SLLSFM0A March 2022 – June 2022 SN6507
The SN6507 is a 36-V, 0.5-A push-pull transformer driver with two integrated n-channel power MOSFETs. It is designed for low cost, small size, low EMI isolated DC/DC power supplies.
The device includes an oscillator that feeds a gate-drive circuit. The gate-drive, comprising a frequency divider and a break-before-make (BBM) logic, provides two complementary output signals which alternately turn the two output NMOS transistors on and off. A subsequent break-before-make logic inserts a dead-time between the high-pulses of the two signals, to avoid shorting out both ends of the transformer's primary windings. The resulting output signals, drive an isolation transformer and a rectifier, converting the input voltage to an isolated output voltage.
To improve performance at wide-input applications, the device implements a Duty Cycle Control (DCC) feature that the duty cyle is dynamically adjusted to compensate for the input variation. It removes the need of pre-regulation if the input variation is within a certain degree. Or even if at wide input conditions where the input variation is out of regulation range, it saves secondary-side LDO size and power loss. The wide switching frequency range allows for better efficiency and smaller output ripple, as well as size optimization when selecting the transformers.
The transformer driver comes with multiple protection features to ensure robust operation, such as programmable overcurrent protection (OCP), input OVP, input UVLO and TSD. The device minimizes excessive output overvoltage transients by taking advantage of the overvoltage comparator. When the overvoltage comparator is activated, the MOSFETs are turned off and prevented from turning on until the overvoltage condition is removed. The device implements overload protection for both MOSFETs which help control the transformer current and avoid transformer saturation. It also shuts down if the junction temperature is higher than the thermal shutdown trip point. A programmable soft-start period reduces the inrush current during start-up and fault recovery.For ultra-low EMI applications, the slew rate control feature provides design flexibility and simplicity to further improve emissions with a resistor-programmable option.