Specifications

 Fast Charge - Constant Current: entered when the battery voltage is above 2.9V.

 Fast Charge - Constant Voltage: entered when the battery has reached V

float

, the

charger switches mode to maintain the cell voltage at V

float

voltage by adjusting the

constant charge current.

 Standby: this is the state when the battery is fully charged and no charging takes

place.

When a voltage is applied to the charger input terminal VDD_CHG, and the battery is not

fully charged, the charger will operate and a LED connected to the terminal LED0 will

illuminate. By default, until the firmware is running, the LED will pulse at a low-duty cycle

to minimize current consumption.

The battery charger circuitry auto-detects the presence of a power source, allowing the

firmware to detect, using an internal status bit, when the charger is powered. Therefore,

when the charger supply is not connected to VDD_CHG, the terminal must be left open

circuit. The VDD_CHG pin, when not connected, must be allowed to float and not be pulled

to a power rail. When the battery charger is not enabled, this pin may float to a low

undefined voltage. Any DC connection will increase current consumption of the device.

Capacitive components such as diodes, FETs, and ESD protection, may be connected.

The battery charger is designed to operate with a permanently connected battery. If the

application permits the charger input to be connected while the battery is disconnected,

the VDD_BAT pin voltage may become unstable. This, in turn, may cause damage to the

internal switch-mode regulator. Connecting a 470μF capacitor to VDD_BAT limits these

oscillations thus preventing damage.

WARNING:

Use good consideration for battery safety. Do not charge with too much current. Do

not charge when the temperature is above 60°C or below 0°C. WT32 is initially

calibrated to stop charging when battery voltage is at 4.2 V. Do not try to charge

batteries above 4.2 V. Do not short circuit the battery or discharge below 1.5 V.

5.4 RESET

WT32 may be reset from several sources: reset pin, power on reset, a UART break

character or through software configured watchdog timer.

The power on reset occurs when the VDD_CORE supply falls below typically 1.26V and is

released when VDD_CORE rises above typically 1.31V. At reset, the digital I/O pins are set

to inputs for bi-directional pins and outputs are tri-state. The pull-down state is shown in

Table 9.

The chip status after a reset is as follows:

 Warm Reset: data rate and RAM data remain available

 Cold Reset(10): data rate and RAM data are not available

Table 9 shows the pin states of WT32 on reset. Pull-up (PU) and pull-down (PD) default to

weak values unless specified otherwise.

Pin Name /

Group I/O Type State on Reset

USB_D+ Digital bi-directional N/A

USB_D- Digital bi-directional N/A