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MAX883C Datasheet(PDF) 11 Page - Maxim Integrated Products |
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MAX883C Datasheet(HTML) 11 Page - Maxim Integrated Products |
11 / 17 page 5V/3.3V or Adjustable, Low-Dropout, Low IQ, 200mA Linear Regulators ______________________________________________________________________________________ 11 Reverse-Current Protection The MAX882/MAX883/MAX884 have a unique protection scheme that limits reverse currents when the input volt- age falls below the output. It monitors the voltages on IN and OUT and switches the IC’s substrate and power bus to the more positive of the two. The control circuitry is then able to remain functioning and turn the pass transis- tor off, limiting reverse currents back through to the input of the device. In this mode, typical current into OUT to GND is 15µA at VOUT = 3.3V and 50µA at VOUT = 5V. Reverse-current protection activates when the voltage on IN falls 6mV (or 20mV max) below the voltage on OUT. Before this happens, currents as high as several milliamperes can flow back through the device. Low-Battery-Detection Comparator The MAX882/MAX883/MAX884 provide a low-battery com- parator that compares the voltage on the LBI pin to the 1.20V internal reference. LBO, an open-drain output, goes low when LBI is below 1.20V. Hysteresis of 7mV has been added to the low-battery comparator to provide noise immunity during switching. LBO remains functional in stand- by mode for the MAX882, but is undefined in OFF mode for the MAX883 and MAX884. Tie LBI to IN when not used. Use a resistor-divider network as shown in Figure 6 to set the low-battery trip voltage. Current into the LBI input is ±50nA (max), so R2 can be as large as 1M Ω. Add extra noise immunity by connecting a small capacitor from LBI to GND. Additional hysteresis can be added by connect- ing a high-value resistor from LBI to LBO. Applications Information The MAX882/MAX883/MAX884 are series linear regula- tors designed primarily for battery-powered systems. Figure 7 shows a typical application. Standby Mode vs. OFF Mode STBY is a comparator input that allows the user to set the standby-mode threshold voltage, while OFF is a logic-level input. When in standby mode, the output is disconnected from the input, but the biasing circuitry (including the low-battery comparator) is kept alive, causing the device to draw approximately 7µA. Standby mode is useful in applications where a low- battery comparator function is still needed in shutdown. A logic low at the OFF pin turns off all biasing circuitry, including the LBI/LBO comparator, and reduces supply current to less than 1µA. OFF mode is useful for maxi- mizing battery life. There is little difference in the time it takes to exit standby mode or OFF mode. Output Capacitor Selection and Regulator Stability An output filter capacitor is required at the MAX882/ MAX883/MAX884 OUT pin. The minimum output capacitance required for stability is 2.2µF. MAX882 MAX883 MAX884 CIN O.1 µF COUT 2.2 µF OUTPUT VOLTAGE BATTERY LBO LBI OFF (STBY) ( ) ARE FOR MAX882. IN POWER- FAIL INDICATION R3 R1 + R2 R2 VLBI TRIP = VLBI , VLBI = 1.20V OUT GND SET R1 R2 MAX882 MAX883 MAX884 CIN O.1 µF COUT 2.2 µF OUTPUT VOLTAGE INPUT VOLTAGE BATTERY OFF (STBY) ON/OFF * * OPTIONAL REVERSE BATTERY PROTECTION ( ) ARE FOR MAX882. IN OUT GND SET LBI Figure 6. Using the Low-Battery Comparator to Monitor Battery Voltage Figure 7. Typical 3.3V or 5V Linear Regulator Circuit |
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