4

FN9239.2

April 10, 2007

Single-Wire Serial Interface

The ISL97632 uses a simple single-wire serial interface for

programming the output brightness of the LEDs. A 5-bit

interface is used to give a total of 32 levels of output

brightness. The interface uses a normally high connection

for use with open-drain driving schemes and Intersil’s

proprietary XSD bus. When held low for between 15µs and

45µs, the interface registers a logic 1. When held low for

between 90µs and 120µs the interface registers a logic 0.

When held low for greater that 215µs, the interface loads the

last 5 bits into the brightness control register and updates

the brightness level. The required minimum high time is 3µs.

This simple single-wire programming is summarized as

follow:

• Logic 0 = Negative pulse >90µs and <120µs

• Logic 1 = Negative pulse >15µs and <45µs

• Load = Negative pulse >215µs

Figure 1 shows an example of programming a binary code of

10100 and load it in to the device serial register.

The serial interface is automatically reset to 0 when the

device is disabled, or enters UVLO. Therefore, when the part

is enabled, the output brightness is automatically set to the

minimum level.

30µs

100µs

220µs

'1'

'0'

'1'

'0'

'0'

'LOAD'

0

200

400

600

800

1000

1200

µs

FIGURE 1. SINGLE-WIRE XSD INTERFACE

ISL97632