MCP6G04 Microchip Technology, MCP6G04 Datasheet - Page 21

• Manufacturer Part Number: MCP6G04
• Description: 110 Selectable Gain Amplifier
• Manufacturer: Microchip Technology

4.3
The MCP6G03 is a single amplifier with chip select
(CS). When CS is high, the internal op amp is shut
down and its output placed in a high-Z state. The
resistive ladder is always connected between V
V
resistance will be 350 kΩ (typ.), with a path for output
signals to appear at the input. The supply current at
V
ladder resistors; it also includes current from the CS pin
to V
is left floating, the amplifier may not operate properly.
Figure 1-2
voltage and supply current response to a CS pulse.
4.4
The amplifier can be set to the gains +1 V/V, +10 V/V,
and +50 V/V using one input pin (GSEL). At the same
time, different compensation capacitors are selected to
optimize the bandwidth vs. slew rate trade-off (see
Table
using a GPIO pin on a microcontroller and
shows how to hard wire the gain (i.e., using PCB
wiring).
TABLE 4-2:
TABLE 4-3:
© 2006 Microchip Technology Inc.
+1 V/V
+10 V/V
+50 V/V
Note 1:
Note 1:
Selected Gain
OUT
SS
Gain
SS
+10 V/V
+50 V/V
includes the current through the load resistor and
+1 V/V
; even in shutdown. This means that the output
4-1).
. When CS is low, the amplifier is enabled. If CS
2:
MCP6G03 Chip Select (CS)
Gain Select (GSEL)
Table 4-2
See Section 4.8.1 “Driving the Gain
Select Pin with a Microcontroller GPIO
Pin”.
See Section 4.8.2 “Driving the Gain
Select Pin with a PWM Signal”
The GSEL pin floats to mid-supply
(V
needed.
and
Output PIC’s V
Digital Output High-Z (Notes 1)
Output V
Digital Output driven Low
Digital Output driven High
DD
/2); a bypass capacitor may be
Figure 2-43
Open Circuit (Note 1)
Low impedance source at V
Tied to GND (0V)
Tied to V
HARD WIRED GAIN
MCU DRIVEN GAIN
SELECTION
SELECTION
DD
Possible GSEL Drivers
shows how to change the gain
/2 PWM signal (Notes 2)
MCU Pin’s State
DD
REF
show how the output
at V
DD
/2
Table 4-3
DD
SS
/2
and
4.5
Large capacitive loads can cause stability problems
and reduced bandwidth for the MCP6G01/2/3/4 family
of SGAs
capacitance increases, there is a corresponding
increase in frequency response peaking and step
response overshoot and ringing. This happens
because a large load capacitance decreases the
internal amplifier’s phase margin and bandwidth.
When driving large capacitive loads with these SGAs
(i.e., > 60 pF), a small series resistor at the output
(R
stability by making the load resistive at higher
frequencies. The bandwidth will be generally lower
than the bandwidth with no capacitive load.
FIGURE 4-5:
Capacitive Loads.
Figure 4-6
different capacitive loads. After selecting R
circuit, double check the resulting frequency response
peaking and step response overshoot on the bench.
Modify R
all gains.
FIGURE 4-6:
ISO
V
IN
1,000
in
100
10
ISO
Capacitive Load and Stability
Figure
(Figure 2-30
10p
10
’s value until the response is reasonable at
gives recommended R
MCP6G0X
MCP6G01/2/3/4
4-5) improves the internal amplifier’s
100p
100
Load Capacitance (F)
SGA Circuit for Large
Recommended R
and
1,000
Figure
1n
R
ISO
2-34). As the load
10,000
DS22004A-page 21
For all gains
10n
ISO
C
ISO
ISO
values for
L
V
100,000
OUT
.
100n
for your