Analogic AAT2842 High-current charge pump with s2cwireâ ¢ control and dual ldo for backlight and flash Datasheet

AAT2842
High-Current Charge Pump with S2Cwire™
Control and Dual LDO for Backlight and Flash
General Description
Features
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 S2Cwire™ (Simple Serial Control™) 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
MicroPower™ 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 85µA quiescent current, making
them ideal for battery-operated applications.
ChargePump™
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
— 85µA Quiescent Current
Built-In Thermal Protection
Automatic Soft Start
-40°C to +85°C Temperature Range
Available in 4x4mm TQFN44-28 Package
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 -40°C to +85°C ambient temperature range.
Camera-Enabled Mobile Devices
Digital Still Cameras
Multimedia Mobile Phones
Typical Application
C1
1μF
C1+
IN
CIN
4.7μF
VBAT
EN_BACKLIGHT
EN_FLASH
C2
1μF
C1- C2+
AAT2842
IN
BENS
FENS
CT
BSET
RSET1
CT
COUT
2.2μF
BL1
BL2
BL3
BL4
FL1
FL2
FL3
FL4
OUTA
VOUT LDOA
FSET
RSET2
REF
CREF
R2A
ENL
AGND
COUTA
FBA
VOUT LDOB
OUTB
EN_LDO
2842.2007.09.1.2
C2-
OUT
R2B
FBB
PGND
R1A
COUTB
R1B
1
AAT2842
High-Current Charge Pump with S2Cwire™
Control and Dual LDO for Backlight and Flash
Pin Descriptions
2
Pin #
Symbol
1
BL1
2
BSET
3
FSET
4
5
AGND
CT
6
REF
7
FBB
8
OUTB
9, 18
IN
10
FBA
11
OUTA
12
13
14
C1C1+
OUT
15
ENL
16
17
19
20
C2+
C2PGND
FL4
21
FL3
22
FL2
23
FL1
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 280kΩ resistor from BSET to AGND sets the maximum backlight current to 30mA.
Flash current setting input. A 280kΩ 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
0.1µF 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 2.2µF 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 4.7µF 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 2.2µF 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 1µF 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 2.2µF 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 1µF 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.
2842.2007.09.1.2
AAT2842
High-Current Charge Pump with S2Cwire™
Control and Dual LDO for Backlight and Flash
Pin Descriptions (continued)
Pin #
Symbol
24
FENS
25
BENS
26
BL4
27
BL3
28
BL2
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.
EP
Pin Configuration
TQFN44-28-0.4
(Top View)
TQFN44-28-0.45
(Top View)
27
26
25
24
23
FL2
FL1
FENS
BENS
BL4
BL3
BL2
FL2
FL1
FENS
BENS
BL4
BL3
BL2
28
BL1
BSET
FSET
AGND
CT
REF
FBB
22
28
1
21
2
20
3
19
4
18
5
17
6
16
7
15
8
9
10
11
12
13
14
FL3
FL4
PGND
IN
C2C2+
ENL
BL1
BSET
FSET
AGND
CT
REF
FBB
27
26
25
24
23
22
1
21
2
20
3
19
4
18
5
17
6
16
15
7
8
9
10
11
12
13
FL3
FL4
PGND
IN
C2C2+
ENL
14
OUT
C1+
C1OUTA
FBA
IN
OUTB
OUT
C1+
C1OUTA
FBA
IN
OUTB
N.B. Not recommended for new designs.
2842.2007.09.1.2
3
AAT2842
High-Current Charge Pump with S2Cwire™
Control and Dual LDO for Backlight and Flash
Absolute Maximum Ratings1
Symbol
TJ
TLEAD
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
Units
-0.3 to 6.0
-0.3 to VOUT + 0.3
V
V
-0.3 to VIN + 0.3
V
-0.3 to 0.3
-40 to 150
300
V
°C
°C
Value
Units
2
50
W
°C/W
Thermal Information2
Symbol
PD
θJA
Description
3
Maximum Power Dissipation
Maximum Thermal Resistance
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 20mW°C above 40°C ambient temperature.
