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Battery Charger Issue

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Full Member level 6
May 10, 2020
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We have used MCP73871-2CCI IC in our design. We have received the hardware. IC is not behaving as per the datasheet.
I connected Only the USB Cable (Battery is not connected) and Measured voltage at input. The voltage measured is 5V. However, The Vbat voltage measures 3.9V instead of 4.2V. Why is there a drop
Observation related to Charge Enable Pin:
  1. I have connected Charge enable to 5V through a Pull up and same pin is also connected to MCU through a series resistor. so that, I can control the IC using MCU. In this configuration, The voltage observed at CE Pin is 1.2V AND VBAT Measures 0.15V.
When I remove the series resistor at MCU End, I am able to obtain Vbat. But Vbat measures 3.9V instead of 4.2V.
Observation related to STAT1, STAT2: With Vbat measuring 3.9V, When we check the STAT1, and STAT2 Pin voltages, We are observing the following.
As per Table 5-1, When No battery is present, The STAT1 and STAT2 should be High-Z, However, When I measure at these pins. I am getting 0.1V. Please clarify why this is happening.
I have attached schematics for your reference.
BATT_CHRG_EN_MCU is the signal that is connected to ATSAMD51N20A MCU Pin PA03 through series resistor. BATT_CHARG_PG# is the power good signal connected to MCU BATT_CHARG_STAT2_MCU is the STAT2 signal connected to MCU. BATT_CHARG_STAT2 is the STAT2 signal connected to LED.
BATT_CHARG_STAT1_MCU is the STAT1 signal connected to MCU. BATT_CHARG_STAT1 is the STAT1 signal connected to LED.
Can you review and let me know if there are issues in the schematics that needs to be corrected.enter image description here

What voltage reading are you expecting when measuring high-Z?

high-Z means you can drive it to any voltage (within a range) with little current. One cannot obtain a reading for impedance just by measuring the voltage on one terminal.

Your Vce pull up resistor is probably too small if you ever intend to disable Vce. The logical inputs to the device should be well below 0.8V for low and 1.8V for high as listed under DC characteristics.

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