A8435: High Efficiency Charge Pump White LED Driver

A8435
High Efficiency Charge Pump White LED Driver
Discontinued Product
This device is no longer in production. The device should not be
purchased for new design applications. Samples are no longer available.
Date of status change: October 31, 2011
Recommended Substitutions:
For existing customer transition, and for new customers or new applications, contact Allegro Sales.
NOTE: For detailed information on purchasing options, contact your
local Allegro field applications engineer or sales representative.
Allegro MicroSystems, Inc. reserves the right to make, from time to time, revisions to the anticipated product life cycle plan
for a product to accommodate changes in production capabilities, alternative product availabilities, or market demand. The
information included herein is believed to be accurate and reliable. However, Allegro MicroSystems, Inc. assumes no responsibility for its use; nor for any infringements of patents or other rights of third parties which may result from its use.
A8435
High Efficiency Charge Pump White LED Driver
Features and Benefits
Description
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The A8435 high efficiency charge pump IC offers a simple,
low-cost white LED driver solution for portable electronics
display applications. Using a proprietary control scheme (1×,
1.5×), the A8435 can output well-matched currents for up to
4 LEDs, while maintaining the highest efficiency over most
of the Li-ion battery lifetime.
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Proprietary adaptive control scheme (1×, 1.5×)
Maximum efficiency, over 92%
0.5% LED current matching
1 MHz operating frequency
Flexible dimming control:
▫ Serial 11-level dimming, down to 5%
▫ PWM
▫ 2-bit parallel
Drives up to 4 white LEDs
30 mA per LED
120 mA total continuous output
Low input ripple and EMI
Soft-start limits inrush current
Short circuit protection
Overvoltage protection
Thermal shutdown protection
Space-saving MLP-16 package: 3 × 3 mm footprint
Very thin 0.75 mm nominal height package
The A8435 accepts an input range of 2.7 to 5.5 V and delivers
up to 30 mA for each of the four regulated current sources. The
A8435 can deliver a total continuous output current of 120 mA,
meeting the requirements of most Li-ion battery-powered white
LED backlight applications. Outputs can also be tied together
for WLED flash/torch applications.
The A8435 offers flexible options for LED current driving.
The LED current can be set by any of the following methods:
(a) choosing an appropriate value for RSET, (b) 2-bit
parallel control with 3 levels, (c) PWM control, or (d) serial
programming
The A8435 is available in a very thin profile 0.75 mm (nominal
height) 3 × 3 mm QFN/MLP-16 package (ES), fitting the needs
of space-conscious applications.
Package: 16 pin QFN/MLP (suffix ES)
Applications include:
▪ White LED backlights for cellular phones, PDAs
▪ Digital cameras, camcorders
▪ Portable audio devices
▪ Other portable device white LED backlighting
▪ 120 mA WLED flash/torch
Approximate Scale
Typical Applications
VBATT
2.7 to 5.5 V
VBATT
2.7 to 5.5 V
C1
1 µF
VIN
VOUT
VIN
CIN
1 µF
C1+
COUT
1 µF
LED1
CIN
1 µF
C1
1 µF
C2+
A8435
C2–
LED2
C2
1 µF
Single-Wire On/Off and
Dimming Control
LED4
EN2
GND
A8435
CTRL
RSET
LED2
LED3
EN1
LED4
EN2
ISET
Figure 1. Typical Circuit. Dual wire control configuration: 2-bit
parallel or PWM dimming.
A8435-DS, Rev. 2
C2+
C2-
LED3
EN1
NC CTRL
On/Off and
Dimming Control
COUT
1 µF
LED1
C1-
C1–
C2
1 µF
VOUT
C1+
GND
ISET
RSET
Figure 2. Typical Circuit. Single wire control configuration.
A8435
High Efficiency Charge Pump White LED Driver
Selection Guide
Part Number
Packaging*
Package Type
A8435EESTR-T
7-in. reel, 1500 pieces/reel
ES, 3 × 3 mm QFN/MLP-16
*Contact Allegro for additional packing options.
Functional Block Diagram
C2
1 µF
C1
1 µF
C1 –
C1+
C2–
C2+
VOUT
VIN
Fractional Charge Pump
(1× and 1.5×)
CIN
1 µF
COUT
1 µF
+
–
EN1
EN2
CTRL
Minimum Select
Control, Clock,
and Reference
LED1
LED2
LED3
Current Mirror
LED4
+
–
ISET
+
–
+
–
+
–
+
–
RSET
GND
Absolute Maximum Ratings
Input or Output Voltage
VIN, VOUT, C1+, C1–, C2+, and C2– pins ..................... –0.3 to 6 V
All other pins..................................................... –0.3 to VIN + 0.3 V
VOUT Short Circuit to GND ....................................................Continuous
Operating Ambient Temperature, TA ..................................... –40°C to 85°C
Maximum Junction Temperature, TJ(max) ............................................. 150°C
Storage Temperature, TS ................................................... –55°C to 150°C
Package Thermal Characteristics
RθJA = 47 °C/W, on a 4-layer board based on JEDEC spec
Additional information is available on the Allegro Web site.
