sgm8545 sg-micro, sgm8545 Datasheet - Page 7

• Manufacturer Part Number: sgm8545
• Description: 1.1mhz, 42?a, Rail-to-rail I/o Cmos Operational Amplifier
• Manufacturer: sg-micro

SGM8545
APPLICATION NOTES
Driving Capacitive Loads
The SGM8545 can directly drive 250pF in unity-gain without
oscillation. The unity-gain follower (buffer) is the most sensitive
configuration to capacitive loading. Direct capacitive loading
reduces the phase margin of amplifiers and this results in ringing
or even oscillation. Applications that require greater capacitive
drive capability should use an isolation resistor between the
output and the capacitive load like the circuit in Figure 1. The
isolation resistor R
increase stability. The bigger the R
stable V
accuracy because R
An improvement circuit is shown in Figure 2, It provides DC
accuracy as well as AC stability. R
connecting the inverting signal with the output, C
to counteract the loss of phase margin by feeding the high
frequency component of the output signal back to the amplifier’s
inverting input, thereby preserving phase margin in the overall
feedback loop.
Figure 2. Indirectly Driving Heavy Capacitive Load with DC
Accuracy
For no-buffer configuration, there are two others ways to
increase the phase margin: (a) by increasing the amplifier’s gain
or (b) by placing a capacitor in parallel with the feedback resistor
to counteract the parasitic capacitance associated with inverting
node.
V
Figure 1. Indirectly Driving Heavy Capacitive Load
V
IN
OUT
IN
will be. Note that this method results in a loss of gain
SG Micro Limited
www.sg-micro.com
SGM8545
C
SGM8545
F
ISO
ISO
and the load capacitor C
forms a voltage divider with the R
R
F
ISO
provides the DC accuracy by
C
ISO
R
L
ISO
resistor value, the more
R
F
C
L
F
R
form a zero to
L
and R
L
V
OUT
V
OUT
Iso
LOAD
serve
.
Power-Supply Bypassing and Layout
The SGM8545 operates from either a single +2.5V to +5.5V
supply or dual ±1.25V to ±2.75V supplies. For single-supply
operation, bypass the power supply V
capacitor which should be placed close to the V
dual-supply operation, both the V
should be bypassed to ground with separate 0.1µF ceramic
capacitors. 2.2µF tantalum capacitor can be added for better
performance.
Vn
Vp
V
SGM8545
Figure 3. Amplifier with Bypass Capacitors
V
CMOS Operational Amplifier
1.1MHz, 42µA, Rail-to-Rail I/O
DD
SS
(GND)
0.1µF
10µF
V
OUT
Vn
Vp
DD
DD
and the V
V
SGM8545
with a 0.1µF ceramic
DD
V
SS
0.1µF
0.1µF
10µF
SS
10µF
DD
supplies
pin. For
V
OUT
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