tc7662a Microchip Technology Inc., tc7662a Datasheet - Page 7

• Manufacturer Part Number: tc7662a
• Description: Charge Pump Dc-to-dc Converter
• Manufacturer: Microchip Technology Inc.

4.2
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 C
charged by C
charged through the load (current flowing out of C
The magnitude of this current change is 2 x I
the total drop is 2 x I
the voltage change across C
the cycle when C
drop at B is I
voltage is the sum of these voltage drops:
FIGURE 4-2:
FIGURE 4-3:
FIGURE 4-4:
 2002 Microchip Technology Inc.
V
0
-(V
V
DD
RIPPLE
)
Output Ripple
OUT
≅
P
(
B
10µF
*V
C
(current flowing into C
2 x f
1
OUT
x t
R
2
A
PUMP
= -nV
supplies current to the load. The
/C
R
OUT
+
t 2
at the instant it goes from being
R
OUTPUT RIPPLE
PARALLELING DEVICES LOWERS OUTPUT IMPEDANCE
INCREASED OUTPUT VOLTAGE BY CASCADING DEVICES
1
DD
volts. The peak-to-peak ripple
x ESR
x C
1
2
3
4
1
2
3
4
R
TC7662A
R
TC7662A
+ 2 x ESR
during time t
"1"
CR
t 1
"1"
volts. Segment B is
R
8
7
6
5
8
7
6
5
CR
) to being dis-
V
DD
2
x I
OUT
, the half of
V
DD
OUT
, hence
)
R
10µF
).
C
10µF
1
+
4.3
Any number of TC7662A voltage converters may be
paralleled to reduce output resistance (Figure 4-3).
The reservoir capacitor, C
each device requires its own pump capacitor, C
resultant output resistance would be approximately:
4.4
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:
V
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 R
OUT
1
2
3
4
1
2
3
4
TC7662A
= – n (V
TC7662A
"n"
Paralleling Devices
Cascading Devices
"n"
R
OUT
IN
8
7
6
5
)
=
8
7
6
5
n (number of devices)
R
OUT
OUT
values.
R
(of TC7662A)
, serves all devices, while
+
+
TC7662A
10µF
C
R
V
2
OUT
L
DS21468B-page 7
*
P
. The