TC682 TELCOM [TelCom Semiconductor, Inc], TC682 Datasheet - Page 4

• Manufacturer Part Number: TC682
• Description: INVERTING VOLTAGE DOUBLER
• Manufacturer: TELCOM [TelCom Semiconductor, Inc]

Capacitor Selection
part, by the ESR of the capacitors used. An expression for
R
equal...
3.3 F low ESR capacitors. The fixed term (16R
80-90 . It can be seen easily that increasing or decreasing
values of C1 and C2 will affect efficiency by changing R
However, be careful about ESR. This term can quickly
become dominant with large electrolytic capacitors. Table 1
shows R
ESR). C1 must be rated at 6VDC or greater while C2 and C3
must be rated at 12VDC or greater.
larger the value of C3 the less the ripple for a given load
current. The formula for
and I
output will be less then 60mV. In most applications (I
= 10mA) a 10-20 F capacitor and 1-5 F pump capacitors
will suffice. Table 2 shows V
(assume 1 ESR).
Table 1. R
4-24
TC682
OUT
R
Assuming all switch resistances are approximately
R
Output voltage ripple is affected by C3. Typically the
V
For a 10 F (0.5 ESR) capacitor for C3, f
R
The output resistance of the TC682 is determined, in
OUT
OUT
RIPPLE
OUT
is derived as shown below:
OUT
C1, C2 ( F)
OUT
= 2(R
= 10mA the peak-to-peak ripple voltage at the
is typically 140
= 16R
OUT
100.00
+2(R
+1/(f
+ESR
+1/(f
10.00
22.00
0.05
0.10
0.47
1.00
3.30
5.00
= {1/[2(f
for various values of C1 and C2 (assume 0.5
SW1
vs. C1, C2
PUMP
PUMP
SW1
SW
C3
+ R
+ 4ESR
+ R
PUMP
x C1) +1/(f
x C1) +1/(f
SW2
SW2
P-P
x C3)] + 2(ESR
+ ESR
+ ESR
C1
V
RIPPLE
at +25 C with V
RIPPLE
+ 4ESR
C1
PUMP
PUMP
C1
+ R
for different values of C3
+ R
is given below:
R
SW3
x C2)
x C2)
OUT
C2
SW3
4085
2084
105
510
285
145
125
94
87
+ ESR
C3
+ R
( )
+ R
)} (I
SW4
IN
PUMP
SW4
SW
OUT
= +5V and
C3
+ ESR
) is about
+ ESR
= 10kHz
)
OUT
OUT
C2
C2
)
<
)
.
Table 2. V
Paralleling Devices
tance of the converter. The effective output resistance is the
output resistance of a single device divided by the number
of devices. As illustrated in Figure 5, each requires separate
pump capacitors C
reservoir capacitor.
–5V Regulated Supply From A Single
3V Battery
battery. The TC682 provides – 6V at V
lated to – 5V by the negative LDO. The input to the TC682
can vary from 3V to 5.5V without affecting regulation appre-
ciably. A TC54 device is connected to the battery to detect
undervoltage. This unit is set to detect at 2.7V. With higher
input voltage, more current can be drawn from the outputs
of the TC682. With 5V at V
regulated output. Assuming 150 source resistance for the
converter, with I
Paralleling multiple TC682s reduces the output resis-
Figure 6 shows a – 5V power supply using one 3V
INVERTING VOLTAGE DOUBLER
C3 ( F)
100.00
RIPPLE
10.00
22.00
0.50
1.00
3.30
5.00
–
L
= 10mA, the charge pump will droop 1.5V.
Peak- to-Peak vs. C3 (I
1
TELCOM SEMICONDUCTOR, INC.
and C
IN
2
, 10mA can be drawn from the
, but all can share a single
V
RIPPLE
1020
520
172
120
OUT
–
70
43
25
OUT
(mV)
, which is regu-
= 10mA)