LT1176/LT1176-5
Step-Down
Switching Regulator
FEATURES
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1.2A On-Board Switch
100kHz Switching Frequency
Excellent Dynamic Behavior
DIP and Surface Mount Packages
Only 8mA Quiescent Current
Preset 5V Output Available
Operates Up to 35V Input
Micropower Shutdown Mode
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 鈥渂uck鈥?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.
APPLICATI
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Buck Converter with Output Voltage Range of
2.5V to 30V
Positive-to-Negative Converter
Negative Boost Converter
Mulitple Output Buck Converter
DESCRIPTIO
The LT1176 is a 1A monolithic bipolar switching regulator
which requires only a few external parts for normal opera-
TYPICAL APPLICATI
Basic 5V Positive Buck Converter
L1*
100碌H
10V T0 35V
V
IN
LT1176-5
SENSE
V
C
R3
2.7k
C3
100碌F
C2
0.01碌F
V
SW
1N5819
EFFICIENCY (%)
5V, 0.8A
GND
+
*COILTRONICS #100-1-52
LT1176/76-5 鈥?TA01
PULSE ENGINEERING, INC. #PE-92102
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 M碌. SEE EFFICIENCY GRAPH.
UO
U
UO
S
5V Buck Converter Efficiency
90
L = 100碌H ON MAGNETICS INC.
SIZE T-50 KOOL M碌 CORE
V
IN
= 10V
80
V
IN
= 20V
+
C1
470碌F
25V
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 鈥?TA02
1
1
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