TC7662ACPA Microchip Technology Inc., TC7662ACPA Datasheet - Page 8

• Manufacturer Part Number: TC7662ACPA
• Description: HI VOLTAGE DC-DC CONVERTER
• Manufacturer: Microchip Technology Inc.

Specifications of TC7662ACPA

• Lead Free Status / Rohs Status: RoHS Compliant part Electrostatic Device

TC7662A
4.5
It
the TC7662A at low load levels by lowering the
oscillator frequency. This reduces the switching losses,
and is shown in Figure 4-5. However, lowering the
oscillator frequency will cause an undesirable increase
in the impedance of the pump (C
capacitors; this is overcome by increasing the values of
C
been reduced. For example, the addition of a 100pF
capacitor between pin 7 (OSC) and V
oscillator frequency to 2kHz from its nominal frequency
of 12kHz (multiple of 6), and thereby necessitate a
corresponding increase in the value of C
10µF to 68µF).
FIGURE 4-5:
4.6
The TC7662A may be employed to achieve positive
voltage doubling using the circuit shown in Figure 4-6.
In this application, the pump inverter switches of the
TC7662A are used to charge C
V
the forward voltage on C
applied through diode D
thus created on C
the supply voltage minus the combined forward voltage
drops of diodes D
The source impedance of the output (V
on the output current, but for V
current of 10 mA, it will be approximately 60Ω.
FIGURE 4-6:
DS21468B-page 8
P
10µF
DD
is possible to increase the conversion efficiency of
and C
– V
1
2
3
4
+
F
Changing the TC7662A Oscillator
Frequency
Positive Voltage Doubling
R
(where V
TC7662A
by the same factor that the frequency has
1
2
3
4
TC7662A
R
1
and D
DD
becomes (2 V
8
7
6
5
LOWERING OSCILLATOR
FREQUENCY
POSITIVE VOLTAGE
MULTIPLIER
is the supply voltage and V
2
P
2
to capacitor C
plus the supply voltage (V
.
D
1
8
7
6
5
V
+
DD
V
DD
DD
P
C
P
P
DD
D
to a voltage level of
) and reservoir (C
= 5V and an output
2
C
) – (2 V
OSC
DD
+
OUT
R
P
V
(2 V
). The voltage
will lower the
+
and C
OUT
C
) will depend
R
DD
F
), or twice
=
10µF
) – (2 V
R
V
(from
OUT
F
DD
F
)
R
is
)
)
4.7
Figure 4-7 combines the functions shown in Figure 4-1
and Figure 4-6 to provide negative voltage conversion
and positive voltage doubling simultaneously. This
approach would be, for example, suitable for generat-
ing +9V and -5V from an existing +5V supply. In this
instance, capacitors C
reservoir functions, respectively, for the generation of
the negative voltage, while capacitors C
pump and reservoir, respectively, for the doubled
positive voltage. There is a penalty in this configuration
which combines both functions, however, in that the
source impedances of the generated supplies will be
somewhat higher due to the finite impedance of the
common charge pump driver at pin 2 of the device.
FIGURE 4-7:
4.8
The same bidirectional characteristics can be used to
split a higher supply in half, as shown in Figure 4-8.
The combined load will be evenly shared between the
two sides. Because the switches share the load in
parallel, the output impedance is much lower than in
the standard circuits, and higher currents can be drawn
from the device. By using this circuit, and then the
circuit of Figure 4-4, +15V can be converted (via +7.5V
series resistance (~250Ω).
FIGURE 4-8:
and -7.5V) to a nominal -15V, though with rather high
+
V
V
C
R
R
DD
OUT
1
L1
L2
2
– V –
=
Combined Negative Voltage
Conversion and Positive Supply
Multiplication
Voltage Splitting
1
2
3
4
50
µF
TC7662A
+
–
50µF
50µF
C
2
+
+
–
–
+
1
COMBINED NEGATIVE
CONVERTER AND
POSITIVE DOUBLER
8
7
6
5
SPLITTING A SUPPLY IN
HALF
 2002 Microchip Technology Inc.
and C
V
DD
1
2
3
4
3
TC7662A
perform the pump and
D
D
1
2
V
(2 V
8
7
6
5
+
+
2
OUT
and C
DD
V
-(V
C
C
OUT
=
) – (2 V
3
4
DD
=
– V
4
V
V –
F
DD
F
are
)
)