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Hello,
I am designing amplifier circuit used OPA4202.
The data sheet of OPAx202 recommends the value of 0.1uF bypass capacitor for each power input terminal of OPAx202.
(Section 9: Power supply recommendations)
Also figure 49 of OPAx202 datasheet shows 4 bypass capacitor (C1, C2, C3, C4) for V+ terminal and V- terminal.
I will use OPA4202 on frequency of DC to 10kHz.
I would like to confirm suggested value of bypass capacitors.
Regards,
MESH
Hi Mesh,
I will use OPA4202 on frequency of DC to 10kHz. I would like to confirm suggested value of bypass capacitors.
It seems that your operating frequency range is from DC to 10kHz. Typically, we use 100nf coupling capacitor for the application. If your power supply is noisy, you may place multiple coupling capacitors in parallel. A standard practice is to select the bypass capacitor in a decade apart. You may also use different size of capacitors in combination with the multiple coupler method. Smaller size will have lower ESL, so its impedance will rise slower with increasing in frequency.
The reasons behind the practices are: First, you want to have multiple low ESR coupling (bypass) capacitors that can filter out unwanted high frequency signals for a noise sensitive application. If op amp's power rails consist of high frequency noises, you want re-direct high frequency signal to ground via low ESR capacitor. Capacitor's spice model consists of ESR + Xc + X_L, and the impedance vs. frequency responses are shown in the impedance plot above.
At higher frequency, capacitor behaves like a short. The voltage ripple is created across ESR*Iac that goes through the capacitor. Lower ESR in capacitor, lower the ripple voltage will develop across an op amp's supply rail. At the op amp's supply rail, power rail prefers to have DC_amplitude + low_ripple_AC_voltage. By implementing multiple bypass capacitors, it may be able to broaden low ESR specification over a frequency range, hence you may remove wider range of unwanted frequency that may couple into op amp's internal circuit (if the application's power supply is noisy, e.g. switching power supply).
This is just one aspect of the use of multiple bypass capacitors. As Kai pointed out, there are other factors when implementing different values of coupling capacitors. It also depends on the type of application. For OPA4202 operating from DC to 10kHz application, 1uf and 0.1uf low ESR capacitors may be adequate for the application.
If the low noise design is required in an application, you also need to check the datasheet of low ESR capacitors used in a design, and make sure that it will perform well over frequency, temperature and load requirements etc..
If you have additional questions, please let us know.
Best,
Raymond
Hi Mesh,
The setup should be stable. It has enough phase margin of 88 degree, which it more than enough. Riso of 51Ω will contribute and maintain an adequate phase margin even capacitive load is increased up to 10nf in the configuration.
OPA202 Step Transient 08202021.TSC
If you have additional questions, please let us know.
Best,
Raymond
Hi Mesh,
with a 200pF load capacitance a simple 100...470n X7R/0805 decoupling cap (per supply voltage) should do. Something like this:
The capacitance loss at +15V supply voltage is only 10%.
Kai
