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MAX4772EUT Datasheet(PDF) 7 Page - Maxim Integrated Products |
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MAX4772EUT Datasheet(HTML) 7 Page - Maxim Integrated Products |
7 / 10 page Reverse-Current Protection The MAX4772/MAX4773 limit the reverse current (VOUT to VIN) from exceeding the maximum IREV value. The switch is shut off and FLAG is asserted if the reverse current-limit condition persists for more than the blanking time. This feature prevents excessive reverse currents from flowing through the device. Switch-On/Off Control Toggle ON high to enable the current-limited switches. When a forward/reverse current fault is present or the die exceeds the thermal-shutdown temperature of +150°C, OUT is internally disconnected from IN and the supply current decreases to 8µA (latch off). The switch is now operating in one of its off states. The switch-off state also occurs when driving ON low, thus reducing the supply current (shutdown) to 0.01µA. Table 1 illustrates the ON/OFF state of the MAX4772/MAX4773 current-limit switches. FLAG Indicator The MAX4772/MAX4773 feature a fault output (FLAG). Whenever an overcurrent condition is encountered, the MAX4772 latches FLAG low and turns the switch off. The MAX4773 latches FLAG low and keeps it low until the overcurrent conditon is removed. During this time, the switch cycles on and off in the autoretry mode. When the overcurrent condition is removed, FLAG deasserts and the switch turns on (Figure 4). FLAG is an open-drain output transistor and requires an external pullup resistor from FLAG to IN. During shut- down (ON is low), the pulldown on FLAG output is released in order to limit power dissipation. FLAG goes low when any of the following conditions occur: • The die temperature exceeds the thermal-shutdown temperature limit of +150°C. • The device is in current limit for more than the fault- blanking period. • The switch is in autoretry. Autoretry (MAX4773) When the forward or reverse current-limit threshold is exceeded, tBLANK timer begins counting (Figure 4). The timer resets if the overcurrent condition disappears before tBLANK has elapsed. A retry time delay (tRETRY) is started immediately after tBLANK has elapsed and during that time, the switch is latched off and FLAG asserts. At the end of tRETRY, the switch is turned on again. If the fault still exists, the cycle is repeated. If the fault has been removed, the switch stays on and FLAG deasserts. 200mA/500mA Selectable Current-Limit Switches _______________________________________________________________________________________ 7 ON FAULT SWITCH ON/OFF SUPPLY CURRENT MODE Low X OFF Shutdown High Thermal OFF immediately (tBLANK period does not apply) Latch off OFF after tBLANK period has elapsed Latch off High Current Limit ON during tBLANK period, OFF during tRETRY period for the MAX4773 cycle repeats until fault is removed See the Autoretry section Table 1. MAX4772/MAX4773 Switch Truth Table Figure 2. MAX4772/MAX4773 Power-Up Sequence (VSEL Rises after Power-Up) VIN VIN ≥ 2V VSEL ISEL 100 µA (MAX) VIH 200mA 500mA Figure 3. MAX4772 Power-Up Sequence (VSEL and VIN Rise Simultaneously) VIN VIN = 2V VSEL ISEL 500mA |
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