HIGH FREQUENCY 7660 DC-TO-DC VOLT AGE CONVERTER
EVALUATION
KIT
AVAILABLE
FEATURES
■ Pin Compatible with 7660, High Frequency
Performance DC-to-DC Converter
■ Low Cost, Two Low Value External Capacitors
Required ........................................................ (1.0µF)
■ Converts +5V Logic Supply to ±5V System
■ Wide Input Voltage Range ....................1.5V to 10V
■ Voltage Conversion........................................ 99.7%
■ Power Efficiency................................................ 85%
■ Available in 8-Pin SOIC and 8-Pin PDIP Packages
FUNCTIONAL BLOCK DIAGRAM
+
V+CAP
82
OSC
7
RC
OSCILLATOR
6
LV
INTERNAL
VOLTAGE
REGULATOR
TC7660H
÷ 2
VOLTAGE–
LEVEL
TRANSLATOR
3
GND
LOGIC
NETWORK
4
CAP
5
V
OUT
GENERAL DESCRIPTION
The TC7660H is a pin-compatible, high frequency upgrade to the Industry standard TC7660 charge pump voltage converter. It converts a +1.5V to +10V input to a
corresponding – 1.5V to -10V output using only two low-cost
capacitors, eliminating inductors and their associated cost,
size and EMI.
The TC7660H operates at a frequency of 120kHz (versus 10kHz for the TC7660), allowing the use of 1.0µF
external capacitors. Oscillator frequency can be reduced
(for lower supply current applications) by connecting an
external capacitor from OSC to ground.
The TC7660H is available in 8-pin DIP and small outline
(SOIC) packages in commercial and extended temperature
ranges.
ORDERING INFORMATION
–
Part No. Package Range
TC7660HCOA 8-Pin SOIC 0°C to +70°C
TC7660HCPA 8-Pin Plastic DIP 0°C to +70°C
TC7660HEOA 8-Pin SOIC – 40°C to +85°C
TC7660HEPA 8-Pin Plastic DIP – 40°C to +85°C
TC7660EV Evaluation Kit for
Charge Pump Family
1
TC7660H
2
3
4
Temperature
5
PIN CONFIGURATION (DIP and SOIC)
NC
1
+
CAP
2
3
4
1
2
3
4
TC7660HCPA
TC7660HEPA
TC7660HCOA
TC7660HEOA
TELCOM SEMICONDUCTOR, INC.
GND
–
CAP
NC
+
CAP
GND
–
CAP
NC = NO INTERNAL CONNECTION
+
8
V
OSC
7
LOW
6
VOLTAGE (LV)
V
5
OUT
+
V
8
OSC
7
LOW
6
VOLTAGE (LV)
5
V
OUT
6
7
8
TC7660H-2 10/1/96
4-63
TC7660H
HIGH FREQUENCY 7660 DC-TO-DC
VOLTAGE CONVERTER
ABSOLUTE MAXIMUM RATINGS*
Supply Voltage ...................................................... +10.5V
LV and OSC Inputs
Voltage (Note 1) ........................ – 0.3V to (V+ + 0.3V)
for V+ < 5.5V
(V+ – 5.5V) to (V+ + 0.3V)
for V+ > 5.5V
Current Into LV (Note 1)......................20µA for V+ > 3.5V
Output Short Duration (V
≤ 5.5V) .........Continuous
SUPPLY
Power Dissipation (TA ≤ 70°C) (Note 2)
SOIC...............................................................470mW
Plastic DIP ......................................................730mW
ELECTRICAL CHARACTERISTICS: Over Operating Temperature Range with V
Operating Temperature Range
C Suffix ..................................................0°C to +70°C
E Suffix ............................................. – 40°C to +85°C
Storage Temperature Range ................– 65°C to +150°C
Lead Temperature (Soldering, 10 sec) .................+300°C
*Static-sensitive device. Unused devices must be stored in conductive
material. Protect devices from static discharge and static fields. Stresses
above those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only and functional
operation of the device at these or any other conditions above those
indicated in the operation sections of the specifications is not implied.
