NSC LM2665 Switched capacitor voltage converter Datasheet

LM2665
Switched Capacitor Voltage Converter
General Description
Features
The LM2665 CMOS charge-pump voltage converter operates as a voltage doubler for an input voltage in the range of
+2.5V to +5.5V. Two low cost capacitors and a diode
(needed during start-up) are used in this circuit to provide up
to 40 mA of output current. The LM2665 can also work as a
voltage divider to split a voltage in the range of +1.8V to
+11V in half.
The LM2665 operates at 160 kHz oscillator frequency to reduce output resistance and voltage ripple. With an operating
current of only 650 µA (operating efficiency greater than 90%
with most loads) and 1µA typical shutdown current, the
LM2665 provides ideal performance for battery powered
systems. The device is in SOT-23-6 package.
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Doubles or Splits Input Supply Voltage
SOT23-6 Package
12Ω Typical Output Impedance
90% Typical Conversion Efficiency at 40 mA
1µA Typical Shutdown Current
Applications
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Cellular Phones
Pagers
PDAs
Operational Amplifier Power Suppliers
Interface Power Suppliers
Handheld Instruments
Basic Application Circuits
Voltage Doubler
DS100049-1
Splitting Vin in Half
DS100049-2
© 1999 National Semiconductor Corporation
DS100049
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LM2665 Switched Capacitor Voltage Converter
November 1999
LM2665
Absolute Maximum Ratings (Note 1)
Continuous Power
Dissipation (TA = 25˚C)(Note 3)
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)
SD
600 mW
TJMax(Note 3)
150˚C
θJA (Note 3)
210˚C/W
Operating Junction
Temperature Range
5.8V
(GND − 0.3V) to (V+ +
0.3V)
−40˚ to 85˚C
Storage Temperature Range
−65˚C to +150˚C
V+ and OUT Continuous Output Current
50 mA
Lead Temp. (Soldering, 10 seconds)
Output Short-Circuit Duration to GND (Note 2)
1 sec.
ESD Rating
300˚C
2kV
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
Condition
Min
Typ
2.5
No Load
650
Max
V
1250
µA
1
Shutdown Mode
IL
Output Current
RSW
Sum of the Rds(on)of the four
internal MOSFET switches
IL = 40 mA
µA
2.0
(Note 5)
Normal Operation
Units
5.5
0.8
(Note 6)
40
V
mA
3.5
8
12
25
Ω
Ω
ROUT
Output Resistance (Note 7)
IL = 40 mA
fOSC
Oscillator Frequency
(Note 8)
80
160
kHz
fSW
Switching Frequency
(Note 8)
40
80
kHz
PEFF
Power Efficiency
RL (1.0k) between GND and
OUT
IL = 40 mA to GND
86
93
VOEFF
Voltage Conversion Efficiency
No Load
%
90
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: The minimum input high for the shutdown pin equals 40% of V+.
Note 6: The maximum input low of the shutdown pin equals 20% of V+.
Note 7: Specified output resistance includes internal switch resistance and capacitor ESR. See the details in the application information for positive voltage doubler.
Note 8: The output switches operate at one half of the oscillator frequency, fOSC = 2fSW.
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LM2665
Test Circuit
DS100049-3
FIGURE 1. LM2665 Test Circuit
Typical Performance Characteristics
(Circuit of Figure 1, V+ = 5V unless otherwise specified)
Supply Current vs
Supply Voltage
Supply Current vs
Temperature
DS100049-4
Output Source
Resistance vs Supply
Voltage
DS100049-5
Output Source
Resistance vs
Temperature
DS100049-6
DS100049-7
3
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LM2665
Typical Performance Characteristics
(Circuit of Figure 1, V+ = 5V unless otherwise
specified) (Continued)
Output Voltage Drop
vs Load Current
Efficiency vs
Load Current
DS100049-9
DS100049-8
Oscillator Frequency vs
Supply Voltage
Oscillator Frequency vs
Temperature
DS100049-10
DS100049-11
Shutdown Supply
Current vs
Temperature
DS100049-12
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LM2665
Connection Diagram
6-Lead SOT (M6)
DS100049-22
Actual Size
DS100049-13
Top View With Package Marking
Ordering Information
Order Number
Package
Number
Package
Marking
Supplied as
LM2665M6
MA06A
SO4A (Note 9)
Tape and Reel (1000 units/rail)
LM2665M6X
MA06A
SO4A (Note 9)
Tape and Reel (3000 units/rail)
Note 9: 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 Description
Pin
Name
Function
Voltage Doubler
1
V+
Voltage Split
Power supply positive voltage input.
