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TLV757P: Why the output of TLV75712P is 1.45V

Shinichi Inoue
Guru 21046 points
Part Number: TLV757P

Dear Specialists,

My customer is evaluating TLV75712PDBVR and has a question.

I would be grateful if you could advise.

---

TLV75712PDBVR was tested as a replacement for TLV117112DCYT.

The output voltage of the TLV75712PDBVR is approximately 1.45V, which is quite high.

Could you please tell me the possible cause?

Input Voltage：3.3V

Output Voltage:1.2V

Output Current：300~500mA

I modified the board that originally mounted TLV117112DCYT and placed TLV75712DBVR.

(1) About the terminals of TLV75712DBVR

The parts that can reach the pattern (pins 2 and 4) are peeled off from the pattern resist and soldered to copper foil.

And 5 pin (output), 1 pin(input) and 3pin(EN) are connected jumper wires.

(2) The 1.2V output is connected to the microcontroller, the current is assumed that the output current is around 300mA to 500mA.

When no load, TLV75712 output 1.2V.

(3)　Power Consumption and Junction Temperature

In this condition.

The power consumption is (3.3-1.2)V x 0.5A =1.05W maximum

On the other hand theta(j-a)=231.1deg/W

Therefoer Junction Temperature =1.05x231.1=115.55deg+25deg =130.55deg > 125deg(Tjmax)

Is there a possibility that the junction temperature exceed Tjmax and is affecting the output voltage?

---

I appreciate your great help and cooperation.

Best regards,

Shinichi

  • 0
    TI__Mastermind 18466 points

    Hey Shinichi, 

    Can I see an image of your test set-up? I don't think I understand:

    Shinichi Inoue said:

    The parts that can reach the pattern (pins 2 and 4) are peeled off from the pattern resist and soldered to copper foil.

    And 5 pin (output), 1 pin(input) and 3pin(EN) are connected jumper wires.

    It is possible that the part is entering thermal shutdown, do you have a scope shot including VIN, VOUT, and IOUT when the LDO is and isn't regulating?

    Shinichi Inoue said:
    Is there a possibility that the junction temperature exceed Tjmax and is affecting the output voltage?

    Best,

    Juliette

  • 0 in reply to Juliette
    Guru 21046 points

    Hi Juliette,

    I could obtain input and output waveform from the customer.

    The customer could not measure Iout. (it is assured 300mA ~500mA)

    As far as we can see from the waveforms, the input voltage and output voltage are almost constant with no large fluctuations.

    It seems to be regulated.

    What could be the reason why the output voltage becomes higher than the original voltage (1.2V)?

    ---

    I appreciate your great help and cooperation.

    Best regards,

    Shinichi

  • 0 in reply to Shinichi Inoue
    TI__Mastermind 18466 points

    Is the load simulated by an electronic load or a resistive load?

  • 0 in reply to Juliette
    Guru 21046 points

    Hi Juliette,

    Thank you for your reply.

    The load is connected actual 1.2V device such as MCU.

    The board is hard to change, the current could not be measured.

    I think Tj is at a fairly high temperature.

    Is there a possibility that the output voltage becomes high(1.45V) when the condition is above Tjmax(125deg) and below Tsd(165deg)?

    I appreciate your great help and cooperation.

    Best regards,

    Shinichi 

  • 0 in reply to Shinichi Inoue
    TI__Mastermind 18466 points

    Hey Shinichi, 

    It is very possible that the device is attempting to protect itself by reducing the power dissipation across the die. The best way to verify this is by taking a thermal image of your application. 

    Our parts typically go into thermal shutdown around 165C, but they can enter thermal shutdown at any temperature above TJMax due to process variation.

    Best,

    Juliette

  • 0 in reply to Juliette
    Guru 21046 points

    Hi Juliette,

    Thank you for your reply.

    I understand that it is possible for temperatures to rise outside the operating temperature range and below the thermal shutdown threshold.

    I’ll ask the customer to measure the device with a thermal imager or infrared thermometer.

    I appreciate your great help and cooperation.

    Best regards,

    Shinichi