LT3506 LINER [Linear Technology], LT3506 Datasheet - Page 18

• Manufacturer Part Number: LT3506
• Description: Dual Monolithic 1.6A Step-Down Switching Regulator
• Manufacturer: LINER [Linear Technology]

LT3506/LT3506A
Single, Low-Ripple 3.2A Output
The LT3506 can generate a single, low-ripple 3.2A output
if the outputs of the two switching regulators are tied
together and share a single output capacitor. By tying the
two FB pins together and the two V
two channels will share the load current. There are several
advantages to this two-phase buck regulator. Ripple cur-
rents at the input and output are reduced, reducing volt-
age ripple and allowing the use of smaller, less expensive
capacitors. Although two inductors are required, each will
be smaller than the inductor required for a single-phase
regulator. This may be important when there are tight
height restrictions on the circuit. The Typical Applications
section shows circuits with maximum heights of 1.4mm,
1.8mm and 2.1mm.
There is one special consideration regarding the two phase
circuit. When the difference between the input voltage and
output voltage is less than 2.5V, then the boost circuits may
APPLICATIO S I FOR ATIO

U
U
W
C
pins together, the
U
prevent the two channels from properly sharing current.
If, for example, channel 1 gets started first, it can supply
the load current, while channel 2 never switches enough
current to get its boost capacitor charged. In this case,
channel 1 will supply the load until it reaches current limit,
the output voltage drops, and channel 2 gets started. The
solution is to generate a boost supply generated from
either SW pin that will service both BOOST pins. The low
profile, single output 5V to 3.3V converter shown in the
Typical Applications section shows how to do this.
Other Linear Technology Publications
Application notes 19, 35 and 44 contain more detailed
descriptions and design information for buck regulators
and other switching regulators. The LT1376 data sheet
has a more extensive discussion of output ripple, loop
compensation and stability testing. Design note 100 shows
how to generate a dual (+ and –) output supply using a
buck regulator
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