Positive voltage output.
2
GND
Power supply ground input
Same as doubler
3
CAP−
Connect this pin to the negative terminal of the
charge-pump capacitor
Same as doubler.
4
SD
Shutdown control pin, tie this pin to ground in normal
operation.
Same as doubler.
5
OUT
Positive voltage output.
Power supply positive voltage
input
6
CAP+
Connect this pin to the positive terminal of the
charge-pump capacitor.
Same as doubler
Circuit Description
The LM2665 contains four large CMOS switches which are
switched in a sequence to double the input supply voltage.
Energy transfer and storage are provided by external capacitors. Figure 2 illustrates the voltage conversion scheme.
When S2 and S4 are closed, C1 charges to the supply voltage V+. During this time interval, switches S1 and S3 are
open. In the next time interval, S2 and S4 are open; at the
same time, S1 and S3 are closed, the sum of the input voltage V+ and the voltage across C1 gives the 2V+ output voltage when there is no load. 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.
DS100049-14
FIGURE 2. Voltage Doubling Principle
Application Information
Positive Voltage Doubler
The main application of the LM2665 is to double the input
voltage. The range of the input supply voltage is 2.5V to
5.5V.
The output characteristics of this circuit can be approximated
by an ideal voltage source in series with a resistance. The
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LM2665
Application Information
Split V+ in Half
Another interesting application shown in the Basic Application Circuits is using the LM2665 as a precision voltage divider. . This circuit can be derived from the voltage doubler
by switching the input and output connections. In the voltage
divider, the input voltage applies across the OUT pin and the
GND pin (which are the power rails for the internal oscillator),
therefore no start-up diode is needed. Also, since the
off-voltage across each switch equals Vin/2, the input voltage
can be raised to +11V.
(Continued)
voltage source equals 2V+. 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:
Shutdown Mode
A shutdown (SD) pin is available to disable the device and
reduce the quiescent current to 1 µA. In normal operating
mode, the SD pin is connected to ground. The device can be
brought into the shutdown mode by applying to the SD pin a
voltage greater than 40% of the V+ pin voltage.
where RSW is the sum of the ON resistance of the internal
MOSFET switches shown in Figure 2.
Capacitor Selection
As discussed in the Positive Voltage Doubler 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
The peak-to-peak output voltage ripple is determined by the
oscillator frequency, the capacitance and ESR of the output
capacitor C2:
High capacitance, low ESR capacitors can reduce both the
output resistance and the voltage ripple.
The Schottky diode D1 is only needed for start-up. The internal oscillator circuit uses the OUT pin and the GND pin. Voltage across OUT and GND must be larger than 1.8V to insure
the operation of the oscillator. During start-up, D1 is used to
charge up the voltage at the OUT 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 D1 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.
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.
Low ESR Capacitor Manufacturers
Manufacturer
Nichicon Corp.
Phone
(708)-843-7500
Capacitor Type
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
Other Applications
Paralleling Devices
Any number of LM2665s 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:
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LM2665
Other Applications
(Continued)
DS100049-19
FIGURE 3. Lowering Output Resistance by Paralleling Devices
Cascading Devices
Note that, the increasing of the number of cascading stages
is pracitically limited since it significantly reduces the efficiency, increases the output resistance and output voltage
ripple.
Cascading the LM2665s is an easy way to produce a greater
voltage (A two-stage cascade circuit is shown in Figure 4).
The effective output resistance is equal to the weighted sum
of each individual device:
Rout = 1.5Rout_1 + Rout_2
DS100049-20
FIGURE 4. Increasing Output Voltage by Cascading Devices
Regulating VOUT
Note that, the following conditions must be satisfied simultaneously for worst case design:
It is possible to regulate the output of the LM2665 by use of
a low dropout regulator (such as LP2980-5.0). The whole
converter is depicted in Figure 5.
A different output voltage is possible by use of LP2980-3.3,
LP2980-3.0, or LP2980-adj.
2Vin_min > Vout_min +Vdrop_max (LP2980) + Iout_max x Rout_max (LM2665)
2Vin_max < Vout_max +Vdrop_min (LP2980) + Iout_min x Rout_min (LM2665)
DS100049-21
FIGURE 5. Generate a Regulated +5V from +3V Input Voltage
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LM2665 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.
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