Rainbow-electronics DS3904 Instrukcja Użytkownika Pobierz pdf (Strona 7)

DS3904

DS3904 Triple 128-Position Nonvolatile

Variable Digital Resistor/Switch

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Detailed Description

The DS3904 contains three, 128-position, NV, low tem-

perature coefficient variable digital resistors. It is con-

trolled through a 2-wire serial interface, and it serves as

a low-cost replacement for designs using conventional

trimming resistors. Furthermore, the address pin allows

two DS3904s to be placed on the same 2-wire bus.

With its low cost and small size, the DS3904 is well tai-

lored to replace larger mechanical trimming variable

resistors. This allows the automation of calibration in

many instances because the 2-wire interface can easily

be adjusted by test/production equipment.

Variable Resistor

Memory Organization

The variable resistors of the DS3904 are addressed by

communicating with the registers in Table 1.

*Writing a value greater than 7Fh to any of the resistor registers

sets the high-impedance mode control bit (RHIZ, the MSB of

the resistor register) resulting in the resistor going into high-

impedance mode.

Device Operation

Clock and Data Transitions

The SDA pin is normally pulled high with an external

resistor or device. Data on the SDA pin can only change

during SCL low time periods. Data changes during SCL

high periods indicates a start or stop condition depend-

ing on the conditions discussed below. See the timing

diagrams for further details (Figures 2 and 3).

Start Condition

A high-to-low transition of SDA with SCL high is a start

condition, which must precede any other command. See

the timing diagrams for further details (Figures 2 and 3).

Stop Condition

A low-to-high transition of SDA with SCL high is a stop

condition. After a read or write sequence, the stop

command places the DS3904 into a low-power mode.

See the timing diagrams for further details (Figures 2

and 3).

Acknowledge

All address and data bytes are transmitted through a

serial protocol. The DS3904 pulls the SDA line low dur-

ing the ninth clock pulse to acknowledge that it has

received each byte.

Pin Description

PIN NAME FUNCTION

1 SDA

2-Wire Serial Data. Open-drain

input/output for 2-wire data.

2 SCL

2-Wire Serial Clock. Input for 2-wire

clock.

Supply Voltage Terminal

4 GND Ground Terminal

5, 6, 7

H2, H1, H0

Resistor High Terminals

8A0Address-Select Input

2-WIRE

INTERFACE

RHIZ CONTROL

EEPROM

RES 0

20kΩ

F8h

MSB

LSB

DATA

GND

SCL

SDA

DS3904

RESISTOR 0

RHIZ CONTROL

RES 1

20kΩ

F9h

MSB LSB

RESISTOR 1

RHIZ CONTROL

RES 2

20kΩ

FAh

MSB LSB

RESISTOR 2

Figure 1. DS3904 Block Diagram

ADDRESS

VARIABLE

RESISTOR

POSITION 7Fh

RESISTANCE

NUMBER OF

POSITIONS*

F8h Resistor 0 20kΩ

128 (00h to

7Fh) + Hi-Z

F9h Resistor 1 20kΩ

128 (00h to

7Fh) + Hi-Z

FAh Resistor 2 20kΩ

128 (00h to

7Fh) + Hi-Z

Table 1. Variable Resistor Registers

1 2 3 4 5 6 7 8 9 10 11

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