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MAX6497 Datasheet(PDF) 7 Page - Maxim Integrated Products |
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MAX6497 Datasheet(HTML) 7 Page - Maxim Integrated Products |
7 / 16 page Detailed Description Overvoltage Monitoring When operating in overvoltage mode, the MAX6495– MAX6499 feedback path (Figure 1) consists of IN, OVSET’s internal comparator, the internal gate charge pump, and the external n-channel MOSFET, resulting in a switch-on/off function. When the programmed over- voltage threshold is tripped, the internal fast compara- tor turns off the external MOSFET, clamping GATE to OUTFB within 0.5µs and disconnecting the power source from the load. When IN decreases below the adjusted overvoltage threshold, the MAX6495–MAX6499 slowly enhance GATE above OUTFB, reconnecting the load to the power source. Overvoltage Limiter (MAX6495/MAX6496/MAX6499) When operating in overvoltage-limiter mode, the MAX6495/MAX6496/MAX6499 feedback path (Figure 2) consists of OUTFB, OVSET’s internal comparator, the internal gate charge pump, and the external n-channel MOSFET, resulting in the external MOSFET operating as a voltage regulator. During normal operation, GATE is enhanced 10V above OUTFB. The external MOSFET source voltage is moni- tored through a resistive divider between OUTFB and OVSET. When OUTFB rises above the adjusted over- voltage threshold, an internal comparator sinks the charge-pump current, discharging the external GATE, regulating OUTFB at the OVSET overvoltage threshold. OUTFB remains active during the overvoltage transients and the MOSFET continues to conduct during the over- voltage event, operating in switched-linear mode. As the transient begins decreasing, OUTFB fall time will depend on the MOSFET’s GATE charge, the internal charge-pump current, the output load, and the tank capacitor at OUTFB. For fast-rising transients and very large-sized MOSFETs, add an additional bypass capacitor from GATE to GND to reduce the effect of the fast-rising voltages at IN. The external capacitor acts as a voltage-divider working against the MOSFET’s drain-to-gate capacitance. For a 6000pF gate-to-source capacitance, a 0.1µF capacitor at GATE will reduce the impact of the fast-rising VIN input. Caution must be exercised when operating the MAX6495/MAX6496/MAX6499 in voltage-limiting mode for long durations. If the VIN is a DC voltage greater than the MOSFET’s maximum gate voltage, the MOSFET dis- sipates power continuously. To prevent damage to the external MOSFET, proper heatsinking should be imple- mented. GATE Voltage The MAX6495–MAX6499 use a high-efficiency charge pump to generate the GATE voltage. Upon VIN exceed- ing the 5V (typ) UVLO threshold, GATE enhances 10V above VIN (for VIN ≥ 14V) with a 100µA pullup current. An overvoltage condition occurs when the voltage at OVSET goes above its VTH+ threshold. When the threshold is crossed, GATE falls to OUTFB within 0.5µs with a 100mA pulldown current. The MAX6495–MAX6499 include an internal clamp to OUTFB that ensures GATE is limited to 18V (max) above OUTFB to prevent gate- to-source damage of the external MOSFET. 72V, Overvoltage-Protection Switches/ Limiter Controllers with an External MOSFET _______________________________________________________________________________________ 7 OVSET GND GATE IN OUTFB R1 VIN VOUT R2 MAX6495– MAX6499 Figure 1. Overvoltage Threshold (MAX6495–MAX6499) OVSET GND GATE IN OUTFB R1 COUT VIN VOUT R2 MAX6495 MAX6496 MAX6499 Figure 2. Overvoltage-Limiter Protection Switch Configuration |
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Similar Description - MAX6497 |
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