TPS7H5001EVM-CVAL: TPS7H5001EVM-CVAL

Tejesh Makanawala

First of all, please advice if we should use OUTA or SRA for input to gate driver if gate driver only needs 1 input. I suspect answer is OUTA, but please confirm.

Main question is tied to controlling duty cycle of OUTA. It is stuck at around 4.6% (note: frequency is 200kHz). How to increase duty cycle?

In discussion board, someone mentioned use COMP, but that pin is an output, so did not attempt to use to avoid damage. Tried using Vsense to control Duty Cycle, but that too does not seem to work. Appreciate your guidance.

over 1 year ago

0 Daniel Hartung over 1 year ago

TI__Mastermind 25435 points

Hey Tejesh,

If there is only one input in converter scheme it is generally OUTA.
Duty cycle is based on What happens in figure 1 of this app note:
https://www.ti.com/lit/an/snva555/snva555.pdf?ts=1689547394097

Error output of COMP in compared to RSC value + CS_ILIM

COMP can be forced as long as the voltage rating is not exceeded.

Thanks,
Daniel

0 Tejesh Makanawala over 1 year ago

Prodigy 10 points

CS_ILIM is “Current sense for PWM control and cycle-by-cycle overcurrent protection. An input voltage over 1.05 V on CS_ILIM will trigger an overcurrent in the PWM controller. The sensed waveform on CS_ILIM contains a 150- mV offset when compared to the COMP/2 voltage at the input of the PWM comparator”

Question: Does 0.0V to 1.0V correspond to 0% to 100% duty cycle? Then 0.5V would be 50% duty cycle.

0 Daniel Hartung over 1 year ago in reply to Tejesh Makanawala

TI__Mastermind 25435 points

Hey Tejesh,

https://www.ti.com/lit/an/snva555/snva555.pdf

Figure 1 of this app note shows how the duty cycle is calculated.
VRAMP is the CS_ILIM pin

COMP is the Vc voltage.

Thanks,
Daniel

0 Tejesh Makanawala over 1 year ago in reply to Daniel Hartung

Prodigy 10 points

Thank you.

Seems like 0.2V corresponds to 25%, 0.5V corresponds to 75%, and 0.8V corresponds to 75% duty cycle.

0 Daniel Hartung over 1 year ago in reply to Tejesh Makanawala

TI__Mastermind 25435 points

Hey Tejesh,

This is not correct.
The value is dependent on what voltage is on your COMP pin, CS_ILIM pin, and RSC value.

The duty cycle is created by a comparison between all three values.

Thanks,
Daniel

0 Tejesh Makanawala over 1 year ago in reply to Daniel Hartung

Prodigy 10 points

A look up table for duty cycle as output and COMP, CS_LIM and RSC value would be beneficial.

0 Daniel Hartung over 1 year ago in reply to Tejesh Makanawala

TI__Mastermind 25435 points

Hey Tejesh,

What you are describing is not how current mode control works.

At the beginning of the clock cycle the duty cycle goes high.

Current mode control is done by comparing COMP (error voltage) to CS_ILIM and terminating the output pulse when that happens.
Thus there could be any number of duty cycles created at the same voltage.
What matters is when the comparison happens in the clock cycle

RSC subtracts voltage from the error voltage in order to create a stable system in reference to this app note:
https://www.ti.com/lit/an/slua101/slua101.pdf

A "look up table" is simply impossible due to the timing aspect.

Thanks,
Daniel

Power management

Power management forum

TPS7H5001EVM-CVAL: TPS7H5001EVM-CVAL