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AAT2842
High-Current Charge Pump with S2CwireTM Control and Dual LDO for Backlight and Flash General Description
The AAT2842 is a highly integrated charge pump with dual linear regulators optimized for systems operating with lithium-ion/polymer batteries. The charge pump provides power for both white LED backlight/keypad and flash. Up to four backlight LEDs can be driven at up to 30mA each and keypad LEDs can be driven using lower currents set by the S2Cwire interface. In addition, up to four flash LEDs can be driven with up to 600mA total. Two separate S2CwireTM (Simple Serial ControlTM) serial digital interfaces are used to enable, disable, and set the current to one of 16 levels for both backlight and flash LEDs. Backlight/keypad and flash current settings are also controlled through external resistors for increased versatility with reduced accuracy and matching. Backlight/keypad current matching is 1% for uniform display brightness, and flash current matching is 4% for uniform power dissipation. An internal flash timer set by an external capacitor protects the flash LED should a fault occur. The AAT2842 offers two high-performance MicroPowerTM low dropout (LDO) linear regulators. A single enable input controls both regulators and each supplies up to 200mA to the load. Both LDOs consume only 85A quiescent current, making them ideal for battery-operated applications. The AAT2842 is equipped with built-in short-circuit and over-temperature protection. The charge pump soft-start circuitry prevents excessive inrush current at start-up. The product is available in a Pb-free, space-saving TQFN44-28 package and operates over the -40C to +85C ambient temperature range.
Features
* *
ChargePumpTM
*
* * * *
VIN Range: 2.7V to 5.5V Tri-Mode Charge Pump: -- Drives up to Four Backlight/Keypad and Four Flash LEDs -- Separate S2Cwire Control for Backlight/Keypad and Flash Currents -- Backlight/Keypad and Flash Current Set by Separate External Resistors -- Flash Timer Set with External Capacitor -- Up to 2MHz Switching Frequency Two Linear Regulators: -- 200mA Output Current -- 200mV Dropout -- Output Voltage Adjustable from 1.2V to VBATTERY -- Output Auto-Discharge for Fast Shutdown -- 85A Quiescent Current Built-In Thermal Protection Automatic Soft Start -40C to +85C Temperature Range Available in 4x4mm TQFN44-28 Package
Applications
* * * Camera-Enabled Mobile Devices Digital Still Cameras Multimedia Mobile Phones
Typical Application
C1 1F
C1+
C2 1F
C1- C2+ C2-
IN VBAT CIN 4.7F EN_BACKLIGHT EN_FLASH
OUT
AAT2842
BL1 BL2 BL3 BL4 FL1 FL2 FL3 FL4 OUTA
COUT 2.2F
IN BENS FENS CT BSET
RSET1 CT RSET2 CREF EN_LDO
VOUT LDOA R2A COUTA
FSET REF FBA OUTB ENL AGND R2B FBB PGND R1B VOUT LDOB COUTB
R1A
2842.2007.09.1.2
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AAT2842
High-Current Charge Pump with S2CwireTM Control and Dual LDO for Backlight and Flash Pin Descriptions
Pin #
1 2 3 4 5 6 7 8 9, 18 10 11 12 13 14
Symbol
BL1 BSET FSET AGND CT REF FBB OUTB IN FBA OUTA C1C1+ OUT
Description
Backlight LED 1 current sink. BL1 controls the current through Backlight LED 1. Connect the cathode of Backlight LED 1 to BL1. If not used, connect BL1 to OUT. Backlight current setting input. A 280k resistor from BSET to AGND sets the maximum backlight current to 30mA. Flash current setting input. A 280k resistor from FSET to AGND sets the maximum flash current to 150mA. Analog ground. Connect AGND to PGND at a single point as close to the AAT2842 as possible. Flash timer control capacitor input. Connect a capacitor from CT to AGND to set the flash timer. A 100nF capacitor sets the timer to 1s. Reference output. For low noise operation, bypass REF to AGND with capacitor. Typically, a 0.1F ceramic capacitor provides sufficient noise reduction. Feedback input for LDOB. FBB measures the output voltage of LDOB. Connect a resistive voltage divider from the output of LDOB to FBB. FBB feedback regulation voltage is 1.2V. LDOB regulated voltage output. OUTB is the voltage output of low dropout regulator B. Bypass OUTB to AGND with a 2.2F or larger ceramic capacitor as close to the AAT2842 as possible. Power input. Connect IN to the input source voltage. Bypass IN to PGND with a 4.7F or larger ceramic capacitor as close to the AAT2842 as possible. Feedback input for LDOA. FBA measures the output voltage of LDOA. Connect a resistive voltage divider from the output of LDOA to FBA. FBA feedback regulation voltage is 1.2V. LDOA regulated voltage output. OUTA is the voltage output of low dropout regulator A. Bypass OUTA to AGND with a 2.2F or larger ceramic capacitor as close to the AAT2842 as possible. Negative node of charge pump capacitor 1. Positive node of charge pump capacitor 1. Connect a 1F ceramic capacitor from C1+ to C1-. Charge pump output. OUT is the output of the charge pump and supplies current to the backlight and flash LEDs. Connect the backlight and flash LED anodes to OUT. Bypass OUT to PGND with a 2.2F or larger capacitor as close to the AAT2842 as possible. LDO enable input. ENL turns on or off the low dropout regulators. Drive ENL high to turn on the regulators, drive it low to turn them off. Positive node of charge pump capacitor 2. Connect a 1F ceramic capacitor from C2+ to C2-. Negative node of charge pump capacitor 2. Power ground. Connect AGND to PGND at a single point as close to the AAT2842 as possible. Flash LED 4 current sink. FL4 controls the current through Flash LED 4. Connect the cathode of Flash LED 4 to FL4. If not used, connect FL4 to OUT. Flash LED 3 current sink. FL3 controls the current through Flash LED 3. Connect the cathode of Flash LED 3 to FL3. If not used, connect FL3 to OUT. Flash LED 2 current sink. FL2 controls the current through Flash LED 2. Connect the cathode of Flash LED 2 to FL2. If not used, connect FL2 to OUT. Flash LED 1 current sink. FL1 controls the current through Flash LED 1. Connect the cathode of Flash LED 1 to FL1. If not used, connect FL1 to OUT.
