AAT2856_08 Datasheet, PDF(9/18 Page) Advanced Analogic Technologies – High Current Charge Pump with Dual LDO for Backlight Applications

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AAT2856_08 Datasheet, PDF (9/18 Pages) Advanced Analogic Technologies – High Current Charge Pump with Dual LDO for Backlight Applications

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PRODUCT DATASHEET

AAT2856

ChargePumpTM High Current Charge Pump with Dual LDO for Backlight Applications

AS2Cwire Serial Interface

The AAT2856 is dynamically programmable by the

AS2Cwire single-wire interface. AS2Cwire records rising

edges detected at the ENS pin to address and load the

data registers. AS2Cwire latches data or address after the

ENS input has been held high for time tLAT (500Î¼s).

Address or data is differentiated by the number of ENS

rising edges. Since the data registers are 4 bits each, the

differentiating number of pulses is 24 or 16, so that

Address 0 is identified by 17 rising edges, Address 1 by

18 rising edges, Address 2 by 19 rising edges, etc. Data

is set to any number of rising edges between 1 and 16. A

typical write protocol is a burst of ENS rising edges iden-

tifying a particular address, followed by a pause with ENS

held high for the tLAT timeout period, then a burst of rising

edges signifying data, and another tLAT timeout after the

data has been sent. Once an address is set, multiple

writes to that address are allowed since the address is not

reset after each write. Address edges are needed when

changing the address, or writing to an address other than

the default after shutdown. Address 0 is the default

address after shutdown. If the part is enabled with only

data edges and no address, then Address 0 will be pro-

grammed and backlight channels BL1-BL6 will turn-on

according to the number of data edges applied.

When ENS is held low for a time longer than tOFF (500Î¼s),

the AAT2856 enters shutdown mode and draws less than

1Î¼A of current from IN. At shutdown, the data and

address registers are reset to 0.

Table 1a contains the AS2Cwire serial interface address

functionality when independent channel control is dis-

abled (independent channel control is disabled by

default) and conversely Table 1b contains the AS2Cwire

serial interface address functionality when independent

channel control is enabled.

AS2Cwire Serial Interface Addressing

Address

ENS Rising

Edges

Function

Backlight Current BL1-BL6

Main Backlight Current BL1-BL5

Sub Backlight Current BL6

Low Current Backlight

Maximum Backlight Current

Scale BL1-BL6

Backlight Independent Channel

Control

Table 1a: AS2Cwire Serial Interface Addressing

with Independent Channel Control Disabled.

Address

ENS Rising

Edges

Function

Not Applicable

Backlight Current BL1-BL6

BL3-BL6 On/Off Control

BL1-BL2 On/Off Control

Maximum Backlight Current

Scale BL1-BL6

Not Applicable

Table 1b: AS2Cwire Serial Interface Addressing

with Independent Channel Control Enabled.

Backlight Current Control (Address 0-3)

Use Addresses 0-3 to program all six backlight LED

channels. All six backlight channels are programmed to

the same current level by writing Address 0 followed by

any Data between 1 and 16. To program only the main

channels BL1 through BL5, use Address 1. Similarly,

use Address 2 to program only the sub channel BL6

independently.

EN/SET

Address

THI

TLO

TLAT

Data

TLAT

2 . . . n <= 16

Data Reg 1

Data Reg 2

Figure 1: AS2Cwire Serial Interface Timing.

2856.2008.02.1.3

www.analogictech.com

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