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PRODUCT DATASHEET
AAT2845
ChargePumpTM
General Description
The AAT2845 is a highly integrated power solution for single-cell lithium-ion-based LCD display applications. It includes a four-channel LED backlight driver and two integrated 200mA LDOs as additional power supplies for display and camera-related chipsets. The backlight driver is a low noise, constant frequency charge pump DC/DC converter that uses a tri-mode load switch (1X), fractional (1.5X), and doubling (2X) conversion to maximize efficiency. Each of the four channels is capable of driving up to 20mA per channel. AnalogicTech's S2CwireTM (Simple Serial ControlTM) serial digital input is used to enable, disable, and set current for each LED with 16 available settings down to 50A. The low current mode supply current can be as low as 50A to save power and maintain high efficiency. Each LED output is equipped with built-in protection for short-circuit and auto-disable functions. Built-in softstart circuitry prevents excessive inrush current during start-up. A low current shutdown feature disconnects the load from the input and reduces quiescent current to less than 1A. The AAT2845 is available in a Pb-free, thermallyenhanced 20-pin 3x4mm TQFN package.
Four-Channel Backlight Driver with Dual LDOs
Features
* Input Voltage Range: 2.7V to 5.5V * Four-Channel LED Driver: Tri-Mode Charge Pump Up to 20mA/Channel Easy Control with Single Wire Interface 16 Current Levels Four Low Current Settings Down to 50A Low IQ (50A) for Low Current Mode >90% Peak Efficiency * Dual, 200mA LDOs User-Programmable Outputs: AAT2845-EE Fixed Output Voltages * AAT2845-QG: 2.8V and 1.5V * AAT2845-QI: 2.8V and 1.8V * Automatic Soft-Start * Over-Temperature Protection * Available in 3x4mm TQFN34-20 Package * -40C to +85C Temperature Range
Applications
* * * * Camera Function Power Supplies Camera Phone Displays LCD Modules White LED Backlighting
Typical Application
CF1 1F C1CF2 1F C2+
CF1 1F C1-
CF2 1F C2+
C1+ C2-
C1+ C2-
OUT IN
VBAT 3.6V
OUT
COUT 1F
AAT2845-EE
CIN 2.2F
WLEDs OSRAM LW M673 or equivalent
IN
VBAT 3.6V
AAT2845-QI
CIN 2.2F
COUT 1F
WLEDs OSRAM LW M673 or equivalent
D1 D2 D3 D4 IN LDOA 200mA
COUTA 2.2F
D1 D2 D3 D4 IN LDOA
COUTA 2.2F VOUTA 2.8V, 200mA
FBA S2Cwire Backlight Control LDO Enable
CBYP 0.1F
EN/SET LDOB ENLDO CBP FBB GND/PGND
200mA
COUTB 2.2F
S2Cwire Backlight Control LDO Enable
CBYP 0.1F
EN/SET LDOB ENLDO CBP GND/PGND
COUTB 2.2F
VOUTB 1.8V, 200mA
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PRODUCT DATASHEET
AAT2845
ChargePumpTM
Pin Descriptions
Symbol Pin #
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 EP AAT2845-EE D2 D1 LDOB IN PGND IN FBA LDOA C2C2+ OUT C1C1+ EN/SET ENLDO D4 D3 GND CBP FBB AAT2845-QG/QI D2 D1 LDOB IN PGND IN N/C LDOA C2C2+ OUT C1C1+ EN/SET ENLDO D4 D3 GND CBP N/C
Four-Channel Backlight Driver with Dual LDOs
Function
Current sink input #2. Current sink input #1. Output of LDO B. Connect a 2.2F or larger ceramic capacitor to GND. Input power supply for charge pump. Requires a 2.2F or larger ceramic capacitor connected between IN and PGND. Power ground. Connect PGND to GND at a single point as close to the AAT2845 as possible. Input power pin for both LDOs. Connect Pin 6 to Pin 4 with as short a PCB trace as practical. AAT2845-EE: Feedback pin for LDOA. Internally regulated at 1.2V. AAT2845-QG/QI: No connection. Do not make any connection to this pin. Output of LDOA. Connect a 2.2F or larger ceramic capacitor to GND. Negative terminal of Charge Pump Capacitor 2. Positive terminal of Charge Pump Capacitor 2. Connect a 1F ceramic capacitor between C2+ and C2-. Charge pump output to drive load circuit. Connect a 1F or larger ceramic capacitor between OUT and PGND. Negative terminal of Charge Pump Capacitor 1. Positive terminal of Charge Pump Capacitor 1. Connect a 1F ceramic capacitor between C1+ and C1-. S2Cwire control pin for backlight LED current control. Enable input pin for LDOA and LDOB. Current sink input #4. Current sink input #3. Ground. Connect GND to PGND at a single point as close to the AAT2845 as possible. Bypass pin for the internal reference. Connect a 0.1F ceramic capacitor from CBP to GND. AAT2845-EE: Feedback pin for LDOB. Internally regulated at 1.2V. AAT2845-QG/QI: No connection. Do not make any connection to this pin. Exposed paddle (bottom). Connect to PGND as close as possible to the device.
