AL9902FDF-13 [DIODES]
LINEAR AND PWM DIMMING HIGH VOLTAGE LED DRIVER;
| 型号： | AL9902FDF-13 |
| 厂家： | 
DIODES INCORPORATED |
| 描述： | LINEAR AND PWM DIMMING HIGH VOLTAGE LED DRIVER 驱动 高压 |
| 文件： | 总18页 (文件大小：729K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
AL9902
LINEAR AND PWM DIMMING HIGH VOLTAGE LED DRIVER
Description
Pin Assignments
The AL9902 high-voltage PWM LED driver provides an efficient
solution for offline high-brightness LED lamps from rectified line
voltages ranging from 85VAC up to 277VAC. The AL9902 has an
internal MOSFET that allows switching frequencies up to 300kHz,
with the switching frequency determined by an external single
resistor. The AL9902 topology creates a constant current through the
LEDs providing constant light output. The output current is
programmed by one external resistor.
SW NC
SO
GND
9
CS
8
VIN
7
12 11 10
EP1
EP2
5
1
NC
2
3
4
6
The LED brightness can be varied by both linear and PWM dimming
using the AL9902’s LD and PWM pins respectively. The PWM input
operates with duty ratio of 0-100% and frequency of up to several
kHz.
NC PWM VDD
LD Rosc
U-DFN6040-12
NC
SO
NC
NC GND CS
11 10
NC VIN
The AL9902 is available in the thermally enhanced U-DFN6040-12
and SO-16 packages.
16 15 14
13 12
9
Features
>90% Efficiency
Universal Rectified 85 to 277VAC Input Range
Internal MOSFET Up to 650V, 2A
1
NC
2
NC
3
5
PWM
6
7
4
8
High Switching Frequency Up to 300kHz
Internal Voltage Regulator Removes Start-Up Resistor
7.5V Regulated Output
SW NC
VDD LD Rosc
SO-16
Tighter Current Sense Tolerance Better Than ±5%
LED Brightness Control with Linear and PWM Dimming
Internal Over-Temperature Protection (OTP)
U-DFN6040-12 and SO-16 Packages
Applications
LED Offline Lamps
High Voltage DC-DC LED Driver
Totally Lead-Free & Fully RoHS compliant (Notes 1 & 2)
Halogen and Antimony Free. “Green” Device (Note 3)
Signage and Decorative LED Lighting
Back Lighting of Flat Panel Displays
General Purpose Constant Current Source
Notes:
1. No purposely added lead. Fully EU Directive 2002/95/EC (RoHS) & 2011/65/EU (RoHS 2) compliant.
2. See http://www.diodes.com/quality/lead_free.html for more information about Diodes Incorporated’s definitions of Halogen- and Antimony-free, "Green"
and Lead-free.
3. Halogen- and Antimony-free "Green” products are defined as those which contain <900ppm bromine, <900ppm chlorine (<1500ppm total Br + Cl) and
<1000ppm antimony compounds.
Typical Applications Circuit
1
AC+
2
3
HD06
Z1
602V
C1
C3
AC-
4
D1
VIN
Rosc
SW
VDD
LD
AL9902
L1
SO
CS
PWM
Rosc
GND
C2
Rsense
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© Diodes Incorporated
AL9902
Document number: DS37878 Rev. 1 - 2
AL9902
Pin Descriptions
Pin Name U-DFN5040-10
SO-16
Functions
NC
NC
1
2
3
14
No connection
1, 2, 4, 10,16 No connection
PWM
5
6
7
Low Frequency PWM Dimming pin, also Enable input. Internal 200kΩ pull-down to GND
Internally regulated supply voltage.
7.5V nominal.
4
VDD
Can supply up to 1 mA for external circuitry. A sufficient storage capacitor is used to provide
storage when the rectified AC input is near the zero crossing.
Linear Dimming input. Changes the current limit threshold at current sense comparator and
changes the average LED current.
LD
5
6
Oscillator control.
A resistor connected between this pin and ground puts the AL9902 into fixed frequency mode and
sets the switching frequency.