Exposure to absolute maximum rating conditions for extended periods
may affect device reliability.
+
= 5V, CI = C2 = 1µF,C
OSC
= 0,
Test Circuit (Figure 1), unless otherwise indicated.
Symbol Parameter Test Conditions Min Typ Max Unit
+
I
+
V
H
+
V
L
R
OUT
F
OSC
P
EFF
V
EFF
NOTES: 1. Connecting any input terminal to voltages greater than V+ or less than GND may cause destructive latch-up. It is recommended that no
Supply Current RL = ∞ — 0.46 1.0 mA
Supply Voltage Range, High Min ≤ TA ≤ Max, 3 — 10 V
RL = 5kΩ, LV Open
Supply Voltage Range, Low Min ≤ TA ≤ Max, 1.5 — 3.5 V
RL = 5kΩ, LV to GND
Output Source Resistance I
= 20mA, TA = 25°C — 55 80 Ω
OUT
I
= 20mA, 0°C ≤ TA ≤ +70°C——95Ω
OUT
(C Device)
I
= 20mA, – 40°C ≤ TA ≤ +85°C — — 110 Ω
OUT
(E Device)
+
V
= 2V, I
= 3mA, LV to GND — 150 250 Ω
OUT
0°C ≤ TA ≤ +70°C
Oscillator Frequency — 120 — kHz
Power Efficiency I
= 10mA, Min ≤ TA ≤ Max 81 85 — %
OUT
Voltage Efficiency RL = ∞ 99 99.7 — %
inputs from sources operating from external supplies be applied prior to "power up" of the TC7660H.
2. Derate linearly above 50°C by 5.5 mW/°C.
4-64
TELCOM SEMICONDUCTOR, INC.
HIGH FREQUENCY 7660 DC-TO-DC
VOLTAGE CONVERTER
I
S
+
V
(+5V)
2
R
L
C
1.0 µF
1
2
+
1
TC7660H
3
4
Figure 1. TC7660H Test Circuit
8
7
6
5
C
1.0 µF
+
Detailed Description
The TC7660H contains all the necessary circuitry to
implement a voltage inverter, with the exception of two
external capacitors, which may be inexpensive 1.0µF nonpolarized capacitors. Operation is best understood by considering Figure 2, which shows an idealized voltage inverter.
Capacitor C1 is charged to a voltage, V+, for the half cycle
when switches S1 and S3 are closed. (Note: Switches S2 and
S4 are open during this half cycle.) During the second half
cycle of operation, switches S2 and S4 are closed, with S
and S3 open, thereby shifting capacitor C1 negatively by V
volts. Charge is then transferred from C1 to C2, such that the
voltage on C2 is exactly V+, assuming ideal switches and no
load on C2.
TC7660H
To improve low-voltage operation, the LV pin should be
connected to GND. For supply voltages greater than 3.5V,
the LV terminal must be left open to ensure latch-up-
proof operation and prevent device damage.
Theoretical Power Efficiency Considerations
In theory, a capacitative charge pump can approach
100% efficiency if certain conditions are met:
(1) The drive circuitry consumes minimal power.
(2) The output switches have extremely low ON
resistance and virtually no offset.
(3) The impedances of the pump and reservoir
capacitors are negligible at the pump frequency.
The TC7660H approaches these conditions for negative voltage multiplication if large values of C1 and C2 are
used. Energy is lost only in the transfer of charge
between capacitors if a change in voltage occurs. The
energy lost is defined by:
2
E = 1/2 C1 (V
V1 and V2 are the voltages on C1 during the pump and
transfer cycles. If the impedances of C1 and C2 are relatively
high at the pump frequency (refer to Figure 1), compared to
the value of RL, there will be a substantial difference in
voltages V1 and V2. Therefore, it is not only desirable to
make C2 as large as possible to eliminate output voltage
ripple, but also to employ a correspondingly large value for
1
C1 in order to achieve maximum efficiency of operation.
+
1
Do's and Don'ts
• Do not exceed maximum supply voltages.