Pin Configuration
AAT2845-EE TQFN34-20 (Top View) AAT2845-QG/-QI TQFN34-20 (Top View)
D3 GND CBP FBB
20 19 18 17
D3 GND CBP N/C
20 19 18 17
D2 D1 LDOB IN PGND IN
1 2 3 4 5 6 10 9 7 8
16 15 14 13 12 11
D4 ENLDO EN/SET C1+ C1OUT
D2 D1 LDOB IN PGND IN
1 2 3 4 5 6 10 9 7 8
16 15 14 13 12 11
D4 ENLDO EN/SET C1+ C1OUT
C2+ C2LDOA FBA
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C2+ C2LDOA N/C
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PRODUCT DATASHEET
AAT2845
ChargePumpTM
Absolute Maximum Ratings1
TA = 25C, unless otherwise noted. Pin descriptions below apply to AAT2845-EE (AAT2845-QG/-QI). Symbol Description
IN, OUT, D1, D2, D3, D4 Voltage to GND/PGND C1+, C1-, C2+, C2- Voltage to GND/PGND LDOA, LDOB, FBA (N/C), FBB (N/C), EN/SET, ENLDO, CBP Voltage to GND/PGND PGND Voltage to GND/PGND Operating Temperature Range Maximum Soldering Temperature (at leads, 10 sec)
Four-Channel Backlight Driver with Dual LDOs
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, 3
Symbol
JA PD
Description
Thermal Resistance Maximum Power Dissipation
Value
50 2
Units
C/W 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. Derate 20mW/C above 40C ambient temperature. 3. Mounted on a FR4 circuit board.
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PRODUCT DATASHEET
AAT2845
ChargePumpTM
Electrical Characteristics1
IN = 3.6V; CIN = COUTA = COUTB = 2.2F; COUT = 1F; C1 = C2 = 1.0F; CBP = 0.1F; TA = 25C, unless otherwise noted. Typical values are at TA = 25C. Symbol Description Conditions Min
2.7 EN/SET = ENLDO = GND 1X Mode, 3.0 VIN 5.5, Active, No Load Current 1.5X Mode, 3.0 VIN 5.5, Active, No Load Current 2X Mode, 3.0 VIN 5.5, Active, No Load Current 50A Setting, 1X Mode 20mA Setting, TA = 25C 1mA Setting, TA = 25C VIN - VF = 1.5V
Four-Channel Backlight Driver with Dual LDOs
Typ
Max
5.5 1.0 1.0 3.0 5.0
Units
V A
Power Supply IN Input Voltage ISHDN Total Shutdown Current at VIN and LDOIN Charge Pump
ICC
Operating Current
mA
IDX I(D-Match)
Average Current Accuracy
2
18 0.9
Current Matching 1X to 1.5X or 1.5X to 2X Transition VTH Threshold at Any DX Pin TSS Soft-Start Time Clock Frequency FCLK TSD Over-Temperature Shutdown Threshold THYS Over-Temperature Shutdown Hysteresis EN/SET Logic Control TEN/SET LO EN/SET Low Time TEN/SET HI MIN Minimum EN/SET High Time TEN/SET HI MAX Maximum EN/SET High Time TOFF EN/SET Off Timeout TLAT EN/SET Latch Timeout EN/SET Input Low Threshold Voltage VIL(EN/SET) VIH(EN/SET) EN/SET Input High Threshold Voltage IEN/SET EN/SET Input Leakage