ROSC
8
9
Input voltage
7
8
VIN
CS
11
12
13
15
3
Senses LED string and internal MOSFET switch current
Device ground
GND
NC
9
11
10
12
EP1
No connection
SO
Source of the internal MOSFET Switch
Drain of the internal MOSFET switch.
Exposed Pad 1(bottom). Drain connection of internal power MOSFET.
SW
EP1
NA
NA
Exposed Pad 2 (bottom). Substrate connection of control IC. Connect to GND directly underneath
the package and large PCB area to minimize junction to ambient thermal impedance.
EP2
EP2
Functional Block Diagram & Typical Application
VIN
D1
VIN
Rosc
SW
LDO
7.5V
OSC
VDD
VDD
250mV
S
Rosc
R
LD
SO
CS
OTP
Rsense
PWM
200K
AL9902
GND
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© Diodes Incorporated
AL9902
Document number: DS37878 Rev. 1 - 2
AL9902
Absolute Maximum Ratings (Note 4) (@TA = +25°C, unless otherwise specified.)
Symbol
VIN(MAX)
VCS
Parameter
Maximum Input Voltage, VIN, to GND
Ratings
-0.5 to +520
-0.3 to +0.45
-0.3 to (VDD +0.3)
-0.3 to (VDD +0.3)
-0.5 to +650
-0.5 to (VDD +0.3)
-0.5 to (VDD +0.3)
8.1
Unit
V
Maximum CS Input Pin voltage Relative to GND
Maximum LD Input Pin Voltage Relative to GND
Maximum PWM input Pin Voltage Relative to GND
Maximum MOSFET Drain Pin Voltage Relative to GND
Maximum MOSFET Source Pin Voltage Relative to GND
Maximum MOSFET GATE pin Voltage Relative to GND
Maximum VDD Pin Voltage Relative to GND
Continuous Power Dissipation (TA = +25C)
V
V
VLD
V
VPWM
VSW
V
V
VSO
V
VGate
VDD(MAX)
-
V
-
-
-
1,000
mW
°C
°C
V
U-DFN6040-12 (derate 10mW/C above +25C)
Junction Temperature Range
+150
TJ
Storage Temperature Range
-65 to +150
2,000
TST
ESD HBM
Human Body Model ESD Protection (Note 5)
Notes:
4. Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional
operation of the device at these or any other conditions above those listed in the operational sections of this specification is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
All voltages are with respect to Ground. Currents are positive into, negative out of the specified terminal.
5. 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.
Maximum Ratings of Internal MOSFET (@TA = +25°C, unless otherwise specified.)
Characteristic
Symbol
VDSS
Value
650
Units
Drain-Source Voltage
Gate-Source Voltage
V
V
±30
VGSS
TC = +25°C
Steady
State
1.6
1
A
Continuous Drain Current (Note 5) VGS = 10V
Pulsed Drain Current (Note 6)
ID
TC = +100°C
3
0.8
22
5
A
A
IDM
IAR
Avalanche Current (Note 7) VDD = 100V, VGS = 10V, L = 60mH
mJ
V/ns
Repetitive Avalanche Energy (Note 7) VDD = 100V, VGS = 10V, L = 60mH
Peak Diode Recovery
EAR
dv/dt
Recommended Operating Conditions (@TA = +25°C, unless otherwise specified.)
Symbol
VINDC
TA
Parameter
Min
Max
500
+105
0.4
Unit
V
Input DC Supply Voltage Range
Ambient Temperature Range
Switch Pin Output Current
20
-40
-
°C
A
ISW
-
8.1
V
VDD
Maximum Recommended Voltage Applied to VDD Pin (Note 6)
Pin PWM input Low Voltage
0
1
VPWM(lo)
VPWM(hi)
V
Pin PWM input High Voltage
2.4
VDD
Note:
6. when using the AL9902 in isolated LED lamps an auxiliary winding might be used.
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AL9902
Document number: DS37878 Rev. 1 - 2
AL9902
Electrical Characteristics (@TA = +25°C, unless otherwise specified.)
