BQ24600: Will not enter charge sequence

Hi Grant,

When you mentioned Iset = 1.4V, do you mean the voltage measured at pin 7 (ISET) is 1.4V? Based on the schematic the voltage at pin 7 (ISET) should be 3.3*(22.1k/(100k+22.1k))~=0.6V.

Can you provide a scope capture of PH pin to see if the converter is working?

Another thing I see in the schematic is that you are using the same GND for both power ground and analog ground which we recommend to be separated. Please refer to datasheet pg. 21 for the schematic and pg. 27 for the layout guideline.

Regards.

Hi Tommy,

Thanks for offering help, I would like to apologize for taking so long to reply, this was another engineer's project before mine so there was a bit of confusion. For the information I gave at first, most of it is right but I double checked values and have a couple updates:

ISET = 0.25V (R25 is actually a 270k resistor to lower charge current)

VFB = 1.9V

TS = 2.2v

Vref = 3.3V

I will attach a scope capture of PH soon, but it appears to be in charge disable mode even though both STAT and PG LEDs are activated.

Above is a scope capture of PH pin it appears to match Figure 3: Charge Disable in datasheet

Hi Grant,

Thank you for providing the capture.

From the capture it looks like the chip might be damaged because the absolute maximum rating (voltage range) for PH is -2 to 36 V according to datasheet.

Can you replace the chip and try it again?

Regards.

Hi Tommy,

I checked again and realized my offset was not good, I took the scope capture again and came up with this, which does look close to the Charge Disable output

Thanks again,

Grant Bracht

Hi Grant,

Can you get a capture with PH, LODRV, CE and the charging current? I want to double check if the device is put into a charge disable state because if the device is charge disabled, the PH output should reduce to a certain voltage (in this case it should go to around 11V) instead of shooting up every 2us.

Regards.

Hi Tommy, 

Without the battery connected these are my readings (All with VoutBoost at 14.7V):

CE 3.3V

LODRV: 0V

PH: 0.8V

With the battery connected:

CE: 3.3V (stays constant so I didn't send the scope capture)

Battery Current: -0.05A (going through VSYS to power MCU and a couple LEDs)

First Capture: PH at 1us

Second Capture PH at 200ms

Third Capture LODRV at 1us

Fourth Capture LODRV at 200ms

Thanks! Hope this helps!

I also took off the previous chip and put on a new one, I got the same results

Hi Grant,

With CE being high and LODRV working, I don't think the charger is in a charge disabled state. However, the waveform from PH does look off to me.

Can you provide the layout file of the board? and I will check on the layout/schematic again to see what may cause this.

I will be out of office tomorrow so please expect delay in responses.

Regards

Hi Tommy,

Thanks so much for the help, I have attached screenshots of the parts related to the charger below.

1. everything around related to the charger (Top)

2. bottom layout

3. Zoomed in on the chip (Top)

Hi Grant,

Thanks for providing the layout.

I will take a look at it when I get back.

Regards.

Hi Grant,

Sorry for the late response.

Can you try to replace R22 with a 2 ohm resistor? R22 and C23 is the snubber circuit but the schematic in the datasheet has an error in it.

Is VSYS connected to any load?

Can you collect the voltage measurement at SRP and SRN?

At the REGN pin (in the layout), since C28 is a decoupling cap, current should not be pulled before C28.

For the polygon connect style, we recommend using direct connect instead of relief connect as relief connect may create current bottleneck in the current path.

Can you send the files of the layout? It is hard to locate the components with only screenshots.

Regards.

Hi Tommy,

Thanks for feedback, I replaced R22 with a 2 ohm resistor and the outcome did not change. VSYS is connected to a 5V and 3.3V switching regulator and a 3-phase motor driver. There is not motor connected right now but the regulator is powering an MCU and a few sensors.

With the battery unplugged, both SRP and SRN are at 0.821V

With the battery in, they are both at 10.76V (battery is at 10.8)

Sorry for the inconvenience, but I cannot put the layout file on the forum, I could give it to you privately though.

Best,

Grant

I have switched to BQ24610 per your recommendations, thank you for all of the help