Dual, 64-Position Nonvolatile Digital

Potentiometer with Buffered Outputs

8

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Writes to this register are similar to writes to the poten-

tiometer register. A stop condition must follow the write

to ensure that the EEPROM is modified. A repeated

start condition before a stop condition following a write

operation will prevent the settings from being stored in

more details.)

Write Protection

The write-protect pin has an internal pullup resistor. To

adjust the potentiometers’ position, this pin must be

grounded. This pin can be left floating or connected to

can be read when the device is write protected.

When writing to the DS3908, the potentiometer will

adjust to the new setting once it has acknowledged the

new data that is being written, and the EEPROM (used

to make the setting nonvolatile) will be written following

the stop condition at the end of the write command. To

change the setting without changing the EEPROM, ter-

minate the write with a repeated start condition before

the next stop condition occurs. Using a repeated start

condition prevents the 20ms (maximum) delay required

for the EEPROM write cycle to finish.

Programmable Amplifier Control

The gain of both DS3908 amplifiers is controlled by

writing to register address FBh. The most significant

nibble of the FBh address controls the PGA1 gain, and

the least significant nibble controls the PGA0 gain. The

format of each nibble is shown in the tables below:

Table 2. Programmable Amplifier Register

REGISTER FORMAT (BINARY)

ADDRESS

PGA1

PGA0

R*

R*

FBh

bit7

bit0

Default value = 11h.

*Reserved for future use, write to zeros.

Table 3. Programmable Amplifier Gain Codes

AMPLIFIER GAIN (V/V)

00X

1

01X

2

1XX

4

X = Don’t care.