4
2842.2007.09.1.2
AAT2842
High-Current Charge Pump with S2Cwire™
Control and Dual LDO for Backlight and Flash
Electrical Characteristics1
VIN = 3.6V; CIN = 4.7µF; COUT = 2.2µF; C1 = C2 = 1.0µF; RBSET = RFSET = 280kΩ; TA = -40°C to +85°C, unless
otherwise noted. Typical values are at TA = 25°C.
Symbol
VIN
IIN(Q)
Description
Conditions
IN Operating Voltage Range
IN Operating Current
IIN(SHDN)
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
ΔI(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
ΔI(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
ΔI(FL_)
FL1-FL4 Current Matching2
FL1-FL4 Charge Pump Mode
VFL_(TH)
Transition Threshold
VFSET
RFSET Pin Voltage
Min
Typ Max Units
2.7
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 = 280kΩ, Data 1, 1X Mode
ENL = BENS = FENS = AGND, TA = 25°C
3.0
50
5.0
27
8.6
°C
15
°C
600
350
mA
mV
2
MHz
350
µs
30
0.5
150
33
1
9.6
150
1
300
0.7
mA
%
mV
V
10.6
2
mA
%
mV
165
4
mA
%
mV
60
135
µA
µA
140
0.7
VIN - VF = 1.5V
VIN - VF = 1.5V
mA
5.0
OUT = 0V to VBAT
VIN - VF = 1.5V
VIN - VF = 1.5V
V
1.0
Data 1
VIN - VF = 1.5V
VIN - VF = 1.5V
5.5
V
1. The AAT2842 is guaranteed to meet performance specifications over the -40°C to +85°C 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
5
AAT2842
High-Current Charge Pump with S2Cwire™
Control and Dual LDO for Backlight and Flash
Electrical Characteristics1
VIN = 3.6V; CIN = 4.7µF; COUT = 2.2µF; C1 = C2 = 1.0µF; RBSET = RFSET = 280kΩ; TA = -40°C to +85°C, unless
otherwise noted. Typical values are at TA = 25°C.
Symbol
Enable/Set
VBENS(L),
VFENS(L)
VBENS(H),
VFENS(H)
IBENS, IFENS
TBENS(L),
TFENS(L)
Description
Conditions
Min
Typ
BENS, FENS Low Threshold
BENS, FENS High Threshold
BENS, FENS Input Leakage
Current
Units
0.4
V
1.4
VBENS or VFENS = VIN = 5V
BENS, FENS Low Time
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
Max
V
-1
1
µA
0.3
75
µs
50
IOUT = 1mA to 200mA
ENL = IN, BENS = FENS = AGND
1.17
1.2
85
ns
75
µs
500
µs
500
µs
1.23
150
V
µA
200
IOUT = 150mA
mA
150
1.4
REF = Open
IOUT =10mA, CREF = 10nF, 1kHz
300
mV
0.4
V
V
15
µs
20
Ω
50
dB
1. The AAT2842 is guaranteed to meet performance specifications over the -40°C to +85°C operating temperature range and is assured
by design, characterization, and correlation with statistical process controls.
6
2842.2007.09.1.2
AAT2842
High-Current Charge Pump with S2Cwire™
Control and Dual LDO for Backlight and Flash
Typical Characteristics
VIN = 3.6V; CIN = 4.7µF; COUT = 2.2µF; C1 = C2 = 1.0µF; RBSET = RFSET = 280kΩ; TA = -40°C to +85°C, unless
otherwise noted. Typical values are at TA = 25°C.