15 16 17 19 20 21 22 23
ENL C2+ C2PGND FL4 FL3 FL2 FL1
2
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AAT2842
High-Current Charge Pump with S2CwireTM Control and Dual LDO for Backlight and Flash Pin Descriptions (continued)
Pin #
24
Symbol
FENS
Description
Flash enable and serial control input. FENS is the on/off control for the flash and the S2Cwire input to serially control the flash LED brightness relative to the maximum current set by the resistor at FSET. Backlight enable and serial control input. BENS is the on/off control for the backlight and the S2Cwire input to serially control the backlight LED brightness relative to the maximum current set by the resistor at BSET. Backlight LED 4 current sink. BL4 controls the current through Backlight LED 4. Connect the cathode of Backlight LED 4 to BL4. If not used, connect BL4 to OUT. Backlight LED 3 current sink. BL3 controls the current through Backlight LED 3. Connect the cathode of Backlight LED 3 to BL3. If not used, connect BL3 to OUT. Backlight LED 2 current sink. BL2 controls the current through Backlight LED 2. Connect the cathode of Backlight LED 2 to BL2. If not used, connect BL2 to OUT. Exposed paddle (bottom); connect to PGND as closely as possible to the device.
25
BENS
26 27 28 EP
BL4 BL3 BL2
Pin Configuration
TQFN44-28-0.4 (Top View) TQFN44-28-0.45 (Top View)
FL2 FL1 FENS BENS BL4 BL3 BL2
28 27 26 25 24 23 22 21 20 19 18 17 16 15 8 9 10 11 12 13 14
FL2 FL1 FENS BENS BL4 BL3 BL2
28 27 26 25 24 23 22 21 20 19 18 17 16 15 8 9 10 11 12 13 14
BL1 BSET FSET AGND CT REF FBB
1 2 3 4 5 6 7
FL3 FL4 PGND IN C2C2+ ENL
BL1 BSET FSET AGND CT REF FBB
1 2 3 4 5 6 7
FL3 FL4 PGND IN C2C2+ ENL
OUT C1+ C1OUTA FBA IN OUTB
N.B. Not recommended for new designs.
OUT C1+ C1OUTA FBA IN OUTB
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AAT2842
High-Current Charge Pump with S2CwireTM Control and Dual LDO for Backlight and Flash Absolute Maximum Ratings1
Symbol Description
IN, OUT, FL1, FL2, FL3, FL4, BL1, BL2, BL3, BL4 Voltage to AGND C1+, C1-, C2+, C2- Voltage to AGND BSET, FSET, CT, FBB, OUTA, FBA, OUTB, ENL, REF, FENS, BENS Voltage to AGND PGND Voltage to AGND Operating Junction Temperature Range Maximum Soldering Temperature (at leads, 10 sec)
Value
-0.3 to 6.0 -0.3 to VOUT + 0.3 -0.3 to VIN + 0.3 -0.3 to 0.3 -40 to 150 300
Units
V V V V C C
TJ TLEAD
Thermal Information2
Symbol
PD JA
Description
Maximum Power Dissipation Maximum Thermal Resistance
3
Value
2 50
Units
W C/W
1. Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at conditions other than the operating conditions specified is not implied. Only one Absolute Maximum Rating should be applied at any one time. 2. Mounted on an FR4 circuit board. 3. Derate 20mWC above 40C ambient temperature.