50 20 1.0 0.5 150 100 1 140 15
A 22 1.1 1.0 mA % mV s MHz C C 75 s ns s s s V V A
0.3 50
75 500 500 0.4 VEN/SET = VIN = 5V 1.4 -1 1
1. The AAT2845 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.
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2845.2008.05.1.2
PRODUCT DATASHEET
AAT2845
ChargePumpTM
Electrical Characteristics1
IN = 3.6V; CIN = COUTA = COUTB = 2.2F; COUT = 1F; C1 = C2 = 1.0F; CBP = 0.1F; TA = 25C, unless otherwise noted. Typical values are at TA = 25C. Symbol Description Conditions
ENLDO = IN, EN/SET = AGND, No Load IOUT = 1mA to 200mA IOUT = 150mA VIN = (VOUT + 1V) to 5.0V IOUT =10mA, 1kHz ENLDO = IN, EN/SET = GND, No Load IOUTA = 1mA to 150mA IOUTB = 1mA to 150mA IOUTA/B = 150mA VIN = (LDOA + 1V) to 5.0V; VIN = (LDOB + 1.2V) to 5.0V
Four-Channel Backlight Driver with Dual LDOs
Min
Typ
80 1.2 150 0.09 50 80 2.8 1.5 150 0.09
Max
150 1.23 300
Units
A V mV %/V dB
LDOs: AAT2845-EE IIN IN Operating Current VFBA, VFBB Feedback Voltage VDO Dropout Voltage VOUT/ Line Regulation VOUT*VIN PSRR Power Supply Rejection Ratio LDOs: AAT2845-QG IN Operating Current IIN LDOA LDOA Voltage Tolerance LDOB LDOB Voltage Tolerance VDO LDOA, LDOB Dropout Voltage2 VLDOA/B/ LDOA, LDOB Line Regulation VLDOA/B*VIN PSRR LDOA, LDOB Power Supply Rejection Ratio LDOs: AAT2845-QI IIN IN Operating Current LDOA LDOA Voltage Tolerance LDOB LDOB Voltage Tolerance VDO LDOA, LDOB Dropout Voltage2 VLDOA/B/ LDOA, LDOB Line Regulation VLDOA/B*VIN PSRR LDOA, LDOB Power Supply Rejection Ratio LDO Logic Control - All Options VIL(ENLDO) ENLDO Pins Logic Low Threshold ENLDO Pins Logic High Threshold VIH(ENLDO) IENLDO ENLDO Input Leakage
1.17
2.716 1.455
150 2.884 1.545 300
A V V mV %
50 ENLDO = IN, EN/SET = GND, No Load IOUTA = 1mA to 150mA IOUTB = 1mA to 150mA IOUTA/B = 150mA VIN = (LDOA/B + 1V) to 5.0V 80 2.8 1.8 150 0.09 50 0.4 VENLDO = VIN = 5V 1.4 -1 1 150 2.884 1.854 300
dB A V V mV % dB V V A
2.716 1.746
1. The AAT2845 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. VDO is defined as VIN - LDOA/B when LDOA/B is 98% of nominal.
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PRODUCT DATASHEET
AAT2845
ChargePumpTM
Typical Characteristics
IN = 3.6V; CIN = COUTA = COUTB = 2.2F; COUT = 1F; C1 = C2 = 1.0F; CBP = 0.1F; TA = 25C, unless otherwise noted. Typical values are at TA = 25C.
Four-Channel Backlight Driver with Dual LDOs
Backlight Efficiency vs. Supply Voltage
100 90
Turn-On to 1X Mode
(VIN = 4.2V; 20mA/ch Load) EN/SET (2V/div) VOUT (2V/div)
Efficiency (%)
80 70 60 50 40 30
20mA/ch
1mA/ch 14.7mA/ch
VSINK (1V/div) IIN (100mA/div)
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)
Time (100s/div)
Turn-On to 1.5X Mode
(VIN = 3.5V; 20mA/ch Load) EN/SET (2V/div) VOUT (2V/div) VSINK (1V/div) IIN (200mA/div)
Turn-On to 2X Mode
(VIN = 2.8V; 20mA/ch Load)
EN/SET (2V/div) VOUT (2V/div) VSINK (500mV/div) IIN (500mA/div)
Time (100s/div)
Time (100s/div)
Turn-Off from 1.5X Mode Backlight
(30mA/ch; Data 1)
EN (2V/div) VDIODE (2V/div)
IIN (200mA/div)
Time (100s/div)
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2845.2008.05.1.2
PRODUCT DATASHEET
AAT2845
ChargePumpTM
Typical Characteristics
IN = 3.6V; CIN = COUTA = COUTB = 2.2F; COUT = 1F; C1 = C2 = 1.0F; CBP = 0.1F; TA = 25C, unless otherwise noted. Typical values are at TA = 25C.
