LT1176_15 Datasheet, PDF (1/8 Pages) Linear Technology – Step-Down Switching Regulator

LT1176/LT1176-5
Step-Down
Switching Regulator
FEATURES
n _{1.2A Onboard Switch}
n _{100kHz Switching Frequency}
n _{Excellent Dynamic Behavior}
n _{DIP and Surface Mount Packages}
n _{Only 8mA Quiescent Current}
n _{Preset 5V Output Available}
n _{Operates Up to 35V Input}
n _{Micropower Shutdown Mode}
APPLICATIONS
n _{Buck Converter with Output Voltage Range of}
2.5V to 30V
n _{Positive-to-Negative Converter}
n _{Negative Boost Converter}
n _{Multiple Output Buck Converter}
DESCRIPTION
The LT^®1176 is a 1A monolithic bipolar switching regulator
which requires only a few external parts for normal opera-
tion. The power switch, all oscillator and control circuitry
and all current limit components are included on the chip.
The topology is a classic positive buck configuration but
several design innovations allows this device to be used as
a positive-to-negative converter, a negative boost converter,
and as a flyback converter. The switch output is specified
to swing below ground.
The LT1176 uses a true analog multiplier in the feedback
loop. This makes the device respond nearly instantaneously
to input voltage fluctuations and makes loop gain indepen-
dent of input voltage. As a result, dynamic behavior of the
regulator is significantly improved over previous designs.
On-chip pulse by pulse current limiting makes the LT1176
nearly bust proof for output overloads or shorts. The input
voltage range as a buck converter is 8V to 35V, but a self
boot feature allows input voltages as low as 5V in the
inverting and boost configurations.
The LT1176 is available in a low cost 8-lead DIP package
with frequency preset at 100kHz and current limit at 1.7A.
An adjustable output is offered as well as a preset 5V ver-
sion. For further design details and application help, see
the LT1074/LT1076 data sheet and Application Note 44.
L, LT, LTC, LTM, Linear Technology, SwitcherCAD and the Linear logo are registered
trademarks of Linear Technology Corporation. All other trademarks are the property of their
respective owners.
TYPICAL APPLICATION
Basic 5V Positive Buck Converter
10V T0 35V
+
V_IN
V_SW
LT1176-5
GND
C3
100µF
SENSE
V_C
R3
2.7k
C2
0.01µF
L1*
100µH
1N5819
5V, 0.8A
+ C1
470µF
25V
*COILTRONICS #100-1-52
PULSE ENGINEERING, INC. #PE-92102
11765 TA01
HURRICANE #HL-AG210LL
THESE ARE LOW COST POWDERED IRON CORES. OPTIMUM EFFICIENCY
AND SMALLEST SIZE IS OBTAINED BY USING A LOW LOSS CORE SUCH
AS MAGNETICS INC. KOOL Mµ. SEE EFFICIENCY GRAPH.
5V Buck Converter Efficiency
90
L = 100µH ON MAGNETICS INC.
SIZE T-50 KOOL Mµ CORE
V_IN = 10V
80
V_IN = 20V
70
60
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
LOAD CURRENT (A)
11765 TA02
11765fb
1