SGM358 sg-micro, SGM358 Datasheet - Page 7

• Manufacturer Part Number: SGM358
• Description: 1mhz, 60?a, Rail-to-rail I/o Cmos Operational Amplifier
• Manufacturer: sg-micro

APPLICATION NOTES
Driving Capacitive Loads
The SGM3XX 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
IN
V
IN
OUT
SGM321
will be. Note that this method results in a loss of gain
C
SGM321
F
ISO
ISO
and the load capacitor C
forms a voltage divider with the R
R
R
ISO
C
ISO
L
F
provides the DC accuracy by
ISO
R
C
F
resistor value, the more
L
V
R
OUT
L
L
F
V
form a zero to
and R
OUT
Iso
LOAD
serve
.
７
Power-Supply Bypassing and Layout
The SGM3XX family 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
0.1µF ceramic capacitor which should be placed close to the
V
supplies should be bypassed to ground with separate 0.1µF
ceramic capacitors. 2.2µF tantalum capacitor can be added for
better performance.
Vn
Vp
DD
pin. For dual-supply operation, both the V
V
Figure 3. Amplifier with Bypass Capacitors
SGM321
V
DD
SS
(GND)
0.1µF
10µF
V
OUT
SGM321/358/324
Vn
Vp
V
SGM321
DD
V
SS
DD
0.1µF
0.1µF
and the V
10µF
10µF
DD
with a
V
OUT
SS