Specifications apply to AL9902 unless otherwise specified
Symbol
Parameter
Conditions
Min
Typ
Max
Unit
mA
Pin PWM to GND,
VIN = 20V
Shut-Down Mode Supply Current
-
0.5
1
Ishdn
VIN =VIN(MIN)~ 500V, (Note 8) lDD(ext) = 0,
Gate pin open
Internally Regulated Voltage
7.2
7.5
8.1
V
VDD
-
-
6.7
500
200
4
1.0
mA
V
IDD(ext)
UVLO
∆UVLO
RPWM
VT
VDD Current Available for External Circuitry VIN = 20 to 100V (Note 7)
6.4
7.2
VDD Under Voltage Lockout Threshold
VDD Under Voltage Lockout Hysteresis
PWM Pull-Down Resistance
VDD rising
-
-
mV
kΩ
V
VDD falling
150
250
VPWM= 5V
MOSFET Threshold Voltage
-
-
ISW = 0.5A
MOSFET Diodes Forward Voltage
Current Sense Threshold Voltage
-
0.85
250
25
100
-
-
V
VFD
ID = 0.5A
237.5
262.5
mV
VCS(hi)
TA = -40°C to +125°C
ROSC = 1MΩ
20
80
-
30
Oscillator Frequency
kHz
fOSC
120
ROSC = 226kΩ
Maximum Oscillator PWM Duty Cycle
Linear Dimming Pin Voltage Range
Thermal Shut-Down (Junction)
100
%
DMAXhf
VLD
fPWMhf = 25kHz, at GATE, CS to GND.
TA = <125°C, VIN = 20V
Use DFN JA when ISW=0.4A, VDS=1V
-
0
-
-
250
mV
141
25
65
5
-
-
-
-
-
-
TSD
°C
Thermal Shut-Down Hysteresis
-
TSDH
JA
Thermal Resistance Junction-to-Ambient
Thermal Resistance Junction-to-Case
Thermal Resistance Junction-to-Ambient
Thermal Resistance Junction-to-Case
-
C/W
C/W
C/W
C/W
U-DFN6040-12 (Note 8)
SO-16
-
JC
-
100
15
JA
-
JC
Notes:
7. Also limited by package power dissipation limit, whichever is lower.
8. Device mounted on FR-4 PCB (25mm x 25mm 1oz copper, minimum recommended pad layout on top. For better thermal performance, larger
copper pad for heat-sink is needed.
Internal MOSFET Characteristic
OFF CHARACTERISTICS (Note 9)
Drain-Source Breakdown Voltage
Zero Gate Voltage Drain Current
Gate-Source Leakage
Symbol
Min
Typ
Max
Unit
Test Condition
650
—
—
—
—
—
1
V
BVDSS
IDSS
VGS = 0V, ID = 250μA
VDS = 650V, VGS = 0V
VGS = ±30V, VDS = 0V
µA
nA
—
±100
IGSS
ON CHARACTERISTICS (Note 9)
Gate Threshold Voltage
3
—
4
5
5
1
V
Ω
V
VGS(th)
RDS (ON)
VSD
VDS = VGS, ID = 250μA
VGS = 10V, ID = 1A
VGS = 0V, IS = 1A
Static Drain-Source On-Resistance
Diode Forward Voltage
—
—
0.7
DYNAMIC CHARACTERISTICS (Note 10)
Input Capacitance
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
pF
pF
pF
Ω
Ciss
Coss
Crss
Rg
479
29
VDS = 25V, VGS = 0V,
f = 1MHz
Output Capacitance
Reverse Transfer Capacitance
1.9
2
Gate Resistance
VDS = 0V, VGS = 0V, f = 1MHz
14
Total Gate Charge
nC
nC
nC
ns
ns
ns
ns
ns
nC
Qg
VDS = 520V, VGS = 10V,
ID = 2A
2.5
7.3
17
Gate-Source Charge
Gate-Drain Charge
Qgs
Qgd
tD(on)
tr
Turn-On Delay Time
33
Turn-On Rise Time
VDS = 325V, VGS = 10V,
31
RG = 25Ω, ID = 2.5A
Turn-Off Delay Time
tD(off)
tf
25
Turn-Off Fall Time
174
884
Body Diode Reverse Recovery Time
Body Diode Reverse Recovery Charge
trr
VDS = 100V, IF = 2A,
di/dt = 100A/μs
Qrr
Notes: 9. Short duration pulse test used to minimize self-heating effect.