Four-Channel Backlight Driver with Dual LDOs
Backlight Operating Characteristic
(VIN = 2.9V; 2X Mode; 14mA/ch Load)
Backlight Operating Characteristic
(VIN = 2.9V; 2X Mode; 20mA/ch Load)
VIN (20mV/div) VCP (40mV/div) VSINK (40mV/div)
VIN (20mV/div) VCP (40mV/div) VSINK (40mV/div)
Time (500ns/div)
Time (500ns/div)
Backlight Operating Characteristic
(VIN = 3.5V; 1.5X Mode; 14mA/ch Load)
Backlight Operating Characteristic
(VIN = 3.7V; 1.5X Mode; 20mA/ch Load)
VIN (20mV/div) VCP (40mV/div) VSINK (20mV/div)
VIN (20mV/div) VCP (40mV/div) VSINK (20mV/div)
Time (500ns/div)
Time (500ns/div)
EN/SET Latch Timeout vs. Supply Voltage
EN/SET Latch Timeout (s) EN/SET Off Timeout (s)
400 350 300 250 200 150 100 50 0 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 5.5 500 450 400 350 300 250 200 150 100 50
EN/SET Off Timeout vs. Supply Voltage
-40C
-40C
25C
85C
25C
85C
0 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)
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PRODUCT DATASHEET
AAT2845
ChargePumpTM
Typical Characteristics
IN = 3.6V; CIN = COUTA = COUTB = 2.2F; COUT = 1F; C1 = C2 = 1.0F; CBP = 0.1F; TA = 25C, unless otherwise noted. Typical values are at TA = 25C.
Four-Channel Backlight Driver with Dual LDOs
EN/SET High Threshold Voltage (V)
EN/SET Low Threshold Voltage (V)
EN/SET and ENLDO Low Threshold Voltage vs. Supply Voltage and Temperature
1 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
EN/SET and ENLDO High Threshold Voltage vs. Supply Voltage and Temperature
1 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
-40C
-40C
25C
85C
25C
85C
Supply Voltage (V)
Supply Voltage (V)
AAT2845-EE LDOA Turn-On Characteristic
(VOUTA = VFBA)
AAT2845-EE LDOB Turn-On Characteristic
(VOUTB = VFBB)
ENLDO (2V/div)
ENLDO (2V/div)
VOUT (500mV/div)
VOUT (500mV/div)
Time (50s/div)
Time (50s/div)
AAT2845-QG/QI LDOA Turn-On Characteristic
(VOUTA = 2.8V)
AAT2845-QI LDOB Turn-On Characteristic
(VOUTB = 1.8V)
ENLDO (2V/div)
ENLDO (2V/div)
VOUT (1V/div)
VOUT (500mV/div)
Time (50s/div)
Time (50s/div)
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2845.2008.05.1.2
PRODUCT DATASHEET
AAT2845
ChargePumpTM
Typical Characteristics
IN = 3.6V; CIN = COUTA = COUTB = 2.2F; COUT = 1F; C1 = C2 = 1.0F; CBP = 0.1F; TA = 25C, unless otherwise noted. Typical values are at TA = 25C.
Four-Channel Backlight Driver with Dual LDOs
AAT2845-QG LDOB Turn-On Characteristic
(VOUTB = 1.5V)
LDOs A and B Line Regulation, All Options
(10mA Load)
0.4 0.3
Error (%)
ENLDO (2V/div)
0.2 0.1 0.0 -0.1 -0.2 -0.3 -0.4 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
OUTA
VOUT (500mV/div)
OUTB
Time (50s/div)
Supply Voltage (V)
LDOs A and B Load Regulation, All Options
1.0 0.8 0.6 0.4 0.2 0.0 -0.2 -0.4 -0.6 -0.8 -1.0 0.1 1 10 100 1000
LDOB Line Transient Response, All Options
(10mA Load)
VIN (400mV/div) VIN = 4.2V OUTA VOUT (10mV/div) VIN = 3.7V
Error (%)
OUTB
Load Current (mA)
Time (40s/div)
LDOB Line Transient Response, All Options
(10mA Load)
VIN (400mV/div) VIN = 4.2V VIN = 3.7V VOUT (10mV/div)
Time (40s/div)
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PRODUCT DATASHEET
AAT2845
ChargePumpTM
Typical Characteristics
IN = 3.6V; CIN = COUTA = COUTB = 2.2F; COUT = 1F; C1 = C2 = 1.0F; CBP = 0.1F; TA = 25C, unless otherwise noted. Typical values are at TA = 25C.
