MOSFET drivers

Linear Technology has introduced two secondary side synchronous n-channel MOSFET drivers, the LTC3900 and LTC3901.

Both have timer and current sense comparators to protect the external MOSFETs during normal and light load operation, power up/down, and when the driver supply voltage drops too low.

A programmable timeout function disables the synchronous drivers when the synchronisation signal between the primary and secondary sides is missing or incorrect. This protects the MOSFETs from overvoltage and electrical overstress.

Additionally, the ICs turn off the MOSFETs if the negative inductor current exceeds a user-programmable level, preventing the buildup of excessive inductor energy.

To ensure proper power up and power down, these drivers shut off the MOSFETs when the driver input voltage is below 4.

The LTC3900 is designed for forward converter topologies and the LTC3901 is for use in push-pull and full-bridge converters.

Applications include 48 V input isolated DC/DC converters, isolated telecom power supplies, industrial control and automotive equipment.

The devices are rectifier drivers that drive two n-channel MOSFETs and accept pulse synchronisation from the primary side controller via a pulse transformer. The timer circuit and VDS current sense comparator in these ICs are used to prevent excessive reverse current buildup in the output inductor.

The timer, which is adjustable, operates using an external RC network to program the time-out period. Strong synchronous gate drivers guarantee 10 ns rise/fall times measured at VCC = 5 with 4700 pF capacitive load.

Synchronous operation improves efficiency when compared with solutions using diodes as secondary side rectification. On every negative transition at the SYNC input, the ICs generate a 200 ns pulse to reset the timer cap. VCC supply range is from 4.5 to 11.