LM2681M6/NOPB [NSC]
IC SWITCHED CAPACITOR CONVERTER, 160 kHz SWITCHING FREQ-MAX, PDSO6, LEAD FREE, SOT-23, 6 PIN, Switching Regulator or Controller;
| 型号： | LM2681M6/NOPB |
| 厂家： | 
National Semiconductor |
| 描述： | IC SWITCHED CAPACITOR CONVERTER, 160 kHz SWITCHING FREQ-MAX, PDSO6, LEAD FREE, SOT-23, 6 PIN, Switching Regulator or Controller 开关 光电二极管 |
| 文件： | 总8页 (文件大小：232K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
January 2003
LM2681
Switched Capacitor Voltage Converter
General Description
Features
n Doubles or Splits Input Supply Voltage
n SOT23-6 Package
The LM2681 CMOS charge-pump voltage converter oper-
ates 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) is used in this circuit to provide up
to 20 mA of output current. The LM2681 can also work as a
voltage divider to split a voltage in the range of +1.8V to
+11V in half.
n 15Ω Typical Output Impedance
n 90% Typical Conversion Efficiency at 20 mA
Applications
n Cellular Phones
n Pagers
The LM2681 operates at 160 kHz oscillator frequency to
reduce output resistance and voltage ripple. With an operat-
ing current of only 550 µA (operating efficiency greater than
90% with most loads) the LM2681 provides ideal perfor-
mance for battery powered systems. The device is in SOT-
23-6 package.
n PDAs
n Operational Amplifier Power Suppliers
n Interface Power Suppliers
n Handheld Instruments
Basic Application Circuits
Voltage Doubler
10096501
Splitting Vin in Half
10096502
© 2003 National Semiconductor Corporation
DS100965
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Absolute Maximum Ratings (Note 1)
T
JMax(Note 3)
150˚C
210˚C/W
θJA (Note 3)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Operating Junction
−40˚ to 85˚C
Temperature Range
Storage Temperature Range
Lead Temp. (Soldering, 10 seconds)
ESD Rating
V+ to GND Voltage:
5.8V
11.6V
−65˚C to +150˚C
300˚C
OUT to GND Voltage:
OUT to V+ Voltage:
5.8V
2kV
V+ and OUT Continuous Output Current
Output Short-Circuit Duration to GND (Note 2)
Continuous Power
30 mA
1 sec.
600 mW
Dissipation (TA = 25˚C)(Note 3)
Electrical Characteristics
Limits in standard typeface are for TJ = 25˚C, and limits in boldface type apply over the full operating temperature range. Un-
less otherwise specified: V+ = 5V, C1 = C2 = 3.3 µF. (Note 4)
Symbol
V+
Parameter
Supply Voltage
Condition
Min
2.5
Typ
Max
5.5
Units
V
IQ
Supply Current
No Load
550
1000
µA
IL
Output Current
20
mA
RSW
Sum of the Rds(on)of the four
internal MOSFET switches
Output Resistance (Note 5)
Oscillator Frequency
Switching Frequency
Power Efficiency
IL = 20 mA
8
16
40
Ω
ROUT
fOSC
fSW
IL = 20 mA
15
160
80
Ω
(Note 6)
80
40
kHz
kHz
(Note 6)
PEFF
RL (1.0k) between GND and
OUT
86
93
%
%
IL = 20 mA to GND
No Load
90
VOEFF
Voltage Conversion Efficiency
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
= (T
− T )/θ , where T
is the maximum junction temperature, T is the
JMax A
DMax
JMax
A
JA
ambient temperature, and θ is the junction-to-ambient thermal resistance of the specified package.
JA
Note 4: In the test circuit, capacitors C and C are 3.3 µF, 0.3Ω maximum ESR capacitors. Capacitors with higher ESR will increase output resistance, reduce
1
2
output voltage and efficiency.
Note 5: Specified output resistance includes internal switch resistance and capacitor ESR. See the details in the application information for positive voltage doubler.
Note 6: The output switches operate at one half of the oscillator frequency, f
= 2f
.
