LM5148: as a Battery Charger

Keith Keller

Part Number: LM5148
Other Parts Discussed in Thread: LM25145, LM5143, LM25148

Hello,
We are designing a multibay charger and would like to use the LM5148 due to the CC control mode for charging batteries.
We need applications help to understand how to configure the circuit.

Design specifications:

Vin 36Vin nominal
Vout 3 - 26V
Iout 0 - 18A
Switching Freq 250kHz
Planning to use a current sense resistor in the 1.5 – 1.8 mOhm range.
Need to support pre-bias start up.
2 DC/DC could be operated in parallel to double the output current

Questions:

How would be interface external op amp to control both voltage and current similar to LM25145 design (attached)?
Should the FB pin be grounded and use the COMP pin?
During standby mode, we would like to disable the Buck converter and hence would use EN pin to enable/disable the converter from external MCU. When we pull the EN pin low to disable the converter, do we lost the VCC 5V internal regulated supply as well or its independent ? We would like to use this 5V supply to power our CC/CV opamps.
Any concerns with pre-bias start up turning converter on/off repetitively with battery attached.
Since we may or may not be using FB pin for external CC/CV control, can we still use PG/SYNCOUT pin to implement 180 phase shift between the 2 buck converters ?
Does PG has to be high (FB pin volage within specified range) to able to enable SYNCOUT clock pulse?

LM25145.pdf
Thank you, Keith

over 1 year ago

0 David Baba over 1 year ago

TI__Mastermind 40040 points

Hello Keith,

I don't recommend a single phase for this much output power. Suggest perhaps the LM5143 which can be configured as a multiphase. please see link to a helpful paper for peak current mode control and CCCV implementation.

https://www.ti.com/lit/an/snvaa85/snvaa85.pdf?ts=1709757230951&ref_url=https%253A%252F%252Fwww.google.com%252F

Hope this helps.

David.

0 Keith Keller over 1 year ago in reply to David Baba

TI__Expert 7230 points

Hi David,

I'm using Webench designer with LM25148 device and entering these parameters: [35 - 37 Vin, 21Vout, 18A, 65oC]

And getting a valid design and design report (attached).

Generally Webench is conservative on its calculations, so I'm wondering the concern at this power level?

Thank you, Keith

LM25148-WBDesign152.pdf

0 David Baba over 1 year ago in reply to Keith Keller

TI__Mastermind 40040 points

Hello Keith,

Its reporting almost 99% efficiency, so I would take that as less conservative. Its doable but will need to manage thermals more aggressively than in a 2-phase single output design.

Hope this helps,

David.

0 Keith Keller over 1 year ago in reply to David Baba

TI__Expert 7230 points

Hi David,

The paper you provided is very helpful. However we need to be able to control current and voltage with 2 MCU PWMs from 0 - 99% Duty Cycle.

Ideally 0% PWM Duty cycle ~ 1V and 99% Duty cycle 27Vout

Could you please help us create an opamp circuit which could do this? (similar to the LM25145 schematic I provided previously & copied below)

0 David Baba over 1 year ago in reply to Keith Keller

TI__Mastermind 40040 points

Hello Keith,

See below concept. RC creates a DC level; the DC level is your Vcontrol voltage. The Vcontrol will adjust VOUT accordingly. if you set feedback resistors to VOUT max and adjust VOUT from there.

Voutadjusted amount = Vcontrol-Vfb/Rinj*RFB top. will cause Vout to reduce.

Hope this helps.

David.

0 Keith Keller over 1 year ago in reply to David Baba

TI__Expert 7230 points

Hello,

Can the FB be grounded on LM5148 and then have the COMP pin driven to control the duty cycle?

Thank you, Keith

0 David Baba over 1 year ago in reply to Keith Keller

TI__Mastermind 40040 points

Hello Keith,

I suggest doing the way I have indicated above.

Thanks,

David.

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LM5148: as a Battery Charger