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LM2662/LM2663
Switched Capacitor Voltage Converter
General Description
The LM2662/LM2663 CMOS charge-pump voltage converter inverts a positive voltage in the range of 1.5V to 5.5V
to thecorresponding negative voltage. The LM2662/LM2663
uses two low cost capacitors to provide 200 mA of output
current without the cost, size, and EMI related to inductor
based converters. With an operating current of only 300 µA
and operating efficiency greater than 90%at most loads, the
LM2662/LM2663 provides ideal performance for battery
powered systems. The LM2662/LM2663 may also be used
as a positive voltage doubler.
The oscillator frequency can be lowered by adding an external capacitor to the OSC pin.Also, the OSC pin may be used
to drive the LM2662/LM2663 with an external clock. For
LM2662, a frequency control (FC) pin selects the oscillator
frequency of 20 kHz or 150 kHz. For LM2663, an external
shutdown (SD) pin replaces the FC pin. The SD pin can be
used to disable the device and reduce the quiescent current
to 10 µA. The oscillator frequency for LM2663 is 150 kHz.
Features
n Inverts or doubles input supply voltage
n Narrow SO-8 Package
n 3.5Ω typical output resistance
n 86%typical conversion efficiency at 200 mA
n (LM2662) selectable oscillator
frequency: 20 kHz/150 kHz
n (LM2663) low current shutdown mode
Applications
n Laptop computers
n Cellular phones
n Medical instruments
n Operational amplifier power supplies
n Interface power supplies
n Handheld instruments
Basic Application Circuits
Voltage Inverter
DS100003-1
Positive Voltage Doubler
DS100003-2
Splitting VINin Half
DS100003-3
January 1999
LM2662/LM2663 Switched Capacitor Voltage Converter
© 1999 National Semiconductor Corporation DS100003 www.national.com
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Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Supply Voltage (V+ to GND, or GND to OUT) 6V
LV (OUT − 0.3V) to (GND + 3V)
FC, OSC, SD The least negative of (OUT − 0.3V)
or (V+ − 6V) to (V+ + 0.3V)
V+ and OUT Continuous Output Current 250 mA
Output Short-Circuit Duration to GND (Note 2) 1 sec.
Power Dissipation (T
A
= 25˚C) (Note 3) 735 mW
T
J
Max (Note 3) 150˚C
θ
JA
(Note 3) 170˚C/W
Operating Junction Temperature
Range −40˚C to +85˚C
Storage Temperature Range −65˚C to +150˚C
Lead Temperature (Soldering, 10 seconds) 300˚C
ESD Rating 2 kV
Electrical Characteristics
Limits in standard typeface are for TJ= 25˚C, and limits in boldface type apply over the full operating temperature range.
Unless otherwise specified: V+ = 5V, FC = Open, C
1=C2
= 47 µF.(Note 4)
Symbol Parameter Condition Min Typ Max Units
V+ Supply Voltage R
L
= 1k Inverter, LV = Open 3.5 5.5
Inverter, LV = GND 1.5 5.5 V
Doubler, LV = OUT 2.5 5.5
I
Q
Supply Current No Load FC = V+ (LM2662)
1.3 4
mALV = Open SD = Ground (LM2663)
FC = Open 0.3 0.8
I
SD
Shutdown Supply Current
10 µA
(LM2663)
V
SD
Shutdown Pin Input Voltage Shutdown Mode 2.0 (Note 5)
V
(LM2663) Normal Operation 0.3
I
L
Output Current 200 mA
R
OUT
Output Resistance (Note 6) IL= 200 mA 3.5 7 Ω
f
OSC
Oscillator Frequency (Note 7) OSC = Open FC = Open 7 20
kHz
FC=V+ 55 150
f
SW
Switching Frequency (Note 8) OSC = Open FC = Open 3.5 10
kHz
FC=V+ 27.5 75
I
OSC
OSC Input Current FC = Open
±
2
µA
FC=V+
±
10
P
EFF
Power Efficiency RL(500) between V+and OUT 90 96
%
I
L
= 200 mA to GND 86
V
OEFF
Voltage Conversion Efficiency No Load 99 99.96
%
Note 1: Absolute maximum ratings indicate limits beyond which damage to the device may occur. Electrical specifications do not apply when operating the device
beyond its rated operating conditions.
Note 2: OUT may be shorted to GND for one second without damage. However, shorting OUT to V+ may damage the device and should be avoided. Also, for temperatures above 85˚C, OUT must not be shorted to GND or V+, or device may be damaged.
Note 3: The maximum allowable power dissipation is calculated by using P
DMax
=(T
JMax−TA
)/θJA, where T
JMax
is the maximum junction temperature, TAis the
ambient temperature, and θ
JA
is the junction-to-ambient thermal resistance of the specified package.