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AAT2842
High-Current Charge Pump with S2CwireTM Control and Dual LDO for Backlight and Flash Electrical Characteristics1
VIN = 3.6V; CIN = 4.7F; COUT = 2.2F; C1 = C2 = 1.0F; RBSET = RFSET = 280k; TA = -40C to +85C, unless otherwise noted. Typical values are at TA = 25C. Symbol
VIN
Description
IN Operating Voltage Range
Conditions
1X Mode, 3.0V VIN 5.5V, Active, No Load; ENL = AGND, FENS = BENS = IN 1.5X Mode, 3.0V VIN 5.5V, Active, No Load; ENL = AGND, FENS = BENS = IN 2X Mode, 3.0V VIN 5.5V, Active, No Load; ENL = AGND, FENS = BENS = IN RBSET = 280k, Data 1, 1X Mode ENL = BENS = FENS = AGND, TA = 25C
Min
2.7
Typ Max Units
5.5 1.0 3.0 5.0 50 5.0 140 15 A A C C mA V
IIN(Q)
IN Operating Current
IN Shutdown Current Over-Temperature Shutdown TSD Threshold Over-Temperature Shutdown TSD(HYS) Hysteresis Charge Pump Section IOUT OUT Maximum Output Current VIN(TH_H) Charge Pump Mode Hysteresis fOSC Charge Pump Oscillator Frequency tSS Charge Pump Soft-Start Delay Backlight LED Outputs, S2Cwire Data = 1 IBL_(MAX) BL1-BL4 Maximum Current I(BL_) BL1-BL4 Current Matching2 BL1-BL4 Charge Pump Mode VBL_(TH) Transition Threshold VBSET RBSET Pin Voltage Backlight LED Outputs, S2Cwire Data = 7 IBL_(MAX) BL1-BL4 Maximum Current I(BL_) BL1-BL4 Current Matching2 BL1-BL4 Charge Pump Mode VBL_(TH) Transition Threshold Flash LED Outputs, S2Cwire Data = 1 IFL_(MAX) FL1-FL4 Maximum Current I(FL_) FL1-FL4 Current Matching2 FL1-FL4 Charge Pump Mode VFL_(TH) Transition Threshold VFSET RFSET Pin Voltage
IIN(SHDN)
Data 1
600 350 2
mA mV MHz s 33 1 mA % mV V 10.6 2 mA % mV
OUT = 0V to VBAT VIN - VF = 1.5V VIN - VF = 1.5V 27
350 30 0.5 150 0.7
VIN - VF = 1.5V VIN - VF = 1.5V
8.6
9.6 60
VIN - VF = 1.5V VIN - VF = 1.5V
135
150 1 300 0.7
165 4
mA % mV V
1. The AAT2842 is guaranteed to meet performance specifications over the -40C to +85C operating temperature range and is assured by design, characterization, and correlation with statistical process controls. 2. Current matching is defined as the deviation of any sink current from the average of all active channels. 2842.2007.09.1.2
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AAT2842
High-Current Charge Pump with S2CwireTM Control and Dual LDO for Backlight and Flash Electrical Characteristics1
VIN = 3.6V; CIN = 4.7F; COUT = 2.2F; C1 = C2 = 1.0F; RBSET = RFSET = 280k; TA = -40C to +85C, unless otherwise noted. Typical values are at TA = 25C. Symbol
Enable/Set VBENS(L), VFENS(L) VBENS(H), VFENS(H) IBENS, IFENS TBENS(L), TFENS(L)
Description
Conditions
Min
Typ
Max
Units
BENS, FENS Low Threshold BENS, FENS High Threshold BENS, FENS Input Leakage Current BENS, FENS Low Time VBENS or VFENS = VIN = 5V 1.4 -1 0.3 50
0.4
V V
1 75
A s ns
TBENS(H-MIN), BENS, FENS Minimum TFENS(H-MIN) High Time TBENS(H-MAX), BENS, FENS Maximum TFENS(H-MAX) High Time TBENS(OFF), BENS, FENS Off Timeout TFENS(OFF) TBENS(LAT), BENS, FENS Latch Timeout TFENS(LAT) Linear Regulators VFBA, VFBB FB Voltage Tolerance IIN IN Operating Current OUTA, OUTB Maximum Load IOUTA(MAX), IOUTB(MAX) Current VOUTA(DO), OUTA, OUTB Dropout Voltage VOUTB(DO) ENL Enable Low Voltage VENL(L) Threshold ENL Enable High Voltage VENL(H) Threshold tENL(DLY) ENL Enable Delay ROUTA(DCHG), OUTA, OUTB Auto-Discharge ROUTA(DCHG) Resistance PSRRA, OUTA, OUTB Power Supply Rejection Ratio PSRRB
75 500 500
s s s
IOUT = 1mA to 200mA ENL = IN, BENS = FENS = AGND
1.17
1.2 85
1.23 150
V A mA
200 IOUT = 150mA 150 300 0.4 1.4 REF = Open 15 20 IOUT =10mA, CREF = 10nF, 1kHz 50
mV V V s dB
1. The AAT2842 is guaranteed to meet performance specifications over the -40C to +85C operating temperature range and is assured by design, characterization, and correlation with statistical process controls.
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2842.2007.09.1.2
AAT2842
High-Current Charge Pump with S2CwireTM Control and Dual LDO for Backlight and Flash Typical Characteristics
VIN = 3.6V; CIN = 4.7F; COUT = 2.2F; C1 = C2 = 1.0F; RBSET = RFSET = 280k; TA = -40C to +85C, unless otherwise noted. Typical values are at TA = 25C.
