Pins functional description

STWBC-EP

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DocID030747 Rev 1

5.3

Half bridge driver: UPBL, DNBL, PWM_QFOD, WAVE_SNS

The power half bridge is driven using the UPBL and DNBL pins. The UPBL pin has to be

connected to a high-side gate driver, while the DNBL pin has to be connected to a low-side

gate driver for the power switches.

The UPBL and DNBL pins are active-high: when 1, the corresponding power switch has to

be ON.

The STWBC-EP integrates programmable dead time between the active states of the UPBL

and DNBL avoiding simultaneous conduction of power switches. The external gate driver

doesn't need to manage dead time.

The STWBC-EP requires the following capability to be supported by the gate driver:



UPBL = 0, DNBL = 0: in such case, the power half bridge must be in the high

impedance state.



UPBL = 1, DNBL = 0: high-side power switch must be ON.



UPBL = 0, DNBL = 1: low-side power switch must be ON.



UPBL = 1, DNBL = 1: optional mode where both high and low-side power switches

must be ON (simultaneous conduction).

While the power half bridge is driven with UPBL and DNBL signals, a low energy drive is

needed to run the coil quality factor estimation. For this function, the bridge is driven by

using the PWM_QFOD pin instead of the UPBL (UPBL is 0 during this operation). The

PWM_QFOD has to be connected to the low energy high-side switch while the DNBL is still

used for the low-side low impedance switch drive.

In many situation the STWBC-EP requires ¼ wave synchronization with the LC tank

connected to the half bridge. A simple passive detector must be connected to the LC tank

and the WAVE_SNS pin. The WAVE_SNS pin should be limited to a 0.6 V swing.

5.4

Wireless power functions: TANK_VOLTAGE, ISENSE,

COIL_TEMP, SYMBOL_DETECT, CURRENT_DEMOD,

CS_CMP_AVG

The STWBC-EP requires monitoring the peak voltage on the LC tank as well as the rectified

current circulating in the tank. To do so, a peak voltage detector of the LC tank must be

connected to the TANK_VOLTAGE pin and a filtered current sensor must be connected to

the ISENSE pin .

For quality factor measurement, a high sensitivity peak voltage detector of the LC tank must

be connected to the CS_CMP_AVG pin.

The STWBC-EP requires external signal conditioning blocks to pre-demodulate the WPC Qi

messages. One of this blocks detects the effect of modulation on the LC tank voltage and it

must be connected to the SYMBOL_DETECT pin. Another block is required to detect the

effect of modulation on the LC tank current and it must be connected to the

CURRENT_DEMOD pin.

For safety reason the STWBC is capable of monitoring the temperature of the transmitting

coil. In order to do so, a NTC thermistor must be connected to the COIL_TEMP pin.