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LM2660M bảng dữ liệu(PDF) 6 Page - National Semiconductor (TI) |
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LM2660M bảng dữ liệu(HTML) 6 Page - National Semiconductor (TI) |
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6 / 12 page  Pin Description Pin Name Function Voltage Inverter Voltage Doubler 1 FC Frequency control for internal oscillator: Same as inverter. (LM2660) FC = open, f OSC = 10 kHz (typ); FC = V+, f OSC = 80 kHz (typ); FC has no effect when OSC pin is driven externally. 1SD (LM2661) Shutdown control pin, tie this pin to the ground in normal operation, and to V+ for shutdown. Same as inverter. 2 CAP+ Connect this pin to the positive terminal of charge-pump capacitor. Same as inverter. 3 GND Power supply ground input. Power supply positive voltage input. 4 CAP− Connect this pin to the negative terminal of charge-pump capacitor. Same as inverter. 5 OUT Negative voltage output. Power supply ground input. 6 LV Low-voltage operation input. Tie LV to GND when input voltage is less than 3.5V. Above 3.5V, LV can be connected to GND or left open. When driving OSC with an external clock, LV must be connected to GND. LV must be tied to OUT. 7 OSC Oscillator control input. OSC is connected to an internal 15 pF capacitor. An external capacitor can be connected to slow the oscillator. Also, an external clock can be used to drive OSC. Same as inverter except that OSC cannot be driven by an external clock. 8 V+ Power supply positive voltage input. Positive voltage output. Circuit Description The LM2660/LM2661 contains four large CMOS switches which are switched in a sequence to invert the input supply voltage. Energy transfer and storage are provided by exter- nal capacitors. Figure 2 illustrates the voltage conversion scheme. When S 1 and S3 are closed, C1 charges to the sup- ply voltage V+. During this time interval switches S 2 and S4 are open. In the second time interval, S 1 and S3 are open and S 2 and S4 are closed, C1 is charging C2. After a number of cycles, the voltage across C 2 will be pumped to V+. Since the anode of C 2 is connected to ground, the output at the cathode of C 2 equals −(V+) assuming no load on C2, no loss in the switches, and no ESR in the capacitors. In reality, the charge transfer efficiency depends on the switching fre- quency, the on-resistance of the switches, and the ESR of the capacitors. Application Information SIMPLE NEGATIVE VOLTAGE CONVERTER The main application of LM2660/LM2661 is to generate a negative supply voltage. The voltage inverter circuit uses only two external capacitors as shown in the Basic Applica- tion Circuits. The range of the input supply voltage is 1.5V to 5.5V. For a supply voltage less than 3.5V, the LV pin must be connected to ground to bypass the internal regulator cir- cuitry. This gives the best performance in low voltage appli- cations. If the supply voltage is greater than 3.5V, LV may be connected to ground or left open. The choice of leaving LV open simplifies the direct substitution of the LM2660/ LM2661 for the LMC7660 Switched Capacitor Voltage Con- verter. The output characteristics of this circuit can be approximated by an ideal voltage source in series with a resistor. The volt- age source equals −(V+). The output resistance R out is a function of the ON resistance of the internal MOS switches, the oscillator frequency, and the capacitance and ESR of C 1 and C 2. A good approximation is: where R SW is the sum of the ON resistance of the internal MOS switches shown in Figure 2. High value, low ESR capacitors will reduce the output resis- tance. Instead of increasing the capacitance, the oscillator frequency can be increased to reduce the 2/(f osc xC1) term. Once this term is trivial compared with R SW and ESRs, fur- ther increasing in oscillator frequency and capacitance will become ineffective. DS012911-21 FIGURE 2. Voltage Inverting Principle www.national.com 6 |
Số phần tương tự - LM2660M |
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Mô tả tương tự - LM2660M |
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