9 Power Supply Recommendations

The bias supply voltage range for which the UCC27614 devices are recommended to operate is from 4.5 V to 26 V. The lower end of this range is governed by the internal UVLO protection feature on the VDD pin supply circuit blocks. Whenever the driver is in UVLO condition when the VDD pin voltage is below the V_(ON) supply start threshold, this feature holds the output low, regardless of the status of the inputs. The upper end of this range is driven by the 26-V recommended maximum voltage rating of the VDD pin of the device. The absolute maximum voltage for the VDD pin is 30 V.

The UVLO protection feature also involves a hysteresis function. This means that when the VDD pin bias voltage has exceeded the threshold voltage and device begins to operate, and if the voltage drops, then the device continues to deliver normal functionality unless the voltage drop exceeds the hysteresis specification. Therefore, ensuring that, while operating at or near the 4.5 V range, the voltage ripple on the auxiliary power supply output is smaller than the hysteresis specification of the device is important to avoid triggering device shutdown.

During system shutdown, the device operation continues until the VDD pin voltage has dropped below the VDD UVLO falling threshold which must be accounted for while evaluating system shutdown timing design requirements. Likewise, at system start-up, the device does not begin operation until the VDD pin voltage has exceeded above the VDD UVLO rising threshold. The quiescent current consumed by the internal circuit blocks of the device is supplied through the VDD pin. Although this fact is well known, recognizing that the charge for source current pulses delivered by the OUT pin is also supplied through the same VDD pin is important. As a result, every time a current is sourced out of the output pin (OUT), a corresponding current pulse is delivered into the device through the VDD pin. Thus ensuring that local bypass capacitors are provided between the VDD and GND pins and located as close to the device as possible for the purpose of decoupling is important. A low-ESR, ceramic surface-mount capacitor is needed. TI recommends having two capacitors; a 100-nF ceramic surface-mount capacitor placed less than 1mm from the VDD pin of the device and another ceramic surface-mount capacitor of few microfarads added in parallel.

UCC27614 is a high current gate driver. If the gate driver is placed far from the switching power device such as MOSFET then that may create large inductive loop. Large inductive loop may cause excessive ringing on any and all pins of the gate driver. This may result in stress exceeding device recommended rating. Therefore, it is recommended to place the gate driver as close to the switching power device as possible. It is also advisable to use an external gate resistor to damp any ringing due to the high switching currents and board parasitic elements.