LM5170: not able to Control the converter output using ISETD. Current stays very low both with Battery and Resistive Load (50-150mA)

Aashiv Vij

Part Number: LM5170
Other Parts Discussed in Thread: LM5171

Tool/software:

Using LM5170 as a Bidirectional Converter to Charge/Discharge a Battery 12V to 24V HV port. Cannot get the Battery Charging to work which is Buck Mode for LM5170, the battery is always discharging to the Circuit.

Using ISETD as the primary control, the max current seen is 50-150mA. The Design Value is up to 2.5A per leg, and I am running Both the Channels.

For Engineering Validation I am trying to Control ISETD with a function Generator using 100KHz PWM with 20-50% Duty Cycle. But the current stays very low.

With Battery Load: 20-80mA Discharge only even in Buck Mode (Charging)

With Resistor Load 24ohms : Max current seen is 170mA (75% Duty Cycle)

Please advice what I can try. Attached is the schematic

over 1 year ago

0 Feng Ji over 1 year ago

TI__Mastermind 22790 points

Hi Aashiv,

What is the DIR voltage and ISETA voltage?

And have you shorted Q2 and Q3 as you disabled fault check mode.

Please share some waveforms like Vin, Vout, IL, DIR, ISETA.

Best Regards,

Feng

0 Aashiv Vij over 1 year ago in reply to Feng Ji

Prodigy 40 points

Hi Feng,

DIR is 3.3V, and we are not using ISETA.

Currently using ISETD, which is 3.3V 100KHz fed from Function Generator

I have not shorted Q2 & Q3, Is that required?

I will gather waveforms to share by tomorrow.

Mostly, data is seen below:

Vin is 24V from Power Supply

Vout is 12V when Battery is connected

Vout is 3.8V when 24ohm resistive load is connected.

Current testing only in Buck Mode to get the circuit running. Next phase will be boost mode from Battery to Input.

Regards,

Aashiv Vij

0 Feng Ji over 1 year ago in reply to Aashiv Vij

TI__Mastermind 22790 points

Hi Aashiv,

Q2 and Q3 need to be shorted according to the schematic.

Best Regards,

Feng

0 Aashiv Vij over 1 year ago in reply to Feng Ji

Prodigy 40 points

During the Test, when powered ON, UVLO is pulled to 3.3V and I can see the BKG at 12.8V (measured to ground, and across Vgs) active with 24ohm resistor load.

ON the other hand, when I plug in the Battery at 12V, and pull UVLO to 3.3V I see a ~24V signal on BKG (measured to ground), and 12.2V (Vgs, looks like there is a clamp inside the LM5170 to save the Gate).

Why do you say that Q2 & Q3 need to be shorted? and by shorted meaning I have to physically short Drain to Source on both?

0 Aashiv Vij over 1 year ago in reply to Aashiv Vij

Prodigy 40 points

These are the waveforms for RAMP2 & COMP2 pins

0 Aashiv Vij over 1 year ago in reply to Aashiv Vij

Prodigy 40 points

I am trying to verify the circuit with open loop control since there is no MCU software yet. Getting Voltage Control to get any output voltage control is what I need help with?

0 Feng Ji over 1 year ago in reply to Aashiv Vij

TI__Mastermind 22790 points

Hi Aashiv.

Then it is OK. You don't have to short Q2 and Q3.

Then I suppose R15 is not populated, right?

Best Regards,

Feng

0 Feng Ji over 1 year ago in reply to Aashiv Vij

TI__Mastermind 22790 points

Hi Aashiv.

Then you can operate in constant current (CC) mode with load set to CV or CR.

Best Regards,

Feng

0 Aashiv Vij over 1 year ago in reply to Feng Ji

Prodigy 40 points

R15 is populated, Is it not suppose to be?

0 Aashiv Vij over 1 year ago in reply to Feng Ji

Prodigy 40 points

I am trying to operate with a standard 12V Battery, but cannot get the right current output to the resistive load. And to the battery load, the current always flows in reverse direction, (low current 50mA). Not sure How to implement voltage control with just ISETD?

0 Feng Ji over 1 year ago in reply to Aashiv Vij

TI__Mastermind 22790 points

Hi Aashiv,

You need to short Q2 and Q3 in boost mode.
It is OK to operate in buck mode.

It is reasonable that it is not switching as COMP is less than 1V.

Best Regards,

Feng

0 Aashiv Vij over 1 year ago in reply to Feng Ji

Prodigy 40 points

Hi Feng,

As per the meeting, I made the following changes and still cannot charge the battery. Testing only BUCK MODE!

The Battery only goes to discharge (not sure why), even in Buck Mode.

L=18uH, below is the new compensation components.

Resistive Load Test: Load 5 ohms, max Duty cycle = 55%, Current output = 650mA, Vout=3.56V. Compensation=4.6V

Battery Load Test: 12V Battery Load, Duty Cycle set to 40%, Converter goes to Discharge within 560us. The Compensation Ramp is limited for some reason.