TC7662A 查看數據表（PDF） - Microchip Technology
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TC7662A Datasheet PDF : 16 Pages
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TC7662A
4.2 Output Ripple
ESR also affects the ripple voltage seen at the output.
The total ripple is determined by 2 voltages, A and B,
as shown in Figure 4-2. Segment A is the voltage drop
across the ESR of CR at the instant it goes from being
charged by CP (current flowing into CR) to being dis-
charged through the load (current flowing out of CR).
The magnitude of this current change is 2 x IOUT, hence
the total drop is 2 x IOUT x ESRCR volts. Segment B is
the voltage change across CR during time t2, the half of
the cycle when CR supplies current to the load. The
drop at B is IOUT x t2/CR volts. The peak-to-peak ripple
voltage is the sum of these voltage drops:
( ) 1
VRIPPLE 2 x fPUMP x CR+ 2 x ESRCR x IOUT
FIGURE 4-2:
OUTPUT RIPPLE
t2
t1
0
V
-(VDD)
B
A
4.3 Paralleling Devices
Any number of TC7662A voltage converters may be
paralleled to reduce output resistance (Figure 4-3).
The reservoir capacitor, CR, serves all devices, while
each device requires its own pump capacitor, CP. The
resultant output resistance would be approximately:
ROUT =
ROUT (of TC7662A)
n (number of devices)
4.4 Cascading Devices
The TC7662A may be cascaded as shown (Figure 4-4)
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 approximately the weighted sum of the
individual TC7662A ROUT values.
FIGURE 4-3:
PARALLELING DEVICES LOWERS OUTPUT IMPEDANCE
VDD
1
8
2
7
TC7662A
C1
3
6
4
"1"
5
1
8
2
7
RL
TC7662A
C1
3
6
4
"n"
5
+ C2
FIGURE 4-4:
INCREASED OUTPUT VOLTAGE BY CASCADING DEVICES
VDD
+
10μF
1
8
2
7
TC7662A
3
6
4
"1"
5
+
10μF
1
8
2 TC7662A 7
3
6
4
"n"
5
10μF
VOUT*
+ 10μF
*VOUT = -nVDD
2001-2012 Microchip Technology Inc.
DS21468B-page 7
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