Issue with TPS7A7300 design not supplying fast transient loads

Andy Pollock73

Other Parts Discussed in Thread: TPS7A7300, TPS7A8300

I have a design using the TPS7A7300 configured per the datasheet notes, using all the ANY-OUT pins to set it at 3.65V output, and using a 5V input. I have a large amount (over 2000 uF) of low ESR input capacitance, and 200uF of low ESR output capacitance. The output is connected to a module that normally requires around 700ma average, but does have peak transient loads (of 1-2 ms) that can reach 2A. The setup is basically working, but when the load (the module) goes into the mode that requires the 2A current pulses, the regulator seems to limit the current output (at around 800ma) and the voltage drops from 3.65 to around 2V for a brief 2ms spike. But the regulator is supposed to support up to 3A or more. Is there something that could be causing the current limiter to trigger prematurely? If I add 2000 uF to the output, the impulse load required by the module is provided by the caps and there is no issue. So it seems the TI is not providing the fast load transient response that I expect. Any suggestions?

over 9 years ago

0 Ryan Eslinger over 9 years ago

TI__Guru 55940 points

Hi Andy,

First it is important to recognize that the ANY-OUT configuration is only to be used up to 3.5V per the datasheet. In order to set the output to 3.65V, please use the traditional adjustable configuration.

Please note that TPS7A8300 has a faster transient response and is pin-to-pin with TPS7A7300. TPS7A8300 is able to be programmed using ANY-OUT to 3.65V.

Very Respectfully,

Ryan

0 Ryan Eslinger over 9 years ago in reply to Ryan Eslinger

TI__Guru 55940 points

Hi Andy,

One additional comment, it appears that 2A with 1.35V of headroom will place your application on the edge of thermal shutdown if not in thermal shutdown. Could you provide a scope shot of Vin, Vout, and Iout?

Very Respectfully,
Ryan

0 Andy Pollock73 over 9 years ago in reply to Ryan Eslinger

Prodigy 100 points

Yes, but there is also a place in the 7300 datasheet where it says that grounding all the ANY-OUT pins will give you 3.65V.

0 Andy Pollock73 over 9 years ago in reply to Ryan Eslinger

Prodigy 100 points

Yes, but the average current is only 700ma worst case. The 2A loads are pulses that may be around 25% duty cycle, and are only occasional, plus we have a lot of PCB heatsinking under the thermal pad. It may be hard to get you a shot of Iout, but I can look at the thermal imaging of the case.

0 Andy Pollock73 over 9 years ago in reply to Ryan Eslinger

Prodigy 100 points

Ryan - while in operation, I measured the case temperature to be 38C.

0 Andy Pollock73 over 9 years ago in reply to Ryan Eslinger

Prodigy 100 points

Ryan: are you concerned at all about the large amount (over 2000 uF) of low ESR input capacitance? I see the comment in the datasheet about a potential unwanted LC resonance, but I'm not sure how to evaluate or determine whether this is an issue for the design.

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Issue with TPS7A7300 design not supplying fast transient loads