TC7660CPA TELCOM SEMICONDUCTOR, TC7660CPA Datasheet - Page 6

• Manufacturer Part Number: TC7660CPA
• Description: IC, VOLT CONVERTER, 7660, DIP8
• Manufacturer: TELCOM SEMICONDUCTOR

Specifications of TC7660CPA

• Primary Input Voltage: 5V
• No. Of Outputs: 1
• Output Voltage: -10V
• Output Current: 20mA
• Voltage Regulator Case Style: DIP
• No. Of Pins: 8
• Operating Temperature Range: 0°C To +70°C
• Operating Temperature: RoHS Compliant

TC7660
4.0
4.1
The TC7660 charge pump converter inverts the voltage
applied to the V
phase operation (Figure 4-1). During the first phase,
switches S
are closed. C
pin, with the load current being supplied from C
ing the second phase, switches S
and switches S
ferred from C
supplied from C
FIGURE 4-1:
Inverter.
In this manner, the TC7660 performs a voltage inver-
sion, but does not provide regulation. The average out-
put voltage will drop in a linear manner with respect to
load current. The equivalent circuit of the charge pump
inverter can be modeled as an ideal voltage source in
series with a resistor, as shown in Figure 4-2.
FIGURE 4-2:
Equivalent Circuit Model.
The value of the series resistor (R
the switching frequency, capacitance and equivalent
series resistance (ESR) of C
tance of switches S
approximation for R
equation:
DS21465B-page 6
V
+
GND S
DETAILED DESCRIPTION
Theory of Operation
2
S
and S
V
1
1
3
1
+
charges to the voltage applied to the V
+
-
+
1
1
.
pin. The conversion consists of a two-
to C
and S
4
are open and switches S
+
OUT
2
Ideal Switched Capacitor
Switched Capacitor Inverter
, with the load current being
1
R
, S
3
S
C
S
OUT
2
4
1
are open. Charge is trans-
is given in the following
2
1
, S
and C
C
3
2
2
OUT
+
and S
2
and S
V
and the on-resis-
) is a function of
OUT
V
4
4
OUT
. A close
are closed
1
= -V
and S
2
. Dur-
IN
3
+
EQUATION
4.2
The overall power loss of a switched capacitor inverter
is affected by four factors:
1.
2.
3.
4.
Figure 4-3 depicts the non-ideal elements associated
with the switched capacitor inverter power loss.
FIGURE 4-3:
Capacitor Inverter.
The power loss is calculated using the following
equation:
EQUATION
V
Where:
+
R
+
-
Losses from power consumed by the internal
oscillator, switch drive, etc. These losses will
vary with input voltage, temperature and
oscillator frequency.
Conduction losses in the non-ideal switches.
Losses due to the non-ideal nature of the
external capacitors.
Losses that occur during charge transfer from
C
capacitors exists.
O UT
f
R
ESR
ESR
1
PU MP
SW
to C
Switched Capacitor Inverter
Power Losses
P
=
C1
C2
I
LO SS
=
R
DD
R
2
SW
=
SW
---------------------------- -
f
on-resistance of the switches
=
=
when a voltage difference between the
PU MP
f
---------- -
ESR
equivalent series resistance of C 1
equivalent series resistance of C
OSC
=
2
1
S
C
S
I
2
O UT
1
C1
3
1
C1
+
Non-Ideal Switched
+
R
R
R
2002 Microchip Technology Inc.
8R
SW
OUT
SW
ESR
SW
+
+
S
C
S
I
DD
2
2
C2
4
4ESR
+
V
C1
I
+
OUT
+
ESR
LOAD
2
C2