ZHCSH30C August 2017 – April 2018 TAS5755M
PRODUCTION DATA.
To facilitate system design, the TAS5755M needs only a 3.3-V supply in addition to the PVDD power-stage supply. An internal voltage regulator provides suitable voltage levels for the gate drive circuitry. Additionally, all circuitry requiring a floating voltage supply, for example, the high-side gate drive, is accommodated by built-in bootstrap circuitry requiring only a few external capacitors.
In order to provide good electrical and acoustical characteristics, the PWM signal path for the output stage is designed as identical half-bridges with separate bootstrap pins (BST_x). The gate-drive voltage (GVDD_OUT) is derived from the PVDD voltage. Special attention must be paid to placing all decoupling capacitors as close to their associated pins as possible. Inductance between the power-supply pins and decoupling capacitors must be avoided.
For a properly functioning bootstrap circuit, a small ceramic capacitor must be connected from each bootstrap pin (BST_x) to the power-stage output pin (OUT_x). When the power-stage output is low, the bootstrap capacitor is charged through an internal diode connected between the gate-drive regulator output pin (GVDD_OUT) and the bootstrap pin. When the power-stage output is high, the bootstrap capacitor potential is shifted above the output potential and thus provides a suitable voltage supply for the high-side gate driver. In an application with PWM switching frequencies in the range from 288 kHz to 384 kHz, it is recommended to use 10-nF, X7R ceramic capacitors, size 0603 or 0805, for the bootstrap supply. These 10-nF capacitors ensure sufficient energy storage, even during minimal PWM duty cycles, to keep the high-side power-stage FET (LDMOS) fully turned on during the remaining part of the PWM cycle.
Special attention must be paid to the power-stage power supply; this includes component selection, PCB placement, and routing. As indicated, each half-bridge has independent power-stage supply pins (PVDD_x). For optimal electrical performance, EMI compliance, and system reliability, it is important that each PVDD_x pin is decoupled with a 100-nF, X7R ceramic capacitor placed as close as possible to each supply pin.
The TAS5755M is fully protected against erroneous power-stage turnon due to parasitic gate charging.