Package is lead (Pb) free, with 100% matte tin leadframe plating.
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
2
A8435
High Efficiency Charge Pump White LED Driver
13 C1–
14 VIN
8
9
LED1
4
10 LED3
7
CTRL
11 GND
EP
LED2
3
6
EN1
12 NC
5
2
EN2
1
ISET
C2+
VOUT
15 C2–
16 C1+
Pin-out Diagram
LED4
(Top View)
Terminal List Table
Name
Pin Number
C1–
13
Function*
Negative terminal of capacitor C1.
C1+
16
Positive terminal of capacitor C1.
C2–
15
Negative terminal of capacitor C2.
C2+
1
Positive terminal of capacitor C2.
CTRL
4
Brightness control scheme toggle. For 2-bit parallel or PWM dimming, leave open or tie to VIN
(see table 1). For single-wire serial input dimming, connect to GND (see figure 2).
EN1
3
When CTRL is open or HIGH: Enable and dimming control input 1 (see table 1).
When CTRL is grounded: single-wire enable and dimming control (see table 1 and figure 2).
(Do not leave unconnected.)
EN2
5
When CTRL is open or HIGH: Enable and dimming control input 2 (see table 1).
When CTRL is grounded: this pin disables shutdown. (Do not leave unconnected.)
EP
–
Exposed metal pad on bottom side. Connect this to ground plane for better thermal
performance.
GND
11
Ground.
ISET
6
Connect RSET resistor to ground to set desired constant current through LEDs.
LED1
8
Current sink for LED1. Connect to VIN or VOUT if not used for LED. (Do not leave unconnected.)
LED2
7
Current sink for LED2. Connect to VIN or VOUT if not used for LED. (Do not leave unconnected.)
LED3
10
Current sink for LED3. Always connect this pin to LED.
LED4
9
Current sink for LED4. Connect to VIN or VOUT if not used for LED. (Do not leave unconnected.)
NC
12
No Connection.
VIN
14
Power supply voltage input.
VOUT
2
Charge pump voltage source output for connection to the LED anodes.
* See Application Information section for cited figure and tables.
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
3
A8435
High Efficiency Charge Pump White LED Driver
ELECTRICAL CHARACTERISTICS1
VIN = VEN1 = VEN2 = 3.6 V, C1 = C2 = 1 μF, TA = –40 to 85°C, typical values at TA = 25°C (unless otherwise noted)
Characteristics
Symbol
Test Conditions
Min.
Typ.
Max.
Input Voltage Range
VIN
Undervoltage Lockout Threshold
UVLO Hysteresis Window
VUVLO
VIN falling, VUVLOHYS = 35 mV
Units
2.7
–
5.5
V
2.25
2.45
2.60
V
–
35
–
mV
Switching, TA = 25°C
–
2.8
4
mA
EN1 = EN2 = GND, TA = 25°C
–
0.1
1
μA
2
–
ms
VUVLOHYS
Quiescent Current
IQ
Soft-Start Completion Time
tSS
–
ISET Bias Voltage
VISETBIAS
0.56
0.6
0.64
V
ISET Leakage in Shutdown
VISETLKG
–
0.01
1
μA
ISET Current Range
IISET
EN1 = EN2 = VIN
ISET to LEDx Current Ratio
ILEDx / IISET
IISET = 60 μA,
EN1 = VIN, EN2 = GND
CTRL = open or HIGH
EN1 = GND, EN2 = VIN
IISET = 60 μA,
CTRL = LOW
Full brightness
40
–
140
μA
190
219
245
A/A
105
121
137
A/A
51
60
69
A/A
–
200
–
A/A
%
ILED Accuracy
EILED
EN1 = EN2 = VIN, RSET = 4.3 kΩ
–
±0.9
–
LED Current Matching2
∆ILED
VIN =3.6 V, ILED = 30 mA per LED
–
±0.5
–
%
Regulation Voltage at LEDx (1.5×)
VLED
EN1 = EN2 = VIN
–
150
–
mV
Open Loop Output Resistance3
ROUT
1× to 1.5× Mode Transition Voltage at LEDx
VTrans
Transition to Dropout Voltage Difference4
LED Leakage in Shutdown
Oscillator Frequency
Output Overvoltage
∆Vdr
VLEDLKG
1× mode: [(VIN – VOUT) / IOUT]
–
1.1
–
Ω
1.5× mode: [(1.5 × VIN – VOUT) / IOUT]
–
3.6
–
Ω
VLEDx Falling
–
100
–
mV
Measured as VTrans – VDropout
–
60
–
mV
EN1 = EN2 = GND, VIN = 5.5 V, TA = 25°C
–
0.01
1
μA
–
1
–
MHz
–
5.74
–
V
V
fosc
Protection5
VOVP
Open circuit at any LED that is programmed to be
in the ON state
CTRL, EN1, EN2 Input High Logic Threshold6
VIH
1.6
–
–
CTRL, EN1, EN2 Input Low Logic Threshold6
VIL
–
–
0.4
V
Input High Current
IIH
VIH = VIN
–
–
1
μA
VIL = GND
Input Low Current
IIL
–
–
1
μA
EN1 Pulse Low Time7
tLO
0.5
–
500
μs
EN1 Pulse High Time7
tHI
0.5
–
–
μs
Initial EN1 Pulse High
Time7
tHI(Init)
First EN1 pulse after shutdown
100
–
–
μs
Shutdown Delay7
tSHDN
Falling edge of EN1 pulse
–
2
3
ms
Thermal-Shutdown Threshold
TSHDN
20°C hysteresis
–
165
–
°C
1Specifications
guaranteed by design over operating temperature range, –40°C to 85°C.
