AirPrime Module Datasheet

Hardware Design Guidelines
Rev 1 Apr.17 17 41110693
VCHG is the input to the battery charger regulator.
VBAT_SENSE is the input to the Battery sensor circuitry.
VBAT is the main supply input to the internal switch mode and LDO regulators
and is the supply domain for VREGEN.
VDD_PADS is the supply to all the I/O domains for PIO, UART, PCM, LED and
RST#.
Boot Modes
The module will boot automatically whenever a voltage greater than 3.1V is
applied to VCHG (for example, when a USB source is plugged in).
The module does not support a soft start supply configuration, for fast transient
supply sources or supply sources with limited sourcing current use a filter (see
R3/C4 in the main schematic above) to slow the rising edge of the supply voltage
at turn on. A large inrush current at turn on can cause a dipping of the supply
voltage applied to the module, in turn causing the module to lock out, adding the
filter as shown keeps the input supply voltage rise monotonic and avoids lock out.
Charging and Battery
In this configuration an external pass transistor is connected between VCHG,
VBAT_SENSE, and CHG_EXT to support an external fast charge configuration.
VBAT_SENSE is connected to VBAT via a 400mR resistor.
The charging current is by default 150mAmp. It can be configured by UART
command to be between 0 and 200mAmp. Please refer to the Melody Manual for
configuration.
R1 and C1 in the main schematic diagram form a RC snubber circuit that is
designed to maintain stability over a wide range of Battery ESRs. The maximum
ESR of the battery should not exceed 1Ω.
The external VBUS voltage connected to VCHG is used to supply the current to
charge the battery. Typically this comes from an external USB source.
In the above circuit VDD_PADS is supplied by a regulated voltage from VBAT, in
the case of batteries that are flat or discharged, the absence of a voltage on
VDD_PADS will halt the booting of the module. Therefore to ensure that a voltage
is available on VDD_PADS to support discharged batteries, the following circuit is
required. This circuit combines the VBAT and VCHG inputs to generate the
supply for VDD_PADS.