ZHCSTD7A December 2021 – November 2023 BQ79631-Q1
PRODUCTION DATA
Pins | Components | Value | Description |
---|---|---|---|
GPIO1, GPIO2, GPIO3 | Resistor (R1) | 1.32 MΩ | Known intentional resistor used to switch in and out of the circuit in order to detemine the unknown values of insulation resistances. |
Resistor string Top (R2) | 1.32 MΩ | Resistor divider to divide down HV measurement to ADC input range. Component values are recommended ones. Other values can be chosen as long as signal is kept within ADC input range. Too large of value resistors will cause more measurement inaccuracy due to leakage at ADC pins. | |
Resistor string Bot (R3//R4) | 12.45 kΩ | ||
SW1 | TPSI2140-Q1 | HV switch used to connect and disconnect R1 in the circuit. | |
Optional MOSFET or Switch (SW2) | 1000-V standoff | Switch to block unwanted leakage current. |
Insulation detection scheme is shown in Figure 9-10
Riso_P and Riso_N are the Insulation resistances in the system that are to be determined.
Riso_P is the resistance between PACK+ and chassis gnd. Riso_N is the resistance btweeen PACK- and chassis gnd.
A low value of Riso_P or Riso_N could provide a low impedance from the HV battery to the LV chassis gnd where sensitive electronics and/or operator could be endangered. Hence it is important to detect a low insulation resistace.
Riso_P and Riso_N are two unknown variables that need to be determined. A single measurement on GPIO1 can give the relation or ratio between Riso_P and Riso_N , but will not be able to determine their absolute resistance values. For this a known reference resistor is needed. R1 in the Figure 9-10 serves that purpose. To solve for the two unknowns Riso_P and Riso_N, two equations are needed. One equation is achieved by connecting R1 in parallel to Riso_P. The other equation is achieved by disconnecting R1 from Riso_P.
The procedure to determine the insulation resistances is as follows:
Step 1: SW_GPIO3 open, measure GPIO1. Get equation1 by deriving the output voltage expression for this configuration of switch.
Step 2: SW_GPIO3 close, measure GPIO1. Get equation2 by deriving the output voltage expression for this configuration of switch.
Step 3: Combine equation1 and 2 solve Riso_P and Riso_N.