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TPS7A88: Question to TPS7A88

Part Number: TPS7A88

Hello, good morning,
I would like to ask you for technical help, it concerns a dual linear voltage regulator "TPS7A88".
In our production department, I create the test programs on our "flying probe" tester.
The component is in the following circuit (see appendix). There are 3.3V at both inputs.
IN1 is connected to EN1. I can measure 1.0V stably at OUT1. I don't measure 1.8V at OUT2. PG1 (voltage monitoring?)
Is connected to EN2. If I understand the circuit correctly, I should also measure 1.0V at PG1. That's not the case.
Is that why regulator2 is not working at the moment? What is the reason for the connection between PG1 and EN2?
I didn't find an example of this in your data sheet. How can I measure the 1.8V at OUT2 in this circuit?
Do I also need 3.3V on R953 and R956? That doesn't seem logical to me, why should voltage be applied externally to a monitor output?

Then also activate IC909 (EN). Many thanks for the help. Best regards Jens Gmeinhart.

  • Hi Jens,

    It looks like this device was connected to have power sequencing during startup in the following order: OUT1 -> OUT2 -> IC909. PG1 is connected to EN2 because once VOUT1 gets up to 93% (max) of VOUT1 (nom), PG1 is pulled to 3.3V through R953, which should assert EN2, thereby turning channel 2 (OUT2) on. What is the voltage you measure on PG1 when OUT1 = 1V? It should ideally be 3.3V (or close to it) if PG1 is working correctly. 

    Just to clarify, PG is an open-drain output, which means that when the condition VOUTx > 93% VOUTx (nom) is not met, the PG pin is low-impedance and is pulled low to near 0V, and when this condition is met, the PG pin is high-impedance and is pulled high (to 3.3V in this case) by the pull-up resistor (R953 and R956 in this case). So, PG is a sort of voltage monitoring pin, but is only represented as a binary value.



  •  Hello Nick,
     thanks for the information. The circuit now works. I measure 1.0V and 1.8V.
    It was the case before that I hadn't measured anything on PG1. I have now activated the whole circuit in front of it.
    Two external voltages are fed in. 12V and 5V. From this, 3.3V and 3.3V_1 are generated with additional voltage regulators.
    If these two voltages are present, the IC908 will also work. IC909 also works. At its output I measure 3.3V_FPGA.
    I therefore assume that the 3.3V must be present so that OUT2 is also active on IC908.
    When supplying, I started with a low current and increased it in small increments. Then the switch-on point was reached.
    The voltages can be measured.
    Many Greetings Jens.
  • Hi Jens,

    That's good to hear. I agree that the 3.3V supplies will need to be active for this power sequencing to work because if they are not, the PG pins will not have a good voltage to pull up to and continue the power up sequence.