10. Guaranteed by design. Not subject to production testing.
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AL9902
Document number: DS37878 Rev. 1 - 2
AL9902
Typical Characteristics
460
440
3.0
2.5
2.0
1.5
V
= 400V
IN
420
400
380
360
340
320
V
= 15V
IN
1.0
0.5
0.0
-0.5
-1.0
-1.5
300
280
-40
-15
10
35
60
85
-40
-15
10
35
60
85
AMBIENT TEMPERATURE (°C)
AMBIENT TEMPERATURE (°C)
Input Current vs. Ambient Temperature
Change in Current Sense Threshold vs. Ambient Temperature
1.5
450
400
I
= 180mA
LED(NOM)
1.0
0.5
350
R
= 226k
OSC
0.0
-0.5
-1.0
300
250
R
= 1M
OSC
200
150
-1.5
-2.0
85 105 125 145 165 185 205 225 245 265
INPUT VOLTAGE (VRMS
-40
-15
10
35
60
85
)
AMBIENT TEMPERATURE (°C)
180mA LED Driver Short Circuit Output Current vs. Input Voltage
Change in Oscillation Frequency vs. Ambient Temperature
IOUT vs. VLD Dimming Control
IOUT vs. PWM Dimming Control at 1KHz
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AL9902
Document number: DS37878 Rev. 1 - 2
AL9902
Typical Characteristics (continued)
180mA LED Driver Output Current vs. Input Voltage
180mA LED Driver Efficiency vs. Input Voltage
180mA LED Driver Power Factor vs. Input Voltage
180mA LED Driver Input Power Dissipation vs. Input Voltage
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AL9902
Document number: DS37878 Rev. 1 - 2
AL9902
Typical Characteristics (cont.)
2.0
10
1
V
= 20V
GS
V
= 20V
DS
V
= 10V
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
GS
V
= 6.0V
GS
V
= 8.0V
GS
V
= 5.5V
0.1
GS
T
= 150°C
A
T
= 25°C
A
T
= 125°C
= 85°C
A
0.01
0.001
T
A
T
= -55°C
A
V
= 5.0V
GS
0
1
2
3
4
5
6
7
8
0
1
2
3
4
5
6
7
8
9
10
VGS, GATE-SOURCE VOLTAGE (V)
VDS, DRAIN-SOURCE VOLTAGE (V)
Typical Transfer Characteristics
Typical Output Characteristics
5
20
4.8
4.6
4.4
4.2
4
18
16
14
12
10
8
I
= 1.0A
D
V
= 10V
GS
3.8
3.6
3.4
3.2
3
6
4
2
0
4
6
8
10
12
14
16
18
20
0
0.2 0.4 0.6 0.8
1
1.2 1.4 1.6 1.8
2
ID, DRAIN-SOURCE CURRENT (A)
VGS, GATE-SOURCE VOLTAGE (V)
Typical On-Resistance vs. Drain Current and Gate Voltage
Typical Transfer Characteristics
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AL9902
Document number: DS37878 Rev. 1 - 2
AL9902
Typical Characteristics (cont.) Internal MOSFET
15
3
2.5
2
V
= 10V
GS
V
= 20V
= 2A
GS
I
D
12
9
T
= 150°C
A
T
= 125°C
A
V
= 10V
GS
T
T
= 85°C
I
= 1A
D
A
1.5
1
6
= 25°C
A
3
0.5
T
= -55°C
A
0
0
0
0.2 0.4 0.6 0.8
1
1.2 1.4 1.6 1.8
2
-50 -25
0
25
50
75 100 125 150
ID, DRAIN CURRENT (A)
TJ, JUNCTION TEMPERATURE (C)
On-Resistance Variation with Temperature
Typical On-Resistance vs. Drain Current and Temperature
15
12
5
4.5
4
I
= 1mA
D
I
= 250µA
V
= 20V
= 2A
D
GS
I
D
9
3.5
3
V
= 10V
= 1A
GS
I
D
6
3
0
2.5
2
-50 -25
0
25
50
75 100 125 150
-50 -25
0
25
50
75 100 125 150
TJ, JUNCTION TEMPERATURE (C)
TJ, JUNCTION TEMPERATURE (C)
On-Resistance Variation with Temperature
Gate Threshold Variation vs. Ambient Temperature
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AL9902
Document number: DS37878 Rev. 1 - 2
AL9902
Typical Characteristics (cont.) Internal MOSFET
