S42
Hardware User Guide
1VV0301303 Rev. 11
Page 31 of 85
2021-05-06
Not Subject to NDA
Note/Tip: It is strongly recommended NOT to switch the module
power supply on/off while other parts of the circuitry stay powered.
This mostly leads to hardly controllable back-feeding issues. Back-
feeding occurs due to connected signal line(s) being >0,3V while the
module power is switched off. Then the I/O protection diodes,
integrated in the I/O ports of the BT IC, will feed the VSUP
“backwards”, which means that the modules power supply is fed via
the I/O lines instead via the power supply. Due to the ultra-low power
design a few µAmps are enough to raise VSUP to an undefined state,
which may cause a hang-up deadlock when then power is switched
on again.
Any I/O pin at a voltage > 0,3V while the supply VSUP is at 0V violates
the abs. max. ratings given in chapter 5.1 Absolute Maximum
Ratings.
It is instead recommended to use the advanced power management
features, which may reduce the supply current to 300nA.
3.12.
Serial Wire Debug Interface
The Serial Wire Debug (SWD) interface (signals SWDIO, SWCLK) is normally not used in
a customer’s product. It is reserved for debugging purposes.
Leave SWDIO, SWCLK unconnected. Only if you intend to use them for debugging
purposes, make them available.
3.13.
DC/DC Converter
The S42 contains a buck DC/DC converter and an LDO for supplying the radio
circuit.
Switching between DC/DC converter and LDO is done automatically based on load to
maximize efficiency.
Used with a 3V coin-cell battery, the peak current drawn from the battery is reduced by
at least 25% by use of the DC/DC converter.
3.14.
Analog/Digital Converter (ADC)
The ADC functionality is FW dependent.
