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WEBENCH® Tools/BQ25606: does not start as it should under load

Andrey Dolgunov
Prodigy 110 points
Part Number: BQ25606


Tool/software: WEBENCH® Design Tools

Good afternoon.
I drew an scheme with bq25606.

 
Made a circuit board(4 layers). I tried to do everything according to the description.

 
In the end: I give to the input 5V (the battery did not connect), at the output I have this picture:
why is the signal waveform (saw) on the output? So it should be?

 
I connect the load 5 ohms, I give to the input 5V. The output voltage is 1.76V. I raise the voltage to 7.2V, the output voltage stabilizes (saw like without load).  Where is the mistake?
If the load is fed to the stabilizer already included, then the voltage remains normal (saw at 3.6V).


 

FB1 is NM.
 

  • 0
    TI__Guru**** 169756 points
    Andrey,

    The square-ish waveform is the charger charging the capacitor at BAT, then terminating charge, then recharging. if you pull /CE high (or use TS pin to disable charge), does the SYS output regulate to a fixed voltage?

    When loaded with 5 ohm on SYS, it appears that the input current limit is too low. Input current limit is the lower the of the ILIM resistor set value or value set by D+/D- pin. If D+/D- pins connected to SDP port (e.g. a PC USB port), the input current limit will be 500mA, which is not enough for your 5 ohm load. If you short D+/D-, does the charger work as you expect?
  • 0 in reply to Jeff F
    Prodigy 110 points

    Good afternoon. Thanks for your reply.
    1. I removed the resistor R55 - the voltage really stabilized.
    2. If the lines USB are short, the current consumption at a load of 5 ohms increases to 1A.
    3. But more often, even without load, the output voltage ceases to be set to the level of 3.6V. Also, a squeak from the chip (or inductor) clearly hear. On the output there is a voltage with a large generation. Does the operating frequency of the installed inductor matter? I installed a inductor with a test frequency of about 8 MHz.

    A month ago I collected a device using the same chip and the trace was almost the same and everything worked perfectly.

  • 0 in reply to Andrey Dolgunov
    TI__Expert 5590 points

    Hi, the switching frequency should not be 8MHz, the switching frequency is 1.5MHz. Do you have battery pack's thermistor connected to TS? The resistors on TS pin should be: 

    • RT1 = 5.23 KΩ
    • RT2 = 30.9 KΩ

    If battery pack thermistor is not used, need to have 10k resistor connected in parallel with RT2. 

  • 0 in reply to Hong Mao
    Prodigy 110 points

    WEBENCH offers a substitute for the SRR4028-1R2Y (and it's at 8MHz).
    I expect to use a battery without a temperature sensor, so I combined two 30.9k and 10k resistors.
    What else can lead to incorrect work of my scheme?

  • 0 in reply to Andrey Dolgunov
    TI__Expert 5590 points

    Hi Andrey:

    This is correct then. Can you elaborate your current issue? I need a little more explanation. 

  • 0 in reply to Hong Mao
    Prodigy 110 points
    Good afternoon.
    I installed resistors:
    • RT1 (R34) = 5.23 KΩ
    • RT2 (R55) = 30.9 KΩ
    I shorted USB D + / D-, and set R26 = 158 Ohm.
    The output voltage is 3.6V without load.
    When the input voltage is applied with the load already switched on (5 Ohm), the output is set at 1.96V 0.2A. If the load is disconnected, the voltage is set to 3.6V. then connected load, the current is set to 0.55A and the voltage is 3.6V.
  • 0 in reply to Andrey Dolgunov
    TI__Expert 5590 points
    Andrey:

    One more question, where do you connect 5 ohm load to? VSYS or BAT pin? Your input current limit and ICHG setting are correct. Do you have a battery connected at BAT pin? Looks like your input power supply has limited current capability and you do not have solid battery at BAT pin. Can you double check your power supply and your battery?
  • 0 in reply to Hong Mao
    Prodigy 110 points
    I connect 5 ohms to VSYS.
    I do not connect the battery. For correct operation, is it necessary to connect the battery?
    I use the source QJ5003C (0-50V, 0-3A).
  • 0 in reply to Andrey Dolgunov
    TI__Expert 5590 points
    Can you double check the power supply's current limit? The current limit is usually programmable.
    I suggest you hook up with a battery or tie BAT pin to ground.
  • 0 in reply to Hong Mao
    TI__Expert 5590 points
    Hi, any update?
  • 0 in reply to Hong Mao
    Prodigy 110 points

    I checked the power supply limit: 3A.
    When connecting the battery, there is no load problem.
    Installation of BAT on the ground does not change the picture.

  • 0 in reply to Andrey Dolgunov
    TI__Expert 5590 points
    Double check D+/D- is short and ICHG resistor value is correct and connect a real battery at BAT pin. You are supposed to see VSYS.