Datasheet LM2767M5X, LM2767M5 Datasheet (NSC)

LM2767
Switched Capacitor Voltage Converter

LM2767 Switched Capacitor Voltage Converter

February 2000

General Description

The LM2767 CMOS charge-pump voltage converter oper­ates as a voltage doubler for an input voltage in the range of
+1.8V to +5.5V. Two low cost capacitors and a diode are
used inthiscircuit to provide at least 15 mAof output current.

The LM2767 operates at 11 kHz switching frequency to
avoid audio voice-band interference. With an operating cur­rent of only 40 µA (operating efficiency greater than 90%with
most loads), the LM2767 provides ideal performance for bat­tery powered systems. The device is manufactured in a
SOT23-5 package.

Basic Application Circuit

Voltage Doubler

Features

n Doubles Input Supply Voltage
n SOT23-5 Package
n 20Ω Typical Output Impedance
n 96%Typical Conversion Efficiency at 15mA

Applications

n Cellular Phones
n Pagers
n PDAs, Organizers
n Operational Amplifier Power Suppliers
n Interface Power Suppliers
n Handheld Instruments

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Ordering Information

Order Number Package

Number

LM2767M5 MA05B S17B (Note 1) Tape and Reel (1000 units/reel)

LM2767M5X MA05B S17B (Note 1) Tape and Reel (3000 units/reel)

Note 1: The small physical size of the SOT-23 package does not allow for the full part number marking. Devices will be marked with the designation shown in
the column Package Marking.

© 2000 National Semiconductor Corporation DS101274 www.national.com

Package

Marking

Supplied as

Connection Diagram

LM2767

Top View With Package Marking

Pin Description

Pin Name Function

1V
2 GND Power supply ground input.
3 CAP− Connect this pin to the negative terminal of the

4 V+ Power supply positive voltage input.
5 CAP+ Connect this pin to the positive terminal of the

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OUT

5-Lead SOT (M5)

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Actual Size

Positive voltage output.

charge-pump capacitor.

charge-pump capacitor.

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LM2767

Absolute Maximum Ratings (Note 2)

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 V+ to V
V

Continuous Output Current 30 mA

OUT

Output Short-Circuit Duration to GND (Note 3) 1 sec.
Continuous Power

Dissipation (T
T

(Note 4) 150˚C

JMax

=

25˚C)(Note 4)

A

) 5.8V

OUT

400 mW

Operating Ratings

θJA(Note 4) 210˚C/W

Junction Temperature Range −40˚C to 100˚C
Ambient Temperature Range −40˚C to 85˚C
Storage Temperature Range −65˚C to 150˚C
Lead Temp. (Soldering, 10 sec.) 240˚C
ESD Rating (Note 5)

Human Body Model
Machine Model

200V

2kV

Electrical Characteristics

Limits in standard typeface are for T
less otherwise specified: V+=5V, C

Symbol Parameter Condition Min Typ Max Units

V+ Supply Voltage 1.8 5.5 V
I

Q

I

L

R

OUT

f

OSC

f

SW

P

EFF

V

OEFF

Note 2: 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 3: V
Note 4: The maximum allowable power dissipation is calculated by using P

ambient temperature, and θ
Note 5: The human body model is a 100pF capacitor discharged through a 1.5kΩ resistor into each pin. The machine model is a 200pF capacitor discharged directly

into each pin.
Note 6: In thetest circuit, capacitors C

voltage and efficiency.

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, f

Supply Current No Load 40 90 µA
Output Current 1.8V ≤ V+ ≤ 5.5V 15 mA
Output Resistance (Note 7) I
Oscillator Frequency (Note 8) 8 22 50 kHz
Switching Frequency (Note 8) 4 11 25 kHz
Power Efficiency RL(5.0k) between GND and

Voltage Conversion Efficiency No Load 99.96

may be shorted toGND for one second without damage. For temperatures above 85˚C, V

OUT

is the junction-to-ambient thermal resistance of the specified package.

JA

=

25˚C, and limits in boldface type apply over the full operating temperature range. Un-

J

=

=

C

1

and C2are 10 µF,0.3Ω maximum ESR capacitors. Capacitors with higher ESR will increase output resistance, reduce output

1

10 µF. (Note 6)

2

L

OUT
I

L

=

15 mA 20 40 Ω

98

=

15 mA to GND 96

must not be shortedto GND or device may be damaged.

OUT

)/θJA, where T

is the maximum junction temperature, TAis the

JMax

DMax

OSC

=

(T

=

2f

JMax−TA

.