2
1000
100
C
iss
1.8
1.6
1.4
T
= 150°C
= 125°C
A
1.2
1
T
= 25°C
A
C
oss
T
A
0.8
0.6
0.4
0.2
0
T
= -55°C
A
10
T
= 85°C
A
C
rss
f = 1MHz
1
0
0.3
0.6
0.9
1.2
1.5
0
5
10
15
20
25
30
35
40
VSD, SOURCE-DRAIN VOLTAGE (V)
Diode Forward Voltage vs. Current
VDS, DRAIN-SOURCE VOLTAGE (V)
Typical Junction Capacitance
10
8
10
1
R
DS(on)
Limited
6
DC
V
I
= 520V
P
= 10s
DS
= 2A
W
0.1
0.01
D
P
= 1s
W
P
4
= 100ms
W
P
= 10ms
W
P
= 1ms
W
T
T
= 150°C
J(max)
= 25°C
2
P
= 100µs
A
W
V
= 10V
GS
Single Pulse
DUT on 1 * MRP Board
0.001
0
1
10
100
1000
0
2
4
6
8
10
12
14
16
V, DRAIN-SOURCE VOLTAGE (V)
Qg, TOTAL GATE CHARGE (nC)
SOA, Safe Operation Area
Gate Charge
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AL9902
Document number: DS37878 Rev. 1 - 2
AL9902
Applications Information
DC-DC and Offline LED Driver
The AL9902 is a cost-effective offline buck LED driver-converter specifically designed for driving LED strings. It is suitable for being used with
either rectified AC line or any DC voltage between 5-500V. See Figure 1 for typical circuit.
1
AC+
2
3
HD06
Z1
602V
C1
C3
AC-
4
D1
VIN
Rosc
SW
VDD
LD
L1
SO
CS
PWM
Rosc
GND
C2
Rsense
Figure 1 Typical Application Circuit (without PFC)
Buck Design Equations:
VLEDs
D
VIN
D
tON
fosc
(VIN VLEDs) tON
0.3ILED
L
0.25
ILED (0.5(ILED 0.3))
RSENSE
Where ILED x 0.3 = IRIPPLE
Design Example
For an AC line voltage of 120V, the nominal rectified input voltage VIN = 120V x 1.41 = 169V. From this and the LED chain voltage the duty cycle
can be determined:
D = VLEDs /VIN = 30/169 = 0.177
From the switching frequency, for example fOSC = 50 kHz, the required on-time of the internal MOSFET can be calculated:
tON = D/fOSC = 3.5 µs
The value of the inductor is determined as follows:
L = (VIN - VLEDs) * tON / (0.3 * ILED) = 4.6mH
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AL9902
Document number: DS37878 Rev. 1 - 2
AL9902
Applications Information (continued)
Input Bulk Capacitor
For offline lamps, an input bulk capacitor is required to ensure that the rectified AC voltage is held above twice the LED string voltage throughout
the AC line cycle. The value can be calculated from:
P (1 Dch
)
in
CIN
2 VLine_min 2fL VDC _max
Where
Dch : Capacity charge work period, generally about 0.2~0.25
fL : Input frequency for full range (85~265VRMS
Should be set 10~15% of 2VLine_ min
)
VDC_max
If the capacitor has a 15% voltage ripple then a simplified formula for the minimum value of the bulk input capacitor approximates to:
ILED VLEDs 0.06
CMIN
=
2
V
IN
Power Factor Correction
If power factor improvement is required then for the input power less than 25W, a simple method for improving the power factor can be
implemented by potential dividing down the rectified mains voltage (resistors R1 and R2 in Figure 2) and feeding it into the LD pin. The current
drawn from the supply voltage will follow an approximate half sine wave. A filter across the LEDs reduces the potential for flicker. This circuit also
significantly reduces the size of input capacitors.
