LM5176-Q1: It is not boosting to 24 V @ Vin=6 to 10 V.

Malakondareddy B

Part Number: LM5176-Q1

Tool/software:

HI everyone,

We have faced few below mentioned problems with LM5176-Q1 when we tested With PCB. The schematic attached for your reference

It is not boosting 24 V from 9 V input but it is working from 10V. However the Vcc voltage is 4.3 V at 9 V and 4.7 V at 10V (as per datasheet it should give 7 V figure 6.4 (VCC vs Vin)). Attached gate to source voltage Q10.
From 9 to 10 V there was inductive noise and the output voltage was 6 to 8 V. (Don't why it is not boosting 24 V)
From 12 V to 15 V there was a proper 24 V but the inductor heated more at this condition. attached image for your reference.
Above 5 A load current @24V there was 3.0 V p-p ripple in output voltage but less ripple at below 5 A.

11 months ago

0 Brigitte 11 months ago

TI__Guru 65300 points

Hello Malakondareddy B,

1. If VCC does not get to the specified value, either there is something discharging VCC, or VIN on the VIN pin is not on the right level, or the device is damaged.

2. With a VCC of only 4.3V, most probable you are not able to turn on the MOSFETs fully.

3. Possibly you have high ripple current on the inductor as the value is relatively low.

4. Please check the measurement method for ripple: How to measure ripple for better design outcomes (ti.com)

Best regards,
Brigitte

0 Malakondareddy B 11 months ago in reply to Brigitte

Prodigy 155 points

Hi Brigitte,

Thanks for quick response

I have attached the schematic that I used in my design and also I follow the datasheet typical application circuit.

Please check the schematic that attached here.

If it is damaged then how it is working at 10-24 V input properly without any issues.

The inductor was chosen based on the bench results and calculation.

0 Brigitte 11 months ago in reply to Malakondareddy B

TI__Guru 65300 points

Hello Malakondareddy B,

Is there the right level on VCC when the input is above 10V?

BTW, please remove the capacitor on BIAS and replace it with a resistor to GND if you are not using a separate BIAS voltage. The capacitor is only necessary if you apply a voltage to BIAS.

Do you have a capacitor close to the VIN pin that is close to the value on VCC? The VCC is taking the energy from the VIN cap, so it might be possible that it is just discharged faster than it can be re-charged from VIN.

Best regards,
Brigitte

0 Malakondareddy B 11 months ago in reply to Brigitte

Prodigy 155 points

Hi Brigitte,

I was observed constant 5 V at input voltage above 10 V. May I know what voltage should be there at VCC when input above 10 V?.

Yes I added 0.1uf capacitor near to the Vin.

0 Brigitte 11 months ago in reply to Malakondareddy B

TI__Guru 65300 points

Hello Malakondareddy B,

The VCC regulator should regulate to 7.35V typically. Something is wrong if it does not regulate to this voltage. Be aware that it is able to deliver 65mA. Do you have some load attached to it?

Best regards,
Brigitte

0 Malakondareddy B 11 months ago in reply to Brigitte

Prodigy 155 points

Hello Brigitte,

Load on VCC or output? Can you send friend request for better communication?

0 Brigitte 11 months ago in reply to Malakondareddy B

TI__Guru 65300 points

Hello Malakondareddy B,

Load on VCC. VCC needs to be above 7V when VIN is above 8V. If this is not the case, you seem to load VCC with too much current.

Best regards,
Brigitte

0 Malakondareddy B 11 months ago in reply to Brigitte

Prodigy 155 points

Yeah but there is no load on VCC except the gate driver supplies. Will I get 7.3 V If I remove all Mosfet from PCB ? Other than is there any method to check VCC ?

0 Brigitte 11 months ago in reply to Malakondareddy B

TI__Guru 65300 points

Hello Malakondareddy,

Please put the device in standby. Then VCC should be charged already. If you still do not get 7.3V, something is wrong with the device and you should exchange it on this board.

Best regards,
Brigitte

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LM5176-Q1: It is not boosting to 24 V @ Vin=6 to 10 V.