• Do not connect LV terminal to GND for supply voltages
greater than 3.5V.
– V
2
)
2
1
2
3
4
5
6
S
+
V
GND
Figure 2. Idealized Charge Pump Inverter
TELCOM SEMICONDUCTOR, INC.
1
S
3
S
2
C
S
2
4
V
OUT
= – V
IN
• Do not short circuit the output to V+ supply for voltages
above 5.5V for extended periods; however, transient
conditions including start-up are okay.
• When using polarized capacitors in the inverting mode,
the + terminal of C1 must be connected to pin 2 of the
TC7660H and the + terminal of C2 must be connected
to GND Pin 3.
7
8
4-65
TC7660H
1
2
3
4
8
7
6
5
TC7660H
1.0 µF
+
V
+
1.0 µF
+
V
OUT
*
1. V
OUT
= –n V+for 1.5V ≤ V+ ≤ 10VNOTES:*
C
1
C
2
Simple Negative Voltage Converter
Figure 3 shows typical connections to provide a negative supply where a positive supply is available. A similar
scheme may be employed for supply voltages anywhere in
the operating range of +1.5V to +10V, keeping in mind that
pin 6 (LV) is tied to the supply negative (GND) only for supply
voltages below 3.5V.
The output characteristics of the circuit in Figure 3 are
those of a nearly ideal voltage source in series with 70Ω.
Thus, for a load current of – 10 mA and a supply voltage of
+5V, the output voltage would be – 4.3V.
The dynamic output impedance of the TC7660H is due,
primarily, to capacitive reactance of the charge transfer
capacitor (C1). Since this capacitor is connected to the
output for only 1/2 of the cycle, the equation is:
XC = = 2.12Ω,
where f = 150 kHz and C1 = 1.0 µF.
2
2πf C
1
HIGH FREQUENCY 7660 DC-TO-DC
VOLTAGE CONVERTER
Figure 3. Simple Negative Converter
Paralleling Devices
Any number of TC7660H voltage converters may be
paralleled to reduce output resistance (Figure 4). The reservoir capacitor, C2, serves all devices, while each device
requires its own pump capacitor, C1. The resultant output
resistance would be approximately:
R
(of TC7660H)
R
OUT
=
OUT
n (number of devices)
+
V
1.0 µF
NOTES:
*
1. V
OUT
1
2
+
= –n V+for 1.5V V 10V
TC7660H
3
4
"1"
8
7
6
5
+
≤≤
Figure 4. Increased Output Voltage by Cascading Devices
Cascading Devices
The TC7660H may be cascaded as shown in (Figure 4)
to produce larger negative multiplication of the initial supply
voltage. However, due to the finite efficiency of each device,
the practical limit is probably 10 devices for light loads. The
output voltage is defined by:
V
= – n (VIN)
OUT
where n is an integer representing the number of devices
cascaded. The resulting output resistance would be approximately the weighted sum of the individual TC7660H
R
4-66
OUT
values.
1.0 µF
+
1
2
3
4
TC7660H
"n"
8
7
6
5
+
1.0 µF
V
OUT
*
Changing the TC7660H Oscillator Frequency
It may be desirable in some applications (due to noise or
other considerations) to increase or decease the oscillator
frequency. This can be achieved by overdriving the oscillator from an external clock, as shown in Figure 6. In order to
prevent possible device latch-up, a 1kΩ resistor must be
used in series with the clock output. In a situation where the
designer has generated the external clock frequency using
TTL logic, the addition of a 10kΩ pull-up resistor to V+ supply
is required. Note that the pump 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.
TELCOM SEMICONDUCTOR, INC.
