inrush current and short circuit protection of both TPS7B6950-Q1 and LP5907-Q1

Muramatsu-san,

For the question about the LP5907-Q1, check this thread: e2e.ti.com/.../381603
and see if it helps. I've also assigned the appropriate applications engineer to answer your question about the TPS7B6950-Q1, and they may be able to answer your question about the LP5907-Q1 as well.

Regards,

For the LP5907 in-rush current at power-up:

Is LP5907 EN pin connected to the IN pin? If yes, then the Vin rise time will affect peak in-rush current. If the Vin rise time is slow enough (> 1 milli-sec) there will not be any noticeable in-rush current. If Vin rise time is very fast, then in-rush current will be the same as if LP5907 EN pin is taken high after Vin is established.

If LP5907 EN pin is taken high after Vin is established then that will be worst case for peak in-rush current . Peak in-rush can generally be in the range of 1A to 1.5A, with a duration of about 10 micro-secs. There is chart for this in the LP5907-Q1 datasheet Typical Performance Characteristics (see: Figure 8. Inrush Current). After about 10 micro-secs the LP5907 control loop will be active and will go into short circuit current limiting (Isc) until nominal Vout is reached.

Charging a 10uF Cout from 0V to 3V at the typical Isc rate of 500mA will take about 60 micro-sec. Then the input current will fall to be same as load current.

For the LP5907 short circuit protection recovery:

The LP5907 Isc current limiting is linear, there is no fold-back limiting, just reduce current demand back to normal range and normal operation will resume. If LP5907 is in current limiting mode for more than a few seconds it is possible that the thermal shutdown may be activated. Normal operation will resume after the device has cooled and current demand is back to normal range.

Muramatsu -san,

1. TPS7B6950-Q1 would recover to normal operating mode automatically when the output overload or shortage condition been removed.
2. This is related with the power up slew rate. If the input voltage ramps up slowly (> several milli-seconds), then the output voltage could follow the input voltage and there is almost no inrush current. If the input voltage rises quickly, the inrush current of TPS7B6950-Q1 would be clamped at the current limit value.
Since there is LP5907-Q1 with higher current limit value at the output and, current limit of TPS7B6950-Q1 would not complete before the output voltage of LP5907-Q1 is stable.

Best regards,
Jason Liu

Dear Donald-san

Thank you for quick response and sorry to late reply.
I went businesstrip last week.

Answer of Q1) about LP5907,I understood that LP5907-Q1 back to normal operation after dropping under Isc current.

But I want to confirm answer of Q2).
I checked start up waveform about fig.9 and fig.15 in datasheet.
fig.15 show rise up time of Vout is near 40uS,does it make over 500mA in-rush current?

I feel start up of LP5907-Q1 usually operate over 250mA current maximum specification.
Can TI grantee LP5907-Q1 device after over 250mA in-rush current?

Regards,
Shinya Muramatsu

Dear Jason-san

Thank you for response and sorry to late reply.

I understood Q1.
And I already got answer about Q2 of LP5907-Q1.
I think answer about TPS7B6950-Q1 is same as LP5907-Q1,and I confirm bellow.

Can TI grantee TPS7B6950-Q1 device after over 150mA in-rush current?

Regards,
Shinya Muramatsu.