Four-Channel Backlight Driver with Dual LDOs
LDOA Load Transient Response, All Options
LDOB Load Transient Response, All Options
IOUT (100mA/div)
IOUT (100mA/div)
VOUT (100mV/div)
VOUT (100mV/div)
Time (20s/div)
Time (20s/div)
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2845.2008.05.1.2
PRODUCT DATASHEET
AAT2845
ChargePumpTM
Functional Block Diagram
C1+ C1- C2+ C2-
Four-Channel Backlight Driver with Dual LDOs
IN
Tri-Mode (1X, 1.5X and 2X) Charge Pump
OUT
Soft-Start Control 1MHz Oscillator Voltage Reference D/A D/A
D1 D2 D3 D4
EN/SET
S2Cwire Interface
6x16 Bit ROM
D/A D/A
IN
LDO A
LDOA FBA
ENLDO
1.2V Reference
CBP
LDO B
LDOB FBB
GND
Functional Description
The AAT2845 is an integrated solution for LCD display applications with a built-in driver for white LED backlight and two LDO voltage regulators for logic power supplies. The backlight driver is a tri-mode load switch (1X) and high-efficiency (1.5X or 2X) charge pump device. To maximize power conversion efficiency, an internal sensing circuit monitors the voltage required on each constant current sink input and sets the load switch and charge pump modes based on the input battery voltage and the current sink input voltage. As the battery discharges over time, the charge pump is enabled when any of the four current sink inputs nears dropout. The charge pump initially starts in 1.5X mode. If the charge pump output droops enough for any current source output to become close to dropout, the charge pump will automatically transition to 2X mode. The charge pump requires only four external components: two 1F ceramic capacitors for the charge pump flying capacitors (C1 and C2), one 1F
ceramic input capacitor (CIN), and one 0.33F to 1F ceramic charge pump output capacitor (COUT). The four constant current sink inputs (D1 to D4) can drive four individual LEDs with a maximum current of 20mA each. The unused sink inputs must be connected to the OUT pin; otherwise the part will operate only in 2X charge pump mode. The S2Cwire serial interface enables the charge pump and sets the current sink magnitudes.
Constant Current Output Level Settings
The constant current sink levels for D1 to D4 are set via the S2Cwire serial interface according to a logarithmic scale for the first 12 codes, and a separate low-current scale for the last four codes. Because the inputs D1 to D4 are true independent constant current sinks, the voltage observed on any single given input will be determined by the difference between VOUT and the actual forward voltage (VF) of the LED being driven.
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PRODUCT DATASHEET
AAT2845
ChargePumpTM Four-Channel Backlight Driver with Dual LDOs
programming, the number of rising edges corresponding to the desired code must be applied on the EN/SET pin. When the EN/SET pin is held low for an amount of time longer than TOFF (500s), the AAT2845 enters shutdown mode and draws less than 1A from the input. An internal data register is reset to zero during shutdown. Since the current level is programmable, no PWM (pulse width modulation) or additional control circuitry is needed to control LED brightness. This feature greatly reduces the burden on a microcontroller or system IC to manage LED or display brightness, allowing the user to "set it and forget it." With its high-speed serial interface (>1MHz data rate), the LED current drive can be changed successively to brighten or dim LEDs in smooth transitions (e.g., to fade out) or in abrupt steps, giving the user complete programmability and real-time control of LED brightness. The last four codes of the current level scale engage a reduced quiescent current mode that enhances the lowcurrent setting efficiency. This mode is especially useful for low-current applications where a continuous, low-current state is maintained for a substantial length of time.
Auto-Disable Feature
The charge pump in the AAT2845 is equipped with an auto-disable feature for each LED channel. After the IC is enabled and started up, a test current of 100A (typical) is forced through each sink channel. The channel will be disabled if the voltage of that particular DX pin does not drop to a certain threshold. This feature is convenient for disabling an unused channel or during an LED fail-short event.
