MCP47DA1 datasheet(43/76 Pages) MICROCHIP

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 2012-2013 Microchip Technology Inc.

DS25118D-page 43

MCP47DA1

6.4

Serial Buffer to Wiper Register

Decode

The I2C’s data byte is 8-bits, where only the lower 7-bits

are implemented. This register is called the Serial Shift

ing of 65 taps (6-bit resolution). This 6-bit resolution is

centered about the 7-bit range (where 40h is mid-

scale). So, SSR values 20h and below are zero-scale

values, and SSR values 60h and above are full-scale

values. Table 6-1 shows the decoding of the serial shift

TABLE 6-1:

SERIAL SHIFT REGISTER

VALUE TO WIPER VALUE

6.5

Resistor Variations

(Voltage and Temperature)

The R1, RAB, and R2 resistors are implemented to have

minimal variations (by design). Any variations should

occur uniformly on all the resistor elements, so the

resistor’s elements will track each other over tempera-

ture and process variations.

The variation of the resistive elements over the operat-

ing voltage range is also minimal. Therefore the VREF

resistance (RVREF) of the device has minimal variation

due to operating voltage.

Since the VOUT pin’s voltage is ratiometric, the resistive

elements change uniformly over temperature, process,

and operating voltage variations. Minimal variation

should be seen on the VOUT pin’s voltage.

6.6

POR Value

A POR/BOR event will load the volatile serial shift

value. Table 6-2 shows the default values offered.

TABLE 6-2:

POR/BOR SETTINGS

Note 1: The I2C Write and Read commands

access the value in the Serial Shift Reg-

ister (SSR).

2: The MSb of the I2C data byte is ignored

and not loaded into the SSR. A write of

C0h, will result in the same VOUT voltage

as a write of 40h (mid-scale). A subse-

quent Read command (of the SSR) will

result in a value of 40h.

3: The 7-bit SSR value is decoded to a 6-bit

(65 taps) value that controls the wiper’s

position.

I2C™ Write

Data

SSR(1)

Wiper

Value(2)

Comment

00h - 20h or

80h - A0h

00h -

20h

00h

Wiper register at

Zero Scale,

VOUT = (1/3) * VREF

21h or A1h

21h

01h

Wiper register =

SSR - 20h

22h or A2h

22h

02h

Wiper register =

SSR - 20h

40h or C0h

40h

20h

Mid-Scale (POR

value),

VOUT = (1/2) * VREF

5Eh or DEh

5Eh

3Eh

Wiper register =

SSR - 20h

5Fh or DFh

5Fh

3Fh

Wiper register =

SSR - 20h

60h - 7Fh or

E0h - FFh

60h -

7Fh

40h

Wiper register at

Full Scale,

VOUT = (2/3) * VREF

Note 1: The Serial Shift Register (SSR) is 7-bits

wide and holds the value written from the

I2C Write command. An I2C Read com-

mand will read the value in this register.

2: The wiper value is the value that controls

the resistor ladder’s wiper position.

Device

Setting

SSR

Wiper

MCP47DA1

Mid-scale

40h

20h

Note 1: Custom POR/BOR wiper setting options

are available; contact the local Microchip

Sales Office for additional information.

Custom options have NRE and minimum

volume requirements.

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