TC7660SCOA Microchip Technology, TC7660SCOA Datasheet - Page 5

• Manufacturer Part Number: TC7660SCOA
• Description: IC CHARGE PUMP DC/DC CONV 8-SOIC
• Manufacturer: Microchip Technology
• Type: Switched Capacitor (Charge Pump), Invertingr

Specifications of TC7660SCOA

• Package / Case: 8-SOIC (3.9mm Width)
• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: -1.5 ~ -12 V
• Current - Output: 20mA
• Frequency - Switching: 10kHz ~ 45kHz
• Voltage - Input: 1.5 ~ 12 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Power - Output: 470mW
• Minimum Operating Temperature: 0 C
• Mounting Style: SMD/SMT
• Function: Inverting/Step Up
• Output Voltage: - 12 V to - 1.5 V or 3 V to 24 V
• Output Current: 20 mA
• Maximum Operating Temperature: + 70 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant
• Other names: 158-1067; 158-1067

SUPER 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 TC7660S
R
Changing the TC7660S 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
© 2001 Microchip Technology Inc.
10 F
OUT
The TC7660S may be cascaded as shown (Figure 5) to
It may be desirable in some applications (due to noise or
values.
+
10 F
1
2
3
4
Figure 6. External Clocking
TC7660S
*
+
NOTES:
1. V
V
DS21467A
OUT
OUT
1
2
3
4
= –n(V
= – n (V
8
7
6
5
TC7660S
"1"
+
) for 1.5V
V +
1 k
IN
Figure 5. Increased Output Voltage by Cascading Devices
)
8
7
6
5
+
V
V
+
+
10 F
12V
V +
V OUT
CMOS
GATE
10 F
+
to
+
5
10 F
+
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
the positive-going edge of the clock.
of the TC7660S 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
values of C
has been reduced. For example, the addition of a 100pF
capacitor between pin 7 (OSC) and pin 8 (V
oscillator frequency to 1kHz from its nominal frequency of
10kHz (a multiple of 10), and necessitate a corresponding
increase in the values of C
Positive Voltage Multiplication
voltage multiplication using the circuit shown in Figure 8. In
this application, the pump inverter switches of the TC7660S
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 TC7660S 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
of the clock frequency. Output transitions occur on
1
TC7660S
and C
"n"
2
) capacitors. To overcome this, increase the
+
+
supply is required. Note that the pump
) is applied through diode D
2
by the same factor that the frequency
1
to a voltage level of V
8
7
6
5
1
1
F
and D
and C
is the forward voltage drop of
+
= 5V and an output current
2
2
2
.
becomes (2V
(from 10 F to 100 F).
+
OSC
10 F
OUT
+
+
–V
) will lower the
TC7660S
V OUT
, as shown in
2
) will depend
TC7660S-14 9/16/96
to capacitor
F
(where V
+
1
) – (2V
*
plus the
1
) and
F
),
+