TC1044 TELCOM [TelCom Semiconductor, Inc], TC1044 Datasheet - Page 5

• Manufacturer Part Number: TC1044
• Description: CHARGE PUMP DC-TO-DC VOLTAGE CONVERTER
• Manufacturer: TELCOM [TelCom Semiconductor, Inc]

CHARGE PUMP DC-TO-DC
VOLTAGE CONVERTER
Cascading Devices
produce larger negative multiplication of the initial supply
voltage. However, due to the finite efficiency of each device,
the practical limit is 10 devices for light loads. The output
voltage is defined by:
where n is an integer representing the number of devices
cascaded. The resulting output resistance would be ap-
proximately the weighted sum of the individual TC1044S
R
Changing the TC1044S Oscillator Frequency
other considerations) to increase the oscillator frequency.
Pin 1, frequency boost pin may be connected to V
increase oscillator frequency to 45kHz from a nominal of
10kHz for an input supply voltage of 5.0 volts. The oscillator
may also be synchronized to an external clock as shown in
Figure 6. In order to prevent possible device latch-up, a 1k
resistor must be used in series with the clock output. In a
10µF
OUT
The TC1044S may be cascaded as shown (Figure 5) to
It may be desirable in some applications (due to noise or
TELCOM SEMICONDUCTOR, INC.
values.
+
10µF
1
2
3
4
*
NOTES:
1. V
Figure 6. External Clocking
TC1044S
+
OUT
V
= –n(V
OUT
1
2
3
4
= –n(V
+
) for 1.5V
8
7
6
5
TC1044S
"1"
IN
V +
Figure 5. Increased Output Voltage by Cascading Devices
)
1k
V
+
8
7
6
5
12V
V +
+
10µF
V +
CMOS
GATE
V OUT
+
10µF
to
+
10µF
+
situation where the designer has generated the external
clock frequency using TTL logic, the addition of a 10k pull-
up resistor to V
frequency with external clocking, as with internal clocking,
will be 1/2 of the clock frequency. Output transitions occur
on the positive-going edge of the clock.
of the TC1044S at low load levels by lowering the oscillator
frequency. This reduces the switching losses, and is achieved
by connecting an additional capacitor, C
Figure 7. Lowering the oscillator frequency will cause an
undesirable increase in the impedance of the pump (C
the reservoir (C
the values of C
frequency has been reduced. For example, the addition of
a 100pF capacitor between pin 7 (OSC) and pin 8 (V
lower the oscillator frequency to 1kHz from its nominal
frequency of 10kHz (a multiple of 10), and necessitate a
corresponding increase in the values of C
10 F to 100 F).
Positive Voltage Multiplication
voltage multiplication using the circuit shown in Figure 8. In
this application, the pump inverter switches of the TC1044S
are used to charge C
is the supply voltage and V
diode D
supply voltage (V
C
or twice the supply voltage minus the combined forward
voltage drops of diodes D
on the output current, but for V
of 10mA, it will be approximately 60 .
2
. The voltage thus created on C
It is also possible to increase the conversion efficiency
The TC1044S may be employed to achieve positive
The source impedance of the output (V
1
1
2
3
4
). On the transfer cycle, the voltage on C
TC1044S
"n"
2
+
) capacitors. To overcome this, increase
1
+
supply is required. Note that the pump
) is applied through diode D
and C
1
to a voltage level of V
8
7
6
5
2
1
F
and D
by the same factor that the
is the forward voltage drop of
+
= 5V and an output current
2
2
.
becomes (2V
+
10µF
OSC
OUT
+
1
– V
V OUT
, as shown in
and C
TC1044S
2
) will depend
to capacitor
F
+
(where V
1
*
) – (2V
plus the
2
1
+
(from
) and
) will
4-47
F
),
+
1
2
3
4
5
6
7
8