Datasheet LM3350MM, LM3350MMX Datasheet (NSC)

LM3350
Switched Capacitor Voltage Converter

General Description

The LM3350 is a CMOS charge-pump voltage converter
which efficiently provides a 3.3V to 5V step-up, or 5V to 3.3V
step-down. The LM3350 uses four small, low cost capacitors
to provide the voltage conversion. It eliminates the cost, size
and radiated EMI related to inductor based circuits, or the
power loss of a linear regulator. Operating power conversion
efficiency greater than 90%provides ideal performance for
battery powered portable systems.

The architecture provides a fixed voltage conversion ratio of
3/2 or 2/3. Thus it can be used for other DC-DC conversions
as well.

Key Specifications

n 800 kHz switch frequency allows use of very small,

inexpensive capacitors.

Ordering Information

n 4.2Ω typical step-up output impedance
n 1.8Ω typical step-down output impedance
n 90%typical power conversion efficiency at 50 mA
n 250 nA typical shutdown current

Features

n Conversion of 3.3V to 5V, or 5V to 3.3V
n Small Mini SO-8 package
n No inductor required

Applications

n Any mixed 5V and 3.3V system
n Laptop computers and PDAs
n Handheld instrumentation
n PCMCIA cards

LM3350 Switched Capacitor Voltage Converter

December 1999

Order Number Package Type

LM3350MMX Mini SO-8 MUA08A S00A 3500k Units on Tape and Reel

LM3350MM Mini SO-8 MUA08A S00A 1000 Units on Tape and Reel

NSC Package

Drawing

Package

Marking

Supplied As

Basic Operating Circuits

Step-Up Converter

DS100002-1

Step-Down Converter

Connection Diagram

Mini SO8 Package

DS100002-3

Top View

DS100002-2

© 1999 National Semiconductor Corporation DS100002 www.national.com

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,

LM3350

please contact the National SemiconductorSalesOffice/
Distributors for availability and specifications.

Maximum Input Voltage, Step-Down 5.5V
Maximum Input Voltage, Step-Up 3.65V
Power Dissipation (P

(Note 2))

(Note 2) 250˚C/W

θ

ja

)(TA=25˚C,

D

500 mW

Storage Temperature −65˚C to +150˚C
Lead Temperature (Soldering, 10

secs)
ESD Susceptibility (Note 3) 2kV
Not short circuit protected.

Operating Conditions (Note 1)

Ambient Temperature Range −40˚C to + 85˚C

Tj Max (Note 2) 150˚C

Electrical Characteristics
3/2 Step-Up Voltage Converter

Specifications in standard type face are for Tj= 25˚C, and those with boldface type apply over full operating temperature
range. Unless otherwise specified, V

Symbol Parameter Conditions Typ (Note 4) Limits (Note 5) Units

V

V

V

I

Q1

I

Q2

Z

f

SW

V

I

Enable

P

out

out

in

out

Enable

η

Output Voltage at

NL

No Load
Output Voltage at

FL

50 mA
Input Supply

Voltage Range

Quiescent Current Shutdown Mode, V

Quiescent Current Normal Mode, I

Output Source
Impedance

Switching
Frequency

Enable Threshold
Voltage

Leakage Current Current into ENABLE pin; ENABLE =

Power Efficiency 90

= 3.3V, V

in

C1, C2, Cinand C

0.33 Ω at 1MHz. I
C1, C2, Cinand C

0.33 Ω at 1MHz. I

Enable

out

load

out

load

= 3.3V, I

load

: 0.33µF, esr ≤

=0A

: 0.33µF, esr ≤

=50mA

=50mA.

5.0 V

4.7 V

3.3 V

2.5 V(Min)

3.65 V(Max)

= 0V,

=0 A; Current into pin V

I

load

pin V

Iow

I

=50mA 4.2 Ω

load

Enable

= 0A; Current into

Ioad

low

0.025 µA
3 µA(Max)

3.75 mA

5 mA(Max)

6.25 Ω (Max)

(Note 6) 800 kHz

500 kHz(Min)

1100 kHz(Max)

1.7 V

1.0 V(Min)

2.5 V(Max)

0.025 µA

5V and all other pins at ground

1 µA(Max)

260˚C

%

Electrical Characteristics
2/3 Step-Down Voltage Converter

Specifications in standard type face are for Tj= 25˚C, and those with boldface type apply over full operating temperature
range. Unless otherwise specified, V

Symbol Parameter Conditions Typ (Note 4) Limits (Note 5) Units

V

out

V

out

V

in

I

Q1

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Output Voltage at

NL

No Load
Output Voltage at

FL

50 mA
Input Supply

Voltage Range

Quiescent Current Shutdown Mode, V

= 5V, V

high

Enable

C1, C2, Cinand C

0.33 Ω at 1MHz. I
C1, C2, Cinand C

0.33Ω at 1MHz. I

=0 A; Current into pin V

I

load

load

= 5V, I

load

: 0.33µF, esr ≤

out

=0A

load

: 0.33 µF, esr ≤

out

=50 mA

= 0V,

Enable

high

=50mA.

