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LM3352MTCX-2.5 Datasheet(PDF) 7 Page - National Semiconductor (TI)

[Old version datasheet] Texas Instruments acquired National semiconductor.
Part No. LM3352MTCX-2.5
Description  Regulated 200 mA Buck-Boost Switched Capacitor DC/DC Converter
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Maker  NSC [National Semiconductor (TI)]
Homepage  http://www.national.com
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Typical Performance Characteristics Unless otherwise specified T
A = 25˚C. (Continued)
Applications Information
Operating Principle
The LM3352 is designed to provide a step-up/step-down
voltage regulation in battery powered systems. It combines
switched capacitor circuitry, reference, comparator, and
shutdown logic in a single 16-pin TSSOP package. The
LM3352 can provide a regulated voltage between 1.8V and
4V from an input voltage between 2.5V and 5.5V. It can sup-
ply a load current up to 200 mA.
As shown in
Figure 1, the LM3352 employs two feedback
loops to provide regulation in the most efficient manner pos-
sible. The first loop is from V
OUT through the comparator
COMP, the AND gate G
1, the phase generator, and the
switch array. The comparator’s output is high when V
OUT is
less than the reference V
REF. Regulation is provided by gat-
ing the clock to the switch array. In this manner, charge is
transferred to the output only when needed. The second
loop controls the gain configuration of the switch array. This
loop consists of the comparator, the digital control block, the
phase generator, and the switch array. The digital control
block computes the most efficient gain from a set of seven
gains based on inputs from the A/D and the comparator. The
gain signal is sent to the phase generator which then sends
the appropriate timing and configuration signals to the switch
array. This dual loop provides regulation over a wide range of
loads efficiently.
Since efficiency is automatically optimized, the curves for
V
OUT vs. VIN and Efficiency vs. VIN in the Typical Perfor-
mance Characteristics section exhibit small variations. The
reason is that as input voltage or output load changes, the
digital control loops are making decisions on how to optimize
efficiency. As the switch array is reconfigured, small varia-
tions in output voltage and efficiency result. In all cases
where these small variations are observed, the part is oper-
ating correctly; minimizing output voltage changes and opti-
mizing efficiency.
Charge Pump Capacitor Selection
A 0.33 µF ceramic capacitor is suggested for C1, C2 and C3.
To ensure proper operation over temperature variations, an
X7R dielectric material is recommended.
V
OUT Ripple vs. COUT
DS101037-31
V
OUT Ripple vs. COUT
DS101037-32
DS101037-3
FIGURE 1. Block Diagram
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