HIGH FREQUENCY 7660 DC-TO-DC
VOLTAGE CONVERTER
+
V
1
2
C
1
3
4
TC7660H
"1"
8
7
6
5
Figure 5. Paralleling Devices Lowers Output Impedance
1
TC7660H
2
1
2
TC7660H
C
1
3
"n"
4
8
R
7
6
5
L
R
L
C
2
+
3
1.0 µF
+
V
1
2
+
3
TC7660H
4
Figure 6. External Clocking
8
1 kΩ
7
6
5
+
V
CMOS
GATE
V
OUT
1.0 µF
+
Positive Voltage Multiplication
The TC7660H may be employed to achieve positive
voltage multiplication using the circuit shown in Figure 7. In
this application, the pump inverter switches of the TC7660H
are used to charge C1 to a voltage level of V+ – VF (where V
is the supply voltage and VF is the forward voltage drop of
diode D1). On the transfer cycle, the voltage on C1 plus the
supply voltage (V+) is applied through diode D2 to capacitor
C2. The voltage thus created on C2 becomes (2 V+) – (2 VF),
or twice the supply voltage minus the combined forward
voltage drops of diodes D1 and D2.
The source impedance of the output (V
on the output current, but for V+ = 5V and an output current
of 10mA, it will be approximately 60Ω.
+
V
1
2
3
4
TC7660H
8
D
7
6
5
1
D
2
+
C
1
) will depend
OUT
V
OUT
(2 V+) – (2 VF)
+
C
2
=
Combined Negative Voltage Conversion
and Positive Supply Multiplication
Figure 8 combines the functions shown in Figures 3 and
8 to provide negative voltage conversion and positive voltage multiplication simultaneously. This approach would be,
for example, suitable for generating +9V and –5V from an
existing +5V supply. In this instance, capacitors C1 and C
perform the pump and reservoir functions, respectively, for
the generation of the negative voltage, while capacitors C
and C4 are pump and reservoir, respectively, for the multiplied 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.
+
+
V
1
2
TC7660H
3
4
+
C
1
Figure 8. Combined Negative Converter and Positive Multiplier
8
7
6
5
+
C
2
+
D
1
V
OUT
(2 V+) – (2 VF)
D
2
+
V
=
OUT
–(V+–VF)
C
3
=
C
4
4
3
2
5
6
7
Figure 7. Positive Voltage Multiplier
TELCOM SEMICONDUCTOR, INC.
8
4-67
TC7660H
HIGH FREQUENCY 7660 DC-TO-DC
VOLTAGE CONVERTER
Efficient Positive Voltage Multiplication/
Conversion
Since the switches that allow the charge pumping operation are bidirectional, the charge transfer can be performed backwards as easily as forwards. Figure 9 shows a
TC7660H transforming – 5V to +5V (or +5V to +10V, etc.).
The only problem here is that the internal clock and switchdrive section will not operate until some positive voltage has
C
1.0 µF
1
1
2
+
3
4
been generated. An initial inefficient pump, as shown in
Figure 9, could be used to start this circuit up, after which it
will bypass the diode and resistor shown dotted in
Figure 9.
Figure 9. Positive Voltage Conversion
TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 1)
Output Source Resistance vs. Supply Voltage
10k
1k
TA = +25°C
Output Source Resistance vs. Temperature
500
I
OUT
450
400
200
TC7660H
= 1 mA
1 MΩ
= –V
V
–
–
INPUT
+
1.0 µF
V
OUT
8
7
6
5
100Ω
OUTPUT SOURCE RESISTANCE (Ω)
10Ω
SUPPLY VOLTAGE (V) TEMPERATURE (°C)
Output Voltage vs. Output Current
µF
=1
C
I C2
0
–1
–2
–3
–4
–5
–6
–7
OUTPUT VOLTAGE (V)
–8
–9
–10
10 20 30 40 50 60 70 80 90 100
0
OUTPUT CURRENT (mA)
78
6543210
TA = +25°C
LV OPEN
150
V+ = +2V
100
V + = +5V
50
OUTPUT SOURCE RESISTANCE (Ω)
0
–55 –25 0 +25 +50 +75 +100 +125
Output Voltage vs. Load Current
5
TA = +25°C
4
V+ = +5V
3
2
1
0
–1
–2
OUTPUT VOLTAGE (V)
–3
–4
–5
10 20 30 40 50 60 70 80
0
SLOPE 55Ω
LOAD CURRENT (mA)
4-68
TELCOM SEMICONDUCTOR, INC.
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