LM5107: LM5107 High Side not turning on

Diandi Zhu

Part Number: LM5107

The schematic is like this:

The following picture shows the input signal to the gate driver. Yellow is input of high side, Green is input of low side from mcu.

In the following picture yellow is the input of high side and green is the output of low side measured at R2. Signal feeding into the gate driver is same as shown in picture 1.

Probe at high side input and R1, the yellow signal below is high side input, the green signal is high side output. Low side input was feeding same signal as shown in Picture 1. High side output is always 12V while is should be HS voltage + 12v.

over 1 year ago

0 Alex Weaver over 1 year ago

TI__Intellectual 2100 points

Hi Diandi,

Thank you for sharing the schematic and relevant waveforms!

It looks like you tried to switch the low-side, and then separately verified if the high-side was switching. Our half-bridge gate drivers are designed so that when the low-side is switched, the boot capacitor stores charge to provide the bias voltage for the high-side. If you switch the high-side without having switched the low-side, the boot capacitor will not be charged and won't be able to provide the bias voltage for the high-side drive.

This issue should be fixed once you verify switching functionality using both the low-side and high-side similar to how your input signals appear in the first waveform image.

Best,

Alex Weaver

0 Diandi Zhu over 1 year ago in reply to Alex Weaver

Prodigy 10 points

Hi Alex,

Thank you for your quick reply. Both low and high switching signal was feeding to the gate driver simultaneously(Please see scope capture 1). I do not have a 4 channel scope. So I cloud not shout the both low and high side inputs in picture 3, but the low side is switching at same time as picture 1 shows.