SLVA997A November 2018 – July 2021 TPS61322
3 Output Ripple Calculation
The TPS613221A, a 3.3-V version from TPS61322xx family is used as the example.
To simplify the calculation, there is no load at the output of TPS613221A, and the efficiency is 100%. All the input energy on the inductor will be discharged to the output capacitor. From the power balance point, the energy discharged to the output capacitor is shown in Equation 1:
where
The peak inductor current at light load is calculated according to the Equation 2:
where
- L is the power inductor inductance
- Ihys is 80 mA typically
- tdelay is 120 ns typically
The inductor current pulse period is calculated according to Equation 2:
where
Finally, the output ripple will be a little higher because of the ESR in the output capacitor, which can be calculated as follow:
where
- ESR is the equivalent series resistance of the output capacitor.
When the input voltage is 1.8 V, the peak inductor current will be 200 mA according to the previous equations. The output ripple is 7.6 mV (ΔV = 6 mV, ESR × Ipeak is 1.6 mV) when using a 10-µF output capacitor with 8-mΩ ESR.