Linear LTC1474 Demo Manual

U
DESCRIPTIO
This demonstration circuit is a step-down (buck) regulator
®
using the LTC 1474/LTC1475. The exclusive use of surface
mount components and the LTC1474/LTC1475 in the tiny
MSOP package results in a highly efficient application in a
small board space. This demo board highlights the
capabilities of the LTC1474/LTC1475, which use a current
mode, constant off-time architecture to switch an internal
P-channel power MOSFET. This results in a power supply
that has low ripple and fast transient response. At low
output currents the LTC1474/LTC1475 automatically
TM
switch to Burst Mode operation to maintain high operating
efficiencies and minimize supply current. At no load,only
PERFORmANCE SU
SYMBOL PARAMETER
V Input Voltage Range
IN
V Output Voltage
OUT
I Maximum Output Current
OUT
I Typical Supply Current
Q
TYPICAL PERFOR A CE CHARACTERISTICS A D BOARD PHOTO
Board A, B, D, E Efficiency
100
V = 5V
IN
90
V = 10V
IN
80
V = 15V
IN
70
60
50
0.03 0.3 3
LOAD CURRENT (mA)
ARY
CONDITIONS
V = 3.3V
OUT
V = 5V
OUT
LTC1474/LTC1475
LTC1474-3.3/LTC1475-3.3
LTC1474-5/LTC1475-5
R
SENSE
R
SENSE
V = 10V, I
IN
V = 10V, I
IN
W U
L = 100µH
V = 3.3V
OUT
R = 0Ω
SENSE
30 300
DM143 TPC
DEMO MANUAL DC143
DEMO MANUAL DC143
10µA I
10µA (typical) is required to regulate the output. The parts
can be shut down to further reduce the supply current to
6µA (typical). In dropout, the internal P-channel MOSFET
is turned on continuously (100% duty cycle), providing
low dropout operation with V
battery detector allows the user to monitor the input
supply through an external resistive divider. This board is
intended for applications such as cellular phones, GSM
systems, 4mA to 20mA current-loop pirate supplies or any
portable battery-powered application. Gerber files for this
circuit board are available. Call the LTC factory.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
= 0Ω
= 0.25Ω
= 0
LOAD
= 0
LOAD
U
Demo Board A
DM143 DB A
NO DESIGN SWITCHER
LTC1474/LTC1475
, High Efficiency,
Q
Step-Down DC/DC
Converter
≅ V
. An onboard low-
OUT IN
BOARD SUFFIX VALUE
A, B, D, E 3.3V to 18V
C, F 5V to 18V
3.3V ± 0.10V
A, D
3.3V ± 0.10V
B, E
5V ± 0.15V
C, F
ALL 300mA
ALL 150mA
A, B, C 10µA
D, E, F 15µA
Demo Board D
DM143 DB D
1