AAT2805 datasheet(12/16 Pages) AAT

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AAT2805

Dual High Efficiency Charge Pump

for White LED and Flash Applications

2805.2006.04.1.7

AS2Cwire Serial Interface

The AS2Cwire single wire interface is used to set the

possible combinations of current levels and LED

channel states. AS2Cwire has addressing capability

for multiple data registers. With multiple data regis-

ters, the main and sub-channel can be programmed

together or independently from one another.

AS2Cwire relies on the number of rising edges of the

EN/SET pin to address and load the registers.

AS2Cwire latches data or address after the EN/SET

pin has been held high for time TLAT. Address or data

is differentiated by the number of EN/SET rising

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

differentiating number of pulses is 24 or 16, so that

Address 1 is signified by 17 rising edges, Address 2

by 18 rising edges, and so forth. Data is set to any

number of rising edges between 1 and including 16.

A typical write protocol is a burst of EN/SET rising

edges, signifying a particular address, followed by a

pause with EN/SET held high for the TLAT timeout

period, a burst of rising edges signifying data, and a

TLAT timeout for the data registers. Once an address

is set, then multiple writes to the corresponding data

When EN/SET is held low for an amount of time

greater than TOFF, the charge pump enters into shut-

down mode and draws less than 1µA from the sup-

ply. Address 1 is the default address on the first ris-

ing edge after the charge pump has been disabled.

Whenever shutdown mode is entered, all registers

are reset to 1.

AS2Cwire Addressing

Five addresses are available to enable all of the

part's functionality (see Table 3). Two 4-bit registers

control the main and sub-channel, giving 16 settings

for each.

The main and sub-channel are pro-

grammed to the same constant current level by using

Address 1. Use Addresses 2 and 3 to program the

main and sub-channel independently. Use Address 4

to program the Max Current register, which sets the

Max Current scale. Lastly, Address 5 programs the

Low Current register. The Low Current register con-

trols the efficient Low Current mode.

When the Max Current register is programmed to 1,

2, or 3, changing the data for Addresses 1-3 will

result in the corresponding values found in Table 1.

When the Max Current register is programmed to 4,

the part is programmed to operate in Low Current

mode and the Data for Addresses 1-3 is irrelevant. In

Low Current mode, the Low Current register takes

precedence. See the Low Current Register Settings

table below for the current level settings and main/

sub-configurations that result.

Table 3: Address Settings.

Max Current and Low Current Registers

Use the Max Current and Low Current registers to

program constant current settings outside of the

20mA Max scale. By default (without changing the

Max Current register), the charge pump operates in

the 20mA Max scale (see Table 1). For example, to

change to the 30mA Max scale, address the Max

Current register with 20 rising edges and pause for

TLAT. Program the Max Current register with 2 rising

edges and pause for TLAT. The part will next operate

in the same Data row, but for the setting found in the

30mA Max column. Next, to change to a different

setting on the 30mA Max scale, address the D1-D4

stant current level with 1-16 rising edges. The part will

update to the new Data setting as shown in Table 1.

The charge pump has a distinct Low Current mode

with ultra-low quiescent current. For drive currents of

2mA or less, the part operates with significantly

reduced quiescent current. This is particularly useful

for applications requiring an "always on" condition

such as transmissive displays. For another example,

to change to Low Current mode, address the Max

Current register with 20 rising edges and pause for

TLAT. Program the Max Current register with 4 rising

edges and pause for TLAT. Address the Low Current

Program the Low Current register with 1-16 rising

edges. The part will update to the new Low Current

mode setting and operate with significantly reduced

quiescent current.

EN/SET

Addressed

Address

Edges

1&2: D1-D4 Current

1: D1-D3 Current

2: D4 Current

3: Max Current

4: Low Current

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