2LED current matching is defined as (I
LEDX – ILED(AVG)) / ILED(AVG) .
3The Open Loop Output Resistance for 1.5× mode is measured with one of the LEDx pins tied to ground or open (thus its voltage is always less
than 80 mV).
4Dropout Voltage, V
Dropout, is defined as the LEDx-to-GND voltage at which ILEDx drops 10% below the value of ILEDX at VLEDX = 200 mV.
5Guaranteed by design.
6EN2 is not used when CTRL is tied to ground.
7Applies only when CTRL is tied to ground. See figure 3 in Application Information section.
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
4
A8435
High Efficiency Charge Pump White LED Driver
Performance Characteristics
Tests performed using application circuit shown in figure 1: dual wire control; and
VIN = 3.6 V, EN1 = EN2 = VIN, CIN = C1 = C2 = COUT = 1 μF, RSET = 7.5 kΩ, TA = 25°C (unless otherwise noted)
Efficiency versus Supply Voltage
Over Range of Dimming Levels, VIN Falling
100
90
Dimming Level
(mA)
4.75
η (%)
80
9.8
17.6 (Full Brightness)
70
60
50
2.70
2.90
3.10
3.30
3.50
3.70
3.90
4.10
VIN (V)
Supply Current versus Supply Voltage
Over Range of Dimming Levels (mA)
120
100
VIN Rising
VIN Falling
17.6 mA
60
VIN Rising
VIN Falling
9.8 mA
40
VIN Rising
20
4.75 mA
VIN Falling
0
2.70
2.90
3.10
3.30
3.50
3.70
3.90
4.10
VIN (V)
LED Current versus Supply Voltage
Matching Between LEDs <1% Over Range of VIN
20
19
18
17
ILED (mA)
IBATT (mA)
80
16
15
14
13
12
11
10
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
VIN (V)
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
5
A8435
High Efficiency Charge Pump White LED Driver
Startup Response
VEN
Symbol
C1
C2
C3
t
Parameter
VEN
IBATT
VOUT
time
Units/Division
5V
50 mA
2V
500 μs
C1
IBATT
C2
C3
VOUT
t
2-Bit (EN1-EN2) Dimming Response
Symbol
C1
C2
t
Conditions
EN2 = VIN
Parameter
VEN1
IOUT
time
Units/Division
2V
50 mA
5 μs
VEN
C1
IOUT
C2
t
11-Level Single-Wire Serial Dimming
Response
Symbol
Parameter Units/Division
2V
C1
VEN1
C2
IOUT
50 mA
C3
VOUT
2V
t
time
10 ms
Conditions
EN2 = CTRL = GND, apply control
signal to EN1
C1
VEN1
IOUT
C2
VOUT
C3
t
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
6
A8435
High Efficiency Charge Pump White LED Driver
Application Information
Setting LED Current
The LED current level, ILEDX, is set by the value chosen for the
external resistor, RSET, which is connected to the ISET terminal.
The full current (100%) level for ILEDX can be calculated using
the following formulas:
Setting
Formula
CTRL = Open or HIGH
RSET (Ω) = 0.6 V × 219 / ILEDX
CTRL = LOW
RSET (Ω) = 0.6 V × 200 / ILEDX
Dimming
The A8435 offers serial, 2-bit parallel, and PWM dimming
control. When the CTRL pin is pulled LOW, the EN1 pin accepts
one-wire serial pulse input both to enable the part, and to select
one of the 11 dimming levels, from 100% down to 5% (see
table 1).
