TC7662BCOA Microchip Technology, TC7662BCOA Datasheet - Page 3

• Manufacturer Part Number: TC7662BCOA
• Description: IC CHARGE PUMP DC/DC CONV 8-SOIC
• Manufacturer: Microchip Technology
• Type: Switched Capacitor (Charge Pump), Invertingr

Specifications of TC7662BCOA

• Package / Case: 8-SOIC (3.9mm Width)
• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: -1.5 ~ -15 V
• Current - Output: 20mA
• Frequency - Switching: 10kHz ~ 35kHz
• Voltage - Input: 1.5 ~ 15 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Power - Output: 470mW
• Minimum Operating Temperature: 0 C
• Mounting Style: SMD/SMT
• Function: Inverting
• Output Voltage: - 15 V to - 1.5 V
• Output Current: 20 mA
• Maximum Operating Temperature: + 70 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant
• Other names: 158-1066; 158-1066

© 2001 Microchip Technology Inc.
CHARGE PUMP DC-TO-DC
VOLTAGE CONVERTER
DETAILED DESCRIPTION
complete a negative voltage converter, with the exception of
two external capacitors which may be inexpensive 1 F
polarized electrolytic types. The mode of operation of the
device may be best understood by considering Figure 2,
which shows an idealized negative voltage converter. Ca-
pacitor C
switches S
are open during this half cycle.) During the second half cycle
of operation, switches S
open, thereby shifting capacitor C
Charge is then transferred from C
voltage on C
load on C
more closely than existing non-mechanical circuits.
power switches; S
are N-channel devices. The main difficulty with this ap-
proach is that in integrating the switches, the substrates of
S
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 (V
be sensed and the substrate bias adjusted accordingly.
Failure to accomplish this would result in high power losses
and probable device latchup.
network which senses the output voltage (V
with the level translators, and switches the substrates of S
and S
bias.
integral part of the anti-latchup circuitry; however, its inher-
ent voltage drop can degrade operation at low voltages.
Therefore, to improve low voltage operation, the “LV” pin
should be connected to GND, disabling the regulator. For
supply voltages greater than 3.5 volts, the LV terminal must
be left open to insure latchup proof operation and prevent
device damage.
3
and S
The TC7662B contains all the necessary circuitry to
In the TC7662B, the four switches of Figure 2 are MOS
The problem is eliminated in the TC7662B by a logic
The voltage regulator portion of the TC7662B is an
NOTE: For large values of C
4
to the correct level to maintain necessary reverse
4
1
10 F
2
of C
is charged to a voltage V
must always remain reverse biased with respect
1
. The TC7662B approaches this ideal situation
C 1
2
and S
1
V +
is exactly V
and C
+
Figure 1. TC7662B Test Circuit
2
1
3
should be increased to 100 µF.
1
2
3
4
is a P-channel device and S
are closed. (Note: Switches S
TC7662B
DS21469A
OSC
2
+
OUT
and S
, assuming ideal switches and no
(>1000 pF), the values
= V
8
7
6
5
4
+
are closed, with S
), the output voltage must
1
+
negatively by V
1
for the half cycle when
to C
+
2
C 2
10 F
such that the
OUT
I L
R L
I S
2
, S
(+5V)
) together
V +
V O
2
1
3
+
and S
and S
and S
volts.
4
3
4
3
3
THEORETICAL POWER EFFICIENCY
CONSIDERATIONS
efficiency if certain conditions are met:
A. The drive circuitry consumes minimal power.
B. The output switches have extremely low ON resistance
C. The impedances of the pump and reservoir capacitors
tive voltage conversion if large values of C
Energy is lost only in the transfer of charge between
capacitors if a change in voltage occurs. The energy lost
is defined by:
where V
transfer cycles. If the impedances of C
high at the pump frequency (refer to Figure 2) compared to
the value of R
voltages V
make C
ripple, but also to employ a correspondingly large value for
C
Dos and Don’ts
1. Do not exceed maximum supply voltages.
2. Do not connect the LV terminal to GND for supply
3. Do not short circuit the output to V
1
and virtually no offset.
are negligible at the pump frequency.
voltages greater than 3.5 volts.
above 5.5 volts for extended periods; however,
transient conditions including start-up are okay.
in order to achieve maximum efficiency of operation.
In theory, a voltage converter can approach 100%
The TC7662B approaches these conditions for nega-
V IN
1
2
Figure 2. Idealized Negative Voltage Capacitor
and V
as large as possible to eliminate output voltage
1
and V
S 1
2
L
S 3
, there will be a substantial difference in
are the voltages on C
E = 1/2 C
2
. Therefore, it is desirable not only to
S 2
1
S 4
C 1
(V
1
2
– V
C 2
1
1
+
2
during the pump and
2
and C
supply for voltages
)
1
and C
TC7662B
2
V OUT = – V IN
are relatively
TC7662B-8 9/11/96
2
are used.