Datasheet LTC1698 (Analog Devices) - 8

LTC1698
W BLOCK DIAGRA
1 VDD VAUX 14 AUX GEN VCC GEN FG V SYNC CC 16 15 SYNC IN CG 2 RMARGIN MARGIN 7 I-TO-V CONVERTER VREF ±5% VREF BANDGAP + OPTODRV 5 OPTO + 20k – ERR VFB 100k – 8 VCOMP M 6 PWRGD PWRGD 10 ISNSGND + 11 MILIM ILIM 25mV + ISNS R – 12 ILIM 3k ICOMP PWRGD 13 – + ROVP + VREF 3k OVP VFB 0.94VREF OVPIN – 9 1698 BD
U OPERATIO (Refer to Block Diagram)
The LTC1698 is a secondary-side synchronous rectifier Schottky diodes, synchronous rectification on the sec- controller designed to work with the LT3781 primary-side ondary offers isolation with high efficiency. It supplies synchronous controller chip to form an isolated synchro- high power without the need of bulky heat sinks, which is nous forward converter. This chip set uses a dual transis- often a problem in any space constrained application. tor forward topology that is predominantly used in distrib- The LTC1698 not only provides synchronous drivers for uted power supply systems where isolated low voltages the external MOSFETs, it comes with other housekeeping are needed to power complex electronic equipment. The functions performed on the secondary side of the power primary stage is a current mode, fixed frequency forward supply, all within a single integrated controller. Figure 1 converter and provides the typical PWM operation. A shows the typical chip-set application. Upon power up, the power transformer is used to provide the functions of LTC1698’s V input/output isolation and voltage step-down to achieve DD input is low, the gate drivers TG and BG are both at the ground potential. The secondary forward and the required low output voltage. Instead of using typical 1698f 8