LT1172MJ8 Linear Technology, LT1172MJ8 Datasheet - Page 4

• Manufacturer Part Number: LT1172MJ8
• Description: SP-SWREG/Monolithic, 100kHz 5A 2.5A And 1.25A High Efficiency Switching Regulato
• Manufacturer: Linear Technology

LT1 170/LT1 171/LT1172
ELECTRICAL CHARACTERISTICS
perature range, otherwise specifications are at T
SYMBOL PARAMETER
f
DC
Note 1: Absolute Maximum Ratings are those values beyond which the life
of the device may be impaired.
Note 2: Minimum effective switch “on” time for the LT1170/71/72 (in current
limit only) is 0.6 s. 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:
V
buck and inverting mode
R = Inductor DC resistance
I
Vf = Output catch diode forward voltage at I
t = 0.6 s, f = 100kHz switching frequency
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.
TYPICAL PERFOR A CE CHARACTERISTICS
4
L
IN
I
I
IN
SW
= 10A for LT1170, 5A for LT1171, and 2.5A for LT1172
MAX
(max, output shorted) = 15V +
16
12
8
4
0
0
Switch Current Limit vs Duty Cycle*
* DIVIDE VERTICAL SCALE BY TWO FOR
10
LT1171, BY FOUR FOR LT1172.
Supply Current Increase
During Switch On-Time
Switching Frequency
Maximum Switch Duty Cycle
Shutdown Mode
Supply Current
Shutdown Mode
Threshold Voltage
Flyback Sense Delay Time (Note 5)
20 30
–55 C
125 C
DUTY CYCLE (%)
40
50 60 70 80 90 100
25 C
(R)(I
W
(t)(f)
L
) + Vf
1170/1/2 G01
L
U
CONDITIONS
3V V
V
3V V
C
= 0.05V
A
IN
IN
2.9
2.8
2.7
2.6
2.5
2.4
2.3
= 25 C. V
–75
V
V
Minimum Input Voltage
MAX
MAX
–50
The
SWITCH CURRENT = 0A
–25
IN
= 15V, V
TEMPERATURE ( C)
SWITCH CURRENT = I
0
denotes the specifications which apply over the full operating tem-
25
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
I
LT1172.
Note 5: Minimum input voltage for isolated flyback mode is 7V. V
55V for HV grade in fully isolated mode to avoid switch breakdown.
LIM
C
50
= 0.5V, V
= 1.67 (2 – DC) for the LT1171, and I
75 100 125
MAX
1170/1/2 G02
FB
= V
150
REF
, output pin open, unless otherwise noted.
C
in hi clamp, V
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
0
Switch Saturation Voltage
LIM
1
100
MIN
88
85
85
50
FB
LIM
= 3.33 (2 – DC) for the LT1170,
= 0.8V. I
* DIVIDE CURRENT BY TWO FOR
2
SWITCH CURRENT (A)*
= 0.833 (2 – DC) for the
LT1171, BY FOUR FOR LT1172.
TYP
100
100
150
3
1.5
25
92
SW
4
= 4A for LT1170,
MAX
112
115
250
250
300
35
97
5
100 C
6
150 C
MAX
–55 C
1170/1/2 G03
UNITS
25 C
7
mA/A
=
kHz
kHz
mV
mV
%
8
A
s