Note 4: In the test circuit, capacitors C
1
and C2are 47 µF, 0.2Ω maximum ESR capacitors. Capacitors with higherESRwillincreaseoutputresistance,reduceoutput
voltage and efficiency.
Note 5: In doubling mode, when V
out
>
5V, minimum input high for shutdown equals V
out
−3V.
Note 6: Specified output resistance includes internal switch resistance and capacitor ESR.
Note 7: For LM2663, the oscillator frequency is 150 kHz.
Note 8: The output switches operate at one half of the oscillator frequency, f
OSC
=
2f
SW
.
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Test Circuits
Typical Performance Characteristics
(Circuit of
Figure 1
)
DS100003-4
DS100003-5
FIGURE 1. LM2662 and LM2663 Test Circuits
Supply Current vs
Supply Voltage
DS100003-37
Supply Current vs
Oscillator Frequency
DS100003-38
Output Source
Resistance vs Supply
Voltage
DS100003-39
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Typical Performance Characteristics (Circuit of
Figure 1
) (Continued)
Output Source
Resistance vs
Temperature
DS100003-40
Output Source
Resistance vs
Temperature
DS100003-41
Efficiency vs Load
Current
DS100003-42
Output Voltage Drop
vs Load Current
DS100003-43
Efficiency vs
Oscillator Frequency
DS100003-44
Output Voltage vs
Oscillator Frequency
DS100003-45
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Typical Performance Characteristics (Circuit of
Figure 1
) (Continued)
Oscillator Frequency
vs External
Capacitance
DS100003-46
Oscillator Frequency
vs Supply Voltage
DS100003-47
Oscillator Frequency
vs Supply Voltage
DS100003-48
Oscillator Frequency
vs Temperature
DS100003-49
Oscillator Frequency
vs Temperature
DS100003-50
Shutdown Supply
Current vs
Temperature
(LM2663 Only)
DS100003-51
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Connection Diagrams
Pin Description
Pin Name Function
Voltage Inverter Voltage Doubler
1 FC Frequency control for internal oscillator: Same as inverter.
(LM2662) FC = open, f
OSC
= 20 kHz (typ);
FC = V+, f
OSC
= 150 kHz (typ);
FC has no effect when OSC pin is driven
externally.
1SD
(LM2663)
Shutdown control pin, tie this pin to the ground
in normal operation.
Same as inverter.
2 CAP+ Connect this pin to the positive terminal of
charge-pump capacitor.
Same as inverter.
3 GND Power supply ground input. Power supply positive voltage input.
4 CAP− Connect this pin to the negative terminal of
charge-pump capacitor.
Same as inverter.
5 OUT Negative voltage output. Power supply ground input.
6 LV Low-voltage operation input. Tie LV to GND
when input voltage is less than 3.5V. Above
3.5V, LV can be connected to GND or left
open. When driving OSC with an external clock,
LV must be connected to GND.
LV must be tied to OUT.
7 OSC Oscillator control input. OSC is connected to an
internal 15 pF capacitor. An external capacitor
can be connected to slow the oscillator. Also,
an external clock can be used to drive OSC.
Same as inverter except that OSC cannot be
driven by an external clock.
8 V+ Power supply positive voltage input. Positive voltage output.
Circuit Description
The LM2662/LM2663 contains four large CMOS switches
which are switched in a sequence to invert the input supply
voltage. Energy transfer and storage are provided by external capacitors.
Figure 2
illustrates the voltage conversion
scheme. When S
1
and S3are closed, C1charges to the sup-
ply voltage V+. During this time interval switches S
2
and S
4
are open. In the second time interval, S1and S3are open
and S
2
and S4are closed, C1is charging C2. After a number
of cycles, the voltage across C
2
will be pumped to V+. Since
the anode of C
2
is connected to ground, the output at the
cathode of C
2
equals −(V+) assuming no load on C2, no loss
in the switches, and no ESR in the capacitors. In reality, the
charge transfer efficiency depends on the switching frequency, the on-resistance of the switches, and the ESR of
the capacitors.
8-Lead SO (M)
DS100003-20
DS100003-21
Top View
Order Number LM2662M, LM2663M
See NS Package Number M08A
DS100003-22
FIGURE 2. Voltage Inverting Principle
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Application Information
SIMPLE NEGATIVE VOLTAGE CONVERTER
The main application of LM2662/LM2663 is to generate a
negative supply voltage. The voltage inverter circuit uses
only two external capacitors as shown in the Basic Application Circuits. The range of the input supply voltage is 1.5V to
5.5V.For a supply voltage less than 3.5V, the LV pin must be
connected to ground to bypass the internal regulator circuitry. This gives the best performance in low voltage applications. If the supply voltage is greater than 3.5V,LV may be
connected to ground or left open. The choice of leaving LV
open simplifies the direct substitution of the LM2662/
LM2663 for the LMC7660 Switched Capacitor Voltage Converter.