Backlight Efficiency vs. Supply Voltage
Flash Efficiency vs. Supply Voltage
100
100
Efficiency (%)
90
80
70
60
7.5mA/ch
VF = 3.1V
50
40
2.1mA/ch
VF = 2.9V
90
Efficiency (%)
30mA/ch
VF = 3.7V
80
70
150mA total
VF = 2.9V
60
50
200mA total
VF = 2.9V
40
30
300mA total
VF = 3.0V
30
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 2.8 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
Supply Voltage (V)
Supply Voltage (V)
Turn On to 1X Mode Backlight
Turn On to 1.5X Mode Backlight
(30mA/ch; Data 1; VIN = 4.2V)
(30mA/ch; Data 1; VIN = 3.5V)
EN
(2V/div)
EN
(2V/div)
OUT
(2V/div)
OUT
(2V/div)
VSINK
(500mV/div)
VSINK
(500mV/div)
IIN
(100mA/div)
IIN
(200mA/div)
Time (200µs/div)
Time (200µs/div)
Turn On to 2X Mode Backlight
Turn Off from 1.5X Mode Backlight
(30mA/ch; Data 1; VIN = 3.2V)
(30mA/ch; Data 1)
EN
(2V/div)
EN
(2V/div)
OUT
(2V/div)
OUT
(2V/div)
VSINK
(500mV/div)
IIN
(200mA/div)
IIN
(200mA/div)
Time (200µs/div)
2842.2007.09.1.2
Time (100µs/div)
7
AAT2842
High-Current Charge Pump with S2Cwire™
Control and Dual LDO for Backlight and Flash
Typical Characteristics
VIN = 3.6V; CIN = 4.7µF; COUT = 2.2µF; C1 = C2 = 1.0µF; RBSET = RFSET = 280kΩ; TA = -40°C to +85°C, unless
otherwise noted. Typical values are at TA = 25°C.
BENS, FENS High Threshold Voltage
vs. Supply Voltage
1.2
1.2
-40°C
1.1
VBENS(L), VFENS(L) (V)
1.1
VBENS(H), VFENS(H) (V)
BENS, FENS Low Threshold Voltage
vs. Supply Voltage
1.0
0.9
0.8
0.7
85°C
0.6
25°C
0.5
0.4
0.3
0.9
0.8
0.7
25°C
85°C
0.6
0.5
0.4
0.3
0.2
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
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
BENS, FENS Off Timeout vs. Supply Voltage
500
350
-40°C
300
25°C
250
85°C
200
TBENS(OFF), TFENS(OFF) (µs)
400
TBENS(LAT), TFENS(LAT) (µs)
-40°C
1.0
450
400
350
300
-40°C
250
200
25°C
85°C
150
150
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 (%)
LDOs A and B Line Regulation
ENL
(2V/div)
VOUT
(500mV/div)
1.00
0.50
OUTA
0.00
OUTB
-0.50
-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 (50µs/div)
8
Input Voltage (V)
2842.2007.09.1.2
AAT2842
High-Current Charge Pump with S2Cwire™
Control and Dual LDO for Backlight and Flash
Typical Characteristics
VIN = 3.6V; CIN = 4.7µF; COUT = 2.2µF; C1 = C2 = 1.0µF; RBSET = RFSET = 280kΩ; TA = -40°C to +85°C, unless
otherwise noted. Typical values are at TA = 25°C.
LDOs A and B Load Regulation
LDOs A and B Line Transient Response
Output Voltage Accuracy (%)
(10mA Load)
1.00
VIN
(400mV/div)
0.50
OUTA
VIN = 4.2V
0.00
VIN = 3.7V
OUTB
-0.50
-1.00
0.1
1
10
100
VOUT
(10mV/div)
1000
Load Current (mA)
Time (40µs/div)
LDOs A and B Load Transient Response
(10mA to 200mA Load Step)
IOUT
(100mA/div)
IOUT = 200mA
VOUT
(100mV/div)
Time (20µs/div)
2842.2007.09.1.2
9
AAT2842
High-Current Charge Pump with S2Cwire™
Control and Dual LDO for Backlight and Flash
Functional Block Diagram
IN
IN
C1+
C1C2+
OUTA
LDO A
Tri-Mode
Charge Pump
(1X/1.5X/2X)
FBA
OUTB
C2-
LDO B
FBB
1.2V
VREF
ENL
To LDO A&B
REF
OUT
BL1
BL2
BENS
BL3
FENS
Control
Logic
CT
BL4
FL1
BSET
FL2
FSET
FL3
FL4
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.
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-
10
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.
