Evaluates: MAX756/MAX757 MAX756 Evaluation Kit General Description Features The MAX756 evaluation kit (EV kit) is a fully assembled Operates Down to 0.7V Input Supply Voltage and tested surface-mount printed circuit board. It can 87% Efficiency at 200mA also be modified to fit the adjustable-output MAX757. The MAX756/MAX757 are CMOS, step-up, DC-DC 60A Quiescent Current switching regulators for small, low input voltage or bat- 20A Shutdown Mode with Active Reference and tery-powered systems. The MAX756 accepts a positive input voltage down to 0.7V and converts it to a higher LBI Detector pin-selectable output voltage of 3.3V or 5V. The 500kHz Maximum Switching Frequency MAX757 is an adjustable version that accepts an input 1.5% Reference Tolerance Over Temperature voltage down to 0.7V and generates a higher adjustable output voltage in the 2.7V to 5.5V range. Typical full- Low-Battery Detector (LBI/LBO) load efficiencies for the MAX756/MAX757 are greater 8-Pin DIP and SO Packages than 87%. A movable jumper selects either 3.3V or 5.0V output Surface-Mount Construction voltage, and additional pads on the bottom of the board Fully Assembled and Tested are provided to place resistors for the LBI/LBO low-bat- tery detector and MAX757 output adjustment. Ordering Information PART TEMP. RANGE BOARD TYPE MAX756EVKIT-SO 0C to +70C Surface Mount EV Kit Quick Reference The MAX756 EV kit is a fully assembled and tested sur- face-mount board. Follow these steps to verify board operation. Do not turn on the power supply until all connec- tions are completed. 1. Connect a 1.8V to 5.5V supply to the pad marked VIN. The ground connects to the GND pad. 2. Connect a voltmeter and load (if any) to the VOUT pad. 3. Place the shunt on J1 across pins 1 and 2. 4. Place the shunt on J2 across pins 1 and 2 for a 5V output voltage. If a 3.3V output is desired, the shunt goes across pins 2 and 3, and the input voltage must be less than 3.6V. 5. Turn on the power and verify that the output voltage is 5V. 6. Refer to the section Using the MAX757 to modify the board for different output voltages. Maxim Integrated Products 1 Call toll free 1-800-998-8800 for free samples or literature. MAX756 Evaluation Kit and a 100mA load. The expected efficiency can be Component List taken from the graphs on the MAX756 data sheet. DESIGNATION QTY DESCRIPTION Under the above conditions, the MAX756 delivers 85% efficiency. C1 1 0.1F, 50V ceramic capacitor Input Power = (5.0V x 100mA) / 85% 100F, 10V, low-ESR tantalum Input Power = 588mW C2, C3 2 capacitors Sprague 595D107X0010D7 and Input Current = 588mW / 2.5V R1, R2, 0 Open Input Current = 235mA R3, R4, R5 Once started, the MAX756 actually operates at 10mA 22H power inductor output from the regulated output voltage. This means Sumida CD54-220, CoilCraft that the input voltage can fall below the 1.8V minimum L1 1 DT3316-223, Coiltronix CTX-20, guaranteed start-up voltage. Typically, the regulated Murata Erie LQH4N150K0M00 output will be maintained even if the input voltage (lower-current 30mA applications) drops to 0.7V. 1A, 20V Schottky diode (1N5817) Nihon EC15QS02L, Jumper Selection D1 1 Motorola MBRS130T3 Two 3-pin headers select the shutdown mode and output Collmer SE014, SE024 voltage. Table 1 lists the selectable jumper options. U1 1 MAX756CSA (8-pin SO) None 2 3-pin headers Using the Low-Battery Indicator None 2 Shunts The MAX756 has an additional comparator useful for None 1 2.00 x 2.00 PC board monitoring the input sources voltage level. Resistor locations R3 and R4 on the bottom of the printed circuit None 1 MAX756 data sheet board are connected as a voltage divider between the Refer to MAX756/MAX757 data sheet for component LBI pad and the MAX756 LBI pin. Note that a printed suppliers phone numbers. circuit board trace across R4 shorts the LBI pin to ground when this function is not used. Cut the trace before installing R4. Refer to the Low-Battery Detection Detailed Description section of the MAX756/MAX757 data sheet for instruc- Input Source tions on selecting values for resistors R3 and R4. The input source for the MAX756 evaluation board must be greater than 1.8V for guaranteed start-up (0.7V Table 1. Jumper Selection for operation once started), and less than the output voltage plus 0.5V. A typical input voltage range would J1 Shunt J2 Shunt SHDN Pin 3V/ Pin MAX756 be the 2.0V to 3.3V range of a 2-cell NiCd battery. An Location Location Connection Output Connection input voltage greater than the selected output voltage (but less than 7V) will not damage the circuit. However, the MAX756 output will equal the input volt- 1 & 2 1 & 2 VOUT GND 5.0V age minus the 0.3V drop of the Schottky diode, D1. 1 & 2 2 & 3 VOUT VOUT 3.3V The input current depends on the power delivered to the load. The following equations show how to calcu- 2 & 3 1 & 2 GND GND VIN -0.3V late the expected input current requirement. Input Power = Output Power / Efficiency 2 & 3 2 & 3 GND VOUT VIN -0.3V and Input Current = Input Power / Input Voltage To calculate the input current for a typical operating cir- cuit, assume a 2.5V input voltage, a 5V output voltage, 2 Evaluates: MAX756/MAX757 5V