LM3352MTC-2.5 National Semiconductor, LM3352MTC-2.5 Datasheet - Page 7

• Manufacturer Part Number: LM3352MTC-2.5
• Description: Regulated 200 mA Buck-Boost Switched Capacitor DC/DC Converter
• Manufacturer: National Semiconductor

Typical Performance Characteristics
V
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
COMP, the AND gate G
switch array. The comparator’s output is high when V
less than the reference V
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
OUT
Ripple vs. C
OUT
REF
1
, the phase generator, and the
. Regulation is provided by gat-
OUT
through the comparator
DS101037-31
FIGURE 1. Block Diagram
OUT
is
Unless otherwise specified T
V
7
OUT
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
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.
Ripple vs. C
OUT
vs. V
IN
OUT
and Efficiency vs. V
A
= 25˚C. (Continued)
IN
DS101037-3
DS101037-32
in the Typical Perfor-
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