MCP6144 Microchip Technology, MCP6144 Datasheet - Page 11

• Manufacturer Part Number: MCP6144
• Description: The MCP6144 is a quad 600nA op amp offering rail to rail input & output over the 1.4 to 5.5V operating range. This amplifier ...
• Manufacturer: Microchip Technology

FIGURE 3-2:
non-inverting amplifier configuration.
Figure 3-2 shows non-inverting and inverting amplifier
circuits. In order for the amplifiers to be stable, the
noise gain should meet the specified requirement:
EQUATION
Note that an inverting signal gain of G = -9 V/V corre-
sponds to a noise gain G
Figure 3-3 shows a unity gain buffer and integrator that
are unstable when used with the MCP6141/2/3/4 fam-
ily. However, they are suitable for the MCP6041/2/3/4
family.
FIGURE 3-3:
suitable for the MCP6141/2/3/4 family.
V
2002 Microchip Technology Inc.
V
IN
Non-inverting noise gain: 1 + R
IN
Inverting noise gain: 1 + R
V
IN
V
R
IN
R
G
R
G
G
MCP604X
n
=
MCP614X
MCP614X
Noise gain for inverting and
Typical Circuits that are not
1
MCP604X
Unity gain buffer:
Unstable for MCP614X
+
n
------ -
R
R
= +10 V/V.
R
Integrator:
Unstable for MCP614X
R
F
G
F
F
C
10V/V
F
/R
F
/R
G
G
+10 V/V
V
+10 V/V
OUT
V
V
OUT
V
OUT
OUT
Note that the integrator circuit in Figure 3-3 becomes
unity gain at high frequencies because of the capaci-
tor. Therefore, this circuit is unstable for the
MCP6141/2/3/4.
3.6
Driving capacitive loads can cause stability problems
with voltage feedback op amps. Figure 2-21 shows how
increasing the load capacitance will decrease the phase
margin. While a phase margin above 60° is ideal, 45° is
on the verge of instability. As can be seen, up to
C
amp outputs without any problems, while 250 pF cre-
ates a 45° phase margin.
When the op amp is required to drive large capacitive
loads (C
Figure 3-4) at the output of the amplifier improves the
phase margin. This resistor makes the output load
resistive at higher frequencies, which improves the
phase margin. The bandwidth reduction caused by the
capacitive load, however, is not changed. To select
R
macro model and bench testing to adjust R
there is a minimum frequency response peaking.
FIGURE 3-4:
capacitive loads.
3.7
The MCP6143 is a single amplifier with a chip select
(CS) option. When CS is pulled high, the supply current
drops to 20 pA (typ.) and goes through the CS pin to
V
impedance state. By pulling CS low, the amplifier is
enabled. If the CS pin is left floating, the amplifier will
not operate properly. Figure 3-5 shows the output
voltage and supply current response to a CS pulse.
SS
L
ISO
= 150 pF can be placed on the MCP6141/2/3/4 op
V
. When this happens, the amplifier is put into a high
, start with 1 k , then use the MCP6141 SPICE
R
IN
2
L
Capacitive Load and Stability
The MCP6143 Chip Select (CS)
Option
>150 pF), a small series resistor (R
MCP614X
MCP6141/2/3/4
R
1
Amplifier circuit for heavy
R
ISO
C
L
21668A-page 11
ISO
V
ISO
OUT
until
in