/0603
SMD 0805/0603
SMD 0805/0603
SMD 0805/0603
R10
R12
R15
15Kꢀ 1%
0ꢀ
2.7Kꢀ
Typical Performance
Efficiency vs Input Voltage
LED Current vs Input Voltage
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
800
700
600
500
400
300
200
100
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 46: Efficiency
Figure 47: Line regulation
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Ordering Information
Part
Marking
Reel
Quantity
Reel
Size
Device
Packaging
Status
Tape Width
16mm
ZXLD1370EST16TC TSSOP-16 EP
Active
ZXLD1370
2500
13”
Package Thermal Data
Thermal Resistance
Package
TSSOP-16 EP
Unit
23
°C/W
Junction-to-Case, θJC
Package Thermal Data
TSSOP-16 EP
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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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