TPS53219A: Input/output capacitor selection

We are designing TPS53219A to support 3.3V/30~40A,

We would like to know how to select the input and output capacitor, does any selection guideline to explain it?

Input capacitors are typically sized to provide 2 different levels of ripple voltage support.

Ceramic Capacitors should be sized to keep the cycle by cycle input voltage ripple at a voltage-ripple level that will not induce excessive RMS ripple current on the bulk electrolytic capacitors on the input supply while the bulk input capacitors need to support transient output loads until the supply generating the input voltage can respond by increasing the current available on the supply.

For Ceramic Capacitors, the maximum allowable ripple voltage is Vpk-pk(max) =  3 x Irms_rated / ESR

Where Irms_rated is the RMS current rating of the bulk input capacitors, derated for margin and operating temperature.

and the capacitance to meet a ripple voltage requirement is: Cin = (1/ Efficiency) * (VOUT/VIN * IOUT)  * (1/ Fsw) /  Vpk-pk(max)

Where Efficiency is the conversion efficiency (you can use 0.90 as an estimate for a 3.3V output), IOUT is the maximum designed load current, Fsw is the programmed switching frequency of the ON-time generator and Vpk-pk(max) is the maximum peak to peak voltage on the bulk capacitors calculated above.

For the Bulk Capacitor, there should be enough bulk capacitors, which can be electrolytic, organic or polymer capacitors to sustain the input current to support the maximum load current (IOUT(max) * VOUT/VIN * (1/Efficiency) through at least 2 periods of the bandwidth of the control loop generating the supply voltage.

For output capacitors, there should be enough output capacitance to limit the under and overshoot of the output voltage in response to a transient.  Typically, the worst case transient occurs during the release of the load when the inductor forces excess current into the output capacitors until the inductors current can respond to the load change.

Cout = Delta_IOUT^2 * L / Delta_Vout

Where:  Delta_IOUT is the worst case load current release (High current to low current), and Delta_VOUT is the allowable output voltage rise in response to that load release.

What is the minimum value of capacitor? What kind the type should be used?

For CIN, generally a mix of Ceramic and Electrolytic, or all Ceramic capacitors are used.

For COUT, the control loop on the TPS53219A  is designed to natively support output capacitors dominated by Organic or Polymer capacitors with a few ceramic capacitors to handle high frequency noise.

In this configuration, the ESR ripple (Inductor current ripple current x Output Capacitor ESR) should be 20mV at the Feedback pin, after the feedback divider.

With some external components - and R-C across the inductor and a capacitor to inject the resulting ripple into the Feedback, all ceramic capacitors can be used.

Could we mix the OS-CON and ceramic capacitor on input and output side?

Yes, but I would recommend comparing the impedance of the ceramic and os-con capacitors at the switching frequency.  If the ceramic capacitors impedance at the switching frequency is less than 2x Os-con capacitor's impedance at the switching frequency, consider the output "ceramic" for the purpose of adding the RC-C injection circuitry.

http://www.ti.com/lit/an/slva453/slva453.pdf