OA1ZHA Datasheet, PDF (21/35 Pages) STMicroelectronics – Fitness and healthcare

OA1ZHA, OA2ZHA, OA4ZHA
Application information
5.7
Capacitive load
Driving large capacitive loads can cause stability problems. Increasing the load
capacitance produces gain peaking in the frequency response, with overshoot and ringing
in the step response. It is usually considered that with a gain peaking higher than 2.3 dB an
op amp might become unstable.
Generally, the unity gain configuration is the worst case for stability and the ability to drive
large capacitive loads.
Figure 43: "Stability criteria with a serial resistor at VDD = 5 V" and Figure 44: "Stability
criteria with a serial resistor at VDD = 1.8 V" show the serial resistor that must be added to
the output, to make a system stable. Figure 45: "Test configuration for Riso" shows the test
configuration using an isolation resistor, Riso.
Figure 43: Stability criteria with a serial resistor at VDD
=5V
Figure 44: Stability criteria with a serial resistor at VDD
= 1.8 V
Figure 45: Test configuration for Riso
5.8
PCB layout recommendations
Particular attention must be paid to the layout of the PCB, tracks connected to the amplifier,
load, and power supply. The power and ground traces are critical as they must provide
adequate energy and grounding for all circuits. Good practice is to use short and wide PCB
traces to minimize voltage drops and parasitic inductance.
In addition, to minimize parasitic impedance over the entire surface, a multi-via technique
that connects the bottom and top layer ground planes together in many locations is often
used.
The copper traces that connect the output pins to the load and supply pins should be as
wide as possible to minimize trace resistance.
DocID025994 Rev 2
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