TC7660EOA Microchip Technology, TC7660EOA Datasheet - Page 8

• Manufacturer Part Number: TC7660EOA
• Description: IC CHARGE PUMP DC/DC CONV 8-SOIC
• Manufacturer: Microchip Technology
• Type: Switched Capacitor (Charge Pump), Invertingr

Specifications of TC7660EOA

• Package / Case: 8-SOIC (3.9mm Width)
• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: -1.5 ~ -10 V
• Current - Output: 20mA
• Frequency - Switching: 10kHz
• Voltage - Input: 1.5 ~ 10 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Power - Output: 470mW
• Minimum Operating Temperature: - 40 C
• Mounting Style: SMD/SMT
• Function: Inverting
• Output Voltage: - 10 V to - 1.5 V
• Output Current: 20 mA
• Maximum Operating Temperature: + 85 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant

TC7660
5.4
The operating frequency of the TC7660 can be
changed in order to optimize the system performance.
The frequency can be increased by over-driving the
OSC input (Figure 5-4). Any CMOS logic gate can be
utilized in conjunction with a 1 k
resistor is required to prevent device latch-up. While
TTL level signals can be utilized, an additional 10 k
pull-up resistor to V
the rising edge of the clock input. The resultant output
voltage ripple frequency is one half the clock input.
Higher clock frequencies allow for the use of smaller
pump and reservoir capacitors for a given output volt-
age ripple and droop. Additionally, this allows the
TC7660 to be synchronized to an external clock, elimi-
nating undesirable beat frequencies.
At light loads, lowering the oscillator frequency can
increase the efficiency of the TC7660 (Figure 5-5). By
lowering the oscillator frequency, the switching losses
are reduced. Refer to Figure 2-3 to determine the typi-
cal operating frequency based on the value of the
external capacitor. At lower operating frequencies, it
may be necessary to increase the values of the pump
and reservoir capacitors in order to maintain the
desired output voltage ripple and output impedance.
FIGURE 5-4:
FIGURE 5-5:
Frequency.
DS21465B-page 8
C
10 µF
1
+
Changing the TC7660 Oscillator
Frequency
+
1
2
3
4
1
2
3
4
TC7660
TC7660
+
“1”
is required. Transitions occur on
External Clocking.
Lowering Oscillator
8
7
6
5
8
7
6
5
V
+
1 k
series resistor. The
+
+
10 µF
V
C
+
V
C
V
2
CMOS
GATE
+
OSC
OUT
V
OUT
5.5
Positive voltage multiplication can be obtained by
employing two external diodes (Figure 5-6). Refer to
the theory of operation of the TC7660 (Section 4.1).
During the half cycle when switch S
tor C
V
D
ing the reference of capacitor C
energy in capacitor C
through diode D
approximately:
EQUATION
FIGURE 5-6:
5.6
Simultaneous voltage inversion and positive voltage
multiplication can be obtained (Figure 5-7). Capacitors
C
tors C
tive voltage multiplication. Capacitors C
the pump capacitors, while capacitors C
the reservoir capacitors for their respective functions.
Both functions utilize the same switches of the TC7660.
As a result, if either output is loaded, both outputs will
drop towards GND.
where:
+
1
1
. During the next half cycle, switch S
- V
and C
1
F1
2
V
and
V
1
2
3
4
of Figure 5-6 is charged up to a voltage of
and C
, where V
F1
F2
Positive Voltage Multiplication
Combined Negative Voltage
Conversion and Positive Supply
Multiplication
3
TC7660
perform the voltage inversion, while capaci-
is the forward voltage drop of diode D
is the forward voltage drop of diode D
V
4
OUT
, plus the two diodes, perform the posi-
F1
2
, producing an output voltage of
=
is the forward voltage drop of diode
8
7
6
5
2
1
Positive Voltage Multiplier.
is transferred to capacitor C
V
2002 Microchip Technology Inc.
+
D
–
1
+
V
V
+
1
F1
C
from GND to V
1
D
+
2
2
V
is closed, capaci-
1
F2
+
is closed, shift-
V
(2 V
1
3
OUT
C
and C
and C
+
2
) - (2 V
=
+
1
2
. The
2
4
.
are
are
F
)
2