MCP6001/2/4
4.0
APPLICATION INFORMATION
–
R
IN
V
IN
MCP600X
+
V
OUT
The MCP6001/2/4 family of op amps is manufactured
using Microchip’s state-of-the-art CMOS process and
is specifically designed for low-cost, low-power and
general-purpose applications. The low supply voltage,
low quiescent current and wide bandwidth makes the
MCP6001/2/4 ideal for battery-powered applications.
This device has high phase margin, which makes it
stable for larger capacitive load applications.
(
Maximum expected V
IN
)
–
V
DD
-
R
IN
≥
------------------------------------------------------------------------------
2 mA
V
SS
–
(
Minimum expected V
IN
)
-
R
IN
≥
---------------------------------------------------------------------------
2 mA
4.1
Rail-to-Rail Input
The MCP6001/2/4 op amps are designed to prevent
phase reversal when the input pins exceed the supply
voltages. Figure 4-1 shows the input voltage exceeding
the supply voltage without any phase reversal.
6
Input, Output Voltages (V)
V
IN
5
V
OUT
4
3
2
1
0
-1
0.E+00
1.E-05
2.E-05
3.E-05
4.E-05
5.E-05
6.E-05
7.E-05
8.E-05
9.E-05
1.E-04
FIGURE 4-2:
Resistor (R
IN
).
Input Current Limiting
4.2
V
DD
= 5.0V
G = +2 V/V
Rail-to-Rail Output
The output voltage range of the MCP6001/2/4 op amps
is V
DD
– 25 mV (min.) and V
SS
+ 25 mV (max.) when
R
L
= 10 kΩ is connected to V
DD
/2 and V
DD
= 5.5V.
Refer to Figure 2-14 for more information.
4.3
Capacitive Loads
Time (10 µs/div)
FIGURE 4-1:
Phase Reversal.
The MCP6001/2/4 Show No
The input stage of the MCP6001/2/4 op amps use two
differential input stages in parallel. One operates at a
low common mode input voltage (V
CM
), while the other
operates at a high V
CM
. With this topology, the device
operates with a V
CM
up to 300 mV above V
DD
and
300 mV below V
SS
. The input offset voltage is
measured at V
CM
= V
SS
– 300 mV and V
DD
+ 300 mV
to ensure proper operation.
Input voltages that exceed the input voltage range
(V
SS
– 0.3V to V
DD
+ 0.3V at 25°C) can cause
excessive current to flow into or out of the input pins,
while current beyond ±2 mA can cause reliability
problems. Applications that exceed this rating must be
externally limited with a resistor, as shown in Figure 4-2.
Driving large capacitive loads can cause stability prob-
lems for voltage feedback op amps. As the load capac-
itance increases, the feedback loop’s phase margin
decreases and the closed-loop bandwidth is reduced.
This produces gain peaking in the frequency response,
with overshoot and ringing in the step response. While
a unity-gain buffer (G = +1) is the most sensitive to
capacitive loads, all gains show the same general
behavior.
When driving large capacitive loads with these op
amps (e.g., > 100 pF when G = +1), a small series
resistor at the output (R
ISO
in Figure 4-3) improves the
feedback loop’s phase margin (stability) by making the
output load resistive at higher frequencies. The band-
width will be generally lower than the bandwidth with no
capacitance load.
–
V
IN
MCP600X
+
R
ISO
V
OUT
C
L
FIGURE 4-3:
Output resistor, R
ISO
stabilizes large capacitive loads.
DS21733F-page 8
©
2005 Microchip Technology Inc.
MICROCHIP [ MICROCHIP TECHNOLOGY ]
