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MAX667CSA Datasheet(PDF) 7 Page - Maxim Integrated Products |
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MAX667CSA Datasheet(HTML) 7 Page - Maxim Integrated Products |
7 / 9 page PNP transistor is turned on fully as regulation is lost. Even with a load current of a few microamperes, the base current will be driven above 5mA. Figure 8 shows how this base current may be significant. Consequently, a mostly discharged battery can be fur- ther discharged at end-of-life. Figure 6 shows how this condition can be modified by connecting DD to SHDN with a 47k Ω resistor, R1, paral- leled with a 0.1µF capacitor to GND. This modification reduces the no-load quiescent current to approximately 160µA when dropout is reached (Figure 9), but increas- es the dropout voltage by about 0.1V. The output volt- age drops to approximately 3V once DD begins to activate SHDN, but it does not fall to zero because SHDN is only partially activated. A second alternate connection (Figure 7) further reduces quiescent current near the dropout voltage, compared to the circuit in Figure 6. The output must be set with external resistors (R1, R2), so DD lowers the output voltage as the input voltage falls by sourcing current into SET via R3. Quiescent current remains low for inputs down to 3.5V, and peaks before falling to 0 at low input voltages. Although the current peak is higher than with the connection in Figure 6, this may be more useful because the quiescent current peaks at an input voltage well below the useful range of most batteries (Figure 9). Also, as IN falls below 5V, OUT tracks IN minus the dropout voltage. This connection still allows separate use of the SHDN input. Power Dissipation The MAX667 can regulate currents as high as 250mA and withstand input-output differential voltages as high as 15.2V, but not simultaneously. The maximum power dissipation is dependent on the package and the tem- perature (see Absolute Maximum Ratings). Figure 10 shows the maximum output current at various input-out- put differential voltages for the plastic DIP and SO packages. The MAX667 can withstand short-circuit loads up to 1 second. Operation from AC Sources The MAX667 is a micropower CMOS regulator intended principally for battery operation. When operating from AC sources, consider power-supply ripple rejection. The MAX667’s error amplifier produces very low gain bandwidth, and the input power-supply rejection ratio +5V/Programmable Low-Dropout Voltage Regulator _______________________________________________________________________________________ 7 +5V/Programmable Low-Dropout Voltage Regulator VIN (V) 800 0 12 4 6 200 600 35 400 CIRCUIT OF FIGURE 7 CIRCUIT OF FIGURE 6 Figure 9. Quiescent Current Below Dropout with Connections of Figures 6 and 7 VIN-VOUT (V) 400 0 015 100 300 200 10 5 GUARANTEED 250mA DIP PACKAGE DISSIPATION LIMIT SO PACKAGE DISSIPATION LIMIT TA = +50˚C Figure 10. MAX667 Load Current vs. Input-Output Differential Voltage Figure 11. Output Response to +4V/100µs Input Step +10V 1ms/div +6V INPUT +2V/div +5V OUTPUT +0.2V/div |
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