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TC660CPA 参数 Datasheet PDF下载

TC660CPA图片预览
型号: TC660CPA
PDF下载: 下载PDF文件 查看货源
内容描述: 百毫安充电泵DC- TO- DC电压转换器 [100mA CHARGE PUMP DC-TO-DC VOLTAGE CONVERTER]
分类和应用: 转换器光电二极管
文件页数/大小: 8 页 / 124 K
品牌: TELCOM [ TELCOM SEMICONDUCTOR, INC ]
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100mA CHARGE PUMP DC-TO-DC  
VOLTAGECONVERTER  
4
TC660  
Circuit Description  
S
S
1
The TC660 contains all the necessary circuitry to com-  
plete a voltage inverter (Figure 1), with the exception of two  
externalcapacitors,whichmaybeinexpensive150µFpolar-  
ized electrolytic capacitors. Operation is best understood by  
considering Figure 2, which shows an idealized voltage  
inverter. Capacitor C1 is charged to a voltage V+ for the half  
cycle when switches S1 and S3 are closed. (Note: Switches  
S2 andS4 areopenduringthishalfcycle.)Duringthesecond  
half cycle of operation, switches S2 and S4 are closed, with  
S1 and S3 open, thereby shifting capacitor C1 negatively by  
V+ volts. Charge is then transferred from C1 to C2, such that  
the voltage on C2 is exactly V+, assuming ideal switches and  
no load on C2.  
2
+
V
C
C
1
2
S
S
3
4
V
= – V  
OUT  
IN  
GND  
The four switches in Figure 2 are MOS power switches;  
S1 is a P-channel device, and S2, S3 and S4 are N-channel  
devices. The main difficulty with this approach is that in  
integrating the switches, the substrates of S3 and S4 must  
always remain reverse-biased with respect to their sources,  
but not so much as to degrade their ON resistances. In  
addition, at circuit start-up, and under output short circuit  
conditions (VOUT = V+), the output voltage must be sensed  
and the substrate bias adjusted accordingly. Failure to  
accomplish this would result in high power losses and  
possible device latch-up. This problem is eliminated in the  
TC660 by a logic network which senses the output voltage  
(VOUT) together with the level translators, and switches the  
substrates of S3 and S4 to the correct level to maintain  
necessary reverse bias.  
Figure 2. Idealized Switched Capacitor  
Theoretical Power Efficiency  
Considerations  
In theory, a voltage multiplier can approach 100%  
efficiency if certain conditions are met:  
(1) The drive circuitry consumes minimal power.  
(2) The output switches have extremely low ON  
resistance and virtually no offset.  
(3) The impedances of the pump and reservoir  
capacitors are negligible at the pump frequency.  
The TC660 approaches these conditions for negative  
voltage multiplication if large values of C1 and C2 are used.  
Energy is lost only in the transfer of charge between  
capacitors if a change in voltage occurs. The energy lost  
is defined by:  
To improve low-voltage operation, the “LV” pin should  
be connected to GND, disabling the internal regulator. For  
supply voltages greater than 3.0V, the LV terminal should  
be left open to ensure latch-up-proof operation and prevent  
device damage.  
2
E = 1/2 C1 (V12 – V2 )  
V1 and V2 are the voltages on C1 during the pump and  
transfer cycles. If the impedances of C1 and C2 are relatively  
high at the pump frequency (refer to Figure 2) compared to  
the value of RL, there will be a substantial difference in  
voltages V1 and V2. Therefore, it is desirable not only to  
make C2 as large as possible to eliminate output voltage  
ripple, but also to employ a correspondingly large value for  
C1 in order to achieve maximum efficiency of operation.  
+
V
I
S
1
2
3
4
8
7
6
5
+
V
(+5V)  
+
C
TC660  
1
150 µF  
R
L
I
L
V
OUT  
C
2
150 µF  
+
Figure 1. TC660 Test Circuit (Inverter)  
TELCOM SEMICONDUCTOR, INC.  
4-9