LM5156: LM5156QDSSRQ1

Hi Aniket,

Thanks for using E2E forum.

The device has an internal wide input VCC regulator which is sourced from the BIAS pin. It should be connected either to input or output of the converter, if VCC is not supplied by external source. 

Kindly, connect the BIAS pin to output of the converter to make the device able to operate at 3V input.

What do you mean with "cut 12V" ?

Best Regards,

Hassan 

I have 2 sources one is main battery which is of 12 V and other is auxiliary battery 3V.

when we cut (Disconnect) 12 V, auxiliary battery should boost the voltage to 12V.

one more thing to add we have a switch IC which has a enable signal coming from Controller.

when 12V is disconnected we turn this enable on from the controller after this enable auxiliary battery comes in picture and boost IC should boost the voltage to 12 in this case.

But in this case, it boosts up to 8V, WHY???

But in other case if i connect enable and auxiliary battery at same time without supplying 12V, it boosts exact 14V which is correct.

Hi Aniket,

Thanks for your detail explanation. 

According to my understanding, when 12V battery is connected, the output of the convert also have 12V from the battery, and the bias pin is connected to the output; thus, the Bias voltage is > 2.7V and the converter boosted the voltage to 12V. 

But when the 12V battery is disconnected, the output of the converter is 3V-V_diode < 2.7V and the converter Bias have not enough voltage to boost the voltage to 12V. 

I recommend to connect the BIAS pin directly to the VCC pin and Vsupply, in this configuration the device can supports inputs from 2.97 V to 16 V.

Best Regards,

Hassan 

HASAN,

I am able to convert 3V to 12V without connecting VBias and VCC.

The issue is when initially 12V is connected, after disconnecting 12V it boosts only upto 8V. 

Is there any issues with timings or sequence of operation.

Thank you in advance.

Aniket Rajput

Hi Aniket,

I have a question regarding your device operation. 

When the 12V battery is connected, what is your converter output? 

Best Regards,

Hassan 

When 12V is connected output voltage is 14V exactly.

Hi Aniket,

Can you please explain the purpose of the marked circuit? 

And can you please attach the FB, SW. Comp, and Bias signal?

Best Regards,

Hassan 

This is a mosfet driven by controller to make one more 10 k in parallel in feedback resistor loop

Hi Aniket,

Doing this, will decrease your FB signal and result into increase in the output voltage.

Best Regards,

Hassan

that is fine that we know.

We have kept that open (Unused).

The Query is to boost the voltage upto 14 in case of Main battery failure

Hi Aniket,

Can you please attach the FB, SW. Comp, and Bias scope plot signals?

Moreover, I would recommend to check your design with the QuickStart calculator.

https://www.ti.com/tool/download/SNVC224

Best Regards,

Hassan 

1. Yellow is your 12V Vsupply.

2. Green is Enable to 3V Aux battery.

3. Pink is VBoost.

When 12V cuts down, Enable turns on boost and voltage is boosted from 3V to 10.8V DC

why its not rising to 14.5V ?

Hi Aniket, 

Did you check your design with the Quick start calculator?

If yes, kindly sent me your Quick start calculator.

Best Regards,

Hassan 

Not yet 

Let me check and share the results

Hi Aniket,

I will wait for your results.

Best Regards,

Hassan