S2Cwire Serial Interface
The current sink magnitude is controlled by AnalogicTech's S2Cwire serial digital input. The interface records rising edges of the EN/SET pin and decodes them into 16 different states. The 16 current level settings available are indicated in Table 1. Output (mA/Ch)
20 18.9 18.0 17.0 15.7 14.8 10.2 8.0
Low Dropout Regulators
The AAT2845 product family includes two LDO linear regulators. The regulators run from the same 2.7V to 5.5V input voltage as the charge pump and have a common ON/OFF control input, ENLDO. For the AAT2845-EE, the LDO output voltages are set through a resistive voltage divider from the output (OUTLDOA or OUTLDOB) to the feedback input (FBA or FBB). The ratio of resistor values determines the LDO output voltage. For the AAT2845-QG option, LDOA is internally set to 2.8V and LDOB is internally set to 1.5V. For the AAT2845-QI option, LDOA is also 2.8V and LDOB is internally set to 1.8V. 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, and both LDOs include current limiting and thermal overload protection to prevent damage to the load or to the LDOs.
Data
1 2 3 4 5 6 7 8
Data
9 10 11 12 13 14 15 16
Output (mA/Ch)
6.0 4.2 2.9 2.0 1.0 0.53 0.10 0.05
Table 1: Current Level Settings. The S2Cwire serial interface has flexible timing. Data can be clocked-in at speeds higher than 1MHz, or much slower, such as 15kHz. After data is applied, EN/SET is held high to latch the data. Once EN/SET has been held in the logic high state for time TLAT (500s), the programmed current becomes active and the internal data register is reset to zero. For subsequent current level
Thermal Protection
The charge pump has a built-in thermal protection circuit that will shut down the charge pump and the LDOs if the die temperature rises above the thermal limit, as is the case during a short-circuit of the OUT pin.
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2845.2008.05.1.2
PRODUCT DATASHEET
AAT2845
ChargePumpTM
T HI T LO TLAT TOFF
Four-Channel Backlight Driver with Dual LDOs
EN/SET
1 2 n-1 n 16
Data Reg
0
n-1
0
Figure 1: S2Cwire Serial Interface Timing.
Applications Information
LED Selection
The AAT2845 is specifically intended for driving white LEDs. However, the device design will allow the AAT2845 to drive most types of LEDs with forward voltage specifications ranging from 2.0V to 4.7V. LED applications may include mixed arrangements for display backlighting, color (RGB) LEDs, infrared (IR) diodes, and any other load needing a constant current source generated from a varying input voltage. Since the D1 to D4 constant current sinks are matched with negligible voltage dependence, the constant current channels will be matched regardless of the specific LED forward voltage (VF) levels. The low dropout current sinks in the AAT2845 maximize performance and make it capable of driving LEDs with high forward voltages. Multiple channels can be combined to obtain a higher LED drive current without complication.
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 the EN/SET input low for longer than TOFF (500s). In this state, the AAT2845 typically draws less than 1A from the input. Data and address registers are reset to 0 in shutdown.
AAT2845-EE LDO Output Voltage Programming
The output voltages for LDOA and LDOB are programmed by an external resistor divider network. As shown below, 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.
LDO(A/B) VOUT(A/B) R2(A/B) FB(A/B) VREF = 1.2V R1(A/B)
Device Switching Noise Performance
The AAT2845 operates at a fixed frequency of approximately 1MHz to control noise and limit harmonics that can interfere with the RF operation of cellular telephone handsets or other communication devices. Back-injected noise appearing on the input pin of the charge pump is 20mV peak-to-peak, typically ten times less than inductor-based DC/DC boost converter white LED backlight solutions. The AAT2845 soft-start feature prevents noise transient effects associated with inrush currents during start-up of the charge pump circuit.
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.
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PRODUCT DATASHEET
AAT2845
ChargePumpTM Four-Channel Backlight Driver with Dual LDOs
The AAT2845 efficiency may be quantified under very specific conditions and is dependent upon the input voltage versus the output voltage seen across the loads applied to outputs D1 through D4 for a given constant current setting. Depending on the combination of VIN and voltages sensed at the current sinks, the device will operate in load switch mode. When any one of the voltages sensed at the current sinks nears dropout, the device will operate in 1.5X or 2X charge pump mode. Each of these modes will yield different efficiency values. Refer to the following two sections for explanations for each operational mode. 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.
