ltc3528-2 Linear Technology Corporation, ltc3528-2 Datasheet - Page 12

• Manufacturer Part Number: ltc3528-2
• Description: Ltc3528-2 - 1a, 2mhz Synchronous Step-up Dc/dc Converter In 2mm ? 3mm Dfn
• Manufacturer: Linear Technology Corporation

LTC3528-2
V
The LTC3528-2 maintains voltage regulation even when
the input voltage is above the desired output voltage. Note
that the efficiency is much lower in this mode, and the
maximum output current capability will be less. Refer to
the Typical Performance Characteristics.
SHORT-CIRCUIT PROTECTION
The LTC3528-2 output disconnect feature allows an output
short circuit while maintaining a maximum internally set
current limit. To reduce power dissipation under short-
circuit conditions, the peak switch current limit is reduced
to 750mA (typical).
SCHOTTKY DIODE
Although not required, adding a Schottky diode from
SW to V
that this defeats the output disconnect and short-circuit
protection features.
PCB LAYOUT GUIDELINES
The high speed operation of the LTC3528-2 demands
careful attention to board layout. A careless layout will
not produce the advertised performance. Figure 2 shows
12
APPLICATIONS INFORMATION
IN
> V
Figure 2. Recommended Component Placement
for Single Layer Board
OUT
OUT
OPERATION
will improve efficiency by about 2%. Note
PGOOD
SHDN
V
C
OUT
OUT
FB
1
2
3
4
LTC3528-2
V
IN
+
C
8
7
6
5
IN
V
SGND
PGND
SW
MULTIPLE VIAS
TO GROUND PLANE
IN
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the recommended component placement. A large ground
copper area with the package backside metal pad properly
soldered will help to lower the chip temperature. A multi-
layer board with a separate ground plane is ideal, but not
absolutely necessary.
COMPONENT SELECTION
Inductor Selection
The LTC3528-2 can utilize small surface mount chip induc-
tors due to its fast 2MHz switching frequency. Inductor
values between 1.5µH and 3.3µH are suitable for most
applications. Larger values of inductance will allow slightly
greater output current capability by reducing the inductor
ripple current. Increasing the inductance above 10µH will
increase size while providing little improvement in output
current capability.
The minimum inductance value is given by:
where:
The inductor current ripple is typically set for 20% to
40% of the maximum inductor current. High frequency
ferrite core inductor materials reduce frequency dependent
power losses compared to cheaper powdered iron types,
improving efficiency. The inductor should have low ESR
(series resistance of the windings) to reduce the I
losses, and must be able to handle the peak inductor cur-
rent without saturating. Molded chokes and some chip
inductors usually do not have enough core area to support
the peak inductor currents of 1.5A seen on the LTC3528-2.
To minimize radiated noise, use a shielded inductor. See
Table 1 for suggested components and suppliers.
Ripple = Allowable inductor current ripple (amps peak-
peak)
V
V
L >
IN(MIN)
OUT(MAX)
V
IN(MIN)
= Minimum input voltage
2 • Ripple • V
= Maximum output voltage
• V
(
OUT(MAX)
OUT(MAX)
– V
IN(MIN)
)
µH
2
R power
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