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ADP2503 - Startup problem where VOUT stays at 0V

Category: Software
Product Number: ADP2503ACPZ-R7

Hi!

I designed a circuit utilizing the ADJ version of the AD2503 buck-boost converter using the Buck-Boost Designer Tool. The output VOUT is approx. 5.4V.

Unfortunately when powering up with no load and pulling EN to VIN the output voltage stays at 0V. At VIN = 3.7V the input current is approx. 250 mA which is not what I expected. I tried PWM and PSM mode but this had no effect. Could the output capacitance be too large? (The capacitance value was suggested by the Designer Tool.)

I measured the resistance of several nodes on the board and wondered if this could be the source of the error:

R(Vin to GND) >= 2 Meg Ohm (looks reasonably)
R(Vout to GND) >= 30 kOhm (looks reasonably because of the feedback network)

Are the switch nodes shorted to GND when the part is not powered up?
R(SW1 to GND) = 0.2 Ohms
R(SW2 to GND) = 0.2 Ohms

I don't have a eval board of this device. Thank you for pointing me into the right direction.



Comment values that looks reasonably or suspiciously.
[edited by: myorbit at 7:06 AM (GMT -4) on 22 Jul 2022]
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  • Hi myorbit,

    Hope you are doing well.

    Are the switch nodes shorted to GND when the part is not powered up?

    The switch nodes (SW1 and SW2) are not shorted to ground since the ADP2503 is a 4-switch converter and the NMOS (see block diagram below) does not conduct when the device is not powered up.

    It seems that there are shorts between the EP (GND) and other pads (mainly on the upper side pins 1 to 5) underneath the IC.

    It seems to me that this may be a layout issue as the pins are shorted to ground or to other pins when the device is soldered on the board. PVIN (pin 5) should not be shorted with VOUT (pin 1) or to GND (pin 3) even when the device is not powered up since the PMOS will not conduct.

    Please consult page 15 of the datasheet for any layout concerns and guidelines. Refer to the link below for the datasheet. Thanks

    ADP2503/ADP2504 (Rev. D) (analog.com)

    Regards,

    Sigs

  • Thanks for coming back to this issue.

    As it turned out there were several solder shorts on different locations between the "upper row of pads". I have performed a CT scan of a couple of PCBs. After fixing the IC works as intended. I tried to stick to the layout guidelines but have not found a footprint suggestion from AD. I possibly need to optimize the pad shape or the paste mask.

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  • Thanks for coming back to this issue.

    As it turned out there were several solder shorts on different locations between the "upper row of pads". I have performed a CT scan of a couple of PCBs. After fixing the IC works as intended. I tried to stick to the layout guidelines but have not found a footprint suggestion from AD. I possibly need to optimize the pad shape or the paste mask.

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