1
LT1170/LT1171/LT1172
100kHz, 5A, 2.5A and 1.25A
High Efficiency Switching Regulators
s
Wide Input Voltage Range: 3V to 60V
s
Low Quiescent Current: 6mA
s
Internal 5A Switch (2.5A for LT1171,
1.25A for LT1172)
s
Shutdown Mode Draws Only 50
A Supply Current
s
Very Few External Parts Required
s
Self-Protected Against Overloads
s
Operates in Nearly All Switching Topologies
s
Flyback-Regulated Mode Has Fully Floating Outputs
s
Comes in Standard 5-Pin Packages
s
LT1172 Available in 8-Pin MiniDIP and Surface Mount
Packages
s
Can Be Externally Synchronized
The LT
1170/LT1171/LT1172 are monolithic high power
switching regulators. They can be operated in all standard
switching configurations including buck, boost, flyback,
forward, inverting and "Cuk." A high current, high effi-
ciency switch is included on the die along with all oscilla-
tor, control and protection circuitry. Integration of all
functions allows the LT1170/LT1171/LT1172 to be built in
a standard 5-pin TO-3 or TO-220 power package as well as
the 8-pin packages (LT1172). This makes them extremely
easy to use and provides "bust proof" operation similar to
that obtained with 3-pin linear regulators.
The LT1170/LT1171/LT1172 operate with supply volt-
ages from 3V to 60V, and draw only 6mA quiescent
current. They can deliver load power up to 100W with no
external power devices. By utilizing current-mode switch-
ing techniques, they provide excellent AC and DC load and
line regulation.
The LT1170/LT1171/LT1172 have many unique features
not found even on the vastly more difficult to use low
power control chips presently available. They use adaptive
antisat switch drive to allow very wide ranging load cur-
rents with no loss in efficiency. An externally activated
shutdown mode reduces total supply current to 50
A
typically for standby operation.
Boost Converter (5V to 12V)
Maximum Output Power*
, LTC and LT are registered trademarks of Linear Technology Corporation.
s
Logic Supply 5V at 10A
s
5V Logic to
15V Op Amp Supply
s
Battery Upconverter
s
Power Inverter (+ to ) or ( to +)
s
Fully Floating Multiple Outputs
USER NOTE:
This data sheet is only intended to provide specifications, graphs, and a general functional description
of the LT1170/LT1171/LT1172. Application circuits are included to show the capability of the
LT1170/LT1171/LT1172. A complete design manual (AN19) should be obtained to assist in
developing new designs. This manual contains a comprehensive discussion of both the LT1070 and
the external components used with it, as well as complete formulas for calculating the values of these
components. The manual can also be used for the LT1170/LT1171/LT1172 by factoring in the higher
frequency. A CAD design program called SwitcherCAD
TM
is also available.
SwitcherCAD is a trademark of Linear Technology Corporation.
DESCRIPTIO
U
FEATURES
APPLICATIO S
U
TYPICAL APPLICATIO
U
1170/1/2 TA01
D1
MBR330
C2
1000
F
C1
1
F
R1
10.7k
1%
R2
1.24k
1%
LT1170
GND
V
IN
5V
R3
1k
*REQUIRED IF INPUT LEADS
2"
** COILTRONICS 50-2-52
PULSE ENGINEERING 92114
V
SW
FB
V
C
OUTPUT
FILTER
L2
10
H
L1**
50
H
C3
100
F
12V
1A
C3*
100
F
+
+
INPUT VOLTAGE (V)
0
POWER (W)
**
100
80
60
40
20
0
40
LT1170/1/2 TA02
10
20
30
50
* ROUGH GUIDE ONLY. BUCK MODE
P
OUT
= (5A)(V
OUT
)
SPECIAL TOPOLOGIES DELIVER
MORE POWER.
** DIVIDE VERTICAL POWER SCALE
BY TWO FOR LT1171, BY FOUR
FOR LT1172.
BOOST
BUCK-BOOST
V
O
= 30V
FLYBACK
BUCK-BOOST
V
O
= 5V
LT1170
2
LT1170/LT1171/LT1172
*
will vary from
approximately
25
C/W with 2.8
sq. in. of 1oz.
copper to 45
C/W
with 0.20 sq. in. of
1oz. copper.
Somewhat lower
values can be
obtained with
additional copper
layers in multilayer
boards.
LT1172MJ8
LT1172CJ8
LT1172CN8
LT1172IN8
LT1172CS8
LT1172IS8
S8 PART MARKING
Supply Voltage
LT1170/71/72HV (Note 2) .................................. 60V
LT1170/71/72 (Note 2) ....................................... 40V
Switch Output Voltage
LT1170/71/72HV ................................................ 75V
LT1170/71/72 ..................................................... 65V
LT1172S8 ........................................................... 60V
Feedback Pin Voltage (Transient, 1ms) ................
15V
Storage Temperature Range ............... 65
C to 150
C
Lead Temperature (Soldering, 10 sec)................. 300
C
ORDER PART
NUMBER
T
JMAX
= 100
C,
JA
= *
C/W
LT1170CQ
LT1170IQ
LT1171CQ
LT1171IQ
T
JMAX
JC
JA
LT1170MK
150
C
2
C/W
35
C/W
LT1170CK
100
C
2
C/W
35
C/W
LT1171MK
150
C
4
C/W
35
C/W
LT1171CK
100
C
4
C/W
35
C/W
LT1172MK
150
C
8
C/W
35
C/W
LT1172CK
150
C
8
C/W
35
C/W
Based on continuous operation.
