2. NTC Iimplementation

2.1. NTC Hardware

The description of the NTC hardware, as mentioned in the DA1469x datasheet (Chapter7.2.6.1):

The JEITA standard defines a battery temperature dependent charge profile. In the normal temperature range, the charge current and voltage are at the maximum level for the selected battery. Above and below this normal temperature range, there are two ranges in which the current (and optionally voltage) is reduced. At very low and very high battery temperatures, charging is stopped altogether. The battery temperature is determined using the NTC in the battery pack (or separate attached to the battery). This NTC is placed in series with an external resistor and a voltage is applied across them, creating a voltage divider. The output of this divider is compared to an internal reference that is created using a programmable resistor ladder that mimics the behavior of the NTC / resistor combination and has programmable taps at ~1 °C intervals, between -10 °C and +55 °C. The NTC battery monitoring connections are shown in the following figure:

_images/ntc_battery_monitor.png

Fig. 2 NTC Battery Monitoring Connections

2.2. NTC Software

The easiest way to check the connections and/or disconnections of the NTC resistor and resistor R1 would have been using the GPADC by measuring the voltage at the connection point of the 2 resistors (P0_07). Unfortunately P0_07 is not connected to the GPADC internally, so another method needs to be implemented for the test. Fortunately, the DA1469x battery temperature monitor circuit is capable of sensing whether the temperature is too high or too low using the reference ladder network and the 2 comparators (see figure 2).

By using the temperature monitor circuit and specific settings of the GPIO’s P1_00 and P0_07, it is possible to test the following cases:

  • NTC & R1 correctly connected
  • NTC not connected to ground
  • NTC not connected to P0_07
  • NTC short circuit
  • R1 not connected to P1_00
  • R1 not connected to P0_07
  • R1 short circuit