L1
1
AC+
AC-
LED+
LED-
2
HD06
Z1
602V
R2
C4
C1
C2
4
D4
VIN
Rosc
SW
LD
VDD
PWM
AL9902
L2
R1
SO
CS
Rosc
GND
C3
Rsense
Figure 2 Typical Application Circuit with Simple PFC
Passive power factor correction using 3 high voltage diodes and 2 identical capacitors can be implemented. For further design information please
see AN75 from the Diodes website.
DC-DC Buck LED Driver
The design procedure for an AC input buck LED driver outlined in the previous chapters equally applies to DC input LED drivers.
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AL9902
Document number: DS37878 Rev. 1 - 2
AL9902
Applications Information (cont.)
DC-DC Boost LED Driver
Due to the topology of the AL9902 LED driver-converter, it is capable of being used in boost configurations as shown in Figure 3 – at reduced
accuracy. The accuracy can be improved by measuring the LED current with an op amp and use the op amp’s output to drive the LD pin.
A Boost LED driver is used when the forward voltage drop of the LED string is higher than the input supply voltage. For example, the Boost
topology can be appropriate when input voltage is supplied by a 48V power supply and the LED string consists of twenty HB LEDs, as the case
may be for a street light.
L1
VIN
Rosc
SW
VDD
VIN
PWM AL9902
D1
SO
CS
C1
LD
Rosc
GND
C3
C2
Rsense
Figure 3 Boost LED driver
In a Boost converter, when the internal MOSFET is ON, the energy is stored in the inductor which is then delivered to the output when the internal
MOSFET switches OFF. If the energy stored in the inductor is not fully depleted by the next switching cycle (continuous conduction mode) the DC
conversion between input and output voltage is given by:
V
VOUT V
IN
IN
VOUT
,
D
1D
VOUT
From the switching frequency, fOSC, the on-time of the MOSFET can be calculated:
D
tON
fOSC
From this the required inductor value can be determined by:
V
IN tON
L
0.3ILED
The Boost topology LED driver requires an output capacitor to deliver current to the LED string during the time that the internal MOSFET is on.
In boost LED driver topologies, if the LEDs should become open circuit damage may occur to the power switch and so some form of detection
should be present to provide overvoltage detection/protection.
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AL9902
Document number: DS37878 Rev. 1 - 2
AL9902
Applications Information (cont.)
General Application
The AL9902 is capable of operating in isolated or non-isolated topologies. It can also be made to operate in continuous as well as discontinuous
conduction mode.
VIN
D1
VIN
Rosc
SW
LDO
7.5V
OSC
VDD
VDD
250mV
S
Rosc
R
LD
SO
CS
OTP
Rsense
PWM
200K
AL9902
GND
Figure 4 Typical Application Circuit
The AL9902 contains a high-voltage LDO (see figure 4), the output of the LDO provides a power rail to the internal circuitry including the gate
driver. A UVLO on the output of the LDO prevents incorrect operation at low input voltage to the VIN pin.
In a non-isolated Buck LED driver when the gate pin goes high, the internal power MOSFET (Q1) is turned on causing current to flow through the
LEDs, inductor (L1) and current sense resistor (RSENSE). When the voltage across RSENSE exceeds the current sense pin threshold, the internal
MOSFET Q1 is turned off. The energy stored in the inductor causes the current to continue to flow through the LEDs via diode D1.
The AL9902’s LDO provides all power to the rest of the IC including gate drive and this removes the need for large high power start-up resistors.
This means that to during normal operation the AL9902 requires around 0.5mA from the high voltage power rail. The LDO can also be used to
supply up to 1mA to external circuits.
