Dual, 256-Tap, Volatile Low-Voltage

Linear Taper Digital Potentiometers

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Detailed Description

The MAX5386/MAX5388 dual, 256-tap, volatile low-volt-

age linear taper digital potentiometers offer three end-to-

end resistance values of 10kI, 50kI, and 100kI. Each

potentiometer consists of 255 fixed resistors in series

between terminals H and L. The potentiometer wiper, W,

is programmable to access anyone of the 256 tap points

on the resistor string.

The potentiometers in each device are programmable

independently of each other. The MAX5386/MAX5388

have an SPI interface.

SPI Digital Interface

The MAX5386/MAX5388 include an SPI interface, which

provides a 3-wire write-only serial data interface to con-

trol the wiper tap position through inputs chip select

(CS), data in (DIN), and data clock (SCLK). Drive CS

low to load data from DIN synchronously into the serial

shift register on the rising edge of each SCLK pulse.

The MAX5386/MAX5388 load the last 9 bits of clocked

data once CS transitions high. See Figures 2 and 3.

After all the data bits are shifted in, data are latched into

the appropriate potentiometer control register when CS

goes from low to high. Data written to a memory register

immediately updates the wiper position. Keep CS low

during the entire data stream to prevent the data from

being terminated.

The first bit A0 (address bit) addresses one of the two

potentiometers; writing a zero in A0 addresses control

register A and writing a one in A0 addresses control reg-

ister B. See Table 1. The power-on reset (POR) circuitry

sets the wiper to midscale (D[7:0] 1000 0000).

The 8 data bits (D7–D0) indicate the position of the

wiper. For D[7:0] = 0000 0000, the wiper moves to the

position closest to L. For D[7:0] = 1111 1111, the wiper

moves closest to H. D[7:0] is 1000 0000 following power-

on for both registers A and B.

Register A: The data byte writes to register A, and the

wiper of potentiometer A moves to the appropriate posi-

tion at the rising edge of CS. D[7:0] indicates the posi-

tion of the wiper. D[7:0] = 0000 0000 moves the wiper to

the position closest to L. D[7:0] = 1111 1111 moves the

wiper to the position closest to H. D[7:0] is 1000 0000

following power-on.

Register B: The data byte writes to register B, and the

wiper of potentiometer B moves to the appropriate posi-

tion at the rising edge of CS. D[7:0] indicates the posi-

tion of the wiper. D[7:0] = 0000 0000 moves the wiper to

the position closest to L. D[7:0] = 1111 1111 moves the

wiper to the position closest to H. D[7:0] is 1000 0000

following power-on.

Table 1. SPI Register Map

Bit Number

1

2

3

4

5

6

7

8

9

Bit Name

A0

D7

D6

D5

D4

D3

D2

D1

D0

Write Wiper Register A

0

D7

D6

D5

D4

D3

D2

D1

D0

Write Wiper Register B

1

D7

D6

D5

D4

D3

D2

D1

D0