ZHCSTD7A December 2021 – November 2023 BQ79631-Q1
PRODUCTION DATA
Pins | Components | Value | Description |
---|---|---|---|
VS1, TSREF, SRP, SRN | R1, R2, R4, R5 | 10 kΩ | Resistors to provide a gain of 10x as well as set the output common mode voltage of V_Tsref/2 on the ADC input pin. |
R3, R6 | 100 kΩ | ||
Amplifier | LM2904QDRQ1 | General purpose op-amplifier. |
A scheme for overcurrent measurement is shown in Figure 9-6.
Often overcurrent detects have large ranges that exceed the dynamic range of the main CSADC.
There are two options for overcurrent detect in the BQ79631-Q1. One option is to use the internal CSAUX ADC that has a wider dynamic range. The MCU then processes the data and compares against an OC threshold.
The other option is to use the OVUV comparator of the VS input. An external amplifier can be used to gain up the voltage across the RShunt and feed this to the OVUV comparator input. The comparator thresholds can be preset. A positive overcurrent event will trip the OV comparator and a negative overcurrent will trip the UV comparator. When either of the comparators trip, a fault is flagged on the nFault pin and in the communication to MCU. These hardware comparators are actively monitoring even when the device is in sleep mode.
As an example of the above scheme, the amplifier gain is set to 10V/V. In order to set an overcurrent fault when the Rsense voltage reaches 50 mV in either the positive or negative direction, an OV threshold of 3000 mV and UV threshold of 2000 mV is programmed. The amplifier gains the 50-mV overcurrent signal to 500 mV at the VS1 input. This signal at VS1 is on either side of the common mode of 2500 mV, which is set by the resistor divider from TSREF. Different values of the OV and UV thresholds can be programmed along with various amplifier gain and common-mode settings in order to achieve the desired overcurrent thresholds.