MP2639A problems led's

Battery Management
1

Hi everyone and thanks in advance.

I am designing a two cell charger with the MP2639A. The operation is quite acceptable since the battery manages to charge but I do not get a good response from the LEDs (LED1, LED2, LED3 and LED4).

The MP2639A is in charging mode and I observe that / CHG_OK = 0 while charging and 3.3 when is charged . The current that exists when the led blinks is 640uA and in the datasheet it gives as an example connecting the leds to VNTC. On the other hand, I observe in the datasheet that when it is in charging mode, there is a MOSFET that connects VCC (4.5V) to VNTC but when i measure the voltage in VNTC is 1.9V so I do not understand where the 2.6V is lost .
If I fix on the bidirectional evaluation board, I observe that the LEDs are connected to VCC.
Could it be that there is an error and instead of connecting the LEDs to VNTC as shown in the datasheet, you have to connect them to VCC? I send you the schematic. (R14 and R15 are not soldered on the PCB).

I attached an image of my schematic and picture of the obsiloscope where show the voltage in the blincking led.

Thanks again

Schematic
Schematic1449×571 132 KB

2

IMAGE
IMAGE4000×3000 1.63 MB

3

Hi gguitierrez,

Thank you for contacting the MPS Forum. The VNTC and VCC are actually internally connected but the switch that connects them is only on during Charge mode:

image
image1144×83 11.6 KB

I do believe the better approach would be to connect the LEDs directly to VCC instead just like the evaluation board. Thank you for noting this for us, we will evaluate this to see if the datasheet needs to be updated.

Thanks,
Brendan Schoemehl
Field Applications Engineer
Monolithic Power Systems | MPS Now