LM3350
LM3350 Switched Capacitor Voltage Converter
Literature Number: SNIS101B
LM3350
Switched Capacitor Voltage Converter
General Description
Features
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.
■
■
■
■
■
Conversion of 3.3V to 5V, or 5V to 3.3V
4.2Ω typical step-up output impedance
1.8Ω typical step-down output impedance
90% typical power conversion efficiency at 50 mA
800 kHz switch frequency allows use of very small,
inexpensive capacitors.
■ No inductor required
■ 250 nA typical shutdown current
■ Small Mini SO-8 package
Applications
■
■
■
■
Any mixed 5V and 3.3V system
Laptop computers and PDAs
Handheld instrumentation
PCMCIA cards
Basic Operating Circuits
Step-Up Converter
10000201
Step-Down Converter
10000202
© 2010 National Semiconductor Corporation
100002
100002 Version 6 Revision 2
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Print Date/Time: 2010/12/28 23:06:13
LM3350 Switched Capacitor Voltage Converter
OBSOLETE
December 28, 2010
LM3350
Connection Diagram
Mini SO8 Package
10000203
Top View
Ordering Information
Order Number
Package Type
NSC Package
Drawing
Package Marking
LM3350MMX
Mini SO-8
MUA08A
S00A
3500k Units on Tape and Reel
LM3350MM
Mini SO-8
MUA08A
S00A
1000 Units on Tape and Reel
Supplied As
Pin Descriptions
Pin
Name
Function
1
Cap1+ Positive terminal for the first charge pump
capacitor.
2
Cap1− Negative terminal for the first charge pump
capacitor.
3
Cap2+ Positive terminal for the second charge
pump capacitor.
4
Cap2− Negative terminal for the second charge
pump capacitor.
5
Vlow
In Step-Up mode, this will be the input
terminal. In Step-Down mode, this will be
the output terminal.
6
Gnd
Ground
7
Vhigh
In Step-Down mode, this will be the input
terminal. In Step-Up mode, this will be the
output terminal.
8
Enable Active high CMOS logic level Enable Input.
Connect to Voltage Input terminal to
enable the IC. Connect to Ground (Pin 6)
to disable.
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100002 Version 6 Revision 2
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Operating Conditions
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Maximum Input Voltage, Step-Down
Maximum Input Voltage, Step-Up
Power Dissipation (PD) (TA=25°C,
(Note 2))
5.5V
3.65V
500 mW
θja (Note 2)
Tj Max (Note 2)
Storage Temperature
Lead Temperature (Soldering, 10 secs)
ESD Susceptibility (Note 3)
Not short circuit protected.
250°C/W
(Note 1)
Ambient Temperature Range
−40°C to + 85°C
150°C
−65°C to +150°C
260°C
2kV
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, Vin = 3.3V, VEnable = 3.3V, Iload = 50 mA.
Conditions
Typ (Note 4)
VoutNL
Output Voltage at No
Load
C1, C2, Cin and Cout: 0.33µF, esr ≤ 0.33 Ω
at 1MHz. Iload = 0 A
5.0
V
VoutFL
Output Voltage at 50
mA
C1, C2, Cin and Cout: 0.33µF, esr ≤ 0.33 Ω
at 1MHz. Iload = 50 mA
4.7
V
Vin
Input Supply Voltage
Range
Symbol
IQ1
IQ2
Zout
fSW
VEnable
IEnable
Pη
Parameter
Quiescent Current
3.3
Shutdown Mode, VEnable = 0V, Iload=0 A;
Current into pin Vlow
0.025
Normal Mode, IIoad = 0A; Current into pin
VIow
3.75
Output Source
Impedance
Iload = 50 mA
4.2
Switching Frequency
(Note 6)
Quiescent Current
V
V(Min)
V(Max)
3
µA
µA(Max)
5
mA
mA(Max)
6.25
Ω (Max)
500
1100
kHz
kHz(Min)
kHz(Max)
1.0
2.5
V
V(Min)
V(Max)
1
µA
µA(Max)
Ω
1.7
Current into ENABLE pin; ENABLE = 5V
and all other pins at ground
Power Efficiency
0.025
90
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Units
2.5
3.65
800
Enable Threshold
Voltage
Leakage Current
Limits (Note 5)
%
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LM3350
Absolute Maximum Ratings (Note 1)
LM3350
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, Vhigh = 5V, VEnable = 5V, Iload = 50 mA.
