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4.1 Low Side and H-Bridge Gate Driver Fundamentals

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Date: April 14, 2017

Low side gate driver can be used to driver the active switch in the PFC stage, and also can be used to drive the synchronous rectification for the bus converter stage, since the power switches are all ground referenced. Low side driver can be implemented in a discrete way with quite a few low voltage transistors for lever-shifter, as well as the totem-pole buffer stage. The drawbacks is obvious due many discrete parts, components size, PCB layout, as well as the parasitics introduced by the non-ideal package and the PCB traces.

All of these discrete devices can be easily integrated in a small chip with optimization of reliability, protection features, as well as driver performance, such as peak driving current, small propagation delay, better pulse width distortion and small quiescent current consumption.

For low side gate drivers, you have the choice for single channel and two-channel. Non-inverting for single channel, as well as two channel. Like the example shown in the lower left, the device leave the two input pin making it universal for non-inverting and inverting by connecting the two input differently. What is more, the output pin is split for programming different turn-on/off, saving the external components if faster turn-off is needed.

Similar to low side gate driver introduced in previous page, the low side gate driver in the half-bridge driver is relative simple and straight forward. Input and output with certain propagation delay. Since the high side drive is not reference with ground, level-shift circuit is need to interface the ground referenced input. To supply the high side power, the most popular way is use bootstrap, charging the boot capacitor when bottom FET is ON. As shown, you have a input referenced with ground, however, the output voltage is referencing with the switch node from 100~700V, difference between HO and HS is the high side gate drive voltage, VDD-VF. Some application even integrate the bootstrap diode for customer convenience. With input filter and splitting on/off, it shows general all the function circuit for high and low side driver.