TS2509

3A / 500KHz PWM Buck Converter

5/9

Version: A09

Function Descriptions (Continue)

Output Capacitor Selection

(EL CAP)

The output capacitor is required to filter the output and provide regulator loop stability. The important capacitor

parameters are; the 100KHz Equivalent Series Resistance (ESR), the RMS ripples current rating, voltage rating, and

capacitance value. For the output capacitor, the ESR value is the most important parameter. The ESR can be

calculated from the following formula.

An aluminum electrolytic capacitor's ESR value is related to the capacitance and its voltage rating. In most case, higher

voltage electrolytic capacitors have lower ESR values. Most of the time, capacitors with much higher voltage ratings

may be needed to provide the low ESR values required for low output ripple voltage. It is recommended to replace this

low ESR capacitor by using a 330µF low ESR values < 110mΩ

(MLCC)

A 33µF MLCC or three 10uF MLCC capacitors for most applications is sufficient.

The current limit threshold is setting by the internal circuit.

4.6V~6V

6V~10V

10V~23V

3A

3.8A

4.0A

2.5A

3A

3A

Layout Guidance

When laying out the PC board, the following suggestions should be taken to ensure proper operation of the TS2509.

These items are also illustrated graphically in below.

1. The power traces, including the PMOS Drain & Source trace, the Schottky and the C2 trace should be kept short,

direct and wide to allow large current flow.

3. Keep the switching node, away from the sensitive FB node.

4. Connect ground side of the C2 & D1 as closely as possible.

5. Connect PMOS Source and R3 as closely as possible.

6. Do not trace signal line under inductor.