Backlight Efficiency vs. Supply Voltage
100 90 100
Flash Efficiency vs. Supply Voltage
Efficiency (%)
80 70 60 50 40 30
Efficiency (%)
30mA/ch VF = 3.7V
90 80 70 60 50 40 30
150mA total VF = 2.9V
7.5mA/ch VF = 3.1V
2.1mA/ch VF = 2.9V
300mA total VF = 3.0V
200mA total VF = 2.9V
2.7 2.8 2.9 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4.0 4.1 4.2
2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5
Supply Voltage (V)
Supply Voltage (V)
Turn On to 1X Mode Backlight
(30mA/ch; Data 1; VIN = 4.2V)
Turn On to 1.5X Mode Backlight
(30mA/ch; Data 1; VIN = 3.5V)
EN (2V/div) OUT (2V/div) VSINK (500mV/div) IIN (100mA/div) Time (200s/div)
EN (2V/div) OUT (2V/div) VSINK (500mV/div) IIN (200mA/div) Time (200s/div)
Turn On to 2X Mode Backlight
(30mA/ch; Data 1; VIN = 3.2V)
Turn Off from 1.5X Mode Backlight
(30mA/ch; Data 1)
EN (2V/div) OUT (2V/div) VSINK (500mV/div) IIN (200mA/div) Time (200s/div)
EN (2V/div) OUT (2V/div)
IIN (200mA/div)
Time (100s/div)
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AAT2842
High-Current Charge Pump with S2CwireTM Control and Dual LDO for Backlight and Flash Typical Characteristics
VIN = 3.6V; CIN = 4.7F; COUT = 2.2F; C1 = C2 = 1.0F; RBSET = RFSET = 280k; TA = -40C to +85C, unless otherwise noted. Typical values are at TA = 25C.
BENS, FENS High Threshold Voltage vs. Supply Voltage
1.2 1.1
BENS, FENS Low Threshold Voltage vs. Supply Voltage
1.2 1.1
-40C
VBENS(H), VFENS(H) (V)
1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5
VBENS(L), VFENS(L) (V)
1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2
-40C
85C
25C
85C
25C
2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5
VIN (V)
VIN (V)
BENS, FENS Latch Timeout vs. Supply Voltage
400
BENS, FENS Off Timeout vs. Supply Voltage
500
TBENS(OFF), TFENS(OFF) (s)
TBENS(LAT), TFENS(LAT) (s)
350 300 250 200 150
450 400 350 300 250 200 150
-40C 25C 85C
-40C 25C 85C
2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5
2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5
VIN (V)
VIN (V)
LDOs A and B Turn On Characteristic
Output Voltage Accuracy (%)
1.00
LDOs A and B Line Regulation
ENL (2V/div)
0.50
OUTA
0.00
OUTB
-0.50
VOUT (500mV/div)
-1.00 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5
Time (50s/div)
Input Voltage (V)
8
2842.2007.09.1.2
AAT2842
High-Current Charge Pump with S2CwireTM Control and Dual LDO for Backlight and Flash Typical Characteristics
VIN = 3.6V; CIN = 4.7F; COUT = 2.2F; C1 = C2 = 1.0F; RBSET = RFSET = 280k; TA = -40C to +85C, unless otherwise noted. Typical values are at TA = 25C.
LDOs A and B Load Regulation
Output Voltage Accuracy (%)
1.00
LDOs A and B Line Transient Response
(10mA Load)
0.50
OUTA
0.00
VIN (400mV/div) VIN = 4.2V VIN = 3.7V
-0.50
OUTB
VOUT (10mV/div)
1000
-1.00 0.1
1
10
100
Load Current (mA)
Time (40s/div)
LDOs A and B Load Transient Response
(10mA to 200mA Load Step)
IOUT (100mA/div)
IOUT = 200mA
VOUT (100mV/div)
Time (20s/div)
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AAT2842
High-Current Charge Pump with S2CwireTM Control and Dual LDO for Backlight and Flash Functional Block Diagram
IN C1+ C1C2+ C2IN OUTA
Tri-Mode Charge Pump (1X/1.5X/2X)
LDO A
FBA OUTB
LDO B
FBB
1.2V VREF
REF OUT BL1 BL2
ENL
To LDO A&B
BENS FENS Control Logic BL3 BL4 FL1 BSET FSET FL2 FL3 FL4
CT
AGND PGND
Functional Description
The AAT2842 is a highly integrated LED driver with two LDO linear regulators. The charge pump LED driver simultaneously drives the backlight and flash LEDs from a 2.7V to 5.5V input voltage. The LDO regulators operate from the same input voltage range and produce regulated output voltages as low as 1.2V.
itors, making a more compact solution than an inductor-based step-up converter solution. Each individual LED is driven by a current sink to GND allowing individual current control with high accuracy over a wide range of input voltages and LED forward voltages while maintaining high efficiency. The charge pump is controlled by the voltage across the LED current sinks. When any one of the active current sinks starts to dropout, the charge pump goes to the next higher mode (from 1X to 1.5X or from 1.5X to 2X mode) to maintain sufficient LED voltage and keep constant LED current. The AAT2842 continuously monitors the LED forward voltages, and the input voltage determines when to reduce the charge pump mode for better efficiency. There is also a 350mV mode-transition hysteresis that prevents the charge pump from oscillating between modes.
