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ISOTMP35-Q1: Supplying ISOTMP35 from AMC3336

Kosta Kotsis
Prodigy 100 points
Part Number: ISOTMP35-Q1
Other Parts Discussed in Thread: AMC3336, ISOTMP35

Tool/software:

Hello all,

I am on the process of designing the evaluation board for a full bridge DC-DC converter.
On this converter, and related to my question posted here, I am interested in measuring the DC-Link voltage, Load voltage, and temperature of the transistors I am using.

For the temperature measurement, I am considering the ISO_TMP35.
For the DC-Link, and Load voltage measurement, I am considering the AMC3336.

One of my objectives is to use as few components as I can. This is why I considered supplying the two ISOTMP35s from the output of one of the AMC3336s (the one that i will use for DC-Link voltage measurement).
I am considering to place these temperature sensors on the HVDC- side of the transistors.
I am doing this because, if I am correct, this should allow me to use one isolated power supply for both of these sensors. The isolated power output of the AMC3336 is referred to HGND, which at the same time is on the same node as the HVDC-. These implications make me consider using one of the AMC3336 as an isolated power supply for the temperature sensors.

Moreover, the MCU that will be reading this data output from the temperature sensors, is not referred to the same ground as the high side (HGND).

My questions are the following:
1. Is it recommended to use the DCDC_OUT and HGND of the AMC3336 to supply these temperature sesnsors? (Their consumption is around 1uA for each one of them)
2. If I try to implement this schematic, are there any other implications that I might not be aware of?

Looking forward to any feedback and input.

Thank you in advance.

Best regards,
Kosta Kotsis High_Level_Schematic_Overview.pdf

  • 0
    TI__Expert 7845 points

    Kosta,

    The ISOTMP35 can draw up to 17uA of IQ across temperature, can the DCDC_OUT pin of the AMC3336 support at least 35uA of current draw? And what voltage would the ISOTMPs be supplied at then?

    -Alex

  • 0 in reply to Alex Thompson
    Prodigy 100 points

    Hello Alex,

    the DCDC_OUT of the AMC3336 has a typical value of 3.5V (min=3.1V & max=4.65V). So the ISOTMP will be supplied with a voltage of around 3.5V. The allowed voltage supply range for the TMPs is between (-0.3V to 6V). SO I am assuming that this should be acceptable. Unless you would recommend putting an LDO between the AMC ant TMP?

    The DCDC_OUT pin of the AMC3336 can supply up to 1mA of DC current to an optional auxiliary circuit. So considering the IQ of the TMPs, it seems that the AMC will be able to handle it. 


  • 0 in reply to Kosta Kotsis
    TI__Expert 7845 points

    Kosta,

    This should work fine then, I don't see a need for an LDO. The ISOTMP35 has a flat PSRR across VDD, so even if there are ripples and noise on VDD, the ISOTMP35 analog output should not be affected.

    Thanks

    -Alex Thompson