The output characteristics of this circuit can be approximated
by an ideal voltage source in series with a resistor. The voltage source equals −(V+). The output resistance R
out
is a
function of the ON resistance of the internal MOS switches,
the oscillator frequency, and the capacitance and ESR of C
1
and C2. Since the switching current charging and discharging C
1
is approximately twice as the output current, the effect
of the ESR of the pumping capacitor C
1
is multiplied by four
in the output resistance. The output capacitor C
2
is charging
and discharging at a current approximately equal to the output current, therefore, its ESR only counts once in the output
resistance. A good approximation is:
where RSWis the sum of the ON resistance of the internal
MOS switches shown in
Figure 2
.
High value, low ESR capacitors will reduce the output resistance. Instead of increasing the capacitance, the oscillator
frequency can be increased to reduce the 2/(f
oscxC1
) term.
Once this term is trivial compared with R
SW
and ESRs, further increasing in oscillator frequency and capacitance will
become ineffective.
The peak-to-peak output voltage ripple is determined by the
oscillator frequency, and the capacitance and ESR of the
output capacitor C
2
:
Again, using a low ESR capacitor will result in lower ripple.
POSITIVE VOLTAGE DOUBLER
The LM2662/LM2663 can operate as a positive voltage doubler (as shown in the Basic Application Circuits). The doubling function is achieved by reversing some of the connections to the device. The input voltage is applied to the GND
pin with an allowable voltage from 2.5V to 5.5V. The V+ pin
is used as the output. The LV pin and OUT pin must be connected to ground. The OSC pin can not be driven by an external clock in this operation mode. The unloaded output
voltage is twice of the input voltage and is not reduced by the
diode D
1
’s forward drop.
The Schottky diode D
1
is only needed for start-up. The internal oscillator circuit uses the V+ pin and the LV pin (connected to ground in the voltage doubler circuit) as its power
rails. Voltage across V+ and LV must be larger than 1.5V to
insure the operation of the oscillator. During start-up, D
1
is
used to charge up the voltage at V+ pin to start the oscillator;
also, it protects the device from turning-on its own parasitic
diode and potentially latching-up. Therefore, the Schottky diode D
1
should have enough current carrying capability to
charge the output capacitor at start-up, as well as a low forward voltage to prevent the internal parasitic diode from
turning-on. A Schottky diode like 1N5817 can be used for
most applications. If the input voltage ramp is less than 10V/
ms, a smaller Schottky diode like MBR0520LT1 can be used
to reduce the circuit size.
SPLIT V+ IN HALF
Another interesting application shown in the Basic Application Circuits is using the LM2662/LM2663 as a precision voltage divider. Since the off-voltage across each switch equals
V
IN
/2, the input voltage can be raised to +11V.
CHANGING OSCILLATOR FREQUENCY
For the LM2662, the internal oscillator frequency can be selected using the Frequency Control (FC) pin. When FC is
open, the oscillator frequency is 20 kHz; when FC is connected to V+, the frequency increases to 150 kHz. A higher
oscillator frequency allows smaller capacitors to be used for
equivalent output resistance and ripple, but increases the
typical supply current from 0.3 mA to 1.3 mA.
The oscillator frequency can be lowered by adding an external capacitor between OSC and GND (See typical performance characteristics). Also, in the inverter mode, an external clock that swings within 100 mV of V+ and GND can be
used to drive OSC. Any CMOS logic gate is suitable for driving OSC. LV must be grounded when driving OSC. The
maximum external clock frequency is limited to 150 kHz.
The switching frequency of the converter (also called the
charge pump frequency) is half of the oscillator frequency.
Note: OSC cannot be driven by an external clock in the voltage-doubling
mode.
TABLE 1. LM2662 Oscillator Frequency Selection
FC OSC Oscillator
Open Open 20 kHz
V+ Open 150 kHz
Open or V+ External Capacitor See Typical
Performance
Characteristics
N/A External Clock External Clock
(inverter mode only) Frequency
TABLE 2. LM2663 Oscillator Frequency Selection
OSC Oscillator
Open 150 kHz
External
Capacitor
See Typical Performance
Characteristics
External Clock External Clock Frequency
(inverter mode only)
SHUTDOWN MODE
For the LM2663, a shutdown (SD) pin is available to disable
the device and reduce the quiescent current to 10 µA. Applying a voltage greater than 2V to the SD pin will bring the device into shutdown mode. While in normal operating mode,
the SD pin is connected to ground.
