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3.1 Voltage Regulator Enable
When using the integrated regulators the voltage regulator enable pin, VREG_ENABLE, enables the LM746 and the following regulators:
-1.8V switch-mode regulator
-1.35V switch-mode regulator
-Low-voltage VDD_DIG linear regulator
-Low-voltage VDD_AUX linear regulator
The VREG_ENABLE pin is active high.
LM746 boots-up when the voltage regulator enable pin is pulled high, enabling the regulators. The firmware then latches the regulators on, it is then
permitted to release the voltage regulator enable pin.
The status of the VREGENABLE pin is available to firmware through an internal connection. VREGENABLE also works as an input line.
3.2 Reset, RST#
LM746 is reset from several sources:
-RST# pin
-Power-on reset
-USB charger attach reset
-Software configured watchdog timer
The RST# pin is an active low reset and is internally filtered using the internal low frequency clock oscillator. LM Developes recommends applying RST#
for a period >5ms. At reset the digital I/O pins are set to inputs for bidirectional pins and outputs are set to tristate.
4.1 Battery Charger hardware Operating Modes
The battery charger hardware is controlled by the VM. The battery charger has 5 modes:
-Disabled
-Trickle charge
-Fast charge
-Standby: fully charged or float charge
-Error: charging input voltage, VCHG, is too low
The battery charger operating mode is determined by the battery voltage and current.
The internal charger circuit can provide up to 200mA of charge current, for currents higher than this the LM746 can control an external pass transistor
4.2 External Mode
The external mode is for charging higher capacity batteries using an external pass device. The current is controlled by sinking a varying current into the
CHG_EXT pin, and the current is determined by measuring the voltage drop across a resistor, Rsense, connected in series with the external pass
device, see Figure 4.2.1. The voltage drop is determined by looking at the dierence between the VBAT_SENSE and VBAT pins. The voltage drop
across Rsense is typically 200mV. The value of the external series resistor determines the charger current. This current can be trimmed with a PS Key.
In Figure 4.2.1, R1 (220mΩ) and C1 (4.7μF) form a RC snubber that is required to maintain stability across all battery ESRs. The battery ESR must be <1.0Ω
LM746 Bluetooth® Dual Mode Audio Module
Standalone (With Embedded Bluetooth® 5 Compliant Stack)
3. Power Control and Regulation
4. Battery Charger
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