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TPS54231 current spike

JimHall
Prodigy 210 points
Other Parts Discussed in Thread: TPS54231, TPS54331

Hi

I am using a TPS54231 with a 12 volt battery input and an output of 5 volts. This regulator powers a cellular radio that draws a large turn on current spike - 4 Amps for about a milli second.

Will the TPS54231 stay regulation when this spike hits.?

As the battery discharges will the TPS54231 stay in regulation when the input voltage drops to 5 volts due to the battery's internal impedance.

I will appreciate any comments.

Thanks

Jim Hall

 

  • 0
    TI__Guru**** 191445 points

    4 msec is a long time relative to the switching time of teh TPS5423.  The current limit is 2.3 A min, 3.5 A typ, so it is likely the device will go into current limit  under a 4 A load for 1 msec.  Even teh TPS54331 may possibly experience OCP at 4 A.  During this OCP operation, teh output voltage will decrease as described below:

    The TPS54231 implements current mode control that uses the COMP pin voltage to turn off the high-side

    MOSFET on a cycle by cycle basis. Every cycle the switch current and the COMP pin voltage are compared;

    when the peak inductor current intersects the COMP pin voltage, the high-side switch is turned off. During

    overcurrent conditions that pull the output voltage low, the error amplifier responds by driving the COMP pin high,

    causing the switch current to increase. The COMP pin has a maximum clamp internally, which limit the output

    current. The TPS54231 provides robust protection during short circuits. There is potential for overcurrent runaway in the

    output inductor during a short circuit at the output. The TPS54231 solves this issue by increasing the off time

    during short circuit conditions by lowering the switching frequency. The switching frequency is divided by 8, 4, 2,

    and 1 as the voltage ramps from 0 V to 0.8 V on VSENSE pin.

    Also you will lose regulation when the input voltage drops.  The TPS54231 can sustain 100% duty cycle for short periods, but even at 100 % duty cycle internal circuit losses will cause the out put voltage to be less than the input voltage.