tc7662b Microchip Technology Inc., tc7662b Datasheet - Page 7

• Manufacturer Part Number: tc7662b
• Description: Charge Pump Dc-to-dc Voltage Converter
• Manufacturer: Microchip Technology Inc.

© 2001 Microchip Technology Inc.
CHARGE PUMP DC-TO-DC
VOLTAGE CONVERTER
Regulated Negative Voltage Supply
can be a problem, particularly if the load current varies
substantially. The circuit of Figure 12 can be used to over-
come this by controlling the input voltage, via an ICL7611
low-power CMOS op amp, in such a way as to maintain a
nearly constant output voltage. Direct feedback is advisable,
since the TC7662B’s output does not respond instanta-
neously to change in input, but only after the switching delay.
The circuit shown supplies enough delay to accommodate
the TC7662B, while maintaining adequate feedback. An
increase in pump and storage capacitors is desirable, and
the values shown provide an output impedance of less than
5
56k
to a load of 10mA.
In some cases, the output impedance of the TC7662B
+8V
100k
50k
Figure 12. Regulating the Output Voltage
100 F
–
+
50k
800k
+8V
+
-
DS21469A
1
2
3
4
TC7662B
VOLTAGE
ADJUST
250K
8
7
6
5
–
+
V+
10 F
100 F
V
OUT
7
TTL DATA
1 F
INPUT
+
–
Figure 13. RS232 Levels from a Single 5V Supply
1
2
3
4
TC7662B
8
7
6
5
1 F
+5 LOGIC SUPPLY
+
16
15
4
IH5142
12
13
14
+5V
-5V
11
TC7662B
1
3
TC7662B-8 9/11/96
RS232
DATA
OUTPUT