SW

BATTERY

VDD1

VDDA

LDO

Analog

supply

voltage

2.8V

LP55281

Digital

supply

voltage

LDO

2.8V

VDD2

10 PF

1 PF

100 nF

LP55281

SNVS458B – JUNE 2007 – REVISED JUNE 2007

www.ti.com

15. Dummy write: 00h to register 0Dh (Only if the incremental write sequence is used)

16. Dummy write: 00h to register 0Eh (Only if the incremental write sequence is used)

17. Set preferred boost voltage (write 00h - FFh to register 0Fh)

18. Set preferred boost frequency (write 00h - 07h to register 10h, PWM frequency can be anything)

19. Enable boost and RGB drivers (write CFh to register 11h)

20. Wait 20 ms for the device and boost startup

Measurement phase:

1. Enable LED test and select output (write 1xh to register 12h)

2. Wait for 128 µs

3. Read ADC output (read register 13h)

4. Go to step 1 of measurement phase and define next output to be measured as many times as needed

5. Disable LED test (write 00h to register 12h) or give reset to the device (see step 1 in basic setup phase)

LED TEST TIME ESTIMATION

the overall test sequence time for the test procedure shown above. This estimation gives the shortest time

Test Phase

Time (ms)

SPI

Setup

0.528

0.024

Boost startup

20

20

14 measurements

4.137

1.831

Total Time

24.7

21.9

7V Shielding

To shield LP55281 from high input voltages (6 to 7.2V), the use of external 2.8V LDO is required. This 2.8V

voltage protects internally the device against high voltage condition. The recommended connection is shown in

the picture below. Internally both logic and analog circuitry works at 2.8V supply voltage. Both supply voltage

pins should have separate filtering capacitors. Note that it is recommended to pull down the external LDO voltage

when it is disabled in order to minimize the leakage current of the LED outputs.

In cases where high voltage is not an issue, the alternative connection is shown below.

20

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