Hi,
I’m checking Figure 29 (STATUS reference circuit) and I have a concern.
The document states the STATUS pin is an open-drain output that goes “high” when the module is powered on. In the reference schematic the STATUS pin drives the base of an NPN through 4.7k with a 47k to ground, and the LED is in the collector to VBAT. My concern is that when the STATUS pin is released (high-Z) the only base bias is through that 47k, which provides only a few microamps. There is therefore no guarantee the transistor will turn on reliably across different transistor hFE values or temperature/variations — so the LED may not reliably light when the module is on.
Questions for the designers / community:
- Is the reference schematic intentionally relying on the base bias through 47k (i.e. trusting the transistor will switch with that tiny current), or is this a mistake in the figure?
- Would you recommend adding a proper pull-up on the STATUS pin (to VBAT or 3.3V) to create a defined logic high and guarantee LED behavior? If yes, what pull-up value is recommended?
- Alternatively, do you consider the current design acceptable (and if so, under what assumptions about the transistor/hFE or LED threshold)?
I’m attaching the figure for context. Thanks for any clarification or recommended changes.