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Application Information (Continued)
CAPACITOR SELECTION
As discussed in the
Simple Negative Voltage Converter
section, the output resistance and ripple voltage are dependent on the
capacitance and ESR values of the external capacitors. The output voltage drop is the load current times the output resistance,
and the power efficiency is
Where IQ(V+) is the quiescent power loss of the IC device, and I
L
2
R
OUT
is the conversion loss associated with the switch on-
resistance, the two external capacitors and their ESRs.
Low ESR capacitors (
Table 3
) are recommended for both capacitors to maximize efficiency, reduce the output voltage drop and
voltage ripple. For convenience, C
1
and C2are usually chosen to be the same.
The output resistance varies with the oscillator frequency and the capacitors. In
Figure 3
, the output resistance vs. oscillator frequency curves are drawn for four difference capacitor values.At very low frequency range, capacitance plays the most important
role in determining the output resistance. Once the frequency is increased to some point (such as 100 kHz for the 47 µF capacitors), the output resistance is dominated by the ON resistance of the internal switches and the ESRs of the external capacitors.
A low value, smaller size capacitor usually has a higher ESR compared with a bigger size capacitor of the same type. Ceramic
capacitors can be chosen for their lower ESR. As shown in
Figure 3
, in higher frequency range, the output resistance using the
10 µF ceramic capacitors is close to these using higher value tantalum capacitors.
TABLE 3. Low ESR Capacitor Manufacturers
Manufacturer Phone Capacitor Type
Nichicon Corp. (708)-843-7500 PL, PF series, through-hole aluminum electrolytic
AVX Corp. (803)-448-9411 TPS series, surface-mount tantalum
Sprague (207)-324-4140 593D, 594D, 595D series, surface-mount tantalum
Sanyo (619)-661-6835 OS-CON series, through-hole aluminum electrolytic
Murata (800)-831-9172 Ceramic chip capacitors
Taiyo Yuden (800)-348-2496 Ceramic chip capacitors
Tokin (408)-432-8020 Ceramic chip capacitors
DS100003-36
FIGURE 3. Output Source Resistance vs Oscillator Frequency
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Other Applications
PARALLELING DEVICES
Any number of LM2662s (or LM2663s) can be paralleled to reduce the output resistance. Each device must have its own pumping
capacitor C
1
, while only one output capacitor C
out
is needed as shown in
Figure 4
. The composite output resistance is:
CASCADING DEVICES
Cascading the LM2662s (or LM2663s) is an easy way to produce a greater negative voltage (as shown in
Figure 5
). If n is the
integer representing the number of devices cascaded, the unloaded output voltage V
out
is (−nVin). The effective output resistance
is equal to the weighted sum of each individual device:
A three-stage cascade circuit shown in
Figure 6
generates −3Vin, from Vin.
Cascading is also possible when devices are operating in doubling mode. In
Figure 7
, two devices are cascaded to generate 3Vin.
An example of using the circuit in
Figure 6orFigure 7
is generating +15V or −15V from a +5V input.
Note that, the number of n is practically limited since the increasing of n significantly reduces the efficiency and increases the output resistance and output voltage ripple.
DS100003-24
FIGURE 4. Lowering Output Resistance by Paralleling Devices
DS100003-25
FIGURE 5. Increasing Output Voltage by Cascading Devices
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Other Applications (Continued)
REGULATING V
out
It is possible to regulate the output of the LM2662/LM2663 by use of a low dropout regulator (such as LP2986). The whole converter is depicted in
Figure 8
. This converter can give a regulated output from −1.5V to −5.5V by choosing the proper resistor ratio:
where, V
ref
= 1.23
V
The error flag on pin 7 of the LP2986 goes low when the regulated output at pin 5 drops by about 5%below nominal. The LP2986
can be shutdown by taking pin 8 low. The less than 1 µA quiescent current in the shutdown mode is favorable for battery powered
applications.
DS100003-26
FIGURE 6. Generating −3Vinfrom +V
in
DS100003-27
FIGURE 7. Generating +3Vinfrom +V
in
DS100003-28
FIGURE 8. Combining LM2662/LM2663 with LP2986 to Make a Negative Adjustable Regulator
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Other Applications (Continued)
Also, as shown in
Figure 9
by operating the LM2662/LM2663 in voltage doubling mode and adding a low dropout regulator (such
as LP2986) at the output, we can get +5V output from an input as low as +3.3V.
DS100003-29
FIGURE 9. Generating +5V from +3.3V Input Voltage
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Physical Dimensions inches (millimeters) unless otherwise noted
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with instructions for use provided in the labeling, can
be reasonably expected to result in a significant injury
to the user.
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device or system whose failure to perform can be reasonably expected to cause the failure of the life support
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8-Lead SO (M)
Order Number LM2662M or LM2663M
NS Package Number M08A
LM2662/LM2663 Switched Capacitor Voltage Converter
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.
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