QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1066 POSITIVE HIGH VOLTAGE IDEAL DIODE-OR LTC4355 DESCRIPTION Demonstration Circuit 1066 showcases the made by 93 mil turrets which if removed, accom- LTC4355 positive high voltage diode-OR controller modate insertion of up to 12 gauge wire for in-situ and monitor in a 200W, 48V application. Included testing. on board are two S-8 ORing MOSFETs and five Design files for this circuit board are available. LEDs to indicate a variety of fault conditions. Call the LTC factory. The 48V inputs are separated from ground and LTC is a trademark of Linear Technology Corporation from each other with at least 60 mils spacing wher- ever possible. Input and output connections are FEATURES APPLICATIONS *Tiny Size Facilitates Grafting into Working System *Servers, Routers, Switches *Two 5A Diode Channels Controlled by One LTC4355 *Mass Storage *Dual Layout for S-8 or D2Pak MOSFETs *Central Office Computing *0.093-inch Turret Holes Accommodate 12 AWG *Fan Trays Wire *ATCA Table 1. Typical Performance Summary (T = 25C) A SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS V Input Operating Range 9 48 77 V IN Peak Input Voltage Clipped by Transient Voltage Suppressor 77 100 V I Maximum Load Current Limited by MOSFET Dissipation 5 A OUT Limited by Fuses 7 A Board Layout Current Capability The 93-mil turrets are not swaged and may be re- The FDS3672 S-8 MOSFETs are capable of handling moved for in-situ testing. The plated-through holes up to 7.5A for short periods, limited by the thermal can accommodate up to 12 gauge wire. The characteristics of the package. A continuous load FDS3672 MOSFETs handle 5A continuous load cur- current of 5A is permissible with the board laying rent with no air flow and a total temperature rise of face-up on a lab bench and convection cooling. about 30-40 Celsius across the board. The bottom Thus situated and carrying 5A load current, either of the board contains pads for optional D2Pak MOSFET experiences a junction temperature rise of MOSFETs for applications up to 20A. Remove the approximately 50-55 Celsius. top-side S-8 MOSFETs if D2Paks are installed. Resistive losses total about 15 milliohms exclusive of MOSFET resistance the fuse accounts for about 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1066 POSITIVE HIGH VOLTAGE IDEAL DIODE-OR 13 milliohms of this figure and is not an insignifi- Operating Voltage Range cant source of dissipation. DC1066 is designed for 48V applications. Neverthe- At 5A load, MOSFET dissipation is approximately less, thediod action of the board operates down 600mW. In contrast, the power loss of an equiva- to the minimum supply voltage for the LTC4355CDE of 9V. Other functionality will be af- lent passive Schottky diode would measure about 3W. This represents a power and thermal area sav- fected or lost including dim LEDs, indication of ings of 5X. At 3A load current the improvement is power faults on each channel (the threshold is even more dramatic. 34.1V), and reduced gate drive. To modify the board for a new operating range simply resize the LED resistors (R5-R9) to a value Fault Pins of Vinmax/5mA, and change R2 and R4 to detect Green LEDs show the status of the five fault pins. If under voltage at the desired point. The simple volt- the LED is on there is no problem extinguished age divider calculations so efficiently covered in the LEDs indicate problems with a fuse, low input volt- LTC4355 data sheet need not be repeated here. For age, or excessive Vds across one or both of the applications below 20V where minimum gate drive MOSFETs. is guaranteed at 4.5V, use logic level MOSFETs. The LTC4355 detects excessive Vds across one or both MOSFETs. Optional resistor R10 located on Modifying for Other Current Ranges the bottom of the board allows for three choices of Vds fault threshold: To modify the board for other current ranges, re- place the fuses and MOSFETs. A good rule of R10=0 Vds fault threshold=250mV thumb for selecting MOSFETs is to select an Rds R10=100k Vds fault threshold=500mV (on) which produces 100 to 200mV drop at maxi- mum load current. This gives a substantial im- R10=open Vds fault threshold=1.5V provement in losses over a Schottky diode solution. DC1066 is built with R10=open for a Vds fault Sufficient copper is available on DC1066 to handle threshold of 1.5V. about 20A. Suggested devices for currents in the 5- Note that the fault pins are limited to 8V abs/max, 20A range include IRFS4710, IRF3710S, yet the pull-up resistors (R5-R9) are powered by IRF1310NS and FDB3632. The bottom of the board the 48V output. The LEDs serve as clamps and if contains pads for D2Pak MOSFETs. Remove the you remove them, the fault pins will be destroyed. If top-side S-8 MOSFETs if D2Paks are installed. you want to interface the fault pins to logic circuits, In high current applications verify your choice of remove BOTH the LED and the attendant pull-up MOSFET by checking its current ratings and calcu- resistor. lating the dissipation. For example, 200mV drop at 20A (4W) makes DC1066 fairly warm with a maxi- mum board temperature rise of 80-90 Celsius. Above 4W, abandon DC1066 and attach the MOS- FETs to a heatsink. 2