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PDF LM3350MMX Data sheet ( Hoja de datos )
| Número de pieza | LM3350MMX | |
| Descripción | Switched Capacitor Voltage Converter | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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December 1999
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.
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
Ordering Information
Order Number
Package Type
LM3350MMX
LM3350MM
Mini SO-8
Mini SO-8
Basic Operating Circuits
NSC Package
Drawing
MUA08A
MUA08A
Step-Up Converter
Package
Marking
S00A
S00A
Supplied As
3500k Units on Tape and Reel
1000 Units on Tape and Reel
Step-Down Converter
Connection Diagram
DS100002-1
Mini SO8 Package
DS100002-3
Top View
© 1999 National Semiconductor Corporation DS100002
DS100002-2
www.national.com
1 page  
Detailed Operation (Continued)
STEP-UP APPLICATIONS NEED AN EXTRA DIODE
The LM3350 is biased from pin Vhigh. Thus for step-up appli-
cations, 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 in-
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 dis-
abled and therefore, all switching action stops. During shut-
down, 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 nor-
mal operation.
Application Information
CAPACITOR SELECTION
The LM3350 requires four capacitors: an input bypass ca-
pacitor (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
ripple. The value of this capacitor (Cout) can be calculated
(approximately) based on the output ripple (∆Vout) require-
ments from:
DS100002-11
A. Step-Up Mode
DS100002-12
B. Step-Down Mode
FIGURE 1. Zout vs. C
PRECAUTIONS
The LM3350 is not short circuit protected.
where Iload is the load current and fO is the oscillator fre-
quency.
In order to ensure superior performance over the entire oper-
ating 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.
5 www.national.com
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| Páginas | Total 8 Páginas | |
| PDF Descargar | [ Datasheet LM3350MMX.PDF ] | |
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