Conditions
Typ (Note 4)
VoutNL
Output Voltage at No
Load
C1, C2, Cin and Cout: 0.33µF, esr ≤ 0.33 Ω
at 1MHz. Iload = 0 A
3.3
V
VoutFL
Output Voltage at 50
mA
C1, C2, Cin and Cout: 0.33 µF, esr ≤ 0.33Ω
at 1MHz. Iload =50 mA
3.2
V
Vin
Input Supply Voltage
Range
Symbol
IQ1
IQ2
Zout
fSW
VEnable
IEnable
Pη
Parameter
Quiescent Current
5
Shutdown Mode, VEnable = 0V, Iload=0 A;
Current into pin Vhigh
0.25
Normal Mode, IIoad = 0A; Current into pin
Vhigh
2.5
Output Source
Impedance
Iload = 50 mA
1.8
Switching Frequency
(Note 6)
Quiescent Current
V
V(Min)
V(Max)
3
µA
µA(Max)
3.3
mA
mA(Max)
3
Ω (Max)
500
1100
kHz
kHz(Min)
kHz(Max)
1.0
2.5
V
V(Min)
V(Max)
1
µA
µA(Max)
Ω
1.7
Current into ENABLE pin; ENABLE = 5V
and all other pins at ground
Power Efficiency
Units
2.2
5.5
800
Enable Threshold
Voltage
Leakage Current
Limits (Note 5)
0.025
90
%
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 be functional, 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 θja and Tj max, Tj = TA+ θjaPD.
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, fOSC = 2fSW.
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LM3350
Typical Performance Characteristics
Vout vs Iload (Step-Up)
Pη vs Iload (Step-Up)
10000204
10000206
Output Source Impedance vs Temperature (Step-Up)
Vout vs Iload (Step-Down)
10000209
10000205
Output Source Impedance vs Temperature (Step-Down)
Pη vs Iload (Step-Down)
10000208
10000207
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LM3350
Switching Frequency vs Temperature
10000210
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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 stepdown 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.
where Iload is the load current and fO is the oscillator frequency.
In order to ensure superior performance over the entire operating 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.
STEP-UP APPLICATIONS NEED AN EXTRA DIODE
The LM3350 is biased from pin Vhigh. Thus for step-up applications, an external Schottky diode (D1) is needed to supply
power to Vhigh during startup (See Figure 2). Note that during
shutdown, this diode will provide a DC path from Vin to Vout.
The load may therefore continue to draw current from the input 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.
10000211
A. Step-Up Mode
Application Information
CAPACITOR SELECTION
The LM3350 requires four capacitors: an input bypass capacitor (connected between Vin and ground), an output hold
capacitor (connected between Vout and ground), and two
sampling capacitors (C1 and C2 in Figures 2, 3). 0.33 µF
(±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 (Cin) is the least critical. Its value
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. Figure
1 shows typical output impedance (Zout) versus capacitor value.
The output hold capacitor value determines the output ripple.
Increasing the value of the hold capacitor decreases the rip-
10000212
B. Step-Down Mode
FIGURE 1. Zout vs. C
PRECAUTIONS
The LM3350 is not short circuit protected.
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LM3350
ple. The value of this capacitor (Cout) can be calculated (approximately) based on the output ripple (ΔVout) requirements
from:
Detailed Operation
LM3350
Typical Application Circuits
10000213
FIGURE 2. Step-Up Converter
10000214
FIGURE 3. Step-Down Converter
and high frequency ringing. Of the four capacitors, Chigh and
Clow have the highest value of di/dt. It is therefore most important to keep them close to the IC. The ground lead that
Chigh and Clow share should also be kept wide and short.
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.
Layout Information
LAYOUT CONSIDERATIONS
The LM3350's high switching frequency (800 kHz) makes a
good layout important. Figure 4 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
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LM3350
10000216
B. Actual Size of the Layout
10000215
A. Copper side (5X)
10000217
C. Copper side with Component Locations (5X)
FIGURE 4. Typical Layout
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LM3350
Physical Dimensions inches (millimeters) unless otherwise noted
8-Lead Mini SO (MM)
Order Number LM3350MMX or LM3350MM
NS Package Number MUA08A
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LM3350
Notes
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LM3350 Switched Capacitor Voltage Converter
Notes
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