LED Drivers
The LEDs are driven from an internal charge pump that, depending on the battery voltage and LED forward voltage, drives the LED directly from the input voltage (1X mode) or steps the input voltage up by a factor of 1.5 (1.5X mode) or 2 (2X mode). The charge pump requires only two tiny ceramic capac-
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2842.2007.09.1.2
AAT2842
High-Current Charge Pump with S2CwireTM Control and Dual LDO for Backlight and Flash
The backlight and flash LED currents are controlled by a combination of an external programming resistor from BSET (for backlight) or FSET (for flash) to AGND and the backlight or flash serial S2Cwire interface BENS or FENS. The programming resistor sets the maximum LED current for each channel, and the serial S2Cwire interface controls the LED current relative to the maximum. To drive backlight LEDs with optimal absolute accuracy and channel-to-channel matching, the maximum output current is set to 30mA with a 280k resistor connected at the BSET pin of the AAT2842. The AAT2842 features separate control interfaces for the backlight and flash current control. The backlight current features 16 current steps, each as a percentage of the maximum backlight current set by the BSET resistance. The flash has 16 current level settings, again as a percentage of the maximum flash current set by the FSET resistance (see Tables 1 and 2). Initiating a flash current also initiates the flash timer which is programmed via an external capacitor CT. Calculate the flash time T by the following equation:
T = 10 * CT
Using Backlight LED Outputs for Low-Current LED Applications
The AAT2842's backlight current outputs can be programmed to drive lower current LEDs, such as those used for keypad applications. For best low-current accuracy and matching, the preferred method is to use a 280k resistor for RBSET and then set the desired current output using the product's S2Cwire interface, as shown in Table 1. If any one of the current sinks is not used, connect the unused current sink to OUT. The current controller monitors the current sink voltage and, if it is connected to OUT, then it is assumed that the current sink is not used or that the LED is shorted, and the controller turns off that current sink.
where T is in seconds and CT is in F. For example, for a 0.1F capacitor:
T = 10 * 0.1F = 1s
To disable the flash timer, connect CT to AGND. Data
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
BL% of BSET
100 82 70 59 49.2 41.0 33.0 28.2 23.5 18.7 15.4 12.3 7.7 4.1 2.4 0.2
S2Cwire Serial Interface
The S2Cwire serial interface records rising edges of the EN/SET pin and decodes them into 16 different states. The S2Cwire interface has flexible timing; data can be clocked-in at speeds greater than 1MHz or much slower, such as 15kHz. After data is submitted, EN/SET is held high to latch the data. Once EN/SET has been held in the logic high state for time TLAT, the programmed current becomes active and the internal data register is reset to zero. For subsequent current level programming, the number of rising edges corresponding to the desired code must be entered on the EN/SET pin.
Table 1: Backlight Current Register: BL1-BL4 (RBSET = 280k).
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AAT2842
High-Current Charge Pump with S2CwireTM Control and Dual LDO for Backlight and Flash Applications Information
LDO Output Voltage Programming
The output voltages for LDOA and LDOB are programmed by an external resistor divider network. As shown in Figure 2, the selection of R1 and R2 is a straightforward matter. R1 is chosen by considering the tradeoff between the feedback network bias current and resistor value. Higher resistor values allow stray capacitance to become a larger factor in circuit performance whereas lower resistor values increase bias current and decrease efficiency.
Data
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
FL% of FSET
100 81 72 66 60 52.5 46.2 41.4 36.6 31.7 28.5 25.0 21.7 18.4 16.7 15.0
OUT(A/B) R2(A/B) FB(A/B) VREF = 1.2V R1(A/B)
VOUT(A/B)
Table 2: Flash Current Register: FL1-FL4 (RFSET = 280k).
Shutdown
Since the sink switches are the only power returns for all loads, there is no leakage current when all of the sink switches are disabled. To activate the shutdown mode, hold both the BENS and FENS inputs low for longer than TBENS(OFF) or TFENS(OFF) (500s). In this state, the AAT2842 typically draws less than 1A from the input. Data and address registers are reset to 0 in shutdown.
Figure 2: Selection of External Resistors. To select appropriate resistor values, first choose R1 such that the feedback network bias current is reasonable. Then, according to the desired VOUT, calculate R2 according to the equation below. An example calculation follows. R1 is chosen to be 120K, resulting in a small feedback network bias current of 1.2V/120K = 10A. The desired output voltage is 1.8V. From this information, R2 is calculated from the equation below.
Low Dropout Regulators
The AAT2842 includes two LDO linear regulators. The regulators run from the same 2.7V to 5.5V input voltage as the charge pump. The regulators use a single on/off control input, ENL. The LDO output voltages are set through a resistive voltage divider from the output (OUTA or OUTB) to the feedback input (FBA or FBB). The ratio of resistor values determines the LDO output voltage. The low 200mV dropout voltage at 200mA load current allows the regulator to maintain output voltage regulation. Each LDO regulator can supply a continuous load current up to 200mA. Both LDOs include current limiting and thermal overload protection to prevent damage to the load or to the LDOs.
R2 =
R1(VOUT - 1.2V) 1.2V
The result is R2 = 60K. Since 60K is not a standard 1% value, 60.4K is selected. From this example calculation, for VOUT = 1.8V, use R1 = 120K and R2 = 60.4K. Example output voltages and corresponding resistor values are provided in Table 3.
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2842.2007.09.1.2
AAT2842
High-Current Charge Pump with S2CwireTM Control and Dual LDO for Backlight and Flash
R2 Standard 1% Values (R1 = 120K) VOUT (V) R2 ()
2.8 2.5 2.0 1.8 1.5 160K 130K 79.6K 60.4K 30.1K
RFSET =
150mA * 280k IFLED(MAX)
This is illustrated graphically in Figure 4.
Maximum Flash LED Current vs. RFSET
180 160 140 120 100 80 60 40 20 0 100 200 300 400 500 600 700 800 900 1000 1100
Table 3: Example Output Voltages and Corresponding Resistor Values.