2842.2007.09.1.2
AAT2842
High-Current Charge Pump with S2Cwire™
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
280kΩ 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 280kΩ 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.
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.
2842.2007.09.1.2
where T is in seconds and CT is in µF.
For example, for a 0.1µF capacitor:
T = 10 · 0.1μF
= 1s
To disable the flash timer, connect CT to AGND.
Data
BL% of BSET
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
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
Table 1: Backlight Current Register: BL1-BL4
(RBSET = 280kΩ).
11
AAT2842
High-Current Charge Pump with S2Cwire™
Control and Dual LDO for Backlight and Flash
Data
FL% of FSET
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
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
Table 2: Flash Current Register: FL1-FL4
(RFSET = 280kΩ).
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.
OUT(A/B)
VOUT(A/B)
R2(A/B)
FB(A/B)
VREF = 1.2V
R1(A/B)
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) (500µs).
In this state, the AAT2842 typically draws less than
1µA from the input. Data and address registers are
reset to 0 in shutdown.
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.
12
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 = 10µA.
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. Example output voltages and corresponding resistor values are provided in Table 3.
2842.2007.09.1.2
AAT2842
High-Current Charge Pump with S2Cwire™
Control and Dual LDO for Backlight and Flash
R2 Standard 1% Values (R1 = 120K)
VOUT (V)
R2 (Ω)
2.8
2.5
2.0
1.8
1.5
160K
130K
79.6K
60.4K
30.1K
RFSET =
This is illustrated graphically in Figure 4.
Maximum Flash LED Current vs. RFSET
180
Table 3: Example Output Voltages and
Corresponding Resistor Values.
The value of RBSET determines the maximum LED
current level for the backlight section. In the typical
application, selecting RBSET = 280kΩ results in
30mA/channel LED current. From this reference
point, the maximum current level can be modified
by calculating an alternative RBSET value:
RBSET =
30mA · 280kΩ
IBLED(MAX)
This is illustrated graphically in Figure 3.
Maximum Backlight LED Current vs. RBSET
35
IBLED (mA)
30
25
160
140
IFLED (mA)
Altering the Maximum LED Current
Level from 30mA for Backlight and
150mA for Flash
150mA · 280kΩ
IFLED(MAX)
120
100
80
60
40
20
0
100
200
300
400
500
600
700
800
900
1000 1100
RFSET (kΩ
Ω)
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.
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.
20
15
10
AAT2842
5
0
100
200
300
400
500
600
700
800
900
1000 1100
RBSET (kΩ
Ω)
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 = 280kΩ results
in 150mA/channel LED current. From this reference point, the maximum current level can be modified by calculating an alternative RFSET value:
2842.2007.09.1.2
HI/LO
or
VDAC
R2
B/FSET
R1
Figure 5: Brightness Control Using Either
BSET or FSET Resistor Pin.
13
AAT2842
High-Current Charge Pump with S2Cwire™
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:
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.
VIO⎞
⎛ 0.7V
ILED(LO) = 12 · 103 R // R - R
⎝ 1
2
2⎠
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 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⎠
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 ⎠
14
η=
POUT
PIN
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:
η=
VF · ILED
VF
≈
VIN · IIN
VIN
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:
η=
VF · ILED
VF
≈
VIN · 1.5IIN 1.5 · VIN
2842.2007.09.1.2
AAT2842
High-Current Charge Pump with S2Cwire™
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:
η=
VF · ILED
VF
≈
VIN · 2IIN 2 · VIN
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.
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 100mΩ.
Ceramic composition capacitors are highly recommended over all other types of capacitors for use
2842.2007.09.1.2
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.
Ceramic Capacitor Materials
Ceramic capacitors less than 0.1µF 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 10µF 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.
15
AAT2842
High-Current Charge Pump with S2Cwire™
Control and Dual LDO for Backlight and Flash
Evaluation Board Layout
Figure 2: AAT2842 Evaluation
Board Top Layer.
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.
16
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.
2842.2007.09.1.2
AAT2842
High-Current Charge Pump with S2Cwire™
Control and Dual LDO for Backlight and Flash
Button(s) Pushed1
Description
DATA
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.