OSC
SW
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2
Test Circuit
10096503
FIGURE 1. LM2681 Test Circuit
Typical Performance Characteristics (Circuit of Figure 1, V+ = 5V unless otherwise specified)
Supply Current vs
Supply Voltage
Supply Current vs
Temperature
10096504
10096505
Output Source
Resistance vs Supply
Voltage
Output Source
Resistance vs
Temperature
10096506
10096507
3
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Typical Performance Characteristics (Circuit of Figure 1, V+ = 5V unless otherwise specified)
(Continued)
Output Voltage Drop
vs Load Current
Efficiency vs
Load Current
10096508
10096509
Oscillator Frequency vs
Supply Voltage
Oscillator Frequency vs
Temperature
10096510
10096511
Connection Diagram
6-Lead SOT (M6)
10096522
Actual Size
10096513
Top View With Package Marking
Ordering Information
Order Number
LM2681M6
Package Number Package Marking
Supplied as
MA06A
MA06A
S10A (Note 7)
S10A (Note 7)
Tape and Reel (250 units/rail)
Tape and Reel (3000 units/rail)
LM2681M6X
Note 7: 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.
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4
Pin Description
Function
Pin
1
Name
V+
Voltage Doubler
Power supply positive voltage input
Power supply ground input
Voltage Split
Positive voltage output
Same as doubler
2
GND
Connect this pin to the negative terminal of the
charge-pump capacitor
3
CAP−
Same as doubler
4
5
GND
OUT
Power supply ground input
Same as doubler
Positive voltage output
Power supply positive voltage input
Connect this pin to the positive terminal of the
charge-pump capacitor
6
CAP+
Same as doubler
mately equal to the output current, therefore, its ESR only
counts once in the output resistance. A good approximation
of Rout is:
Circuit Description
The LM2681 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 capaci-
tors. 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 capaci-
tors) and the charge transfer loss between capacitors. De-
tails will be discussed in the following application information
section.
where RSW is the sum of the ON resistance of the internal
MOSFET switches shown in Figure 2.
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 reslistance 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.
10096514
FIGURE 2. Voltage Doubling Principle
SPLIT V+ IN HALF
Application Information
Another interesting application shown in the Basic Applica-
tion Circuits is using the LM2681 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.
POSITIVE VOLTAGE DOUBLER
The main application of the LM2681 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
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 ca-
pacitor C2 is charging and discharging at a current approxi-
5
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Where IQ(V+) is the quiescent power loss of the IC device,
and IL Rout is the conversion loss associated with the switch
Application Information (Continued)
2
CAPACITOR SELECTION
on-resistance, the two external capacitors and their ESRs.
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 selection of capacitors is based on the specifications of
the dropout voltage (which equals Iout Rout), the output volt-
age 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
Capacitor Type
PL & PF series, through-hole aluminum electrolytic
TPS series, surface-mount tantalum
593D, 594D, 595D series, surface-mount tantalum
OS-CON series, through-hole aluminum electrolytic
Ceramic chip capacitors
(708)-843-7500
(803)-448-9411
(207)-324-4140
(619)-661-6835
(800)-831-9172
(800)-348-2496
(408)-432-8020
AVX Corp.
Sprague
Sanyo
Murata
Taiyo Yuden
Tokin
Ceramic chip capacitors
Ceramic chip capacitors
Other Applications
PARALLELING DEVICES
Any number of LM2681s 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:
10096519
FIGURE 3. Lowering Output Resistance by Paralleling Devices
CASCADING DEVICES
Rout = 1.5Rout_1 + Rout_2
Cascading the LM2681s is an easy way to produce a greater
voltage (A two-stage cascade circuit is shown in Figure 4).
Note that, the increasing of the number of cascading stages
is pracitically limited since it significantly reduces the effi-
ciency, increases the output resistnace and output voltage
ripple.
The effective output resistance is equal to the weighted sum
of each individual device:
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6
Other Applications (Continued)
10096520
FIGURE 4. Increasing Output Voltage by Cascading Devices
REGULATING VOUT
Note that, the following conditions must be satisfied simulta-
neously for worst case design:
It is possible to regulate the output of the LM2681 by use of
a low dropout regulator (such as LP2980-5.0). The whole
converter is depicted in Figure 5.
>
2Vin_min Vout_min +Vdrop_max (LP2980) + Iout_max x Rout
-
_max (LM2681)
<
A different output voltage is possible by use of LP2980-3.3,
LP2980-3.0, or LP2980-adj.
2Vin_max Vout_max +Vdrop_min (LP2980) + Iout_min x Rout
_min (LM2681)
-
10096521
FIGURE 5. Generate a Regulated +5V from +3V Input Voltage
7
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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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