ZHCSF60K June 2016 – July 2020 BQ77904 , BQ77905
PRODUCTION DATA
The device detects temperature by checking the voltage divided by RTS_PU and RTS, with the assumption of using 10-KΩ RTS_PU and 103AT NTC for RTS. System designers should always check the thermistor resistance characteristics and refer to the temperature protection threshold specifications in the Electrical Characteristics table to determine if a different pullup resistor should be used. If a different temperature trip point is required, it is possible to scale the threshold using this equation: Temperature Protection Threshold = RTS / (RTS + RTS_PU).
Example: Scale OTC trip points from 50°C to 55°C
The OTC protection can be set to 45°C or 50°C. When the device's OTC threshold is set to 50°C, it is referred to configure the VOTC parameter to 29.38% of VTB (typical), with the assumption of RTS_PU = 10 KΩ and RTS = 103AT or similar NTC (which the NTC resistance at 50°C = 4.16 KΩ). The VOTC specification is the resistor divider ratio of RTS_PU and RTS.
The VOTC, VOTD, VUTC, and VUTD configuration options are fixed in the device; thus, the actual temperature trip point can only adjust by using a different B-value NTC and/or using a different RTS_PU.
In this example, the 103AT NTC resistance at 55°C is 3.536 KΩ. By changing the RTS_PU from 10 KΩ to 8.5 KΩ, users can scale the actual OTC temperature trip point from 50°C to 55°C. Because the RTS_PU value is smaller, this change affects all the other temperature trip points and scales OTD, UTC, and UTD to ~5°C higher as well.