LP3883: Input bypass capacitor

Stephen Kenna

Part Number: LP3883

I am using the LP3883-1.2 as described in the datasheet's typical application circuit for several similar CCA designs. The input voltage being used is 5VDC and the load is very light at ~1ma. Unfortunately after most of the product was delivered it was discovered that the input bypass capacitor had been inadvertently installed with a 1800pf capacitor instead of the datasheet's called-out 4.7uf capacitor. However, in each design there a nearby 68uf capacitor across the same 5VDC and ground planes used by the LP3883-1.2 input. The 68uf capacitor is a low-ESR chip tantalum and is located between 1.5 to 2.5 inches from the LP3883-1.2. Is the condition I just described adequate to meet the input capacitance requirement noted in the datasheet?

over 8 years ago

0 Daddio over 8 years ago

Intellectual 515 points

Without actual in-circuit dynamic testing it's not possible to give any absolute 100% iron-clad assurance for this situation.

However, if the copper trace from the 68uF tantalum capacitor to the LP3883 Vin pin is of a reasonable dimension with reasonably direct routing, there is a fairly good likelihood that there will not be any problem.

0 Stephen Kenna over 8 years ago in reply to Daddio

Prodigy 30 points

The 68uf capacitor is connected between a 5V plane and a ground plane as are the IN and GND pins of the LP3883. Does this improve the situation as opposed to having copper traces from the capacitor to the LP3883?

0 Daddio over 8 years ago in reply to Stephen Kenna

Intellectual 515 points

Yes, using 5V PWR plane and GND plane will be better than copper traces.

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LP3883: Input bypass capacitor