Datasheet LM2765M6 Datasheet (NSC)

LM2765
Switched Capacitor Voltage Converter

LM2765 Switched Capacitor Voltage Converter

March 2000

General Description

The LM2765 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 in this circuit to provide up to 20 mAof output current.

The LM2765 operates at 50 kHz switching frequency to re­duce output resistance and voltage ripple. With an operating
current of only130 µA (operating efficiency greater than 90%
with most loads) and 0.1µA typical shutdown current, the
LM2765 provides ideal performance for battery powered
systems. The device is manufactured in a SOT-23-6 pack­age.

Basic Application Circuits

Voltage Doubler

Features

n Doubles Input Supply Voltage
n SOT23-6 Package
n 20Ω Typical Output Impedance
n 90% Typical Conversion Efficiency at 20 mA
n 0.1µA Typical Shutdown Current

Applications

n Cellular Phones
n Pagers
n PDAs
n Operational Amplifier Power Supplies
n Interface Power Supplies
n Handheld Instruments

DS101281-1

Connection Diagram

6-Lead SOT (M6)

DS101281-22

Actual Size

DS101281-13

Top View With Package Marking

Ordering Information

Order Number Package

Number

LM2765M6 MA06A S15B (Note 1) Tape and Reel (1000 units/reel)

LM2765M6X MA06A S15B (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 DS101281 www.national.com

Package

Marking

Supplied as

Pin Description

LM2765

Pin Name Function

1 V+ Power supply positive voltage input.
2 GND Power supply ground input.
3 CAP− Connect this pin to the negative terminal of the charge-pump

4 SD Shutdown control pin, tie this pin to ground in normal operation.
5V
6 CAP+ Connect this pin to the positive terminal of the charge-pump

OUT

capacitor.

Positive voltage output.

capacitor.

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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

) 5.8V

OUT

SD (GND − 0.3V) to (V+ +

0.3V)

V

Continuous Output Current 40 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

600 mW

Operating Ratings

θJA(Note 4) 210˚C/W

Junction Temperature Range −40˚ to 100˚C
Ambient Temperature Range −40˚ to 85˚C
Storage Temperature Range −65˚C to 150˚C
Lead Temp. (Soldering, 10

seconds) 240˚C
ESD Rating (Note 5)

Human body model
Machine model

200V

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, C

Symbol Parameter Condition Min Typ Max Units

V+ Supply Voltage 1.8 5.5 V
I

Q

I

SD

V

SD

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
peratures above 85˚C, OUT must not be shorted to GND or V+, or device may be damaged.

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 the test 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 130 450 µA
Shutdown Supply Current 0.1 0.5

Shutdown Pin Input Voltage Shutdown Mode 2.0

Output Current 2.5V ≤ VIN≤ 5.5V 20

Output Resistance (Note 7) IL=20mA 20 40 Ω
Oscillator Frequency (Note 8) 40 100 200 kHz
Switching Frequency (Note 8) 20 50 100 kHz
Power Efficiency IL= 20 mA to GND 92 %
Voltage Conversion Efficiency No Load 99.96 %

may be shorted to GND for one second without damage. However, shorting V

OUT

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

JA

and C2are 3.3 µF, 0.3Ω maximum ESR capacitors. Capacitors with higher ESR will increase output resistance, reduce output

1

= 3.3 µF. (Note 6)

1=C2

= 85˚C 0.2

T

A

Normal Operation 0.6

<

1.8V ≤ V

2.5V 10

IN

to V+ may damage the device and should be avoided. Also, for tem-

OUT

DMax

OSC

=(T

=2fSW.

JMax−TA

)/θJA, where T

is the maximum junction temperature, TAis the

JMax

mA

LM2765

µA

V

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Test Circuit

LM2765

DS101281-3

FIGURE 1. LM2765 Test Circuit

Typical Performance Characteristics

specified)

Supply Current vs
Supply Voltage

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Output Resistance vs
Supply Voltage

(Circuit of Figure 1, VIN=5V,TA= 25˚C unless otherwise

Output Resistance vs
Capacitance

DS101281-5

Output Resistance vs
Temperature

DS101281-6

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DS101281-7

LM2765

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

= 5V, TA= 25˚C unless otherwise

IN

DS101281-9

Output Ripple vs
Load Current

DS101281-10

DS101281-12

DS101281-11

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Circuit Description

The LM2765 contains four large CMOS switches which are

LM2765

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 S

and S4are closed, C1charges to the supply volt-

2

age V+. During this time interval, switches S
open. In the next time interval, S
same time, S

and S3are closed, the sum of the input volt-

1

age V+ and the voltage across C

and S4are open; at the

2

gives the 2V+ output volt-

1

age when there is no load. The output voltage drop when a
load is added is determined by the parasitic resistance (R

of the MOSFET switches and the ESR of the capacitors)

s(on)

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

FIGURE 2. Voltage Doubling Principle

Application Information

Positive Voltage Doubler

The main application of the LM2765 is to double the input
voltage. The range of the input supply voltage is 1.8V 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 R
function of the ON resistance of the internal MOSFET
switches, the oscillator frequency, and the capacitance and
ESR of C
discharging C
the effect of the ESR of the pumping capacitor C
multiplied by four in the output resistance. The output ca­pacitor C
mately equal to the output current, therefore, its ESR only
counts once in the output resistance. A good approximation
of R

and C2. Since the switching current charging and

1

is approximately twice as the output current,

1

is charging and discharging at a current approxi-

2

is:

out

and S3are

1

out

will be

1

-

d

DS101281-14

is a

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

is typically 8Ω for

SW

the LM2765.
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.

Shutdown Mode

A shutdown (SD) pin is available to disable the device and
reduce the quiescent current to 0.1 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.

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

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 specifications of

the dropout voltage (which equals I

), the output volt-

outRout

age ripple, and the converter efficiency. Low ESR capacitors
(

Table 1

) are recommended to maximize efficiency, reduce

the output voltage drop and voltage ripple.

1

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

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Application Information (Continued)

TABLE 1. Low ESR Capacitor Manufacturers (Continued)

Manufacturer Phone Website Capacitor Type

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

Other Applications

Paralleling Devices

Any number of LM2765s can be paralleled to reduce the out­put resistance. Each device must have its own pumping ca­pacitor C
shown in Figure 3. The composite output resistance is:

, while only one output capacitor C

1

is needed as

out

LM2765

FIGURE 3. Lowering Output Resistance by Paralleling Devices

Cascading Devices

Cascading the LM2765s 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

DS101281-19

R

= 1.5R

out

out_1+Rout_2

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.

DS101281-20

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Other Applications (Continued)

Regulating V

LM2765

It is possible to regulate the output of the LM2765 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.

OUT

>

2V

2V

in_min

in_max

V

out_min+Vdrop_max

<

V

out_max+Vdrop_min

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

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

(LP2980) + I

(LP2980) + I

out_max

out_min

xR

xR

out_max

out_min

(LM2765)

(LM2765)

DS101281-21

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Physical Dimensions inches (millimeters) unless otherwise noted

LM2765 Switched Capacitor Voltage Converter

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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