AAT3151B

High Efficiency 1X/1.5X Charge Pump

For White LED Applications

3151B.2007.09.1.0

9

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 program-

mability and real-time control of LED brightness.

For each Max Current scale, there are 16 current

level settings separated from one another by

approximately 1dB. Code 1 is full-scale current and

Code 15 is full-scale current attenuated by roughly

14dB. Code 16 is reserved as a "no current" setting

(see Table 1).

The AAT3151B has an additional Low Current

mode with reduced quiescent current. This mode is

especially useful for low-current applications where

a continuous, low-current state is maintained. The

reduction in quiescent current significantly reduces

the impact due to maintaining a continuous back-

lighting state.

Table 1: Constant Current Programming

Levels (mA)

AS

The AS

the possible combinations of current levels and

LED channel states.

AS

the EN/SET pin to address and load the registers.

AS

pin has been held high for time T

Address or

data is differentiated by the number of EN/SET ris-

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

the differentiating number of pulses is 2

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 T

edges signifying data, and a T

data registers. Once an address is set, then multi-

ple writes to the corresponding data register are

allowed.

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

greater than T

mode and draws less than 1µA from the supply.

Address 1 is the default address on the first rising

edge after the AAT3151B has been disabled.

Whenever shutdown mode is entered, all registers

are reset to 1.

20mA Max

1

30mA Max

15mA Max

Data

I

I

I

1

20.0

30.0

15.0

2

17.8

26.7

13.3

3

15.9

23.8

11.9

4

14.3

21.4

10.7

5

12.7

19.0

9.5

6

11.1

16.7

8.3

7

10.2

15.2

7.6

8

8.9

13.3

6.7

9

7.9

11.9

6.0

10

7.0

10.5

5.2

11

6.3

9.5

4.8

12

5.7

8.6

4.3

13

5.1

7.6

3.8

14

4.4

6.7

3.3

15

4.1

6.2

3.1

16

0.0

0.0

0.0

1. The device defaults to the 20mA Max scale. Use the Max Current Register to change the Max Scale.

2. There is an additional Low Current mode with currents down to 50µA. See the Low Current Register Settings section.