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TPS61220: Standby current is too high when enable pin is LOW (Vin=3V, EN=0, No load at Vout)

Yilmaz Kalafat
Prodigy 20 points
Part Number: TPS61220

Dear TI team,

I use the TPS61220 to boost a 3V battery to 5V, which works fine. In my application the TPS61220 is always in standby (enable pin 'low') and there is no load connected at Vout. I use a FET switch to isolate the load.  TPS61220 is only activate when the auxiliary  power (24VDC) is off, which will happen once a year maybe.  When i measure the TPS61220 standby current (EN=0, Vin=3V, no load) i get values between 2,5uA and 3uA, which I am very happy with. Now i have a batch which draws 10uA to 12uA, roughly 15% of my ciruict boards failed during final test due to this high current. I double checked the design, but couldn't find anything. Circuit is an exact copy of the reference design. We also checked our production process for ESD or other type disturbance, nothing. 

When i measure the standby current, I see that most of the current (6 to 9uA) is drawn by pin 5. Only a little goes to Vin. The 'good' TPS61220 doesnt show this behaviour. 

My questions are:

1 - What is the normal standby current when EN=0, Vin=3V and no load connected. 

2 - Is it normal to have spread for standby current? normal values are 2,5uA, 15% (of 300 boards) are above 10uA

3 - We bought these booster IC from a distributor. Is it possible that we have parts which didn't go through quality checkor could be a copy?

4 - Any other suggestions?

Thanks in advance,

Yilmaz 

  • 0
    TI__Genius 9046 points

    Hi Yilmaz,

    Could you please kindly see my comments to below questions? Thank you.

    1 - What is the normal standby current when EN=0, Vin=3V and no load connected. 

    [WW]The normal current into the circuitry should be below 0.5A+0.2uA=0.7uA. It is also called shutdown current because your EN=0. However, because HSFET is a N-FET, so its body diode produces a way for VIN to VOUT. So FB resistor can influence this current measurement. If you want to measure this current accurately, not only down-streaming load should be disconnected, but also FB resistors need to be unpopulated.

    2 - Is it normal to have spread for standby current? normal values are 2,5uA, 15% (of 300 boards) are above 10uA

    [WW]No. Shutdown current is influenced more by temperature. Input voltage does not effect it too much.

    3 - We bought these booster IC from a distributor. Is it possible that we have parts which didn't go through quality checkor could be a copy?

    [WW]You can check through CSC below.

    ticsc.service-now.com/csm

    4 - Any other suggestions?

    [WW]Would you please help share your schematic and layout to me for review? Also if you have disconnected the load, do you have value of FB resistors?

    -Wenhao

  • 0 in reply to Wenhao Wu
    Prodigy 20 points

    Hello Wenhao,

    Thank you for your quick reply. Below you can find the circuit diagram.  

    Normally our device is powered by an auxiliary supply (24VDC). In case the supply is cut off, the supply monitoring circuit will trigger the uC and BATT_EN will be set 'high'. TPS61220 is turned ON and at the same FET switch T202/T201 also. FET switch is there to isolate C262 (2200uF) from the TPS output.

    As long as the Aux power is good, the TPS61220 stays in power off mode. Current through the FB resistors is roughly 2,13uA, which gives a total of  2,83uA (2,13uA + 0,7uA). This is also what i measure, but i can't explain the currents ≥ 10uA. Another strange thing I observed is that this current fluctuates a lot and has some ripple. Almost like the internal FET wants to switch. 

    Ps: There is a ground plane directly under the TPS.

    Best regards,

    Yilmaz

  • 0 in reply to Yilmaz Kalafat
    TI__Genius 9046 points

    Hi Yilmaz,

    You could measure the SW-GND waveform. If the SW is not always high. Then it indicates LSFET is trying to turn on;

    Another thing you need to note is your layout looks not good. The VOUT capacitor's connecting to GND pin should use polygon and solid connections. See below layout example for your reference. Thank you.

    -Wenhao

  • 0 in reply to Wenhao Wu
    TI__Genius 9046 points

    Hi Sir,

    Any updates?

    -Wenhao