Milpitas, Calif. - Linear Technology's LTC3900 and LTC3901 are two secondary-side synchronous N-channel MOSFET drivers designed to go the extra mile to protect the external MOSFETs of a DC/DC converter 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 synchronization signal between the primary and secondary sides is missing or incorrect. This feature protects the MOSFETs from over-voltage and excessive electrical stress. Additionally, the ICs turn off the MOSFETs if inductor current exceeds a user-programmable level. Moreover, to ensure proper power up and power down, these drivers shut off the MOSFETs when the driver input voltage is below 4 volts.
The LTC3900 is designed for use in forward converter topologies and the LTC3901 is suited 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.
In operation, these rectifier drivers drive two N-channel MOSFETs and accept pulse synchronization from the primary-side controller via a pulse transformer. The chips' timer circuit and VDS current-sense comparator 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. On every negative transition at the SYNC input, the ICs generate a 200 ns pulse to reset the timer capacitor.
The LTC3900 is offered in an 8-lead SO package. The LTC3901 is housed in a 16-lead SSOP. Both are rated for operation from -40 to +85°C. The LTC3900 and LTC3901 are priced at $2.50 and $2.60 each, respectively, in 1k pieces.