LP5569ARTWR datasheet(83/93 Pages) TI2

83 / 93 page

LP5569

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SNVSAP8A – JULY 2017 – REVISED SEPTEMBER 2017

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11 Layout

11.1 Layout Guidelines

The charge pump basically has three areas of concern regarding component placement:

•

The flying capacitors

•

The output capacitor

•

The input capacitor

11.1.1 Flying Capacitor Placement

The charge pump flying capacitors must quickly charge up and then supply current to the output every switching

cycle. Because the charge-pump switching frequency is 1.25 MHz, the capacitor must be a low-inductance and

low-resistance ceramic. Additionally, there must be a low-inductive connection between the flying capacitors and

LP5569 pins C1P, C2P, C1M, and C2M.

11.1.2 Output Capacitor Placement

The charge-pump output capacitor is charged by the flying capacitor every switching cycle (1.25 MHz). This fast

switching action requires that a low-inductance and low-resistance capacitor (ceramic) be used and that the

output capacitor be connected to the LP5569 VOUT pin with a low-inductance connection. This is done by

placing the output capacitor as close as possible to the VOUT and PGND pins of the LP5569 device, with

connections on the same layer to avoid vias.

11.1.3 Input Capacitor Placement

The charge pump input capacitor is discharged by the flying capacitor every switching cycle (0.8 µs). This fast

switching action requires that a low-inductance and low-resistance capacitor (ceramic) be used and that the input

capacitor be connected to the LP5569 VIN pin with a low-inductive connection. This is done by placing the output

capacitor as close as possible to the VOUT and AGND pins of the LP5569 device, with connections on the same

layer to avoid vias.

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