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MAX1697 Datasheet(PDF) 7 Page - Maxim Integrated Products |
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MAX1697 Datasheet(HTML) 7 Page - Maxim Integrated Products |
7 / 12 page Detailed Description The MAX1697 capacitive charge pumps invert the volt- age applied to their input. For highest performance, use low equivalent series resistance (ESR) capacitors (e.g., ceramic). During the first half-cycle, switches S2 and S4 open, switches S1 and S3 close, and capacitor C1 charges to the voltage at IN (Figure 2). During the second half- cycle, S1 and S3 open, S2 and S4 close, and C1 is level shifted downward by VIN volts. This connects C1 in par- allel with the reservoir capacitor C2. If the voltage across C2 is smaller than the voltage across C1, charge flows from C1 to C2 until the voltage across C2 reaches -VIN. The actual voltage at the output is more positive than -VIN, since switches S1–S4 have resistance and the load drains charge from C2. Efficiency Considerations The efficiency of the MAX1697 is dominated by its qui- escent supply current (IQ) at low output current and by its output impedance (ROUT) at higher output current; it is given by: η≅ + − ⋅ I II IR V OUT OUT Q OUT OUT IN 1 60mA, SOT23 Inverting Charge Pump with Shutdown _______________________________________________________________________________________ 7 0 100 50 200 150 300 250 350 450 400 500 0 234 1 567 9 810 MAX1697T OUTPUT RIPPLE vs. CAPACITANCE CAPACITANCE ( µF) VIN = +1.9V, VOUT = -1.5V VIN = +3.15V, VOUT = -2.5V VIN = +4.75V, VOUT = -4.0V 0 100 50 200 150 300 250 350 450 400 500 0 234 1 567 9 810 MAX1697U OUTPUT RIPPLE vs. CAPACITANCE CAPACITANCE ( µF) VIN = +1.9V, VOUT = -1.5V VIN = +3.15V, VOUT = -2.5V VIN = +4.75V, VOUT = -4.0V Pin Description 6 Positive Terminal of the Flying Capacitor 1 Inverting Charge-Pump Output 2 Power-Supply Voltage Input. Input range is 1.5V to 5.5V. 3 Negative Terminal of the Flying Capacitor 4 Ground 5 Shutdown Input. Drive this pin high for normal operation; drive it low for shutdown mode. OUT is actively pulled to ground during shutdown. PIN FUNCTION NAME C1+ OUT IN C1- GND SHDN Typical Operating Characteristics (continued) (Circuit of Figure 1, capacitors from Table 2, VIN = +5V, SHDN = IN, TA = +25°C, unless otherwise noted.) TE: ( C1 C2 21 5 ON OFF 3 RL 6 4 C3 C1+ C1- IN SHDN OUT GND INPUT 1.5V to 5.5V NEGATIVE OUTPUT -1 · VIN MAX1697 Figure 1. Typical Application Circuit |
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