Laird BL654 User Manual page 12

The development board power supply circuitry special feature is it resolves whether the BL654 VDD pin is an input supply
pin (in Normal Voltage mode) or becomes an output supply voltage pin (in High Voltage mode).
On the development board, the power circuity net names are as follows:
▪
VCC_3V3 – Supplies regulated 3.3V power to the FTDI chip as well as temperature sensor (U1).
▪
VSUPPLY – Supplies regulated 3.3V or 1.8V via selection switch SW5 to net VSUPPLY which is connected to input of
Load switch U21.
▪
VCC_2V5_5V5 – Selection switch SW8 supplies either regulated 2.5V or 3x AAA battery voltage (4.5V) can be used for
when BL654 is powered in High Voltage mode (using the VDD_HV pin).
▪
V5V – The main development board power supply's buck-boosted output (that is 5V) supplies a discrete regulator
made up of Q3 and U19. U19 OpAmp drives Q3 to generate regulated voltage (that then is connected to input of load
switch U20) that tracks control signal VDD_nRF_SENSE.
▪
VDD_VSRC_nRF – Supplies the FTDI chip IO and all other sensors and circuitry. VDD_VSRC_nRF is generated from load
switches U20 or U19.
▪
VDD_nRF_SENSE – Used as control signal to drive control pin of load switches U20 and U19. The source of
VDD_nRF_SENSE is the BL654 VDD pin. When BL654 is powered in High Voltage mode (using the VDD_HV pin), the
BL654 VDD pin becomes an output.
▪
VDD_nRF_SW – Selection switch SW6 supplies either VDD_SRC_nRF or coin-cell (J34). When the BL654 operated in
Normal Voltage mode (SW7 in middle position and voltage source is either 1.8V or 3.3V selected by SW5). Also
supplies the I2C RTC chip (U16). The use case for powering this is that the RTC chip can be configured so that, after the
pre-determined time, the RTC chip outputs (via RTC_ALARM pin) a transition level that can be used to wake up the
BL654 module up from deep sleep.
▪
VDD_nRFp – Supplies the BL654 series module only. Current measuring block on the development board only
measures the current into power domain VDD_nRFp (that is current going into header J7 pin 1).
▪
VDD_nRF – Supplies the BL654 series module only and is to the current that has come out of the current measuring
block on the development board on header connector J7 pin 2.
▪
VDD_HVp – Supplies the BL654 series module only. Current measuring block on the development board only measures
the current into power domain VDD_nRFp (that is current going into header J9 pin1).
▪
VDD_HV – Supplies the BL654 series module only and is to the current that has come out of the current measuring
block on the development board on header connector J9pin2.
▪
VBUS_nRFp – This voltage from USB cable plugged into connector USB3, that is directly fed to BL654 VBUS pin (via 0R
resistor R50) on net VBUS_nRF.
TIP: If operating the development board at temperature of 75°C or above there is an issue related to Q2 (it starts turning
on) which results in VDD_VSRC_nRF supplying heading towards 0V or turning off. To overcome this issue 75°C or above
issue, bridge with solder the open-solderbridge SB24 which connects 1MOhms resistor to ground onto the gate of Q2.
The 1-MOhm resistor results in extra current consumption of (= VDD_nRF_SENSE/1Mohms) added to any current
measurements made when operating the BL654 module on devboard in High voltage mode (VDD_HV pin) ONLY which
is when SW7 in Top position or Bottom position (and in that case by default VDD_nRF_SENSE is 1.8V).
PCB location of SB24 and schematic showing SB24.
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