LM27313: OUTPUT shows sawtooth wave

zhang ping

Part Number: LM27313

When the OLED brightness reaches 30%, the OUTPUT of LM27313 is normal, as shown in Figure 2. However, when the OLED brightness reaches 60%, the output of LM27313 is unstable, and the oscillometer shows sawtooth wave, as shown in Figure 3. Figure 4 shows the power parameters of THE OLED screen.

over 2 years ago

0 Zack Liu over 2 years ago

TI__Mastermind 34201 points

Hi Ping,

May i know the load current when OLED brightness reaches 30% and 60%?

0 zhang ping over 2 years ago in reply to Zack Liu

Genius 3195 points

7mA 30%-15mA 60%

0 Zack Liu over 2 years ago in reply to zhang ping

TI__Mastermind 34201 points

Hi Ping,

Can you also share the layout?

0 zhang ping over 2 years ago in reply to Zack Liu

Genius 3195 points

0 Zack Liu over 2 years ago in reply to zhang ping

TI__Mastermind 34201 points

Hi Ping,

There are several possible reason that causes this unstable Vout:

1. Layout: Layout is always very critical for a SMPS. The GND pin is better to be connected to the negative sides of output capacitors directly on top layer. Connect the lower FB resistor negative side to GND pin directly on top layer.

2. Is there any inrush current when the OLED draw current? If possible, please use current probe to measure the load current and inductor current.

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LM27313: OUTPUT shows sawtooth wave