MCP4716 datasheet(39/70 Pages) MICROCHIP

39 / 70 page

 2012 Microchip Technology Inc.

DS25154A-page 39

MCP47A1

6.3

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 Register (SSR). The Wiper register supports

addressing of 65 taps (6-bit resolution). Table 6-1

shows the decoding of the Serial Shift Register to the

Wiper Register value.

TABLE 6-1:

SERIAL SHIFT REGISTER

VALUE TO WIPER VALUE

6.4

Resistor Variations

(Voltage and Temperature)

The RAB 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 temperature 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, and the

resistive elements change uniformly over temperature,

process, and operating voltage variations. Minimal

variation should be seen on the VOUT pin’s voltage.

6.5

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 Regis-

ter (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

Wiper Register at

Zero Scale,

VOUT = VSS

01h or 81h

01h

02h or 82h

02h

20h or A0h

20h

Mid-Scale (POR

value),

VOUT = (1/2) * VREF

3Eh or BEh

3Eh

Wiper Register =

SSR - 20h

3Fh or BFh

3Fh

Wiper Register =

SSR - 20h

40h - 7Fh or

C0h - FFh

40h -

7Fh

40h

Wiper Register at

Full Scale,

VOUT = 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

MCP47A1

Mid-scale

20h or A0h

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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