The AL9902 operates and regulates by limiting the peak current of the internal MOSFET; the peak current sense threshold is nominally set at
250mV. The AL9902 is capable of operating in a fixed frequency (PWM) mode and also variable frequency (fixed off-time) mode to regulate the
LED current.
The same basic operation is true for isolated topologies; however in these the energy stored in the transformer delivers energy to LEDs during the
off-cycle of the internal MOSFET.
The on-resistance of the AL9902’s internal power MOSFET means that it can drive up to 2A.
Design Parameters
Setting the LED Current
In the non-isolated buck converter topology, figure 4, the average LED current is not the peak current divided by 2 - however, there is a certain
error due to the difference between the peak and the average current in the inductor. The following equation accounts for this error:
250mV
RSENSE
.
ILED (0.5 *IRIPPLE))
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© Diodes Incorporated
AL9902
Document number: DS37878 Rev. 1 - 2
AL9902
Applications Information (cont.)
Setting Operating Frequency
The AL9902 is capable of operating between 25 and 450kHz switching frequency range. The switching frequency is programmed by connecting
an external resistor between ROSC pin and ground. The corresponding oscillator period is:
Rosc 22
tOSC
=
µs
with ROSC in kΩ
25
The switching frequency is the reciprocal of the oscillator period. Typical values for ROSC vary from 75kΩ to 1MΩ.
VLEDs
In buck mode the duty cycle, D, is
; so when driving small numbers of LEDs from high-input voltages, the duty cycle will be reduced and
VIN
care should be taken to ensure that tON > tBLANK. The simplest way to do this is to reduce/limit the switching frequency by increasing the ROSC
value. Reducing the switching frequency will also improve the efficiency.
When operating in buck mode, the designer must keep in mind that the input voltage must be maintained higher than two times the forward
voltage drop across the LEDs. This limitation is related to the output current instability that may develop when the AL9902 operates at a duty cycle
greater than 0.5. This instability reveals itself as an oscillation of the output current at a sub-harmonic (SBO) of the switching frequency.
Inductor Selection
The non-isolated buck circuit, Figure 4, is usually selected and has two operation modes: continuous and discontinuous conduction modes. A
buck power stage can be designed to operate in continuous mode for load current above a certain level usually 15% to 30% of full load. Usually
the input voltage range, the output voltage and load current are defined by the power stage specification. This leaves the inductor value as the
only design parameter to maintain continuous conduction mode. The minimum value of inductor to maintain continuous conduction mode can be
determined by the following example.
The required inductor value is determined from the desired peak-to-peak LED ripple current in the inductor; typically around 30% of the nominal
LED current.
V
VLEDs
D
IN
L =
, where D is duty cycle
0.3ILED
fOSC
The next step is determining the total voltage drop across the LED string. For example, when the string consists of 10 High-Brightness LEDs and
each diode has a forward voltage drop of 3.0V at its nominal current; the total LED voltage VLEDS is 30V.
Dimming
The LED brightness can be dimmed either linearly (using the LD pin) or via pulse width modulation (using the PWM-D pin); or a combination of
both - depending on the application. Pulling the PWM pin to ground will turn off the AL9902. When disabled, the AL9902’s quiescent current is
typically 0.5mA. Reducing the LD voltage will reduce the LED current but it will not entirely turn off the external power transistor and hence the
LED current – this is due to the finite blanking period. Only the PWM pin will turn off the power transistor.
Linear dimming is accomplished by applying a 45 to 250mV analog signal to the LD pin. This overrides the default 250mV threshold level of the
CS pin and reduces the output current. If an input voltage greater than 250mV is applied to the LD then the output current will not change.
The LD pin also provides a simple cost-effective solution to soft start; by connecting a capacitor to the LD pin down to ground at initial power up,
the LD pin will be held low causing the sense threshold to be low. As the capacitor charges up the current sense threshold will increase thereby
causing the average LED current to increase.
PWM dimming is achieved by applying an external PWM signal to the PWM pin. The LED current is proportional to the PWM duty cycle and the
light output can be adjusted between 0 and 100%. The PWM signal enables and disables the AL9902 - modulating the LED current. The ultimate
accuracy of the PWM dimming method is limited only by the minimum gate pulse width, which is a fraction of a percentage of the low frequency
duty cycle. PWM dimming of the LED light can be achieved by turning on and off the converter with low frequency 50Hz to 1000Hz TTL logic level
signal.
