Evaluates: MAX256 19-0715 Rev 0 12/06 MAX256 Evaluation Kit General Description Features The MAX256 evaluation kit (EV kit) is a fully assembled +3V to +5VDC Input Range and tested PCB that contains a 3W isolated H-bridge Isolated Outputs DC-DC converter. The circuit is configured for unregu- lated output voltages of approximately +5V and -5V +VOUT: +5V Provides Up to 300mA (with respect to an isolated ground). Output current is -VOUT: -5V Provides Up to 300mA up to 600mA from either output, or 300mA from each of the two outputs. Input power for the circuit is provided 87% Overall Efficiency at +5V Input and 200mA from a +5VDC source, or operates at any input voltage Load down to +3V with a corresponding reduction in the out- Center-Tapped, Full-Wave Rectifier Output put voltages. The EV kit provides greater than 85% overall efficiency 400kHz Switching Frequency at +5V between 250mW and 2W output power using an 2.7V Undervoltage Lockout (UVLO) H-bridge DC-DC converter topology. Input ripple cur- rent and radiated noise are minimized by the inherent Designed for 1500V Isolation RMS balanced nature of the design with no interruption in the Low-Cost, Integrated-FET H-Bridge Design input current. Undervoltage lockout (UVLO) and ther- mal shutdown provide for a robust 3W isolated supply. Fully Assembled and Tested The surface-mount transformer provides up to 1500V galvanic isolation with each output powered RMS from a center-tapped full-wave rectifier circuit to reduce Ordering Information output voltage ripple. PART TEMP RANGE IC PACKAGE Operation at 400kHz allows the use of ceramic output capacitors and a small transformer. MAX256EVKIT+ 0C to +70C* 8 SO-EP +Denotes a lead-free and RoHS-compliant EV kit. *This limited temperature range applies to the EV kit PCB only. The MAX256 IC temperature range is -40C to +125C. EP = Exposed paddle. Component List DESIGNATION QTY DESCRIPTION DESIGNATION QTY DESCRIPTION JU2 1 2-pin header 10F 10%, 10V X7R ceramic C1 1 capacitor (1206) R1 1 39.2k 1% resistor (0603) Murata GRM31CR71A106K R2 1 100k 5% resistor (0603) 0.47F 10%, 16V X7R ceramic Not installed, resistors (0805) R3, R4 0 (0 5% resistors recommended) C2 1 capacitor (0805) Murata GRM219R71C474K R5 1 0 5% resistor (0805) 0.1F 10%, 25V X7R ceramic 3W 1:1:2.6:2.6 turn transformer C3, C4 2 capacitors (0805) T1 1 (8-pin gull wing) Murata GRM21BR71E104K HALO Electronics TGM-H281NF U1 1 MAX256ASA+ (8-pin SO-EP) 30V, 1A Schottky diodes (SOD-123) D1D4 4 Diodes Inc. B130LAW 2 Shunts (JU1, JU2) JU1 1 3-pin header 4 Rubber bumpers 1 PCB: MAX256EVKIT+ Maxim Integrated Products 1 For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct at 1-888-629-4642, or visit Maxims website at www.maxim-ic.com.MAX256 Evaluation Kit Component Suppliers SUPPLIER PHONE WEBSITE Diodes Inc. 805-446-4800 www.diodes.com HALO Electronics 650-903-3800 www.haloelectronics.com Murata Mfg. Co., Ltd. 770-436-1300 www.murata.com Note: Indicate that you are using the MAX256 when contacting these component suppliers. Quick Start Detailed Description The MAX256 EV kit is a 3W, isolated H-bridge DC-DC Required Equipment converter that provides approximately +5V and -5V with One 5V, 1A current-limited power supply with a respect to an isolated ground. Either of the outputs built-in current meter provides up to approximately 600mA when operated Two voltmeters from a +5V supply. The total current is limited to approximately 600mA. The EV kit circuit should be Two 1A meters powered from a +5V source capable of at least 800mA, Two 100mA loads (or 51 resistors) but can also be operated at lower voltages consistent with the 2.7V UVLO limit. Procedure The MAX256 EV kit is fully assembled and tested. The MAX256 is an integrated primary-side controller Follow the steps below to verify board operation. and H-bridge driver for isolated power-supply circuits. Caution: Do not turn on the power supply until all con- The device contains an on-board oscillator, protection nections are completed. circuitry, and internal H-bridge FET drivers to provide up to 3W of power to the primary winding of a trans- 1) Connect a voltmeter to the +VOUT pad and SGND. former. The MAX256 operates using the internal pro- 2) Connect the second voltmeter to the -VOUT pad grammable oscillator, or can be driven by an external and SGND. clock for improved EMI performance. Regardless of the 3) Connect a 1A meter in series with the 100mA load clock source used, an internal flip-flop stage guaran- to +VOUT. Connect the load ground to the SGND tees a fixed 50% duty cycle to prevent DC current flow PC pad. in the transformer. 4) Connect the second 1A meter in series with the The MAX256 operates from a single-supply voltage and 100mA load to -VOUT. Connect the load ground to includes UVLO for controlled startup. The device pre- the SGND PC pads. vents cross-conduction of the H-bridge MOSFETs by implementing break-before-make switching. Thermal 5) Verify that a shunt is installed across pins 2-3 of shutdown circuitry provides additional protection jumper JU1 (400kHz internal oscillator) and that a against damage due to overtemperature conditions. shunt is not installed across the pins of jumper JU2 (mode = enabled). The MAX256 ICs UVLO provides controlled turn-on during power-up and during brownouts. If the input 6) Connect the +5V power supply to the VCC pad. voltage at VCC falls below 1.9V (typ), the MAX256 IC Connect the power supplys ground to the GND shuts down. The MAX256 driver switches nominally at pad. 400kHz frequency, set by resistor R1. The switching- 7) Turn on the power supply and verify that the volt- frequency duty cycle is fixed at 50% to control energy meter at +VOUT reads approximately +6V. transfer to the isolated outputs. 8) Verify that the voltmeter at -VOUT reads approxi- The PCB is designed for 1500V isolation, with 300 RMS mately -6V. mils spacing between the GND and SGND planes. The The +5V supply powering the MAX256 EV kit must be bottom PCB GND plane under U1 is utilized as a ther- current-limited at 1A and the output load current for mal heatsink for power dissipation of the MAX256 ICs each output limited to less than 300mA. 2 Evaluates: MAX256