LT1172CQ Linear Technology, LT1172CQ Datasheet - Page 5

IC SWTCHNG REGULATOR HI-EFF 5-DD

LT1172CQ

Manufacturer Part Number
LT1172CQ
Description
IC SWTCHNG REGULATOR HI-EFF 5-DD
Manufacturer
Linear Technology
Type
Step-Down (Buck), Step-Up (Boost), Inverting, Cuk, Flyback, Forward Converterr
Datasheet

Specifications of LT1172CQ

Internal Switch(s)
Yes
Synchronous Rectifier
No
Number Of Outputs
1
Voltage - Output
1.25 ~ 40 V
Current - Output
1.25A
Frequency - Switching
100kHz
Voltage - Input
3 ~ 40 V
Operating Temperature
0°C ~ 100°C
Mounting Type
Surface Mount
Package / Case
D²Pak, TO-263 (5 leads + tab)
Power - Output
100W
Lead Free Status / RoHS Status
Contains lead / RoHS non-compliant

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ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER
DC
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: Minimum effective switch “on” time for the LT1170/LT1171/
LT1172 (in current limit only) is ≈ 0.6μs. This limits the maximum safe
input voltage during an output shorted condition. Buck mode and inverting
mode input voltage during an output shorted condition is limited to:
Maximum input voltage can be increased by increasing R or Vf.
External current limiting such as that shown in AN19, Figure 39, will
provide protection up to the full supply voltage rating. C1 in Figure 39
should be reduced to 200pF .
temperature range, otherwise specifications are at T
MAX
V
buck and inverting mode
R = Inductor DC resistance
I
Vf = Output catch diode forward voltage at I
t = 0.6μs, f = 100kHz switching frequency
L
IN
= 10A for LT1170, 5A for LT1171, and 2.5A for LT1172
(max, output shorted) =
Maximum Switch Duty Cycle
Shutdown Mode
Supply Current
Shutdown Mode
Threshold Voltage
Flyback Sense Delay Time (Note 5)
15V +
( )
R
( )
( )
t
I
L
( )
f
L
+ Vf
CONDITIONS
3V ≤ V
V
3V ≤ V
C
= 0.05V
A
= 25°C. V
IN
IN
≤ V
≤ V
The
MAX
MAX
l
IN
denotes the specifications which apply over the full operating
= 15V, V
Transformer designs will tolerate much higher input voltages because
leakage inductance limits rate of rise of current in the switch. These
designs must be evaluated individually to assure that current limit is well
controlled up to maximum input voltage.
Boost mode designs are never protected against output shorts because
the external catch diode and inductor connect input to output.
Note 3: Measured with V
2A for LT1171, and 1A for LT1172.
Note 4: For duty cycles (DC) between 50% and 80%, minimum guaranteed
switch current is given by I
(2 – DC) for the LT1171, and I
Note 5: Minimum input voltage for isolated flyback mode is 7V. V
for HV grade in fully isolated mode to avoid switch breakdown.
C
= 0.5V, V
LT1170/LT1171/LT1172
FB
= V
REF
C
, output pin open, unless otherwise noted.
in hi clamp, V
LIM
LIM
= 3.33 (2 – DC) for the LT1170, I
= 0.833 (2 – DC) for the LT1172.
l
l
MIN
100
FB
85
50
= 0.8V. I
TYP
100
150
1.5
92
SW
= 4A for LT1170,
MAX
250
250
300
97
LIM
MAX
= 1.67
117012fg
UNITS
= 55V
5
mV
mV
μA
μs
%

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