TC660 TELCOM [TelCom Semiconductor, Inc], TC660 Datasheet - Page 5

• Manufacturer Part Number: TC660
• Description: 100mA CHARGE PUMP DC-TO-DC VOLTAGE CONVERTER
• Manufacturer: TELCOM [TelCom Semiconductor, Inc]

Circuit Description
plete a voltage inverter (Figure 1), with the exception of two
external capacitors, which may be inexpensive 150 F polar-
ized electrolytic capacitors. Operation is best understood by
considering Figure 2, which shows an idealized voltage
inverter. Capacitor C
cycle when switches S
S
half cycle of operation, switches S
S
V
the voltage on C
no load on C
S
devices. The main difficulty with this approach is that in
integrating the switches, the substrates of S
always remain reverse-biased with respect 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
and the substrate bias adjusted accordingly. Failure to
accomplish this would result in high power losses and
possible device latch-up. This problem is eliminated in the
TC660 by a logic network which senses the output voltage
(V
substrates of S
necessary reverse bias.
be connected to GND, disabling the internal regulator. For
supply voltages greater than 3.0V, the LV terminal should
be left open to ensure latch-up-proof operation and prevent
device damage.
100mA CHARGE PUMP DC-TO-DC
VOLTAGE CONVERTER
2
1
+
1
150 µF
OUT
and S
and S
volts. Charge is then transferred from C
is a P-channel device, and S
The TC660 contains all the necessary circuitry to com-
The four switches in Figure 2 are MOS power switches;
To improve low-voltage operation, the “LV” pin should
TELCOM SEMICONDUCTOR, INC.
C 1
) together with the level translators, and switches the
V +
4
3
are open during this half cycle.) During the second
+
open, thereby shifting capacitor C
2
OUT
Figure 1. TC660 Test Circuit (Inverter)
.
1
2
3
4
2
3
is exactly V
= V
and S
TC660
1
+
), the output voltage must be sensed
is charged to a voltage V
1
and S
4
to the correct level to maintain
+
, assuming ideal switches and
3
8
7
6
5
are closed. (Note: Switches
2
, S
2
3
and S
and S
+
4
1
I L
4
are closed, with
C 2
150 µF
to C
1
are N-channel
3
negatively by
and S
+
I S
R L
2
for the half
, such that
(+5V)
V +
V OUT
4
must
Theoretical Power Efficiency
Considerations
efficiency if certain conditions are met:
voltage multiplication 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:
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
1
in order to achieve maximum efficiency of operation.
V +
In theory, a voltage multiplier can approach 100%
(1) The drive circuitry consumes minimal power.
(2) The output switches have extremely low ON
(3) The impedances of the pump and reservoir
The TC660 approaches these conditions for negative
V
1
and V
2
resistance and virtually no offset.
capacitors are negligible at the pump frequency.
GND
as large as possible to eliminate output voltage
1
and V
Figure 2. Idealized Switched Capacitor
2
are the voltages on C
S 3
L
, there will be a substantial difference in
S 1
E = 1/2 C
2
. Therefore, it is desirable not only to
C 1
1
(V
1
S 2
2
– V
S 4
1
1
2
during the pump and
2
and C
)
1
and C
C 2
V OUT = – V IN
2
are relatively
2
TC660
are used.
4-9
1
2
3
4
5
6
7
8