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TC660CPA 数据表(PDF) 7 Page - TelCom Semiconductor, Inc |
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TC660CPA 数据表(HTML) 7 Page - TelCom Semiconductor, Inc |
7 / 8 page 4-11 TELCOM SEMICONDUCTOR, INC. 7 6 5 4 3 1 2 8 TC660 100mA CHARGE PUMP DC-TO-DC VOLTAGE CONVERTER 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 TC660 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 GND 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. Positive Voltage Doubler Figure 5. Increased Output Voltage by Cascading Devices 1 2 3 4 8 7 6 5 V + 1 2 3 4 8 7 6 5 150 µF 150 µF 150 µF "n" "1" 150 µF VOUT . VOUT = –n(V+) for 1.5V ≤ V+ ≤ 5.5V NOTE: * * + + + + TC660 TC660 Figure 6. External Clocking 1 2 3 4 8 7 6 5 TC660 + V + + CMOS GATE 150 µF VOUT 150 µF OSC V + Cascading Devices The TC660 may be cascaded as shown (Figure 5) 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 TC660 ROUT values. Changing the TC660 Oscillator Frequency It may be desirable in some applications (due to noise or other considerations) to increase the oscillator frequency. Pin 1, the FC pin, may be connected to V + to increase oscillator frequency to 90kHz from a nominal of 10 kHz for an input supply voltage of 5.0 volts. The oscillator may also be synchronized to an external clock as shown in Figure 6 and LV must be grounded when overdriving OSC. In a situation where the designer has generated the external Figure 7. Lowering Oscillator Frequency 1 2 3 4 8 7 6 5 + V + VOUT C1 COSC + C2 TC660 |
类似零件编号 - TC660CPA |
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类似说明 - TC660CPA |
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