參數(shù)資料
型號(hào)： TL7660IP
廠商： TEXAS INSTRUMENTS INC
元件分類(lèi)： 穩(wěn)壓器
英文描述： SWITCHED CAPACITOR CONVERTER, 9 kHz SWITCHING FREQ-MAX, PDIP8
封裝： ROHS COMPLIANT, PLASTIC, DIP-8
文件頁(yè)數(shù)： 22/22頁(yè)
文件大?。?/td> 566K
代理商： TL7660IP
www.ti.com
Typical Applications
Simple Negative Voltage Converter
1
2
3
4
8
7
6
5
+
TL7660
+
-
10 F
V+
10 F
V
= –V+
OUT
CMOS VOLTAGE CONVERTER
SCAS794 – JUNE 2006
APPLICATION INFORMATION (continued)
The majority of applications will undoubtedly utilize the TL7660 for generation of negative supply voltages.
Figure 3 shows typical connections to provide a negative supply negative (GND) for supply voltages below
3.5 V.
Figure 3. Simple Negative-Voltage Converter
The output characteristics of the circuit in Figure 3 can be approximated by an ideal voltage source in series with
a resistance. The voltage source has a value of –VCC. The output impedance (RO) is a function of the ON
resistance of the internal MOS switches (shown in Figure 2), the switching frequency, the value of C1 and C2,
and the ESR (equivalent series resistance) of C1 and C2. A good first order approximation for RO is:
RO ≈ 2(RSW1 + RSW3 + ESRC1) + 2(RSW2 + RSW4 + ESRC1)
RO ≈ 2(RSW1 + RSW3 + ESRC1) + 1/fPUMPC1 + ESRC2
Where fPUMP = fOSC/2 , RSWX = MOSFET switch resistance.
Combining the four RSWX terms as RSW, we see that:
RO ≈ 2 (RSW) + 1/fPUMPC1 + 4 (ESRC1) + ESRC2
RSW, the total switch resistance, is a function of supply voltage and temperature (See the Output Source
Resistance graphs). Careful selection of C1 and C2 reduces the remaining terms, minimizing the output
impedance. High value capacitors reduce the 1/fPUMPC1 component, and low ESR capacitors lower the ESR
term. Increasing the oscillator frequency reduces the 1/fPUMPC1 term but may have the side effect of a net
increase in output impedance when C1 > 10 F and there is no longer enough time to fully charge the capacitors
every cycle. In a typical application where fOSC = 10 kHz and C = C1 = C2 = 10 F:
RO ≈ 2(23) + 1/(5 × 10
3)(10–5) + 4(ESR
C1) + ESRC2
RO ≈ 46 + 20 + 5 (ESRC)
Because the ESRs of the capacitors are reflected in the output impedance multiplied by a factor of 5, a high
value could potentially swamp out a low 1/fPUMPC1 term, rendering an increase in switching frequency or filter
capacitance ineffective. Typical electrolytic capacitors may have ESRs as high as 10
.
9
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
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