Altering the Maximum LED Current Level from 30mA for Backlight and 150mA for Flash
The value of RBSET determines the maximum LED current level for the backlight section. In the typical application, selecting RBSET = 280k results in 30mA/channel LED current. From this reference point, the maximum current level can be modified by calculating an alternative RBSET value:
30mA * 280k IBLED(MAX)
IFLED (mA)
RFSET (k)
Figure 4: Maximum Flash Current vs. RFSET. Selection of set resistor values outside of the typical application must be carefully evaluated to ensure that the application's performance requirements can still be met.
RBSET =
This is illustrated graphically in Figure 3.
Maximum Backlight LED Current vs. RBSET
35 30
Brightness Control Using the BSET and FSET Pins
An alternative method can be used for brightness control of the flash and/or backlight sections by utilizing the corresponding set resistor pin. By using a digital I/O port or DAC output, an alternative brightness control technique can be created for each lighting section, as shown in Figure 5.
IBLED (mA)
25 20 15 10 5 0 100 200 300 400 500 600 700 800 900 1000 1100
AAT2842
RBSET (k)
Figure 3: Maximum LED Current vs RBSET. Similarly, the value of RFSET determines the maximum LED current level for the flash section. In the typical application, selecting RFSET = 280k results in 150mA/channel LED current. From this reference point, the maximum current level can be modified by calculating an alternative RFSET value:
HI/LO or VDAC
R2 B/FSET R1
Figure 5: Brightness Control Using Either BSET or FSET Resistor Pin.
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AAT2842
High-Current Charge Pump with S2CwireTM Control and Dual LDO for Backlight and Flash
Using an additional resistor to connect the BSET pin with a digital output provides a LO/HI control. When the digital output is asserted high, the resulting brightness level for the backlighting section is LO and the individual LED current levels are:
VIO 0.7V ILED(LO) = 12 * 103 R // R - R 1 2 2
Device Power Efficiency
The AAT2842 power conversion efficiency depends on the charge pump mode. By definition, device efficiency is expressed as the output power delivered to the LEDs divided by the total input power consumed.
=
POUT PIN
The same can be applied to the FSET pin. When the digital output is asserted high, the resulting brightness level for the flash section is LO and the individual LED current levels are:
VIO 0.7V ILED(LO) = 60 * 103 R // R - R 1 2 2
When the input voltage is sufficiently greater than the LED forward voltages, the device optimizes efficiency by operating in 1X mode. In 1X mode, the device is working as a bypass switch and passing the input supply directly to the output. By simplifying the conditions such that the LEDs have uniform VF, the power conversion efficiency can be approximated by:
VF * ILED VF VIN * IIN VIN
When the digital output is asserted low, the resulting brightness level for the backlighting section is HI and the individual LED current levels are:
0.6V ILED(HI) = 12 * 103 R // R 1 2
=
The same can be applied to the FSET pin. When the digital output is asserted low, the resulting brightness level for the flash section is HI and the individual LED current levels are:
0.6V ILED(HI) = 60 * 103 R // R 1 2
Due to the very low 1X mode quiescent current, the input current nearly equals the total output current delivered to the LEDs. Further, the low resistance bypass switch introduces negligible voltage drop from input to output. The AAT2842 further maintains optimized performance and efficiency by detecting when the input voltage is not sufficient to sustain LED drive current. The device automatically switches to 1.5X mode when the input voltage drops too low in relation to the LED forward voltages. In 1.5X mode, the output voltage can be boosted to 3/2 the input voltage. The 3/2 conversion ratio introduces a corresponding 1/2 increase in input current. For ideal conversion, the 1.5X mode efficiency is given by:
VF * ILED VF VIN * 1.5IIN 1.5 * VIN
Additionally, the output from a digital-to-analog converter can be used with either SET pin to control the brightness level. The result is like the equations above, where VIO is replaced with VDAC. Using the flash section as an example:
VDAC 0.7V ILED = 60 * 103 R // R - R 1 2 2
=
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AAT2842
High-Current Charge Pump with S2CwireTM Control and Dual LDO for Backlight and Flash
Similarly, when the input falls further, such that 1.5X mode can no longer sustain LED drive current, the device will automatically switch to 2X mode. In 2X mode, the output voltage can be boosted to twice the input voltage. The doubling conversion ratio introduces a corresponding doubling of the input current. For ideal conversion, the 2X mode efficiency is given by:
VF * ILED VF VIN * 2IIN 2 * VIN
with the AAT2842. Ceramic capacitors offer many advantages over their tantalum and aluminum electrolytic counterparts. A ceramic capacitor typically has very low ESR, is lowest cost, has a smaller PCB footprint, and is non-polarized. Low ESR ceramic capacitors help maximize charge pump transient response. Since ceramic capacitors are non-polarized, they are not prone to incorrect connection damage.
=
Equivalent Series Resistance
ESR is an important characteristic to consider when selecting a capacitor. ESR is a resistance internal to a capacitor that is caused by the leads, internal connections, size or area, material composition, and ambient temperature. Capacitor ESR is typically measured in milliohms for ceramic capacitors and can range to more than several ohms for tantalum or aluminum electrolytic capacitors.
LED Selection
The AAT2842 is designed to drive high-intensity white LEDs. It is particularly suitable for LEDs with an operating forward voltage in the range of 4.2V to 1.5V. The charge pump device can also drive other loads that have similar characteristics to white LEDs. For various load types, the AAT2842 provides a highcurrent, programmable, ideal constant current source.
