TC7662ACPA Microchip Technology, TC7662ACPA Datasheet - Page 5

• Manufacturer Part Number: TC7662ACPA
• Description: IC CHARGE PUMP DC/DC CONV 8-DIP
• Manufacturer: Microchip Technology
• Type: Switched Capacitor (Charge Pump), Invertingr

Specifications of TC7662ACPA

• Package / Case: 8-DIP (0.300", 7.62mm)
• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: -3 ~ -18 V
• Current - Output: 40mA
• Frequency - Switching: 12kHz
• Voltage - Input: 3 ~ 18 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Through Hole
• Power - Output: 730mW
• Minimum Operating Temperature: 0 C
• Mounting Style: Through Hole
• Function: Inverting
• Output Voltage: - 18 V to - 3 V
• Output Current: 40 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: 158-1138; 158-1138

3.0
The TC7662A is a capacitive charge pump (sometimes
called a switched-capacitor circuit), where four
MOSFET switches control the charge and discharge of
a capacitor.
The functional block diagram shows how the switching
action works. SW1 and SW2 are turned on simulta-
neously, charging C
assumes that the ON resistance of the MOSFETs in
series with the capacitor produce a charging time
(3 time constants) less than the ON time provided by
the oscillator frequency, as shown:
3 (R
In the next cycle, SW1 and SW2 are turned OFF and,
after a very short interval with all switches OFF
(preventing large currents from occurring due to cross
conduction), SW3 and SW4 are turned ON. The charge
in C
inverted. In this way, a negative voltage is derived.
An oscillator supplies pulses to a flip-flop that is fed to
a set of level shifters. These level shifters then drive
each set of switches at one-half the oscillator
frequency.
The oscillator has a pin that controls the frequency
of oscillation. Pin 7 can have a capacitor added that
is connected to ground. This will lower the frequency
of the oscillator by adding capacitance to the
internal timing capacitor of the TC7662A. (See Typical
Characteristics – Oscillator Frequency vs. C
FIGURE 3-1:
 2002 Microchip Technology Inc.
NC
C
P
DS(ON)
P
+
is then transferred to C
10µF
DETAILED DESCRIPTION
C
P
) <C
1
2
3
4
TC7662A
P
/(0.5 f
P
to the supply voltage, V
TC7662A TEST CIRCUIT
OSC
8
7
6
5
NC
).
R
, but with the polarity
C
OSC
C
R
+
OSC
R
10µF
I
S
I
L
DD
L
V
(-5V)
.)
V
(+5V)
. This
OUT
DD
3.1
In theory, a voltage converter can approach 100%
efficiency if certain conditions are met:
1.
2.
3.
The TC7662A approaches these conditions for
negative voltage conversion if large values of C
C
V
transfer cycles. If the impedances of C
relatively high at the pump frequency (refer to Figure 3-
1), compared to the value of R
substantial difference in voltages V
it is desirable not only to make C
to eliminate output voltage ripple, but also to employ a
correspondingly large value for C
maximum efficiency of operation.
3.2
• Do not exceed maximum supply voltages.
• Do not short circuit the output to V
• When using polarized capacitors in the inverting
• If the voltage supply driving the TC7662A has a
The energy lost is defined by:
1
R
Note:
voltages above 5.5V for extended periods;
however, transient conditions including start-up
are okay.
mode, the + terminal of C
pin 2 of the TC7662A and the + terminal of C
must be connected to GND (pin 3).
large source impedance (25-30 ohms), then a
2.2µF capacitor from pin 8 to ground may be
required to limit the rate of rise of the input voltage
to less than 2V/µsec.
and V
are used.
The drive circuitry consumes minimal power.
The output switches have extremely low ON
resistance and virtually no offset.
The impedances of the pump and reservoir
capacitors are negligible at the pump frequency.
Theoretical Power Efficiency
Considerations
2
Dos and Don’ts
are the voltages on C
Energy is lost only in the transfer of charge
between capacitors if a change in voltage
occurs.
E = 1/2 C
P
(V
P
1
must be connected to
2
TC7662A
P
– V
R
P
during the pump and
1
as large as possible
L
in order to achieve
2
and V
, there will be a
+
2
)
DS21468B-page 5
supply for
P
2
and C
. Therefore,
R
P
R
and
are