MCP4902-ESLASHST datasheet(28/48 Pages) MICROCHIP

28 / 48 page

MCP4902/4912/4922

DS22250A-page 28

 2010 Microchip Technology Inc.

6.4

Single-Supply Operation

The MCP4902/4912/4922 family of devices are rail-to-

rail voltage output DAC devices designed to operate

with a VDD range of 2.7V to 5.5V. Its output amplifier is

robust enough to drive small-signal loads directly.

Therefore, it does not require any external output buffer

for most applications.

6.4.1

DC SET POINT OR CALIBRATION

A common application for the DAC devices is

digitally-controlled set points and/or calibration of

variable parameters, such as sensor offset or slope.

For example, the MCP4922 provides 4096 output

steps. If the external voltage reference (VREF) is

4.096V, the LSb size is 1 mV. If a smaller output step

size is desired, a lower external voltage reference is

needed.

6.4.1.1

Decreasing Output Step Size

If the application is calibrating the bias voltage of a

diode or transistor, a bias voltage range of 0.8V may be

desired with about 200 µV resolution per step. Two

common methods to achieve a 0.8V range is to either

reduce VREF to 0.82V or use a voltage divider on the

DAC’s output.

Using a VREF is an option if the VREF is available with

the

desired

output

voltage

range.

However,

occasionally, when using a low-voltage VREF, the noise

floor causes SNR error that is intolerable. Using a

voltage divider method is another option and provides

some advantages when VREF needs to be very low or

when the desired output voltage is not available. In this

case, a larger value VREF is used while two resistors

scale the output range down to the precise desired

level.

Example 6-1 illustrates this concept. Note that the

bypass capacitor on the output of the voltage divider

plays a critical function in attenuating the output noise

of the DAC and the induced noise from the

environment.

EXAMPLE 6-1:

EXAMPLE CIRCUIT OF SET POINT OR THRESHOLD CALIBRATION

VDD

SPI

3-wire

VTRIP

0.1 uF

Comparator

G = Gain selection (1x or 2x)

Dn = Digital value of DAC (0-255) for MCP4901/MCP4902

VOUT

VREF G

------



VCC+

VCC–

VOUT

Vtrip

VOUT

R1 R2

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







VDD

RSENSE

DAC

= Digital value of DAC (0-1023) for MCP4911/MCP4912

= Digital value of DAC (0-4095) for MCP4921/MCP4922

N = DAC Bit Resolution

VREF

MCP4901

MCP4911

MCP4921

(a) Single Output DAC:

(b) Dual Output DAC:

MCP4902

MCP4912

MCP4922

MCP4902-E/ST 数据表(PDF) 28 Page - Microchip Technology

MCP4902-E/ST 数据表(HTML) 28 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

数据表下载

链接网址

MCP4902-E/ST 数据表(PDF) 28 Page - Microchip Technology

MCP4902-E/ST 数据表(HTML) 28 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

数据表 下载

链接网址

数据表下载