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. A table of example output voltages and corresponding resistor values is provided below. R2 Standard 1% Values (R1 = 120K) VOUT (V)
2.8 2.5 2.0 1.8 1.5
1X Mode Efficiency
The AAT2845 1X mode is operational at all times and functions alone to enhance device power conversion efficiency when VIN is higher than the voltage across the load. When in 1X mode, voltage conversion efficiency is defined as output power divided by input power:
R2 ()
160K 130K 79.6K 60.4K 30.1K
Table 2: Example Output Voltages and Corresponding Resistor Values
=
POUT PIN
Power Efficiency and Device Evaluation
The charge pump efficiency discussion in the following sections accounts only for efficiency of the charge pump section itself. Due to the unique circuit architecture and design of the AAT2845, it is very difficult to measure efficiency in terms of a percent value comparing input power over output power. Since the AAT2845 outputs are pure constant current sinks and typically drive individual loads, it is difficult to measure the output voltage for a given output (D1 to D4) to derive an overall output power measurement. For any given application, white LED forward voltage levels can differ, yet the output drive current will be maintained as a constant. This makes quantifying output power a difficult task when taken in the context of comparing to other white LED driver circuit topologies. A better way to quantify total device efficiency is to observe the total input power to the device for a given LED current drive level. The best white LED driver for a given application should be based on trade-offs of size, external component count, reliability, operating range, and total energy usage...not just % efficiency.
The expression to define the ideal efficiency () can be rewritten as:
=
-or-
POUT VOUT * IOUT VOUT = = PIN VIN * IOUT VIN VOUT VIN
(%) = 100
1.5X and 2X Charge Pump Mode Efficiency
The AAT2845 contains a fractional charge pump which will boost the input supply voltage in the event where VIN is less than the voltage required to supply the output. The efficiency () can be simply defined as a linear voltage regulator with an effective output voltage that is equal to one and one half or two times the input voltage. Efficiency () for an ideal 1.5X charge pump can typically be expressed as the output power divided by the input power.
=
POUT PIN
In addition, with an ideal 1.5X charge pump, the output current may be expressed as 2/3 of the input current.
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PRODUCT DATASHEET
AAT2845
ChargePumpTM Four-Channel Backlight Driver with Dual LDOs
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. The expression to define the ideal efficiency () can be rewritten as:
=
-or-
POUT VOUT * IOUT VOUT = = PIN VIN * 1.5IOUT 1.5VIN (%) = 100 VOUT 1.5VIN
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 (i.e., larger than 2.2F) are often available in low-cost Y5V and Z5U dielectrics, but capacitors larger than 1F are not typically required for AAT2845 applications. Capacitor area is another contributor to ESR. Capacitors that are physically large will have a lower ESR when compared to an equivalent material smaller capacitor. These larger devices can improve circuit transient response when compared to an equal value capacitor in a smaller package size.
For a charge pump with an output of 5V and a nominal input of 3.5V, the theoretical efficiency is 95%. Due to internal switching losses and IC quiescent current consumption, the actual efficiency can be measured at 93%. These figures are in close agreement for output load conditions from 1mA to 100mA. Efficiency will decrease substantially as load current drops below 1mA or when the voltage level at VIN approaches the voltage level at VOUT. The same calculations apply for 2X mode, where the output current then becomes 1/2 of the input current.
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. A value of 1F for all four capacitors is a good starting point when choosing capacitors. If the constant current sinks are only programmed for light current levels, then the capacitor size may be decreased.
Evaluation Board User Interface
The user interface for the AAT2845 evaluation board is provided by three buttons and two connection terminals. The board is operated by supplying external power and pressing individual buttons or button combinations. The table below indicates the function of each button or button combination. To power-on the evaluation board, connect a power supply or battery to the DC- and DC+ terminals. Close the board's supply connection by positioning the J1 jumper to the ON position. A red LED indicates that power is applied. The evaluation board is made flexible so that the user can disconnect the enable lines from the microcontroller and apply external enable signals. By removing the jumpers from J2, and/or J3, external enable signals can be applied to the board. External enable signals must be applied to the ON pin of each J2, or J3 terminal. When applying external enable signals, consideration must be given to the voltage levels. The externally applied voltages should not 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.
Capacitor Characteristics
Ceramic composition capacitors are highly recommended over all other types of capacitors for use with the AAT2845. 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
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PRODUCT DATASHEET
AAT2845
ChargePumpTM
Evaluation Board Layout
Four-Channel Backlight Driver with Dual LDOs
Figure 3: AAT2845 Evaluation Board Top Layer. Button(s) Pushed1
DATA LIGHT LIGHT+DATA ENLDO DATA+LIGHT+ENLDO
Figure 4: AAT2845 Evaluation Board Bottom Layer.
Description
Increment the backlight data setting. 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. Decrement the backlight data setting. Hold down to auto-cycle. Toggle ON/OFF the LDOs. Reset. Clear data and bring all enable lines low.
