DEMO CIRCUIT 786 LTC4260CGN QUICK START GUIDE LTC4260CGN 200W Positive 48V Hot Swap Controller with Current and Voltage FEATURES DESCRIPTION n Configured for 200W, 36 to 72V Demonstration Circuit 786 showcases the n Provision for Short Pin Control of Turn-on LTC 4260CGN positive high voltage Hot Swap n I2C Monitoring of Load Current, Input and Output controller with I2C compatible monitoring in a 200W, Voltage 36 to 72V application. Included on board is an input n I2C Control of Device Features and Reporting of clamp and snubber, input and output voltage dividers Device Status for UV, OV, and PWRGD, LEDs to indicate the n Provision for On-Board Input and Output Bypassing presence of various voltages and signals, high voltage n layout rules and turret terminals for critical signals to High Voltage Layout Enforces 60 mil Minimum facilitate evaluation in a working system. Spacing n LEDs Indicate +48V Input, +48V/5A Output, Power A distinct line of demarcation runs the length of the Bad, Alert Status, and I2C Port Logic States board, separating high voltage +48V referred n Input Clamping Included On Board potentials from ground. Input and output connections are made by 93 mil turrets which if removed, APPLICATIONS accommodate insertion of up to 12 gauge wires for in-situ testing. An I2C port designed to interface with n Servers, Routers, Switches DC590A allows control of DC786A with LTC s Quick n Mass Storage Eval software. n Central Office Computing n Fan Trays Design files for this circuit board are available. Call the LTC factory. , LTC and LT are registered trademarks of Linear Technology Corporation. ThinSOT and PowerPath are trademarks of Linear Technology Corporation.I2C is a trademark of Philips Electronics N.V. ers, and LED current limiting resistors. Also on the BOARD LAYOUT bottom is the LTC4260CGN supply bypass capacitor, The top of the board contains the core Hot Swap con- C3, and space for optional input and output bypassing. troller and associated components, along with LEDs. Except for C3, the other components are largely unre- Also on top are various configuration jumpers and all lated to the core application and are included for the connection turrets. The large turrets may be removed purposes of the demo board itself. to permit installation of up to 12 gauge wire for direct, low resistance connections to the board. None of the Thermal layout requirements for the FDB3632 MOSFET turrets are swaged. are modest, as the maximum, continuous worst-case dissipation is less than 600mW. Typical dissipation is The bottom of the board contains components for less than 150mW, resulting in a temperature rise of software identification of the board, provision for A to less than 10C. D converter input scaling dividers, I2C line LED driv- 1 LTC4260CGN The board is designed with two ground planes, on lay- The A/D external monitor input (pin 13, ADIN) is con- ers 2 and 3. Layer 2 is a small signal ground plane nected to a jumper, JP8, ADIN SELECT. As shipped this which picks up ground for dividers, PROBE GND, the jumper connects ADIN to a divider (R11, R12) which small GND turrets, C3 and the timing capacitor, CT, as in turn connects to the +48V input, and gives a full well as all I2C and configuration jumper related scale of approximately 100V. Moving the jumper to grounding. Layer 3 is reserved for large signal EXT connects R14 and R17. The board is stuffed with grounding, including CIN, COUT, 3 large GND turrets, R14=10kW and R17 is omitted in this condition the input and output LEDs, and the input clamp and snub- ADIN turret connected to the LTC4260 s ADIN pin ber. These two ground planes join at PROBE GND. The through 10kW and as shown, gives a 2.56V full scale large GND turrets are provided to accommodate multi- sensitivity. R11, R12, R14, and R17 may be changed ple ground connections of meters, power supplies, to accommodate different scaling factors. The ADIN loads, etc., and there is no need for load current to be pin full scale is 2.56V, 2%. routed through the circuit board. The R11-R12 divider is built with 1% resistors, which A clear line of demarcation separates +48V copper add up to 2% measurement error. Up to 4% total from ground, passing under R9, CIN, Z1, CSNUB, R27, measurement error is possible, or 2V error out of a R1, U1, R7, C1 COUT, and R10. 55-60 mils spacing on 50V input. unpassivated surfaces is generally recommended for 48V circuits. This rule is bent in the vicinity of the MORE CURRENT LTC4260CGN s pins 2, 3 and 4, where the spacing necks down to about 30 mils. In practice this area Space is provided for up to three 2010 surface mount could be passivated with conformal coating, or one of sense resistors, and a TO-247 (TO-3P) MOSFET. This the other package options could be used (see the allows modification of the board for higher current ap- LTC4260 data sheet). plications. There is more copper between +48V INPUT and +48V/5A OUTPUT than the turrets and a TO-247 CIRCUIT NOTES can handle. The limitation is at the source of Q1, where the trace narrows to about 200 mils X 4 layers, all 1 DC786A uses an 8mW, 5% sense resistor (R5). Cou- ounce. This is good for about 40A continuous. There is pled with the LTC4260 s minimum current limit sense an equivalent of about 1 to 1.5 squares of 1-ounce voltage threshold of 40mV, this guarantees a minimum copper between the input and output turret terminals. current of 4.76A before the onset of current limiting or circuit breaker action. Thus 200W is available down to Kelvin sensing is located under the center R5 position. approximately 42V, dropping to 170W at 36V. Using a If using 1 resistor, put it in the middle if using 2 resis- less common sense resistor value of 7mW increases tors (ideally equal value) put them in the outside posi- the power at 36V to 195W. tions if using a high value resistor totri a low value unit, put the low value component in the middle and The UV and OV trip points are set by separate dividers the high value component on the outside. to facilitate modification. The trip points are as follows: Q1 is best removed with two large, hot soldering irons, UV turning on = 43V such as a Weller WTCPS controlled temperature iron UV turning off = 38.5V with a PTE8 tip. First cut the leads (or desolder and OV turning off = 71V lift), then apply the heat along Q1 s tab shear line, and OV turning on = 69.2V pluck the part from the board using a pliers and a third hand, immediately removing the soldering irons. Tab A/D CONVERTER INPUT OPTIONS removal should take only a few seconds. 2