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TC7660IJA データシート(PDF) 7 Page - Microchip Technology |
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TC7660IJA データシート(HTML) 7 Page - Microchip Technology |
7 / 12 page 7 TC7660 CHARGE PUMP DC-TO-DC VOLTAGE CONVERTER © 2001 Microchip Technology Inc. DS21465A TC7660-7 9/30/96 Figure 5. Increased Output Voltage by Cascading Devices Figure 4. Paralleling Devices Lowers Output Impedance device latch-up, a 1k Ω resistor must be used in series with the clock output. In a situation where the designer has generated the external clock frequency using TTL logic, the addition of a 10k Ω pull-up resistor to V+ supply is required. Note that the pump frequency with external clocking, as with internal clocking, will be 1/2 of the clock frequency. Output transitions occur on the positive-going edge of the clock. It is also possible to increase the conversion efficiency of the TC7660 at low load levels by lowering the oscillator frequency. This reduces the switching losses, and is achieved by connecting an additional capacitor, COSC, as shown in Figure 7. Lowering the oscillator frequency will cause an undesirable increase in the impedance of the pump (C1) and the reservoir (C2) capacitors. To overcome this, increase the values of C1 and C2 by the same factor that the frequency has been reduced. For example, the addition of a 100pF capacitor between pin 7 (OSC) and pin 8 (V+) will lower the oscillator frequency to 1kHz from its nominal frequency of 10kHz (a multiple of 10), and necessitate a corresponding increase in the values of C1 and C2 (from 10µF to 100µF). Cascading Devices The TC7660 may be cascaded as shown (Figure 6) to produce larger negative multiplication of the initial supply voltage. However, due to the finite efficiency of each device, the practical limit is 10 devices for light loads. The output voltage is defined by: VOUT = –n (VIN) where n is an integer representing the number of devices cascaded. The resulting output resistance would be ap- proximately the weighted sum of the individual TC7660 ROUT values. Changing the TC7660 Oscillator Frequency It may be desirable in some applications (due to noise or other considerations) to increase the oscillator frequency. This is achieved by overdriving the oscillator from an exter- nal clock, as shown in Figure 6. In order to prevent possible 1 2 3 4 8 7 6 5 TC7660 V + 1 2 3 4 8 7 6 5 TC7660 C1 RL C2 C1 "n" "1" + 1 2 3 4 8 7 6 5 V + 1 2 3 4 8 7 6 5 10 µF 10 µF "n" "1" 10 µF VOUT 1. VOUT = –n V + for 1.5V V 10V + NOTES: * * + + + TC7660 TC7660 |
同様の部品番号 - TC7660IJA |
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同様の説明 - TC7660IJA |
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