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PDF AAT2842 Data sheet ( Hoja de datos )
| Número de pieza | AAT2842 | |
| Descripción | High-Current Charge Pump | |
| Fabricantes | ANALOGICTECH | |
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AAT2842
High-Current Charge Pump with S2Cwire™
Control and Dual LDO for Backlight and Flash
General Description
Features
ChargePump™
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 key-
pad 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 resis-
tors for increased versatility with reduced accuracy
and matching. Backlight/keypad current matching
is 1% for uniform display brightness, and flash cur-
rent matching is 4% for uniform power dissipation.
An integral 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.
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.
• 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
• Camera-Enabled Mobile Devices
• Digital Still Cameras
• Multimedia Mobile Phones
Typical Application
VBAT
CIN
4.7µF
EN_BACKLIGHT
EN_FLASH
RSET1
CT RSET2
CREF
EN_LDO
C1 C2
1µF 1µF
C1+ C1- C2+ C2-
IN OUT
AAT2842
BL1
IN BL2
BENS
BL3
BL4
FENS
FL1
FL2
CT
BSET
FSET
FL3
FL4
OUTA
REF
FBA
OUTB
ENL FBB
AGND PGND
COUT
2.2µF
R2B
R1B
VOUT LDOB
COUTB
VOUT LDOA
R2A
COUTA
R1A
2842.2006.10.1.0
1
1 page  
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; TA = -40°C to +85°C, unless otherwise noted. Typical
values are at TA = 25°C.
Symbol Description
Conditions
Min Typ Max Units
VIN IN Operating Voltage Range
1X Mode, 3.0V ≤ VIN ≤ 5.5V, Active, No
Load; ENL = AGND, FENS = BENS = IN
2.7
5.5 V
1.0
IIN(Q)
IN Operating Current
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
3.0 mA
5.0
IIN(SHDN)
TSD
IN Shutdown Current
Over-Temperature Shutdown
Threshold
RBSET = 280kΩ, Data 1, 1X Mode
ENL = BENS = FENS = AGND, TA = 25°C
50
5.0
140
µA
µA
°C
TSD(HYS)
Over-Temperature Shutdown
Hysteresis
15 °C
Charge Pump Section
IOUT
VIN(TH_H)
OUT Maximum Output Current
BL1-BL4, FL1-FL4 Charge Pump RBSET = 280kΩ, Data 1
Mode Transition Hysteresis
600 mA
500 mV
fOSC Charge Pump Oscillator
Frequency
2 MHz
Backlight LED Outputs, S2Cwire Data = 1
IBL_(MAX)
ΔI(BL_)
VBL_(TH)
BL1-BL4 Maximum Current
BL1-BL4 Current Matching2
BL1-BL4 Charge Pump Mode
Transition Threshold
RBSET = 280kΩ, VIN - VF = 1.5V
VIN - VF = 1.5V
27 30 33
0.5 1
150
mA
%
mV
Backlight LED Outputs, S2Cwire Data = 7
IBL_(MAX)
ΔI(BL_)
VBL_(TH)
BL1-BL4 Maximum Current
BL1-BL4 Current Matching2
BL1-BL4 Charge Pump Mode
Transition Threshold
RBSET = 280kΩ, VIN - VF = 1.5V
VIN - VF = 1.5V
8.6 9.6 10.6 mA
2%
60 mV
Flash LED Outputs, S2Cwire Data = 1
IFL_(MAX)
ΔI(FL_)
VFL_(TH)
FL1-FL4 Maximum Current
FL1-FL4 Current Matching2
FL1-FL4 Charge Pump Mode
Transition Threshold
RFSET = 280kΩ, VIN - VF = 1.5V
VIN - VF = 1.5V
135 150 165
14
300
mA
%
mV
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.
2842.2006.10.1.0
5
5 Page 
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 program-
ming resistor sets the maximum LED current for
each channel, and the serial S2Cwire interface con-
trols 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. Depending upon the application and the
white LEDs chosen, the preferred method to
decrease the maximum BL output current is to use
a 280kΩ resistor for RBSET and then set the desired
current output using the product's S2Cwire inter-
face, as shown in Table 1.
Using Backlight LED Outputs for
Low-Current LED Applications
The AAT2842's backlight current outputs can be pro-
grammed 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 con-
troller monitors the current sink voltage and, if it is
connected to OUT, then it is assumed that the cur-
rent 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.
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 maxi-
mum flash current set by the FSET resistance (see
Tables 1 and 2). Initiating a flash current also initi-
ates the flash timer which is programmed via an
external capacitor CT.
Calculate the flash time T by the following equation:
T = 10 × CT
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
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
Table 1: Backlight Current Register: BL1-BL4
(RBSET = 280kΩ).
2842.2006.10.1.0
11
11 Page | ||
| Páginas | Total 21 Páginas | |
| PDF Descargar | [ Datasheet AAT2842.PDF ] | |
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