MCP4716 datasheet(50/70 Pages) MICROCHIP

50 / 70 page

MCP47A1

DS25154A-page 50

 2012 Microchip Technology Inc.

8.3

Building Programmable Current

Source

Figure 8-6

shows

example

building

programmable current source using a voltage follower.

The current sensor resistor is used to convert the DAC

voltage output into a digitally-selectable current source.

The smaller RSENSE is, the less power is dissipated

across it. However, this also reduces the resolution that

the current can be controlled.

FIGURE 8-6:

Digitally-Controlled Current

Source.

8.4

Serial Interface Communication

Times

Table 8-1 shows time for each I2C serial interface

command as well as the effective data update rate that

can be supported by the digital interface (based on the

two I2C serial interface frequencies). The continuous

write command allows a higher data update frequency

since

for

the

fixed

overhead

bytes

are

transferred. The Serial Interface performance, along

with the VOUT output performance (such as slew rate),

would be used to determine the application’s volatile

DAC register update rate.

TABLE 8-1:

SERIAL INTERFACE TIMES / FREQUENCIES

RSENSE

Load

VCC+

VCC–

VOUT

OUT

sense

---------------



 1

-------------





----

Common-Emitter Current Gain

where

VDD

I2C™

2-wire

VREF

MCP47A1

VDD

(or VREF)

Command

# of Serial

Interface bits(1)

Example

Command

Time (µs)

Effective Data Update

Frequency (kHz) (2)

# Bytes

Transferred

# of Serial

Interface bits

100kHz

400kHz

100kHz

400kHz

Write Single Byte

290.0

72.5

3.4

13.8

Write Continuous Bytes

20 + N * 9

650.0

162.5

7.7

30.8

Read Byte

390.0

97.5

2.6

10.3

Note 1:

Includes the Start or Stop bits.

This is the command frequency multiplied by the number of bytes transferred.

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