MP2797 Design Queries

Battery Management
1

I am in the early design stages of a Battery Management System and we are considering MP2797 as our AFE chip. However, there is some information in the datasheet that is not clear to me:

  1. “Drives up to 100A DC with Parallel N-Channel MOSFETs”. Is this not a limitation of external FETs rather than AFE?
  2. DSG gate drive is given with a Typical value of 10V, yet Charge Pump Output Voltage as 14.7V. Does the charge pump not generated the DSG gate voltage? If so, where does the voltage difference come from?
  3. How many FETs can be driven by DSH and CHG pins? How does the VCP capacitor increase relate to this number?
  4. What is the power consumption in Active mode? Only Shutdown and Safe State supply current values are given.
  5. Can this chip support high-side (positive) current sensor measurements?
  6. How are external FETs driven for balancing? Does cell voltage drive FET gate?
2

Hi, our team is working to help answer your questions. Thank you for your patience!

3

  1. This is a limitation of the hardware that carries over to the driving capacity.

  2. The charge pump and DSG are biased by separate sources. This causes a difference in output voltages.

  3. The number of MOSFETs that can be used in parallel on the DSH/CHG pins depends on your particular MOSFET. The DSG/CHG gate drive voltages and gate drive turn-on/off resistances are provided. Additionally, the VCP capacitor is directly correlated with the Cvcp in a 1:1 ratio. If you share your desired configuration and part specs, we may be able to assist you further with this problem.

  4. The active mode current is ~380uA. The 380uA does not include any current drawn by an external device from the integrated LDO. NTCB_ DYNAMIC_ON is a configuration that keeps the bias voltage on the NTCs during ADC conversion and can increase AM current. CC_PWR_SAVE is a configuration that can reduce AM current by taking fewer current measurements (so this is a tradeoff against current measurement accuracy).

  5. Whether the part takes high-side current sensor measurements depends on the output mode of your high-side current measurement device. The component has several GPIO pins, as well as one GPIOHV pin that can measure up to 86V. The normal GPIO pins can be assigned special functions, which may include reading your current sensor’s output. The high-voltage GPIO pin Is normally used by safe mode to provide a P-channel MOSFET bypass function. Additionally, an I2C interface is available on the component. If any of the GPIO are set as digital inputs, they should not be floating otherwise this can increase power consumption.

  6. Internal FETs are driven at up to 58mA with a 4V cell voltage. This is based on the internal balancing MOSFETs’ Rdson. External MOSFETs are driven using a minimum gate threshold voltage of 1.8V, assuming a 4.2V lithium cell.