TS2509
3A / 500KHz PWM Buck Converter
5/9 Version: B09
Function Descriptions (Continue)
Output Capacitor Selection
(EL CAP)
The output capacitor is required to maintain the DC output voltage stability. The important capacitor parameters are;
the 100KHz ESR (Equivalent Series Resistance), 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.
V
RIPPLE
= ∆I
L
x ESR = 0.4A x 110mΩ = 44mV
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 is most sufficient for applications.
R
DS(ON)
Current Limiting
The current limit threshold is setting by the internal circuit.
Layout Guidance
When laying out the PC board, the following suggestions should be taken to ensure proper operation of the TS2509.
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.
2. Connect the C5 to the V
CC
& EN pins of the TS2509 as closely as possible to get good power filter effect.
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.
