LM2663: I apply +5.5V as V+, but Vout had been dropped to -4.3V with loading

The datasheet guarantees an output impedance of at most 7 Ω under the specified test conditions (47 µF low-ESR capacitors).

What kind of capacitors are C19/C21? Are they right near the chip? (show the board layout)

Hi, Clemens

Many thanks to your help.

I used X5R 47uF capacitor for C19/C21. And I test LM2663 on PCB board like below picture show.

But also found voltage drop down to -4.5V @ 20.6mA while connected to LCD loading.

If LCD IC input pin have something wrong? to make LM2663 voltage drop?

The datasheet's layout guidelines say:

• Place C_IN on the top layer (same layer as the LM2662/2663) and as close to the device as possible. Connecting the input capacitor through short, wide traces to both the V+ and GND pins reduces the inductive voltage spikes that occur during switching which can corrupt the V+ line.
• Place C_OUT on the top layer (same layer as the LM2662/2663) and as close as possible to the OUT and GND pin. The returns for both C_IN and C_OUT should come together at one point, as close to the GND pin as possible. Connecting C_OUT through short, wide traces reduce the series inductance on the OUT and GND pins that can corrupt the V_OUT and GND lines and cause excessive noise in the device and surrounding circuitry.
• Place C₁ on the top layer (same layer as the LM2662/2663) and as close to the device as possible. Connect the flying capacitor through short, wide traces to both the CAP+ and CAP– pins.

On this board, there is no input capacitor, and all the traces/wires are long and thin.