LP5907-Q1: Ask about the output capacitor selection

Hi Jack,

Thanks for the questions. Following are my responses:

Jack Li said:

1. As shown in datasheet, the output capacitor limit to 10uF, I wonder if it's valid value in 3.3V or nominal value.

As described in the datasheet, for all voltage options, the maximum output capacitor value for which the device is guaranteed to be stable is 10uF, given it also meets the ESR requirements. This is assuming the fact that the capacitor tolerance should be 30% or better over the full temperature range (as described in the footnote of section 6.6).

Jack Li said:

2. What may happen if we use 4pcs 10uF capacitors at LP5907 output? Will it be less risk if the length from output PIN to device A/B/C is long enough?

The LP5907 has a risk of becoming unstable and oscillating with higher values of load capacitance. The risk remains the same for different lengths. You can test the stability of the LP5907 with this much Cout by using an EVM and placing your actual Cout onto the EVM and conducting a load transient or NISM test. Just letting you know, this is not a recommended operating condition for the device.

Jack Li said:

3. Shall we need to reduce these 10uF capacitor?

10uF Output cap is the max value with which regular operation is guaranteed by the datasheet.

Alternatively, you can choose to use a newer device TPS7A20. This was designed to replace the LP5907 and the TPS7A20 is stable with this much capacitance, and is cheaper.

Regards,

Bobby

Hi Jack,

Sorry, I misunderstood your question earlier.

From datasheet, the max 'capacitance' the device is guaranteed to handle at output is 10uF.

This means not the nominal value, but the actual capacitance (de-rated) value at the point of operation (3.3V in your case)

Regards,

Bobby