Ceramic Capacitor Materials
Ceramic capacitors less than 0.1F are typically made from NPO or C0G materials. NPO and C0G materials generally have tight tolerance and are very stable over temperature. Larger capacitor values are usually composed of X7R, X5R, Z5U, or Y5V dielectric materials. Large ceramic capacitors are often available in lower-cost dielectrics, but capacitors greater than 10F are not typically required for AAT2842 applications. Capacitor area is another contributor to ESR. Capacitors that are physically larger will have a lower ESR when compared to an equivalent material smaller capacitor. These larger devices can improve circuit performance when compared to an equal value capacitor in a smaller package size.
Capacitor Selection
Careful selection of the four external capacitors CIN, C1, C2, and COUT is important because they will affect turn-on time, output ripple, and transient performance. Optimum performance will be obtained when low equivalent series resistance (ESR) ceramic capacitors are used. In general, low ESR may be defined as less than 100m. Ceramic composition capacitors are highly recommended over all other types of capacitors for use
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AAT2842
High-Current Charge Pump with S2CwireTM Control and Dual LDO for Backlight and Flash Evaluation Board Layout
Figure 2: AAT2842 Evaluation Board Top Layer.
Figure 3: AAT2842 Evaluation Board Bottom Layer. The evaluation board is flexible so that the user can disconnect the enable lines from the microcontroller and apply external enable signals. By removing the jumpers from J2, J3, and/or J4, external enable signals can be applied to the board. External enable signals must be applied to Pin 1 of each J2, J3, or J4 terminal. When applying external enable signals, consideration must be given to the voltage levels. The externally applied voltages cannot exceed the supply voltage that is applied to the IN pins of the device (DC+). The LDO loads can be connected directly to the evaluation board. For adequate performance, be sure to connect the load between OUTA/OUTB and DC-, as opposed to some other GND in the system.
Evaluation Board User Interface
The user interface for the AAT2842 evaluation board is provided through four buttons and a number of connection terminals. The board is operated by supplying external power and pressing individual buttons or button combinations. Table 4 indicates the function of each button or button combination. To power-on the board, connect a power supply or battery to the DC- and DC+ terminals. Close the board supply connection by positioning the J1 jumper to the ON position. A red LED indicates that power is applied.
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AAT2842
High-Current Charge Pump with S2CwireTM Control and Dual LDO for Backlight and Flash
Button(s) Pushed1
DATA LIGHT LIGHT+DATA MOVIE MOVIE+DATA FLASH DATA+FLASH LIGHT+MOVIE+FLASH
Description
Increment the data setting for the most recently activated mode. With backlight or movie mode activated, hold down the button to auto-cycle through the brightness levels. Toggle ON/OFF the backlighting section. Set the brightness level using the DATA button (defaults to Data 1). Decrement the brightness setting for backlight mode. Hold down to auto-cycle. Toggle ON/OFF movie mode illumination. Set the brightness level using the DATA button (defaults to Data 10). Decrement the brightness setting for movie mode. Hold down to auto-cycle. Generate a flash pulse. Pulse duration is the lesser of 2 seconds or the CT value result. Set the brightness level using the DATA button (defaults to Data 1). Toggle ON/OFF the LDOs. Reset. Clear all data and bring all enable lines low.
Table 4: Evaluation Board User Interface.
Evaluation Board Schematics
VOUT
D1
D2
D3
D4
D5
D6
ENBL ENFL U1 AAT2842 DC+ FL3 FL4 PGND IN C2C2+ ENL
21 20 19 18 17 16 15
28 27 26 25 24 23 22
280K yields 30mA/ch max backlighting 280K yields 150mA/ch max flash
FL1 FENS BENS
FL2
BL4 BL3 BL2
1 2 3
BL1 BSET FSET AGND CT REF FBB
R9 280K
R10 280K C8 1.0F C9 1.0F
4 5 6 7
VIN C2 1.0F C4 4.7F
J1
3 2 1
CTRL_CT
C12 100F optional 100F lab supply bypass ENL
FBA IN OUTB
8 9 10
C1+ C1OUTA
11 12 13
OUT
14
VOUT R11 160K R12 120K R13 60.4K R14 120K C7 2.2F Programmed for 1.8V output by default C6 2.2F
OUTB Programmed for 2.8V output by default
C1 1.0F
C3 2.2F
C5 2.2F
OUTA
Figure 4: AAT2842 Section Schematic.
1. The "+" indicates that these buttons are pressed and released together. 2842.2007.09.1.2
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AAT2842
High-Current Charge Pump with S2CwireTM Control and Dual LDO for Backlight and Flash
VIN C11 0.1F U3
1 IN 2 NC 3 NC 4
J2
ENBL ENBL
EN/SET GND
OUT3 8 7 OUT2 6 OUT1 5
J3
ENFL ENFL
J4
ENL ENL R6 R7 R8 100K 100K 100K
AAT4291
VIN VIN R1 R2 R3 R4 1K 1K 1K 1K
1 2 3 4
U2 VDD GP5 GP4 GP3 VSS 7 GP0 GP1 6 5 GP2
8
C10 0.1F
R5 330 LED7 RED
DATA LIGHT MOVIE FLASH
SW1 SW2 SW3 SW4
PIC12F675
CTRL_CT
DC-
Figure 5: MCU and I/O Expander Section Schematic.
