TI LM2664M6X Switched capacitor voltage converter Datasheet

LM2664
Switched Capacitor Voltage Converter
General Description
Features
The LM2664 CMOS charge-pump voltage converter inverts
a positive voltage in the range of +1.8V to +5.5V to the
corresponding negative voltage of −1.8V to −5.5V. The
LM2664 uses two low cost capacitors to provide up to 40 mA
of output current.
The LM2664 operates at 160 kHz oscillator frequency to
reduce output resistance and voltage ripple. With an operating current of only 220 µA (operating efficiency greater than
91% with most loads) and 1 µA typical shutdown current, the
LM2664 provides ideal performance for battery powered
systems. The device is in SOT-23-6 package.
n
n
n
n
n
Inverts Input Supply Voltage
SOT23-6 Package
12Ω Typical Output Impedance
91% Typical Conversion Efficiency at 40 mA
1µA Typical Shutdown Current
Applications
n
n
n
n
n
n
Cellular Phones
Pagers
PDAs
Operational Amplifier Power Suppliers
Interface Power Suppliers
Handheld Instruments
Basic Application Circuits
Voltage Inverter
10003101
+5V to −10V Converter
10003125
© 2005 National Semiconductor Corporation
DS100031
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LM2664 Switched Capacitor Voltage Converter
September 2005
LM2664
Absolute Maximum Ratings (Note 1)
TJMax(Note 3)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
θJA (Note 3)
Supply Voltage (V+ to GND, or GND to OUT)
SD
Output Short-Circuit Duration to GND (Note 2)
Continuous Power
Dissipation (TA = 25˚C)(Note 3)
210˚C/W
Operating Junction
Temperature Range
5.8V
−40˚ to 85˚C
Storage Temperature Range
(GND − 0.3V) to (V+ +
0.3V)
V+ and OUT Continuous Output Current
150˚C
−65˚C to +150˚C
Lead Temp. (Soldering, 10 seconds)
300˚C
ESD Rating
2kV
50 mA
1 sec.
600 mW
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, C1 = C2 = 3.3 µF. (Note 4)
Symbol
Parameter
V+
Supply Voltage
IQ
Supply Current
ISD
Shutdown Supply Current
VSD
Shutdown Pin Input Voltage
Min
(Note 5)
Condition
Typ
(Note 6)
1.8
No Load
220
IL
Output Current
RSW
Sum of the Rds(on)of the four
internal MOSFET switches
ROUT
Output Resistance (Note 9)
IL = 40 mA
fOSC
Oscillator Frequency
(Note 10)
fSW
Switching Frequency
(Note 10)
PEFF
Power Efficiency
RL (1.0k) between GND and
OUT
µA
µA
0.8
(Note 8)
40
80
No Load
V
mA
4
8
12
25
Ω
Ω
160
kHz
40
80
kHz
90
94
%
IL = 40 mA to GND
Voltage Conversion Efficiency
V
500
2.0
(Note 7)
IL = 40 mA
Units
5.5
1
Normal Operation
Shutdown Mode
VOEFF
Max
(Note 5)
91
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 PDMax = (TJMax − TA)/θJA, where TJMax is the maximum junction temperature, TA is the
ambient temperature, and θJA is the junction-to-ambient thermal resistance of the specified package.
Note 4: In the test circuit, capacitors C1 and C2 are 3.3 µF, 0.3Ω maximum ESR capacitors. Capacitors with higher ESR will increase output resistance, reduce
output voltage and efficiency.
Note 5: Min. and Max. limits are guaranteed by design, test, or statistical analysis.
Note 6: Typical numbers are not guaranteed but represent the most likely norm.
Note 7: The minimum input high for the shutdown pin equals 40% of V+.
Note 8: The maximum input low for the shutdown pin equals 20% of V+.
Note 9: Specified output resistance includes internal switch resistance and capacitor ESR. See the details in the application information for simple negative voltage
converter.
Note 10: The output switches operate at one half of the oscillator frequency, fOSC = 2fSW.
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2
LM2664
Test Circuit
10003103
*C1 and C2 are 3.3 µF, SC series OS-CON capacitors.
FIGURE 1. LM2664 Test Circuit
Typical Performance Characteristics
(Circuit of Figure 1, V+ = 5V unless otherwise specified)
Supply Current vs
Supply Voltage
Supply Current vs
Temperature
10003121
10003113
Output Source
Resistance vs Supply
Voltage
Output Source
Resistance vs
Temperature
10003115
10003114
3
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LM2664
Typical Performance Characteristics (Circuit of Figure 1, V+ = 5V unless otherwise specified)
(Continued)
Output Voltage Drop
vs Load Current
Efficiency vs
Load Current
10003116
10003117
Oscillator Frequency vs
Supply Voltage
Oscillator Frequency vs
Temperature
10003119
10003118
Shutdown Supply
Current vs
Temperature
10003120
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4
LM2664
Connection Diagrams
6-Lead Small Outline Package (M6)
10003122
Actual Size
10003104
Top View With Package Marking
Ordering Information
Order Number
Package Number
Package Marking
Supplied as
LM2664M6
MA06A
SO3A (Note 11)
Tape and Reel (1000 units/rail)
LM2664M6X
MA06A
SO3A (Note 11)
Tape and Reel (3000 units/rail)
Note 11: The first letter "S" identifies the part as a switched capacitor converter. The next two numbers are the device number. The fourth letter "A" indicates the
grade. Only one grade is available. Larger quantity reels are available upon request.
