LM43601-Q1: OUTPUT IS NOT GENERATED AUTOMATICALLY

Hello Ravi,

My knee jerk reaction is it is not a phenomena you are seeing, it is instability in the design.

With the device regulating, can you preform a couple no load to full load transients, at the fastest possible slew? Ensure that you don't hit the current limit of the device.

Looking at your feedforward network, the zero and pole combo it establishes are pretty much right on top of one another.

With a lower Z feedback divider, I can provide further separation between the two, and allow hopefully for some phase boost prior to the crossover frequency which I anticipate to be sub 20kHz.

If you find the regulator to be unstable per the suggested load transient, then I recommend

RFBT = 100k

RFBB = 9.2K

CFF = 470p

This puts the zero at 3k, pole at 40k

Hello Marshall,

Thanks for your quick reply.As per your suggestion I made the suggested changes in the our board and tested it but still the same instability issue is been observed.

Pls. suggest how to resolve the instability issue.

Pls. note that I am not a Power Electronics Expert, so as per my requirement I had designed the power supply using TI Workbench Tool.

The generated -12V is given to TLV4197QPWRQ1 OPAMP VEE to generate PWM of +12V and -12V Voltage levels.

So the load current will be around 10mA max since we need 2 channels of pwm.So we won't be able to ON and OFF the load on the fly.

Thanks and Regards

Ravi Chawda

Will we need some additional circuit to enable the output of the Regulator

Hello Ravi,

I need to see waveforms to confirm the problem you are seeing. Please share a report if you can.

I would like to see Vin voltage, En voltage, SW voltage, and Vout voltage.

The claim is that device UVLO is exceeded and the device is not regulating. With the  plots above, I should be able to confirm that.

Hello Marshall,

At power On following are the voltages observed on the Multimeter, since I do not have a DSO to capture the required waveforms.

VIN => 12.19V

EN PIN => 12.19V

SW VOLTAGE => 0.020V

VOUT (i.e negative terminal of cout C40) => 0.610v

After Reinserting the input Jumper JP5 we get the following voltage levels

VIN => 12.15V

EN PIN => 12.15V

SW VOLTAGE => 0.101V

VOUT (i.e negative terminal of cout C40) => "-12.10V"

Thanks and Regards

Ravi Chawda

Hello Ravi,

This would be nearly impossible to debug without an oscilloscope to see IC behavior, respectfully.

To me, it seems odd that a power cycle resolves the issue. I believe something is being overlooked.

These are the VIN and EN Pin Power On Waveforms. There is no output during these waveforms

SW pin waveforms at power ON, NO OUTPUT during these waveforms

VOUT pin waveform an POWER ON,NO OUTPUT During this waveform

VIN AND EN PIN WAVEFORMS WHEN JP5 IS REINSERTED AND WE START GETTING THE OUTPUT

SW PIN WAVEFORMS when JP5 is reinserted and we start getting the output

VOUT PIN WAVEFORMS when JP5 is reinserted and we start getting the output

Hello Marshall

I hope the waveforms captured are sufficient for your analysis and to get your valuable feedback to resolve our problem.

Pls. let me now if you need any further Information/Waveforms.

Thanks and Regards

Ravi Chawda

Hello Ravi, is this waveform correspond to the output regulating waveform? It does not appear to be -12V?

Hello Ravi,

This waveform appears to be regulating to -12V.

Hello Ravi,

I tried to replying to your individual posts, but it wont allow me to. It seems you may have mixed up the captions for some of your captures, so I was just confirming. Thanks for sharing them.

It seems to me that your input supply might be current limiting?

Have you ever tried the same experiment with lab power supply?

It is odd to me that power cycle the device would solve the issue...Startup issues usually arise from device hitting current limit. 

Hello Marshall,

At present we are using Lab Power supply only and have kept the max current delivery settings in the power Supply which is around 2A(POWER SUPPLY 1) and 5A(POWER SUPPLY2),

We have tested using 2 different Power Supplies and in both the cases we are observing the same behavior.

I am also not able to understand how come the output is getting enabled by reinserting the Jumper VIN Jumper.

My Email ID is : ravi.chawda@threemediatech.com

and: ravi.m.chawda@gmail.com

Can you pls. share me your email Id so that we can communicate much more faster.

Thanks and Regards

Ravi Chawda