SW

%

%

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Test Circuit

LM2767

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FIGURE 1. LM2767 Test Circuit

Typical Performance Characteristics

specified)

Supply Current vs
Supply Voltage

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Output Resistance vs
Supply Voltage

(Circuit of Figure 1, V

Output Resistance vs
Capacitance

Output Resistance vs
Temperature

=

IN

5V, T

=

25˚C unless otherwise

A

DS101274-5

DS101274-6

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DS101274-7

LM2767

Typical Performance Characteristics (Circuit of Figure 1, V

specified) (Continued)

Output Voltage vs
Load Current

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Switching Frequency vs
Supply Voltage

Efficiency vs
Load Current

Switching Frequency vs
Temperature

=

IN

5V, T

=

25˚C unless otherwise

A

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Output Ripple vs
Load Current

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DS101274-23

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Circuit Description

The LM2767 contains four large CMOS switches which are

LM2767

switched in a sequence to double the input supply voltage.
Energy transfer and storage are provided by externalcapaci­tors. Figure 2 illustrates the voltage conversion scheme.
When S
age V+. During this time interval, switches S
open. In the next time interval, S
same time, S
age V+ and the voltage across C
age when there is no load. The output voltage drop when a
load is added is determined by the parasitic resistance (R

s(on)

and the charge transfer loss between capacitors. Details will
be discussed in the following application information section.

and S4are closed, C1charges to the supply volt-

2

and S4are open; at the

and S3are closed, the sum of the input volt-

1

2

gives the 2V+ output volt-

1

of the MOSFET switchesand the ESRof the capacitors)

FIGURE 2. Voltage Doubling Principle

and S3are

1

-

d

DS101274-14

equal to the output current, therefore, its ESR only counts
once in the output resistance. A good approximation of R

out

is:

where RSWis the sum of the ON resistances of the internal
MOSFET switches shown in Figure 2. R

is typically 4.5Ω

SW

for the LM2767.
The peak-to-peak output voltage ripple is determined by the

oscillator frequency as well as the capacitance and ESR of
the output capacitor C

:

2

High capacitance, low ESR capacitors can reduce both the
output resistance and the voltage ripple.

The Schottky diode D

is only needed to protect the device

1

from turning-on its own parasitic diode and potentially
latching-up. During start-up, D
the output capacitor to V

IN

will also quickly charge up

1

minus the diode drop thereby de­creasing the start-up time. Therefore, the Schottky diode D
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.

1

Application Information

Positive Voltage Doubler

The main application of the LM2767 is to double the input
voltage. The range of the input supply voltage is 1.8V to

5.5V.

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 output characteristics of this circuit can beapproximated
by an ideal voltage source in series with a resistance. The
voltage source equals 2V+. The output resistance R

is a

out

function of the ON resistance of the internal MOSFET
switches, the oscillator frequency, and the capacitance and
ESR of C
discharging C
effect of the ESR of the pumping capacitor C

and C2. Since the switching current charging and

1

is approximately twice the output current, the

1

will be multi-

1

plied by four in the output resistance. The output capacitor
C

is charging and discharging at a current approximately

2

Where IQ(V+) is the quiescent power loss of the IC device,

2

and I

R

is the conversion loss associated with the switch

L

out

on-resistance, the two external capacitors and their ESRs.
The selection of capacitors is based on the allowable voltage

droop (which equals I
age ripple. Low ESR capacitors (

), and the desired output volt-

outRout

Table 1

) are recommended
to maximize efficiency, reduce the output voltage drop and
voltage ripple.

TABLE 1. Low ESR Capacitor Manufacturers

Manufacturer Phone Website Capacitor Type

Nichicon Corp. (847)-843-7500 www.nichicon.com PL & PF series, through-hole aluminum

electrolytic
AVX Corp. (843)-448-9411 www.avxcorp.com TPS series, surface-mount tantalum
Sprague (207)-324-4140 www.vishay.com 593D, 594D, 595D series, surface-mount tantalum
Sanyo (619)-661-6835 www.sanyovideo.com OS-CON series, through-hole aluminum

electrolytic
Murata (800)-831-9172 www.murata.com Ceramic chip capacitors
Taiyo Yuden (800)-348-2496 www.t-yuden.com Ceramic chip capacitors
Tokin (408)-432-8020 www.tokin.com Ceramic chip capacitors

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Other Applications

Paralleling Devices

Any number of LM2767s can be paralleled to reduce the out­put resistance. Since there is no closed loop feedback, as
found in regulated circuits, stable operation is assured. Each
device must have its own pumping capacitor C
one output capacitor C

is needed as shown in Figure 3.

out

The composite output resistance is:

FIGURE 3. Lowering Output Resistance by Paralleling Devices

, while only

1

LM2767

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Cascading Devices

Cascading the LM2767s 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:

FIGURE 4. Increasing Output Voltage by Cascading Devices

Regulating V

OUT

It is possible to regulate the output of the LM2767 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.

>

2V

2V

in_min

in_max

V

out_min+Vdrop_max

<

V

out_max+Vdrop_min

Note that increasing the number of cascading stages is prac­itically limited since it significantly reduces the efficiency, in­creases the output resistance and output voltage ripple.

Note that the following conditions must be satisfied simulta­neously for worst case design:

(LP2980) + I

(LP2980) + I

out_max

out_min

xR

xR

R

out_max

out_min

=

out

(LM2767)

(LM2767)

1.5R

out_1+Rout_2

DS101274-20

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Other Applications (Continued)

LM2767

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FIGURE 5. Generate a Regulated +5V from +3V Input Voltage

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Physical Dimensions inches (millimeters) unless otherwise noted

LM2767 Switched Capacitor Voltage Converter

5-Lead Small Outline Package (M5)

NS Package Number MA05B

For Order Numbers, refer to the table in the ″Ordering Information″ section of this document.

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can be reasonably expected to cause the failure of
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labeling, can be reasonably expected to result in a
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