With EN2 low, when EN1 is pulled high, the IC turns on. The
initial LED current defaults to 100% after softstart is complete.
The tLO must be < 500 ms to avoid shutdown. With EN2 high,
the operation of EN1 is the same as when EN2 is low, except
shutdown is disabled (TLO = ∞).
Table 1. CTRL, EN1, and EN2 Pin States
CTRL
EN1
EN2
Open or HIGH
LOW
LOW Shutdown
Brightness
LED Current, ILED
0
Open or HIGH
LOW HIGH 27% Brightness
60 × IISET
Open or HIGH
HIGH LOW 55% Brightness
121 × IISET
Open or HIGH
HIGH HIGH Full Brightness
219 × IISET
LOW
Adjustable; 11 levels of dimming from
Pulse No
100% to 5% (see figure 3; 100% corinput effect
responds to 200 × IISET)
LOW
LOW
LOW Shutdown
> 2 ms
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
7
A8435
High Efficiency Charge Pump White LED Driver
When changing from one specific brightness level to another, the
user may not want to keep the existing brightness level stored
in memory. A simpler method is to program a shutdown and
re-enable, followed by an appropriate number of pulses (from
100%) to reach the target brightness level. The total “LED off”
time during shutdown, re-enable, and brightness programming
can be kept sufficiently short such that no delay is discernable to
the eye.
Shutdown
If the CTRL pin is unconnected or HIGH, the device enters the
shutdown mode when EN1 and EN2 are pulled LOW. When
configured to have a serial pulse dimming control (the CTRL pin
is grounded), the EN1 and the EN2 pins must be pulled LOW for
longer than tSHDN (2 ms typical) in order to enter shutdown mode.
0
EN1
tHI(Init)
2
3
4
tSS
100%
IILEDX SHDN
1
5
The output is high impedance after shutdown.
Disabling Unused LEDs
If any WLED is not used, connect the corresponding pin to either
VIN or VOUT to disable it. Never leave open any unused WLED
pin. LED pins will sink 30 μA typical when connected to VIN or
VOUT and the IC is enabled.
LED3 must always be selected. For example, to drive 2 LEDs,
select LED3 and one of either LED1, LED2, or LED4.
Component Selection
Ceramic capacitors with X5R or X7R dielectric are recommended
for the input capacitor, CIN, the output capacitor, COUT, and the
charge pump capacitors, C1 and C2.
6
t LO
90%
80%
70%
7
8
9
10
11
tSHDN
t HI
100% 90%
60%
50%
40%
30% 20%
10%
5%
SHDN
Figure 3. Single-Wire Serial Dimming Control, at pin EN1; CTRL = LOW, EN2 = LOW.
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
8
A8435
High Efficiency Charge Pump White LED Driver
Package ES, 3 × 3 mm 16-Pin QFN/MLP
0.30
3.00 ±0.15
0.90
16
1
2
A
0.50
16
1
3.00 ±0.15
1.70
3.10
1.70
17X
D
SEATING
PLANE
0.08 C
+0.05
0.25 –0.07
C
3.10
C
PCB Layout Reference View
0.75 ±0.05
0.50
For reference only
(reference JEDEC MO-220WEED)
Dimensions in millimeters
Exact case and lead configuration at supplier discretion within limits shown
+0.15
0.40 –0.10
A Terminal #1 mark area
B
1.70
2
1
16
1.70
B Exposed thermal pad (reference only, terminal #1
identifier appearance at supplier discretion)
C Reference land pattern layout (reference IPC7351
QFN50P300X300X80-17W4M);
All pads a minimum of 0.20 mm from all adjacent pads; adjust as
necessary to meet application process requirements and PCB layout
tolerances; when mounting on a multilayer PCB, thermal vias at the
exposed thermal pad land can improve thermal dissipation (reference
EIA/JEDEC Standard JESD51-5)
D Coplanarity includes exposed thermal pad and terminals
Copyright ©2005-2008, Allegro MicroSystems, Inc.
Allegro MicroSystems, Inc. reserves the right to make, from time to time, such departures from the detail specifications as may be required to permit improvements in the performance, reliability, or manufacturability of its products. Before placing an order, the user is cautioned to verify that the
information being relied upon is current.
Allegro’s products are not to be used in life support devices or systems, if a failure of an Allegro product can reasonably be expected to cause the
failure of that life support device or system, or to affect the safety or effectiveness of that device or system.
The information included herein is believed to be accurate and reliable. However, Allegro MicroSystems, Inc. assumes no responsibility for its use;
nor for any infringement of patents or other rights of third parties which may result from its use.
For the latest version of this document, visit our website:
www.allegromicro.com
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
9
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