SSM2311CBZ-R2 datasheet(16/20 Pages) AD

16 / 20 page

SSM2311

Rev. 0 | Page 16 of 20

INPUT CAPACITOR SELECTION

The SSM2311 does not require input coupling capacitors if the

input signal is biased from 1.0 V to VDD − 1.0 V. Input capacitors

are required if the input signal is not biased within this recom-

mended input dc common-mode voltage range, if high-pass

filtering is needed (Figure 43), or if using a single-ended source

(Figure 44). If high-pass filtering is needed at the input, the input

capacitor along with the input resistor of the SSM2311 forms a

high-pass filter whose corner frequency is determined by the

following equation:

fC = 1/(2π × RIN × CIN)

The input capacitor can significantly affect the performance of

the circuit. Not using input capacitors degrades both the output

offset of the amplifier and the PSRR performance.

PROPER POWER SUPPLY DECOUPLING

To ensure high efficiency, low THD, and high PSRR, proper power

supply decoupling is necessary. Noise transients on the power

supply lines are short-duration voltage spikes. Although the actual

switching frequency can range from 10 kHz to 100 kHz, these

spikes can contain frequency components that extend into the

hundreds of megahertz. The power supply input needs to be

decoupled with a good quality low ESL, low ESR capacitor—usually

of around 4.7 μF. This capacitor bypasses low frequency noises

to the ground plane. For high frequency transients noises, use a

0.1 μF capacitor as close as possible to the VDD pin of the device.

Placing the decoupling capacitor as close as possible to the SSM2311

helps maintain efficiency performance.

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