LT1776_15 Datasheet, PDF (1/20 Pages) Linear Technology – Wide Input Range, High Efficiency, Step-Down Switching Regulator

LT1776
Wide Input Range,
High Efficiency, Step-Down
Switching Regulator
FEATURES
s _{Wide Input Range: 7.4V to 40V}
s _{Tolerates Input Transients to 60V}
s _{700mA Peak Switch Rating}
s _{Adaptive Switch Drive Maintains Efficiency at High}
Load Without Pulse Skipping at Light Load
s _{True Current Mode Control}
s _{200kHz Fixed Operating Frequency}
s _{Synchronizable to 400kHz}
s _{Low Supply Current in Shutdown: 30µA}
s _{Available in 8-Pin SO and PDIP Packages}
U
APPLICATIONS
s _{Automotive DC/DC Converters}
s _{Cellular Phone Battery Charger Accessories}
s _{IEEE 1394 Step-Down Converters}
DESCRIPTION
The LT^®1776 is a wide input range, high efficiency Buck
(step-down) switching regulator. The monolithic die in-
cludes all oscillator, control and protection circuitry. The
part can accept input voltages as high as 60V and contains
an output switch rated at 700mA peak current. Current
mode control delivers excellent dynamic input supply
rejection and short-circuit protection.
The LT1776 contains several features to enhance effi-
ciency. The internal control circuitry is normally powered
via the V_CC pin, thereby minimizing power drawn directly
from the V_IN supply (see Applications Information). The
action of the LT1776 switch circuitry is also load depen-
dent. At medium to high loads, the output switch circuitry
maintains fast rise time for good efficiency. At light loads,
rise time is deliberately reduced to avoid pulse skipping
behavior.
The available SO-8 package and 200kHz switching fre-
quency allow for minimal PC board area requirements.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATION
V_IN
8V TO 40V
+
5
1
V_IN
2
SHDN V_CC
3
V_SW
39µF
63V
LT1776
6
SYNC
7
FB
8
V_C
100µH*
+
MBR160
100µF
10V
2200pF
GND
22k
100pF
4
*43T #30 ON MAGNETICS
MPP #55030
Figure 1
5V
400mA
36.5k
1%
12.1k
1%
1776 F01
Efficiency vs V_IN and I_LOAD
90
80
70
60
50
40
V_IN = 10V
30 ^{VIN = 20V}
V_IN = 30V
20 ^{VIN = 40V}
1
10
100
LOAD CURRENT (mA)
1000
1776 TA01
1