LT1176 Datasheet, PDF (1/4 Pages) Linear Technology – Step-Down Switching Regulator

LT1176/LT1176-5
Step-Down
Switching Regulator
FEATURES
s _{1.2A On-Board Switch}
s _{100kHz Switching Frequency}
s _{Excellent Dynamic Behavior}
s _{DIP and Surface Mount Packages}
s _{Only 8mA Quiescent Current}
s _{Preset 5V Output Available}
s _{Operates Up to 35V Input}
s _{Micropower Shutdown Mode}
APPLICATI S
s _{Buck Converter with Output Voltage Range of}
2.5V to 30V
s _{Positive-to-Negative Converter}
s _{Negative Boost Converter}
s _{Mulitple Output Buck Converter}
DESCRIPTIO
The LT1176 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 con-
verter, 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 version.
For further design details and application help, see the
LT1074/LT1076 data sheet and Application Note 44.
TYPICAL APPLICATI
Basic 5V Positive Buck Converter
10V T0 35V
V_IN
V_SW
L1*
100µH
5V, 0.8A
LT1176-5
1N5819
GND
+ _C3
100µF
SENSE
V_C
R3
2.7k
C2
0.01µF
+ C1
470µF
25V
*COILTRONICS #100-1-52
PULSE ENGINEERING, INC. #PE-92102
LT1176/76-5 • 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)
LT1176/76-5 • TA02
1