LIGHT
LIGHT+DATA
MOVIE
MOVIE+DATA
FLASH
DATA+FLASH
LIGHT+MOVIE+FLASH
Table 4: Evaluation Board User Interface.
Evaluation Board Schematics
VOUT
D1
D2
D3
D4
D5
D6
ENBL
ENFL
22
FL2
7
23
6
DC+
BL1
FL3
BSET
FL4
FSET
PGND
AGND
IN
CT
C2C2+
FBB
ENL
21
20
19
J1
VIN
18
17
C2
1.0μF
16
15
OUT
C4
4.7μF
3
2
C12
100μF
optional 100μF
lab supply bypass
1
ENL
14
13
12
11
10
9
8
C9
1.0μF
C1+
C1OUTA
REF
FBA
IN
OUTB
C8
1.0μF
24
5
25
4
FL1
FENS
BENS
2
R10
280K
CTRL_CT
26
BL4
BL3
BL2
1
3
R9
280K
27
28
280K yields 30mA/ch
max backlighting
280K yields 150mA/ch
max flash
U1
AAT2842
VOUT
OUTB
Programmed for
2.8V output by default
R11
160K
C6
2.2μF
C1
1.0μF
C3
2.2μF
C5
2.2μF
R12
120K
OUTA
R13
60.4K
C7
2.2μF
Programmed for
1.8V output by default
R14
120K
Figure 4: AAT2842 Section Schematic.
1. The “+” indicates that these buttons are pressed and released together.
2842.2007.09.1.2
17
AAT2842
High-Current Charge Pump with S2Cwire™
Control and Dual LDO for Backlight and Flash
VIN
C11
0.1μF
J2
ENBL
J3
ENFL
J4
ENL
ENBL
U3
1
IN
2
NC
3
NC
4
OUT3 8
7
OUT2 6
OUT1 5
ENFL
EN/SET GND
AAT4291
ENL
R6
R7
R8
100K 100K 100K
VIN
VIN
R1 R2 R3 R4
1K 1K 1K 1K
DATA
SW1
LIGHT
SW2
MOVIE
SW3
FLASH
SW4
U2
1
2
3
4
VDD
GP5
GP4
GP3
8
VSS 7
GP0
GP1 6
5
GP2
PIC12F675
C10
0.1μF
R5
330
LED7
RED
CTRL_CT
DC-
Figure 5: MCU and I/O Expander Section Schematic.
18
2842.2007.09.1.2
AAT2842
High-Current Charge Pump with S2Cwire™
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
2842.2007.09.1.2
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
Manufacturer
2
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
1.0µF, 10V, X5R, 0603, Ceramic
2.2µF, 10V, X5R, 0603, Ceramic
4.7µF, 10V, X5R, 0603, Ceramic
0.1µF, 16V, X7R, 0603, Ceramic
100µF, 10V, 10µA, 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
AnalogicTech
Microchip
AnalogicTech
OSRAM
Lumileds
Murata
Murata
Murata
Murata
AVX
Vishay
Vishay
Vishay
Vishay
Vishay
Vishay
Vishay
Sullins Electronics
Chicago Miniature Lamp
ITT Industries
19
AAT2842
High-Current Charge Pump with S2Cwire™
Control and Dual LDO for Backlight and Flash
Ordering Information
Package
Marking1
Part Number (Tape and Reel)2
TQFN44-28-0.45
TQFN44-28-0.4
TGXYY
XUXYY
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
Code
1.2
E
1. XYY = assembly and date code.
2. Sample stock is generally held on part numbers listed in BOLD.
20
2842.2007.09.1.2
AAT2842
High-Current Charge Pump with S2Cwire™
Control and Dual LDO for Backlight and Flash
Package Information1
TQFN44-28-0.4
Pin 1 Dot
by Marking
C0.3
2.600 ± 0.050
4.000 ± 0.050
Detail "A"
4.000 ± 0.050
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
21
AAT2842
High-Current Charge Pump with S2Cwire™
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)
2.60 ± 0.05
4.00 ± 0.05
Detail "A"
4.00 ± 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.
© 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