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AAT2842
High-Current Charge Pump with S2CwireTM Control and Dual LDO for Backlight and Flash Evaluation Board Component Listing
Component
U1 U2 U3 D1 - D4 D5, D6 C1, C2, C10 C3, C5, C6, C7 C4 C8, C9, C11 C12 R1 - R4 R5 R6 - R8 R9, R10 R11 R12, R14 R13 J1 - J4 LED7 SW1 - SW4
Part Number
AAT2842INJ-EE-T1, AAT2842IBJ-EE-T1 PIC12F675 AAT4291IJS-1-T1 LW M673 LXCL-PWF1 GRM18x GRM18x GRM18x GRM18x TAJBx Chip Resistor Chip Resistor Chip Resistor Chip Resistor Chip Resistor Chip Resistor Chip Resistor PRPN401PAEN CMD15-21SRC/TR8 PTS645TL50
Description
High-Current Charge Pump with S Cwire Control and Dual LDO for Backlight and Flash 8-bit CMOS, FLASH MCU; 8-pin PDIP I/O Expander Mini TOPLED White LED; SMT Luxeon Flash LED 1.0F, 10V, X5R, 0603, Ceramic 2.2F, 10V, X5R, 0603, Ceramic 4.7F, 10V, X5R, 0603, Ceramic 0.1F, 16V, X7R, 0603, Ceramic 100F, 10V, 10A, Tantalum 1K, 5%, 1/4W; 1206 330, 5%, 1/4W; 1206 100K, 5%, 1/4W; 1206 280K, 1%, 1/10W; 0603 160K, 1%, 1/10W; 0603 120K, 1%, 1/10W; 0603 60.4K, 1%, 1/10W; 0603 Conn. Header, 2mm Zip Red LED; 1206 Switch Tact, SPST, 5mm
2
Manufacturer
AnalogicTech Microchip AnalogicTech OSRAM Lumileds Murata Murata Murata Murata AVX Vishay Vishay Vishay Vishay Vishay Vishay Vishay Sullins Electronics Chicago Miniature Lamp ITT Industries
2842.2007.09.1.2
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AAT2842
High-Current Charge Pump with S2CwireTM Control and Dual LDO for Backlight and Flash Ordering Information
Package
TQFN44-28-0.45 TQFN44-28-0.4
Marking1
TGXYY XUXYY
Part Number (Tape and Reel)2
AAT2842IBJ-EE-T1 AAT2842INJ-EE-T1
Comments
Not recommended for new designs Recommended for new designs
All AnalogicTech products are offered in Pb-free packaging. The term "Pb-free" means semiconductor products that are in compliance with current RoHS standards, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. For more information, please visit our website at http://www.analogictech.com/pbfree.
Legend
Voltage 1.2 Code E
1. XYY = assembly and date code. 2. Sample stock is generally held on part numbers listed in BOLD.
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2842.2007.09.1.2
AAT2842
High-Current Charge Pump with S2CwireTM Control and Dual LDO for Backlight and Flash Package Information1
TQFN44-28-0.4
Pin 1 Dot by Marking Detail "A"
2.600 0.050
4.000 0.050
4.000 0.050
C0.3
2.600 0.050
Top View
Bottom View
0.400 0.050
0.430 0.050
0.750 0.050
0.230 0.050
0.203 REF 0.050 0.050
Side View
Pin 1 Indicator
Detail "A"
All dimensions in millimeters.
1. The leadless package family, which includes QFN, TQFN, DFN, TDFN and STDFN, has exposed copper (unplated) at the end of the lead terminals due to the manufacturing process. A solder fillet at the exposed copper edge cannot be guaranteed and is not required to ensure a proper bottom solder connection. 2842.2007.09.1.2
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AAT2842
High-Current Charge Pump with S2CwireTM Control and Dual LDO for Backlight and Flash
TQFN44-28-0.45 N.B.: Not recommended for new designs.
Index Area (D/2 x E/2)
Detail "A"
4.00 0.05
4.00 0.05
2.60 0.05
2.60 0.05
Top View
Bottom View
0.45 0.05
0.35 0.05
0.75 0.05 0.203 0.025 0.05 0.05
0.18 0.05
Side View
Pin 1 Indicator
0.425 0.050
Detail "A"
All dimensions in millimeters.
(c) Advanced Analogic Technologies, Inc. AnalogicTech cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an AnalogicTech product. No circuit patent licenses, copyrights, mask work rights, or other intellectual property rights are implied. AnalogicTech reserves the right to make changes to their products or specifications or to discontinue any product or service without notice. Except as provided in AnalogicTech's terms and conditions of sale, AnalogicTech assumes no liability whatsoever, and AnalogicTech disclaims any express or implied warranty relating to the sale and/or use of AnalogicTech products including liability or warranties relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right. In order to minimize risks associated with the customer's applications, adequate design and operating safeguards must be provided by the customer to minimize inherent or procedural hazards. Testing and other quality control techniques are utilized to the extent AnalogicTech deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarily performed. AnalogicTech and the AnalogicTech logo are trademarks of Advanced Analogic Technologies Incorporated. All other brand and product names appearing in this document are registered trademarks or trademarks of their respective holders.
Advanced Analogic Technologies, Inc.
3230 Scott Boulevard, Santa Clara, CA 95054 Phone (408) 737- 4600 Fax (408) 737- 4611 22
2842.2007.09.1.2

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