DRV8838: Can this part family drive CAP Loads?

Seth,

Without output inductance to slow down the output current ramp-up and without motor back EMF to against the input voltage to limit the winding current going up, only the loop resistance plus the parasitic inductance and OCP current threshold limits the output current. After triggers OCP, the converter would wait for 1ms to retry. The average maximum load current could be 1us/1ms = 1000 times smaller than the average startup current during the deglitch time.  So, we have to limit the output current below 1.9A for this application. What is VM voltage? Can you put a series resistor to limit the current below 1.9A?

Af

Hi Wang,

Thanks for your reply. I've tried simulations using 3 volts as the VM voltage, at 100 kHz with 200nS rise/fall times.
with 10uF load and no current limiting - that works out to 150A? So i think that would correlate to a 0.02 Ohm output impedance.
If i current limit using a 2 Ohm resistor, would that limit it to 1.5A?

Is there a SPICE model available for this family of part?

Thanks again,

Seth

Seth,

The current cannot go 150A high due to the capacitor voltage change and parasitic loop inductance.
2ohm series resistor could limit the current below 1.5A. Does any load on that capacitor? If there is a load on the output capacitor, the 2ohm resistor could affect the load voltage.
Do you put the capacitor load between the OUTx and ground? When you run 100kHz PWM, you may add an inductor to limit the current below OCP and charge the output capacitor voltage up. It could reduce the loss comparing 2ohm series resistor solution.

Hi Wang,

There will be a load on the capacitor eventually. This is for an N stage charge pump. The capacitor is one of the pumping capacitors, and the DRV8388 would be driving one of the clock phases.
Adding the inductor is an interesting idea. I will take a look at that.