3.3 V

3.2 V

5V

2.2 V(Min)

5.5 V(Max)

0.25 µA

3 µA(Max)

Electrical Characteristics
2/3 Step-Down Voltage Converter

Specifications in standard type face are for Tj= 25˚C, and those with boldface type apply over full operating temperature
range. Unless otherwise specified, V

Symbol Parameter Conditions Typ (Note 4) Limits (Note 5) Units

I

Q2

Z

out

f

SW

V

Enable

I

Enable

P

η

Note 1: Absolute maximum ratings indicate limits beyond which damage to the device may occur. Operating ratings indicate conditions for which the device is in­tended to befunctional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see Electrical Characteristics. The guar­anteed specifications apply only for the test conditions listed. Some performance characteristics may degrade when the device is not operated under the listed test
conditions.

Note 2: For operation at elevated temperatures, LM3350 must be derated based on package thermal resistance of θ
Note 3: The human body model is a 100 pF capacitor discharged through a 1.5 kW resistor into each pin.
Note 4: Typical numbers are at 25˚C and represent the most likely parametric norm.
Note 5: Limits are 100%production tested at 25˚C. Limits over the operating temperature range are guaranteed through correlation using Statistical Quality Control

(SQC) methods. The limits are used to calculate National’s Averaging Outgoing Quality Level (AOQL).
Note 6: The internal oscillator runs at 1.6 MHz, the output switches operate at one half of the oscillator frequency, f

Quiescent Current Normal Mode, I

Output Source
Impedance

Switching
Frequency

Enable Threshold
Voltage

Leakage Current Current into ENABLE pin; ENABLE =

Power Efficiency 90

= 5V, V

high

pin V

high

I

=50mA 1.8 Ω

load

(Note 6) 800 kHz

5V and all other pins at ground

(Continued)

= 5V, I

Enable

= 0A; Current into

Ioad

load

=50mA.

2.5 mA

3.3 mA(Max)

3 Ω(Max)

500 kHz(Min)

1100 kHz(Max)

1.7 V

1.0 V(Min)

2.5 V(Max)

0.025 µA
1 µA(Max)

and Tjmax, Tj=TA+θjaPD.

ja

=

.

2f

OSC

SW

%

LM3350

Typical Performance Characteristics

V

vs I

load

(Step-Up)

DS100002-4

out

Pηvs I

load

(Step-Up)

DS100002-6

Output Source Impedance vs
Temperature (Step-Up)

DS100002-9

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Typical Performance Characteristics (Continued)

LM3350

V

vs I

out

(Step-Down)

load

Pηvs I

(Step-Down)

load

Output Source Impedance vs
Temperature (Step-Down)

DS100002-5

Switching Frequency vs
Temperature

DS100002-10

Pin Description

Pin Name Function

1 Cap1+ Positive terminal for the first charge

2 Cap1− Negative terminal for the first charge

3 Cap2+ Positive terminal for the second charge

4 Cap2− Negative terminal for the second charge

5V

6 Gnd Ground
7V

8 Enable Active high CMOS logic level Enable

pump capacitor.

pump capacitor.

pump capacitor.

pump capacitor.
In Step-Up mode, this will be the input

low

terminal. In Step-Down mode, this will
be the output terminal.

In Step-Down mode, this will be the

high

input terminal. In Step-Up mode, this
will be the output terminal.

Input. Connect to Voltage Input terminal
to enable the IC. Connect to Ground
(Pin 6) to disable.

DS100002-7

DS100002-8

Detailed Operation

OPERATING PRINCIPLE

The LM3350 is a charge-pump voltage converter that pro­vides a voltage conversion ratio of 3/2 in step-up mode and
a conversion ratio of 2/3 in the step-down mode. Thus it can
be used in the step-down mode to provide a 3.3V output
from a regulated 5V input or in the step-up mode to provide
a 5V output from a regulated 3.3V input. Other values of in­put voltages can be used as long as they are within the lim­its.

