tc7660h Microchip Technology Inc., tc7660h Datasheet - Page 3

• Manufacturer Part Number: tc7660h
• Description: High Frequency 7660 Dc-to-dc Voltage Converte
• Manufacturer: Microchip Technology Inc.

HIGH FREQUENCY 7660 DC-TO-DC
VOLTAGE CONVERTER
© 2001 Microchip Technology Inc.
Detailed Description
implement a voltage inverter, with the exception of two
external capacitors, which may be inexpensive 1.0 F
non-polarized 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
1.0 F
2
1
+
GND
and S
and S
volts. Charge is then transferred from C
C 1
The TC7660H contains all the necessary circuitry to
V +
+
4
3
are open during this half cycle.) During the second
open, thereby shifting capacitor C
Figure 2. Idealized Charge Pump Inverter
1
2
3
4
2
.
TC7660H
Figure 1. TC7660H Test Circuit
2
is exactly V
S 1
S 3
1
is charged to a voltage, V
1
DS21466A
and S
8
7
6
5
+
, assuming ideal switches and
3
are closed. (Note: Switches
2
and S
S 2
S 4
+
4
1
C 2
1.0 F
C 2
are closed, with
to C
1
negatively by
+
, for the half
2
, such that
I S
R L
(+5V)
V OUT
= – V IN
V +
3
connected to GND. For supply voltages greater than 3.5V,
the LV terminal must be left open to ensure latch-up-
proof operation and prevent device damage.
Theoretical Power Efficiency Considerations
100% efficiency if certain conditions are met:
tive voltage multiplication if large values of C
used. 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 1), compared to
the value of R
voltages V
make C
ripple, but also to employ a correspondingly large value for
C
Do's and Don'ts
• Do not exceed maximum supply voltages.
• Do not connect LV terminal to GND for supply voltages
• Do not short circuit the output to V
• When using polarized capacitors in the inverting mode,
1
greater than 3.5V.
above 5.5V for extended periods; however, transient
conditions including start-up are okay.
the + terminal of C
TC7660H and the + terminal of C
to GND Pin 3.
in order to achieve maximum efficiency of operation.
To improve low-voltage operation, the LV pin should be
In theory, a capacitative charge pump can approach
(1) The drive circuitry consumes minimal power.
(2) The output switches have extremely low ON
(3) The impedances of the pump and reservoir
The TC7660H approaches these conditions for nega-
V
1
and V
2
resistance and virtually no offset.
capacitors are negligible at the pump frequency.
as large as possible to eliminate output voltage
1
and V
2
are the voltages on C
L
, there will be a substantial difference in
E = 1/2 C
2
. Therefore, it is not only desirable to
1
must be connected to pin 2 of the
1
(V
1
2
– V
2
1
+
1
must be connected
2
during the pump and
supply for voltages
2
and C
)
TC7660H
2
1
are relatively
and C
TC7660H-2 10/1/96
2
are