Pin Descriptions
Pin
Name
1
GND
Function
Power supply ground input.
2
OUT
Negative voltage output.
3
CAP−
Connect this pin to the negative terminal of the charge-pump capacitor.
4
SD
5
V+
6
CAP+
Shutdown control pin, tie this pin to V+ in normal operation, and to GND for shutdown.
Power supply positive voltage input.
Connect this pin to the positive terminal of the charge-pump capacitor.
Circuit Description
The LM2664 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 S1 and S3 are closed, C1 charges to the supply
voltage V+. During this time interval, switches S2 and S4 are
open. In the second time interval, S1 and S3 are open; at the
same time, S2 and S4 are closed, C1 is charging C2. After a
number of cycles, the voltage across C2 will be pumped to
V+. Since the anode of C2 is connected to ground, the output
at the cathode of C2 equals −(V+) when there is no load
current. The output voltage drop when a load is added is
determined by the parasitic resistance (Rds(on) of the MOSFET switches and the ESR of the capacitors) and the charge
transfer loss between capacitors. Details will be discussed in
the following application information section.
10003105
FIGURE 2. Voltage Inverting Principle
5
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LM2664
Application Information
SIMPLE NEGATIVE VOLTAGE CONVERTER
SHUTDOWN MODE
The main application of LM2664 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 1.8V to 5.5V.
A shutdown (SD ) pin is available to disable the device and
reduce the quiescent current to 1µA. Applying a voltage less
than 20% of V+ to the SD pin will bring the device into
shutdown mode. While in normal operating mode, the pin is
connected to V+.
The output characteristics of this circuit can be approximated
by an ideal voltage source in series with a resistance. The
voltage source equals −(V+). The output resistance Rout is a
function of the ON resistance of the internal MOSFET
switches, the oscillator frequency, the capacitance and ESR
of C1 and C2. Since the switching current charging and
discharging C1 is approximately twice as the output current,
the effect of the ESR of the pumping capacitor C1 will be
multiplied by four in the output resistance. The output capacitor C2 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
of Rout is:
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 IL2Rout is the conversion loss associated with the switch
on-resistance, the two external capacitors and their ESRs.
The selection of capacitors is based on the specifications of
the dropout voltage (which equals Iout Rout), the output voltage ripple, and the converter efficiency. Low ESR capacitors
(Table 1) are recommended to maximize efficiency, reduce
the output voltage drop and voltage ripple.
where RSW is the sum of the ON resistance of the internal
MOSFET switches shown in Figure 2.
High capacitance, low ESR capacitors will reduce the output
resistance.
The peak-to-peak output voltage ripple is determined by the
oscillator frequency, the capacitance and ESR of the output
capacitor C2:
Again, using a low ESR capacitor will result in lower ripple.
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
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LM2664
Other Applications
PARALLELING DEVICES
Any number of LM2664s can be paralleled to reduce the
output resistance. Each device must have its own pumping
capacitor C1, while only one output capacitor Cout is needed
as shown in Figure 3. The composite output resistance is:
10003110
FIGURE 3. Lowering Output Resistance by Paralleling Devices
CASCADING DEVICES
Cascading the LM2664s is an easy way to produce a greater
negative voltage (e.g. A two-stage cascade circuit is shown
in Figure 4).
If n is the integer representing the number of devices cascaded, the unloaded output voltage Vout is (-nVin). The effective output resistance is equal to the weighted sum of
each individual device:
Rout = nRout_1 + n/2 Rout_2 + ... + Rout_n
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.
10003111
FIGURE 4. Increasing Output Voltage by Cascading Devices
COMBINED DOUBLER AND INVERTER
In Figure 5, the LM2664 is used to provide a positive voltage
doubler and a negative voltage converter. Note that the total
current drawn from the two outputs should not exceed 50
mA.
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LM2664
Other Applications
(Continued)
10003112
FIGURE 5. Combined Voltage Doubler and Inverter
Note that, the following conditions must be satisfied simultaneously for worst case design:
Vin_min > Vout_min +Vdrop_max (LP2980)
+ Iout_max x Rout_max (LM2664)
Vin_max < Vout_max +Vdrop_min (LP2980)
+ Iout_min x Rout_min (LM2664)
REGULATING VOUT
It is possible to regulate the negative output of the LM2664
by use of a low dropout regulator (such as LP2980). The
whole converter is depicted in Figure 6. This converter can
give a regulated output from −1.8V to −5.5V by choosing the
proper resistor ratio:
Vout = Vref (1 + R1/R2)
where, Vref = 1.23V
10003124
FIGURE 6. Combining LM2664 with LP2980 to Make a Negative Adjustable Regulator
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LM2664 Switched Capacitor Voltage Converter
Physical Dimensions
inches (millimeters) unless otherwise noted
6-Lead Small Outline Package (M6)
NS Package Number MA06A
For Order Numbers, refer to the table in the "Ordering Information" section of this document.
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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