The LM3350 contains an array of CMOS switches which are
operated in a certain sequence to provide the step-up or
step-down of the input supply. An internal RC oscillator pro­vides the timing signals.

Energy transfer and storage are provided by four inexpen­sive ceramic capacitors. The selection of these capacitors is
explained in the Capacitor Selection section under Applica­tion Information.

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Detailed Operation (Continued)

STEP-UP APPLICATIONS NEED AN EXTRA DIODE

The LM3350 is biased from pin V
cations, an external Schottky diode (D1) is needed to supply
power to V
shutdown, this diode will provide a DC path from V

during startup (See

high

The load may therefore continue to draw current from the in-

. Thus for step-up appli-

high

Figure 2

). Note that during

in

to V

out

put voltage source. This Schottky diode is not required for
step-down applications (See

Figure 3

).

SHUTDOWN MODE

When ENABLE is a logic low (ground), the LM3350 enters a
low power shutdown mode. In this mode, all circuitry is dis­abled and therefore, all switching action stops. During shut­down, the current consumption drops to 250 nA (typical).
When ENABLE is a logic high, (i.e. 3.3V for step-up mode
and 5.0V for step-down mode), the LM3350 returns to nor­mal operation.

Application Information

CAPACITOR SELECTION

The LM3350 requires four capacitors: an input bypass ca­pacitor (connected between V
capacitor (connected between V
sampling capacitors (C1 and C2 in

±

(

20%) ceramic chip type capacitors are recommended for
all four capacitors. The usable operating frequency should
be greater than 5 MHz for all capacitors.

The input bypass capacitor (C
should be at least that of the sampling capacitors.

While the recommended sampling capacitor values are 0.33
µF, other values may be selected. Values other than 0.33 µF
affect maximum output current rating and efficiency.
shows typical output impedance (Z
value.

The output hold capacitor value determines the output ripple.
Increasing the value of the hold capacitor decreases the
ripple. The value of this capacitor (C
(approximately) based on the output ripple (∆V
ments from:

and ground), an output hold

in

and ground), and two

out

Figures 2, 3

) is the least critical. Its value

in

). 0.33 µF

Figure 1

) versus capacitor

out

) can be calculated

out

) require-

out

.

A. Step-Up Mode

B. Step-Down Mode

FIGURE 1. Z

PRECAUTIONS

The LM3350 is not short circuit protected.

LM3350

DS100002-11

DS100002-12

vs. C

out

where I
quency.

is the load current and fOis the oscillator fre-

load

In order to ensure superior performance over the entireoper­ating temperature range, capacitors made of X7R dielectric
material are suggested. However, capacitors made of other
dielectric materials that still meet the

±

20%specification

over the entire temperature range can also be used.

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Typical Application Circuits

LM3350

Layout Information

DS100002-13

FIGURE 2. Step-Up Converter

DS100002-14

FIGURE 3. Step-Down Converter

LAYOUT CONSIDERATIONS

Figure 4

The LM3350’s high switching frequency (800 kHz) makes a good layout important.

illustrates a typical layout. It is im­portant to keep the distance short between the four capacitors and the IC. Wide traces and grounding are also recommended.
These steps will minimize trace inductance and high frequency ringing. Of the four capacitors, C
value of di/dt. It is therefore most important to keep them close to the IC. The ground lead that C
be kept wide and short.

high

high

and C

and C

have the highest

low

share should also

low

The location of the diode (D1) used in the step-up configuration is not critical. This diode is only used during the initial turn on of
the IC. D1 is not needed in step-down applications.

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Layout Information (Continued)

A. Copper side (5X)

LM3350

DS100002-16

B. Actual Size of the Layout

DS100002-15

C. Copper side with Component Locations (5X)

FIGURE 4. Typical Layout

DS100002-17

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Physical Dimensions inches (millimeters) unless otherwise noted

LM3350 Switched Capacitor Voltage Converter

Order Number LM3350MMX or LM3350MM

8-Lead Mini SO (MM)

NS Package Number MUA08A

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NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT
DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL
COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:

1. Life support devices or systems are devices or
systems which, (a) are intended for surgical implant
into the body, or (b) support or sustain life, and
whose failure to perform when properly used in
accordance with instructions for use provided in the

2. A critical component is any component of a life
support device or system whose failure to perform
can be reasonably expected to cause the failure of
the life support device or system, or to affect its
safety or effectiveness.

labeling, can be reasonably expected to result in a
significant injury to the user.

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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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