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TPS40170: Hello, I am about to use TPS40170 but would like to use external error amplifier instead of built-in error amplifier in the IC since I’d need much higher accuracy. The chip input pins, FB and COMP and TRK are presented in a block diagram. Can I

Dejan Simovic
Prodigy 40 points
Part Number: TPS40170

Hello,

I am about to use TPS40170  but would like to use external error amplifier instead of built-in error amplifier in the IC since I’d need much higher accuracy.

The chip input pins, FB and COMP and TRK are presented in  a block diagram (not a real schematic).

Can I make a unity gain for internal error amplifier and feed it with external error amplifier and if yes how?

Is there any other idea I may use to avoid internal E/A?

Many thanks,

Dejan

  • 0
    TI__Guru**** 191445 points
    Yes you should be able to configure the internal amplifier for a fixed or unity gain and control the regulation using an external error amplifier. Alternately you could use an external precision reference at the TRK pin so long as the TRK voltage is lower than the internal reference of 0.6V and still use the internal error amplifier
  • 0
    TI__Expert 4365 points

    TPS40170_Ext_Error_amp_Ref.pdf

    Here is a suggested approach:  The error amplifier internal to the TPS40170 is a conventional type of voltage output op amp.(Not a trans-conductance current output type) This type of op amp can't be over driver. As John suggests configure it for unity gain. But this is an inverting stage; so equal valued input and feedback resistors will give you a gain of roughly -1. Next you will need an additional unity gain inverting stage that is offset to nearly the same reference voltage as the 0.6 Vref internal to the device.  Next you add your own error amplifier and precision external reference. Both op amps must run directly from the 3.3V Vdd pin of the controller. Total current drawn for all this external circuitry must be less than 5mA. Op amps that have rail-to-rail output swing and that don't suffer from phase inversion are a necessity. Important that the output of the external unity gain inverter not swing higher than 3.6V and overdrive the FB input. Your choice of series or shunt type external reference driven from 3.3V VDD or 8.0V VBP source. The external feedback network will be based on the new external reference voltage chosen. Use an additional divider to derive the 0.6V offset for the external unity gain inverter.

    In theory this should work. In practice there may be issues having three amplifier stages in the path. Selection of the compensation parts should be confirmed using a frequency response analyzer. Be sure to confirm proper operation during start-up. The external error amp may hit the rail during startup and cause output overshoot at the end of the start-up interval.

  • 0 in reply to Alan Martin
    Prodigy 40 points

    Since I am not tied-up for this particular chip let me rephrase my question, can you suggest synchronous buck driver that could work as a current source on the fixed load, controlled with an external error amplifier (in order to achieve extra precision/ accuracy/temp stability and low noise)

    Sync option is a plus but not necessary.

    any demo board available?

    Application is DC/DC Vin range 7-18Vdc, output programmable 0-6A, 0-6V many thanks.