LTC3528B Linear Technology Corporation, LTC3528B Datasheet - Page 10

• Manufacturer Part Number: LTC3528B
• Description: 1MHz Synchronous Step-Up DC/DC Converters
• Manufacturer: Linear Technology Corporation

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LTC3528/LTC3528B
V
The LTC3528/LTC3528B will maintain voltage regulation
even when the input voltage is above the desired output
voltage. Note that the effi ciency 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/LTC3528B 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/LTC3528B de-
mands careful attention to board layout. A careless layout
will not produce the advertised performance. Figure 1
shows the recommended component placement. A large
ground copper area with the package backside metal pad
APPLICATIONS INFORMATION
10
IN
> V
OUT
OUT
OPERATION
will improve effi ciency by about 2%. Note
Figure 1. Recommended Component Placement for Single Layer Board
PGOOD
SHDN
V
C
OUT
OUT
FB
1
2
3
4
LTC3528
V
IN
+
properly soldered will help to lower the chip temperature.
A multilayer board with a separate ground plane is ideal,
but not absolutely necessary.
COMPONENT SELECTION
Inductor Selection
The LTC3528/LTC3528B can utilize small surface mount
chip inductors due to their fast 1MHz switching frequency.
Inductor values between 2.2μH and 4.7μH are suitable for
most applications. Larger values of inductance will allow
slightly greater output current capability (and lower the
Burst Mode threshold) by reducing the inductor ripple cur-
rent. Increasing the inductance above 10μH will increase
size while providing little improvement in output current
capability.
The minimum inductance value is given by:
where:
Ripple = Allowable inductor current ripple (amps peak-
peak)
V
V
C
L >
8
7
6
5
IN
IN(MIN)
OUT(MAX)
V
SGND
PGND
SW
MULTIPLE VIAS
TO GROUND PLANE
IN
V
IN(MIN)
1.2 • Ripple • V
= Minimum input voltage
= Maximum output voltage
3528 F01
• V
(
OUT(MAX)
OUT(MAX)
– V
IN(MIN)
)
µH
3528fa