Hi
I have a question about TPS73701 current limit.
When I was testing TPS73701 OCP, the output current retried as red below.
Is this normal behavior?
Ch1: Vin
Ch2: Vout
Ch3: En
Ch4: Iout
schematic:
Thanks
BR,
Hank
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Hi
I have a question about TPS73701 current limit.
When I was testing TPS73701 OCP, the output current retried as red below.
Is this normal behavior?
Ch1: Vin
Ch2: Vout
Ch3: En
Ch4: Iout
schematic:
Thanks
BR,
Hank
Hi Hank,
The LDO may be unstable. It looks like the output capacitors are low ESR variants and the design is not following the datasheet guidance. Please note that there is a typo in the datasheet, it should read "the product of Cout and total ESR drops below 50nF-ohms".
If it is unstable, you may be able to stabilize it by removing all output capacitors except one 10uF cap. For 10uF capacitance, this assumes that the ESR of the capacitor is greater than 5 milliohms.
Thanks,
Stephen
Hi Stephen
But I had made transient test as below, it seem be stable.
Ch2: Vout
Ch4: Iout
Thanks
BR,
Hank
Hi Hank,
It looks to me like the current limit circuit may be oscillating. Can you try the same test but with just one 10uF on Vout? The load transient test is not stressing the current limit loop as that loop is not engaged with the level of current applied in the load transient test data (I'm reading the oscilloscope data as max 280mA current which does not engage the current limit).
If using just one 10uF capacitor on Cout does not improve these results, then I would also short the L372 ferrite bead on the input, as this looks like a lossy inductor at low frequencies and I want to be sure this is not impacting the stability of the LDO.
Please respond with your findings. I will be regularly monitoring this thread.
Thanks,
Stephen
Hi Stephen
I had only used one 22uF cap, but the output current still retried.
But I tried CCL mode for E-load, the OCP is as below.
Is this normal behavior? or What will be normal behavior when OCP happens?
Is current limit of TPS73701 retry or latch mode?
Thanks
BR,
Hank
Hi Hank,
Are you using an electronic load? If so, I would recommend retesting with a physical resistor that is switched on using a switch (relay, MOSFET, BJT, etc). Electronic loads can interfere with the measurement as the control loop of the e-load reacts with the control loop of the LDO. So what you may have been seeing is the electronic load oscillating, and not the LDO.
Thanks,
Stephen