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TC7660HCOA 数据表(PDF) 4 Page - Microchip Technology |
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TC7660HCOA 数据表(HTML) 4 Page - Microchip Technology |
4 / 8 page 4 TC7660H HIGH FREQUENCY 7660 DC-TO-DC VOLTAGE CONVERTER TC7660H-2 10/1/96 © 2001 Microchip Technology Inc. DS21466A 2 2 πf C1 XC = = 2.12 Ω, where f = 150kHz and C1 = 1.0µF. ROUT (of TC7660H) n (number of devices) ROUT = Paralleling Devices Any number of TC7660H voltage converters may be paralleled to reduce output resistance (Figure 4). The reser- voir capacitor, C2, serves all devices, while each device requires its own pump capacitor, C1. The resultant output resistance would be approximately: Cascading Devices The TC7660H may be cascaded as shown in (Figure 4) to produce larger negative multiplication of the initial supply voltage. However, due to the finite efficiency of each device, the practical limit is probably 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 TC7660H ROUT values. Changing the TC7660H Oscillator Frequency It may be desirable in some applications (due to noise or other considerations) to increase or decease the oscillator frequency. This can be achieved by overdriving the oscilla- tor from an external clock, as shown in Figure 6. In order to prevent possible 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. Simple Negative Voltage Converter Figure 3 shows typical connections to provide a nega- tive supply where a positive supply is available. A similar scheme may be employed for supply voltages anywhere in the operating range of +1.5V to +10V, keeping in mind that pin 6 (LV) is tied to the supply negative (GND) only for supply voltages below 3.5V. The output characteristics of the circuit in Figure 3 are those of a nearly ideal voltage source in series with 70 Ω. Thus, for a load current of – 10 mA and a supply voltage of +5V, the output voltage would be – 4.3V. The dynamic output impedance of the TC7660H is due, primarily, to capacitive reactance of the charge transfer capacitor (C1). Since this capacitor is connected to the output for only 1/2 of the cycle, the equation is: 1 2 3 4 8 7 6 5 TC7660H 1.0 µF + V + 1.0 µF + VOUT* 1. VOUT = –n V + for 1.5V V + 10V NOTES: * C1 C2 Figure 3. Simple Negative Converter Figure 4. Increased Output Voltage by Cascading Devices 1 2 3 4 8 7 6 5 V + 1 2 3 4 8 7 6 5 1.0 µF 1.0 µF "n" "1" 1.0 µF VOUT 1. VOUT = –n V + for 1.5V V 10V + NOTES: * * + + + TC7660H TC7660H |
类似零件编号 - TC7660HCOA |
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类似说明 - TC7660HCOA |
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