MCP48FVB21 datasheet(41/84 Pages) MICROCHIP

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 2015 Microchip Technology Inc.

DS20005466A-page 41

MCP48FVBXX

5.3.2

OUTPUT VOLTAGE

The volatile DAC Register values, along with the device

configuration bits, control the analog VOUT voltage. The

volatile DAC Register’s value is unsigned binary. The

formula for the output voltage is given in Equation 5-2.

Table 5-3 shows examples of volatile DAC register

values and the corresponding theoretical VOUT voltage

for the MCP48FVBXX devices.

EQUATION 5-2:

CALCULATING OUTPUT

VOLTAGE (VOUT)

The following events update the DAC register value

and therefore the analog voltage output (VOUT):

• Power-on Reset

• Brown-out Reset

• Write command

The VOUT voltage will start driving to the new value

after any of these events has occurred.

5.3.3

STEP VOLTAGE (VS)

The Step Voltage is dependent on the device resolution

and the calculated output voltage range. 1 LSb is

defined as the ideal voltage difference between two

successive codes. The step voltage can easily be

calculated by using Equation 5-3. Theoretical step

voltages are shown in Table 5-2 for several VREF

voltages.

EQUATION 5-3:

VS CALCULATION

Note:

When Gain = 2 (VRL = VREF) and

if VREF > VDD / 2, the VOUT voltage will be

limited to VDD. So if VREF = VDD, then the

VOUT voltage will not change for volatile

DAC Register values mid-scale and greater,

since the op amp is at full-scale output.

Where:

# of Resistors in

Resistor Ladder

= 4096 (MCP48FVB2X)

= 1024 (MCP48FVB1X)

=256 (MCP48FVB0X)

OUT

DAC Register Value



# of Resistors in Resistor Ladder

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

Gain



TABLE 5-2:

THEORETICAL STEP

VOLTAGE (VS)

(1)

VREF

5.0

2.7

1.8

1.5

1.0

1.22 mV

659 µV

439 µV

366 µV

244 µV 12-bit

4.88 mV

2.64 mV 1.76 mV 1.46 mV

977 µV 10-bit

19.5 mV

10.5 mV

7.03 mV

5.86 mV

3.91 mV

8-bit

Note 1:

When Gain = 1x, VFS = VRL, and VZS = 0V.

Where:

# of Resistors in

Resistor Ladder

= 4096 (12-bit)

= 1024 (10-bit)

256 (8-bit)

# of Resistors in Resistor Ladder

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

Gain



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