NCV8502DEMO/D Demonstration Note for NCV8502 Adding Additional Current Capability to the NCV8502 (Adjustable Output Voltage Option) http://onsemi.com DEMONSTRATION NOTE Description The NCV8502A High Current Demo board highlights the procedure for increasing the output current capability of the NCV8502. This is accomplished by adding a discrete driver to the application with the adjustable version of the NCV8502. The combination of the NCV8502 and the MJD31C will supply greater than 1.0 A of current to the user programmable output voltage. It is intended for the user to make use of the flexibility of the parts output voltage using a discrete resistor feedback divider. In this demonstration board, a potentiometer has been added to display the parts’ output availability in fixed output voltages from 2.5 V to 10 V. The capability of the output voltage has an absolute maximum voltage of 20 V on the IC, and must be maintained below this level. This demo board uses a 16 V capacitor on the output limiting its use to 16 V. The NCV8502’s capability extends up to 60 V, but should be avoided here to prevent damage to the capacitor. Connection to the parts Flag/Monitor function has been made available via two external posts on the board. The intention of this function is to provide an early warning signal to the microprocessor that there is an impending reset that will occur, and the microprocessor should finish its current instruction. This comparator may also be used as a general use comparator. The positive input terminal is connected to the parts temperature stable reference (refer to the NCV8502/D data sheet for details). This demonstration board is also a valid evaluation constituent for evaluation of the NCV8501 series of parts. Features • Automotive Grade • User Selectable Output Voltage • 1.0 A Capability • Early Warning through Flag/Monitor Function Figure 1. NCV8502A High Current Demonstration Board Semiconductor Components Industries, LLC, 2004 April, 2004 − Rev. 3 1 Publication Order Number: NCV8502DEMO/D NCV8502DEMO/D MON FLAG U1 VIN C2 0.1 µF VIN VOUT MON VADJ N/C FLAG N/C GND Q1 MJD31C VOUT C3* 0.01 µF R1 294 k NCV8502A C1 47 µF GND R2 39 k CW R4 750 k R3 500 k *Eliminates potential overshoot. Figure 2. Demonstration Circuit Schematic OPERATION GUIDELINES • There is no current limiting for the MJD31C. Do not • • • • • A minimum 10 mA load is required for this board for overstress the device. Consider your power dissipation before running tests. The VADJ reference voltage is typically 1.20 V. Design your output voltage around that voltage. Thermal effects will affect the potentiometer at a different rate than the discrete surface mount resistors. The output capacitor C1 is rated at 16 V. Maintain operation below this level. • stability considerations. Your output capacitor value may differ depending on board layout and loading. Your capacitor value may actually decrease with the removal of the trim potentiometer. R4 is mounted under the board across the potentiometer. Alternatively, R3 and R4 may be replaced by a single 250 k potentiometer, but doing so may not show the full range of output voltage. BOARD USE Simply connect a power supply from VIN to ground in addition to your load (10 mA minimum) on VOUT to ground. Turning the adjustment screw of the potentiometer will move your output voltage to the voltage extremes of 2.5 V and 10 V. Using the flag/monitor function will require a pull−up resistor on the FLAG output as it is an open collector output. Switching of the FLAG output will occur as the voltage threshold on the monitor (MON) input is crossed at about 1.20 V. http://onsemi.com 2 NCV8502DEMO/D VIN 1 8 VOUT VADJ FLAG MON NC NC GND Figure 3. Pin Connections, SO−8 VOUT VIN Current Source (Circuit Bias) IBIAS Current Limit Sense + + − RADJ IBIAS + − VBG Error Amplifier RESET VBG + − Fixed Voltage only 1.8 V Thermal Protection 3.0 µA Delay IBIAS Bandgap Reference VBG VADJ VBG 20 k Adjustable Version only GND IBIAS FLAG + − MON Figure 4. Block Diagram BILL OF MATERIALS Item Qty Reference Part Mfg. & P/N 1 1 C1 47 µF, 16 V, SMT, Tantalum Kemet Digikey, 800−344−4539 2 1 C2 0.1 µF, 50 V, 1206, Ceramic Kemet Digikey, 800−344−4539 3 1 C3 0.01 µF, 50 V, 1206, Ceramic Kemet Digikey, 800−344−4539 4 1 Q1 NPN Power Transistor ON Semiconductor, MJD31C ON Semiconductor, 800−282−9855 5 1 R1 Resistor 1206, Surface Mount Panasonic, 294 k, 1% Digikey, 800−344−4539 6 1 R2 Resistor 1206, Surface Mount Panasonic, 39 k, 1% Digikey, 800−344−4539 7 1 R3 Resistor Potentiometer Bournes Trimpot, 3006P−1−504 Mouser, 800−346−6873 8 1 R4 Resistor, Carbon Composition Ohmite, 750 k, 1/4 W, 5% Digikey, 800−344−4539 9 1 U1 150 mA Linear Regulator ON Semiconductor, NCV8502DADJ ON Semiconductor, 800−282−9855 http://onsemi.com 3 Distributor NCV8502DEMO/D PRINT CIRCUIT BOARD LAYOUT Figure 5. Top Layer and Top Silk Figure 6. Bottom Layer Shown from Top Perspective with Top Silk ON Semiconductor and are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC reserves the right to make changes without further notice to any products herein. SCILLC makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does SCILLC assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidental damages. “Typical” parameters which may be provided in SCILLC data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. All operating parameters, including “Typicals” must be validated for each customer application by customer’s technical experts. SCILLC does not convey any license under its patent rights nor the rights of others. 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