Evaluates: MAX6397 MAX6397 Evaluation Kit General Description Quick Start The MAX6397 evaluation kit (EV kit) demonstrates a Procedure high-voltage overvoltage protection circuit for applications The MAX6397 EV kit is fully assembled and tested. that must survive load dump and high-voltage transient Follow these steps to verify operation. Do not turn on conditions. This EV kit is a fully assembled and tested the power supply until all connections are completed. surface-mount board. 1) Connect a DC power supply (0 to 20V or above, 5A or The EV kit supports high-output currents up to 5A, runs depending on load) to VIN1 and GND. at voltages up to 72V, and can withstand temperatures 2) Connect a voltmeter or oscilloscope and a load (if ranging from -40C to +105C. Two alternate voltage desired) to OUT and GND. inputs implement two different schemes for reverse- battery protection. Connections to the on-chip linear 3) Make sure the J2 shunt connects pins 1 and 2 regulator, capable of driving 100mA, and the power-good (overvoltage-protect mode). The J4 shunt should con- (POK) signal are also provided. nect pins 1 and 2. 4) Turn on the power supply and increase the input Features voltage. The output turns on when the input voltage 5.5V to 72V Wide Supply Voltage Range reaches 5.5V. Increase the supply voltage further the Up to 5A Output Current Capacity output turns off when the input voltage reaches 17V. Selectable Overvoltage Mode and Overvoltage- 5) The above steps can be followed for a power supply Limiter Mode connected to VIN2 or VIN3. The thresholds for turn on Adjustable Overvoltage Threshold and turn off for inputs VIN2 and VIN3 are higher due to 100V Reverse-Battery Protection the voltage drop across the reverse-battery protection. Always-On Linear Regulator Output 6) Check the linear regulator output and POK signal. Power-Good Signal Output Ordering Information PART TYPE MAX6397EVKIT EV Kit 19-4003 Rev 2 4/15Evaluates: MAX6397 MAX6397 Evaluation Kit The minimum output voltage in overvoltage-limiter mode Detailed Description depends on load current, output capacitance, and the The MAX6397 EV kit demonstrates a high-voltage MOSFETs switching period. The MAX6397 EV kit comes overvoltage-protection circuit for applications that must with one 22F capacitor at the output to supply the survive load dump and high-voltage transient conditions. load during the time when the MOSFET is off. Connect This EV kit can be configured in overvoltage mode or the optional electrolytic capacitor C13 (150F, 100V) to overvoltage limiter mode by setting jumper J2 (see Table 1 support load currents higher than 0.5A when the EV kit for the jumper settings), and can supply up to 5A of output operates in overvoltage limiter mode. current. Add capacitor C3 on the gate of MOSFET M1 to decrease The MAX6397 EV kit has three positive power-supply the frequency of the sawtooth waveform. This process inputs: VIN1, VIN2, and VIN3. Inputs VIN2 and VIN3 helps limit the devices power dissipation. have diode-based and p-channel MOSFET-based reverse- battery protections, respectively, and VIN1 bypasses all Linear Regulator Output and Power-Good reverse-battery protections. Signal Connections are also included for the linear regulator Overvoltage Mode output and the power-good (POK) signal. The linear In overvoltage mode, the MAX6397 monitors the input regulator supplies up to 100mA at 5V, limited by the voltage and turns off the series-pass n-channel MOSFET ambient temperature, the input/output voltages, and the (M1) when the input voltage exceeds the programmed package power dissipation. The POK signal has a 100k threshold voltage. As soon as the input voltage drops resistor (R3) to the regulator output. The linear regulator is below the overvoltage threshold, the MAX6397 charge always on regardless of the state of SHDN. pump fully enhances MOSFET M1 to turn the output back on. The voltage-divider formed by R1 and R2 sets the Jumper Selection threshold voltage. The resistors provided in the MAX6397 To filter fast transients that may be present at the input EV kit set the threshold at 17V. If inputs VIN2 or VIN3 are from reaching the MAX6397, place a small resistor, R4, used, this threshold is higher due to the voltage drop in (10, for example) on the board, and cut jumper J1. D1 or M2. Three-pin jumper J2 selects between overvoltage mode The overvoltage threshold can be adjusted by varying R1 and overvoltage limiter mode do not leave this jumper or R2 using the equation below: unconnected. Three-pin jumper J3 controls the gate drive of p-channel MOSFET M3 used as a reverse- battery V OV protection. Use J3 to disconnect resistor R5 when M3 is R1 1 R2 1.215 not used to avoid supply leakage through R5. Three-pin jumper J4 controls the SHDN pin of the MAX6397 and where V is the desired overvoltage threshold. To main- OV can enable or disable the MOSFET M1 enhancement. tain threshold accuracy, R2 must be less than 250k. Table 1 lists the jumper options. Since the EV kit ships with R2 set at 49.9k, use the for- mula above to change the threshold by changing R1 only. Table 1. Jumper Function Overvoltage-Limiter Mode SHUNT POSITION AND FUNCTION JUMPER In overvoltage-limiter mode, the MAX6397 monitors 1 and 2 2 and 3 the output voltage instead of the input voltage. The J1 Shorted: RC input filter disabled* output voltage is sensed through the same voltage- divider formed by R1 and R2, so the equation given for Overvoltage limiter J2 Overvoltage mode* mode overvoltage mode also applies to the threshold voltage in overvoltage limiter mode. During an input overvoltage M2 gate drive is M2 gate drive is J3 transient in this mode, the MOSFET switches off until the disabled* enabled output voltage falls to 95% of the threshold voltage, and J4 U1 is enabled* U1 is disabled then the MOSFET switches back on. This cycle repeats, *Default position. generating a sawtooth waveform on the output. Maxim Integrated 2 www.maximintegrated.com =