MCP6G01-ESLASHMS datasheet(23/38 Pages) MICROCHIP

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DS22004B-page 23

MCP6G01/1R/1U/2/3/4

4.7

Unused Amplifiers

An unused amplifier in a quad package (MCP6G04)

should be configured as shown in Figure 4-8. This

circuit prevents the output from toggling and causing

crosstalk. Because the VIN pin looks like an open

circuit, the GSEL voltage is automatically set at VDD/2,

and the gain is 1 V/V. The output pin provides a

buffered VDD/2 voltage and minimizes the supply

current draw of the unused amplifier.

FIGURE 4-8:

Unused Amplifiers.

4.8

Typical Applications

4.8.1

DRIVING THE GAIN SELECT PIN

WITH A MICROCONTROLLER GPIO

The circuit in Figure 4-9 uses a microcontroller GPIO

pin to drive the Gain Select input (GSEL). Setting the

GPIO pin to logic low, high-Z or logic high gives a GSEL

voltage of 0V, VDD/2 or VDD, respectively (G = 10, 1 or

50).

FIGURE 4-9:

Driving the GSEL Pin.

The microcontroller’s GPIO pin cannot produce a

leakage current of more than ±1 µA for this circuit to

function properly. In noisy environments, a capacitor

may need to be added to the GPIO pin.

4.8.2

DRIVING THE GAIN SELECT PIN

WITH A PWM SIGNAL

The circuit in Figure 4-10 uses a PWM output on a PIC

microcontroller (100 kHz clock rate) to drive the Gain

Select input (GSEL). Setting the PWM duty cycle to

0%, 50% or 100% gives a GSEL voltage of 0V, VDD/2

or VDD, respectively (G = 10, 1 or 50).

FIGURE 4-10:

Driving the GSEL Pin.

The PWM clock rate needs to be fast so it is easily

filtered and does not interfere with the desired signal,

and it needs to be slow enough for good accuracy and

low crosstalk. This filter reduces the ripple at the GSEL

pin to about 7 mVP-P at VDD = 5.0V. The 10% settling

time is about 200 µs; the filter limits how quickly the

gain can be changed. Scale the resistors and/or

capacitors for other clock rates, or for different ripple.

4.8.3

GAIN RANGING

Figure 4-11 shows a circuit that measures the current

IX. The circuit’s performance benefits from changing

the gain on the SGA. Just as a hand-held multimeter

uses different measurement ranges to obtain the best

results, this circuit makes it easy to set a high gain for

small signals and a low gain for large signals. As a

result, the required dynamic range at the SGA’s output

is less than at its input (by up to 34 dB).

FIGURE 4-11:

Wide Dynamic Range

Current Measurement Circuit.

¼ MCP6G04

VOUT

MCP6G0X

VIN

GSEL

VDD

VOUT

MCP6G0X

VIN

GSEL

MCU

GPIO

VDD

VOUT

MCP6G0X

VIN

GSEL

PIC MCU

PWM

Output

4.7 nF

VDD

10 k

4.7 nF

10 k

VOUT

MCP6G0X

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