Table 3: Evaluation Board User Interface.
1. The "+" indicates that these buttons are pressed and released together.
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PRODUCT DATASHEET
AAT2845
ChargePumpTM
DC+
Four-Channel Backlight Driver with Dual LDOs
1
2
3
VOUT C9 100F
J1 Optional 100F capacitor to bypass lab supply
D1
D2
D3
D4
C7 0.1F
20 19 18 17
CBYP
FBB
GND
1 2
D3
U1 AAT2845 D4
16 15 14 13 12 11
D2 D1 LDOB IN PGND IN LDOA FBA C2-
ENLDO EN/SET C1+ C1OUTCP C2+
ENL C1 1.0F EN/SET
OUTB Programmed for 2.8V output R10 160K R11 120K C6 2.2F
3 4 5 6
C4 2.2F
C3 1.0F
7
8
9
10
C2 1.0F
OUTA R8 60.4K R9 120K C5 2.2F Programmed for 1.8V output
Figure 5: AAT2845-EE Section Schematic.
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PRODUCT DATASHEET
AAT2845
ChargePumpTM Four-Channel Backlight Driver with Dual LDOs
J2 R6 220
3 2 1
EN/SET R7 100K
VIN VIN R1 R2 R3 1K 1K 1K U2
1 2 3 4
DATA SW1 LIGHT SW2 ENLDO SW3
VDD GP5 GP4 GP3 PIC12F675
VSS GP0 GP1 GP2
8 7 6 5
C8 1F
R5 330 LED7 RED
J3 ENL
3 2 1
R4 100K DC-
Figure 6: MCU Section Schematic.
Evaluation Board Component Listing
Component
U1 U2 D1 - D4 C1 - C3 C4 - C6 C7 C8 C9 R1 - R3 R4, R7 R5 R6 R8 R9, R11 R10 J1 - J3 LED7 SW1 - SW3
Part#
AAT2845IML-EE-T1 PIC12F675 LW M673 GRM18x GRM18x GRM18x GRM31x TAJBx Chip Resistor Chip Resistor Chip Resistor Chip Resistor Chip Resistor Chip Resistor Chip Resistor PRPN401PAEN CMD15-21SRC/TR8 PTS645TL50
Description
Four-Channel Backlight Driver with Dual LDOs 8-bit CMOS, FLASH MCU; 8-pin PDIP Mini TOPLED White LED; SMT 1.0F, 10V, X5R, 0603, ceramic 2.2F, 10V, X5R, 0603, ceramic 0.1F, 16V, X7R, 0603, ceramic 1F, 10V, X5R, 1206, ceramic 100F, 10V, 10A, tantalum 1K, 5%, 1/4W; 1206 100K, 5%, 1/4W; 1206 330, 5%, 1/4W; 1206 220, 5%, 1/4W; 1206 60.4K, 1%, 1/10W; 0603 120K, 1%, 1/10W; 0603 160K, 1%, 1/10W; 0603 Conn. Header, 2mm zip Red LED; 1206 Switch Tact, SPST, 5mm
Manufacturer
AnalogicTech Microchip OSRAM Murata Murata Murata Murata AVX Vishay Vishay Vishay Vishay Vishay Vishay Vishay Sullins Electronics Chicago Miniature Lamp ITT Industries
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PRODUCT DATASHEET
AAT2845
ChargePumpTM
Ordering Information
Low Dropout Regulators Package
TQFN34-20 TQFN34-20 TQFN34-20 LDOA Programmable 2.8V 2.8V LDOB Programmable 1.5V 1.8V
Four-Channel Backlight Driver with Dual LDOs
Marking
UHXYY XEXYY XFXYY
Part Number (Tape and Reel)
AAT2845IML-EE-T1 AAT2845IML-QG-T1 AAT2845IML-QI-T1
Package Information3
TQFN34-20
3.00 0.05 1.55 0.05 Detail "A" 0.40 0.100
4.00 0.05
2.55 0.05
0.24 0.060
Top View
Bottom View Detail "A"
0.025 0.025
0.75 0.05
Side View
0.214 0.036
All dimensions in millimeters.
1. XYY = assembly and date code. 2. Sample stock is generally held on part numbers listed in BOLD. 3. 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.
Advanced Analogic Technologies, Inc. 3230 Scott Boulevard, Santa Clara, CA 95054 Phone (408) 737-4600 Fax (408) 737-4611
(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.
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