Schematic guidelines

AN4324

14/31

DocID024963 Rev 2.0

4.3

RSTIO pin system integration

The STC3115 RSTIO is an open drain pin which, to operate, must always be pulled-up to a

The STC3115 RSTIO feature maintains the accuracy of the first open circuit voltage (OCV)

measurement in all application start-up sequences. This feature prevents the first OCV

measurement from a fast application start-up. If the main application reset signal is

detected as low before the beginning of the first OCV measurement, it is forced low by the

RSTIO pin until the end of the measurement to guarantee measurement accuracy. In this

reset state, the application consumption is low and no battery voltage drop is implied. This

operation takes a maximum of 500 ms.

Several typical application implementations are described below.

The Vbatt voltage used to pull-up the RSTIO signal can be another system voltage such as

an IO voltage (see Figure 7: "STC3115 RSTIO schematic if the RSTIO feature is

disabled"). If the RSTIO pin is pulled-up to a fixed positive voltage or if it is grounded, this

feature is disabled.

Figure 7: STC3115 RSTIO schematic if the RSTIO feature is disabled

1.

Typical R1 value = 1 kΩ

In the architecture of Figure 8: "STC3115 RSTIO feature integration in a PMU based

application", it is assumed that the application processor (AP) consumes the most power.

Once the PMU is ready to provide the voltage and clock to the AP, the RESETN signal is

relaxed by the PMU (which informs the AP that the PMU is ready). The STC3115 RSTIO

pin relaxes this signal at the end of the first OCV measurement.