With both modes of dimming it is not possible to achieve average brightness levels higher than the one set by the current sense threshold level of
the AL9902. If a greater LED current is required then a smaller sense resistor should be used.
Output Open Circuit Protection
The non-isolated buck LED driver topology provides inherent protection against an open circuit condition in the LED string due to the LEDs being
connected in series with the inductor. Should the LED string become open circuit then no switching occurs and the circuit can be permanently left
in this state with damage to the rest of the circuit.
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© Diodes Incorporated
AL9902
Document number: DS37878 Rev. 1 - 2
AL9902
Ordering Information
AL9902 XXX - 13
Package
Packing
FDF : U-DFN6040-12
S16 : SO-16
13 : Tape & Reel
13” Tape and Reel
Part Number
Package Code
Packaging
VCS Tolerance
Quantity
Part Number Suffix
AL9902FDF-13
AL9902S16-13
±5%
±5%
FDF
S16
U-DFN6040-12
SO-16
3,000/Tape & Reel
3,000/Tape & Reel
-13
-13
Marking Information
( Top View )
YY : Year : 15, 16,17~
WW : Week : 01~52; 52
represents 52 and 53 week
Logo
Part Number
AL9902
YYWWX X
X X : Internal Code
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© Diodes Incorporated
AL9902
Document number: DS37878 Rev. 1 - 2
AL9902
Package Outline Dimensions (All dimensions in mm.)
Please see AP02002 at http://www.diodes.com/datasheets/ap02002.pdf for latest version.
U-DFN6040-12
A1
A3
U-DFN6040-12
Dim Min Max Typ
A
Seating Plane
A
A1
A3
b
0.55 0.65 0.60
0
-
0.05 0.02
0.15
D
-
e
0.35 0.45 0.40
5.95 6.05 6.00
D
D1 1.95 2.15 2.05
D2 2.35 2.55 2.45
D2
e
-
-
1.00
D1
E
3.95 4.05 4.00
E2
E
E1
E1 2.10 2.30 2.20
E2 1.80 2.00 1.90
L
L
Z
0.35 0.45 0.40
0.30
-
-
All Dimensions in mm
b
Z
SO-16
SO-16
Dim
A
A1
A2
B
C
D
E
Min
1.40
0.10
1.30
0.33
0.19
9.80
3.80
Max
1.75
0.25
1.50
0.51
0.25
10.00
4.00
H
E
Gauge Plane
L
Detail ‘A’
e
H
L
1.27 Typ
D
A
5.80
0.38
0
6.20
1.27
8
A2
All Dimensions in mm
C
e
B
A1
Detail ‘A’
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© Diodes Incorporated
AL9902
Document number: DS37878 Rev. 1 - 2
AL9902
Suggested Pad Layout
Please see AP02001 at http://www.diodes.com/datasheets/ap02001.pdf for the latest version.
U-DFN6040-12
X3
Value
(in mm)
0.500
0.650
0.350
0.250
1.075
1.275
2.750
0.400
1.150
1.000
2.300
Dimensions
Y
C
C
G
G1
X
X1
X2
X3
Y
Y1
Y2
Y3
G
Y3
Y1
Y2
G1
X1
X2
Pin1
X
SO-16
X1
Value
(in mm)
1.270
Dimensions
C
X
Y1
0.670
X1
Y
9.560
1.450
Y1
6.400
Y
Pin 1
C
X
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© Diodes Incorporated
AL9902
Document number: DS37878 Rev. 1 - 2
AL9902
IMPORTANT NOTICE
DIODE 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).
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website, harmless against all damages.
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This document is written in English but may be translated into multiple languages for reference. Only the English version of this document is the
final and determinative format released by Diodes Incorporated.
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 © 2015, Diodes Incorporated
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© Diodes Incorporated
AL9902
Document number: DS37878 Rev. 1 - 2
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