printed circuit board (PCB) components in descending order of priority:
1. The switch-mode power supply (SMPS) components
2. Bluetooth® radio frequency (RF) trace and band-pass filter
3. Bluetooth RF decoupling
4. Crystal (XTAL)
5. Audio BGBYP capacitor
6. VDD_DIG decoupling
7. The quad serial peripheral interface (QSPI) flash devices and decoupling
8. All other decoupling
SMPS
1.8 V SMPS output
digital SMPS changes between 1.1 V and 0.85 V depending on the power mode of the integrated circuit
three modes PWM PFM ULP(PFM)
PWM frequency 2 MHz PWM max load current 350 mA 150 mA
PFM / ULP max load current 40 mA 55 mA
QTIL recommends to use inductors with a minimum saturation current rating that is at least 30% higher than the target Max inductor current in PWM mode.
Inductor ESR / DCR 290 mΩ,
QCC5124 VFBGA SMPS circuits can be powered from SMPS_VCHG or SMPS_VBAT using low
impedance on chip switches to SMPS_DCPL. The typical impedance of the on chip VBAT switch is
600 mΩ and the VCHG switch is 1.2 Ω.
The placement of the SMPS_DCPL capacitor is important. The 2.2 μF capacitor must be placed as close as possible to the QCC5124 VFBGA device to close the high frequency current loop and minimize EMI
Charge current enters through the SMPS_VCHG pin, which should be locally decoupled with a 2.2 μF ceramic capacitor. As SMPS_VCHG is a high-voltage node, the capacitor must be appropriately voltage rated. QTIL recommends use of a capacitor rated for at least 10 V.
VBAT_SENSE
This Kelvin connection avoids the IR drop in the battery PCB traces, which can lead to early termination, from affecting the charge process. As this is a sense connection, thick PCB tracks are not required.
When choosing transistors, note that transistor Hfe values are usually quoted with 2 V Vce.
SYS_CTRL
has no internal pull resistor, and requires an external pull-down if left undriven.
In analog input mode, LED pads the input range is 0 to VDD_AUX_ADC. Damage may be caused if
input voltages exceed 1.8 V.
usb
Over longer distances, USB data lines should be routed as a 90 Ω differential pair. They should have a single ended impedance to ground of around 45 Ω and a track length matched to avoid skew.