T
JMAX
= 125
C for intermittent fault conditions.
LT1170MK
LT1170CK
LT1171MK
LT1171CK
LT1172MK
LT1172CK
T
JMAX
= 150
C,
JA
= 100
C/W (J)
T
JMAX
= 100
C,
JA
= 100
C/W (N)
T
JMAX
= 100
C,
JA
= 120
C/W to 150
C/W
depending on board layout (S)
1172
N8 PACKAGE
8-LEAD PDIP
1
2
3
4
8
7
6
5
TOP VIEW
GND
V
C
FB
NC*
E2
V
SW
E1
V
IN
J8 PACKAGE
8-LEAD CERDIP
S8 PACKAGE
8-LEAD PLASTIC SO
* Do not connect Pin 4 of the LT1172 DIP or SO to external
circuitry. This pin may be active in future revisions.
Operating Junction Temperature Range
LT1170/71/72M ......................... 55
C to 150
C
LT1170/71/72HVC,
LT1170/71/72C (Oper.) .............. 0
C to 100
C
LT1170/71/72HVC
LT1170/71/72C (Sh. Ckt.) .......... 0
C to 125
C
LT1170/71/72HVI,
LT1170/71/72I (Oper.) .......... 40
C to 100
C
LT1170/71/72HVI,
LT1170/71/72I (Sh. Ckt.) ...... 40
C to 125
C
(Note 1)
T
JMAX
JC
JA
LT1170CT/LT1170HVCT
100
C
2
C/W
75
C/W
LT1171CT/LT1171HVCT
100
C
4
C/W
75
C/W
LT1172CT/LT1172HVCT
100
C
8
C/W
75
C/W
Based on continuous operation.
T
JMAX
= 125
C for intermittent fault conditions.
LT1170CT
LT1170IT
LT1170HVCT
LT1170HVIT
LT1171CT
LT1171IT
LT1171HVCT
LT1172CT
LT1172HVCT
T
JMAX
= 100
C,
JA
= 150
C/W
Based on continuous operation.
T
JMAX
= 125
C for intermittent fault conditions.
LT1172CSW
ORDER PART
NUMBER
ORDER PART
NUMBER
ORDER PART
NUMBER
2
4
1
3
V
SW
V
C
FB
CASE
IS GND
V
IN
K PACKAGE
4-LEAD TO-3 METAL CAN
BOTTOM VIEW
Q PACKAGE
5-LEAD DD
V
IN
V
SW
GND
FB
V
C
FRONT VIEW
5
4
3
2
1
ORDER PART
NUMBER
TOP VIEW
SW PACKAGE
16-LEAD PLASTIC SO WIDE
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
NC
NC
GND
V
C
FB
NC
NC
NC
NC
NC
E2
V
SW
E1
V
IN
NC
NC
T PACKAGE
5-LEAD PLASTIC TO-220
V
IN
V
SW
GND
FB
V
C
FRONT VIEW
5
4
3
2
1
1172I
LT1171HVCQ
LT1172CQ
LT1172HVIQ
C
I
PACKAGE/ORDER I FOR ATIO
U
U
W
ABSOLUTE AXI U RATI GS
W
W
W
U
3
LT1170/LT1171/LT1172
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
REF
Reference Voltage
Measured at Feedback Pin
1.224
1.244
1.264
V
V
C
= 0.8V
q
1.214
1.244
1.274
V
I
B
Feedback Input Current
V
FB
= V
REF
350
750
nA
q
1100
nA
g
m
Error Amplifier
I
C
=
25
A
3000
4400
6000
mho
Transconductance
q
2400
7000
mho
Error Amplifier Source or
V
C
= 1.5V
150
200
350
A
Sink Current
q
120
400
A
Error Amplifier Clamp
Hi Clamp, V
FB
= 1V
1.80
2.30
V
Voltage
Lo Clamp, V
FB
= 1.5V
0.25
0.38
0.52
V
Reference Voltage Line
3V
V
IN
V
MAX
q
0.03
%/V
Regulation
V
C
= 0.8V
A
V
Error Amplifier Voltage Gain
0.9V
V
C
1.4V
500
800
V/V
Minimum Input Voltage (Note 5)
q
2.6
3.0
V
I
Q
Supply Current
3V
V
IN
V
MAX
, V
C
= 0.6V
6
9
mA
Control Pin Threshold
Duty Cycle = 0
0.8
0.9
1.08
V
q
0.6
1.25
V
Normal/Flyback Threshold
0.4
0.45
0.54
V
on Feedback Pin
V
FB
Flyback Reference Voltage
I
FB
= 50
A
15.0
16.3
17.6
V
(Note 5)
q
14.0
18.0
V
Change in Flyback Reference
0.05
I
FB
1mA
4.5
6.8
9
V
Voltage
Flyback Reference Voltage
I
FB
= 50
A
0.01
0.03
%/V
Line Regulation (Note 5)
7V
V
IN
V
MAX
Flyback Amplifier
I
C
=
10
A
150
300
650
mho
Transconductance (g
m
)
Flyback Amplifier Source
V
C
= 0.6V
Source
q
15
32
70
A
and Sink Current
I
FB
= 50
A
Sink
q
25
40
70
A
BV
Output Switch Breakdown
3V
V
IN
V
MAX
,
LT1170/LT1171/LT1172
q
65
90
V
Voltage
I
SW
= 1.5mA
LT1170HV/LT1171HV/LT1172HV
q
75
90
V
LT1172S8
q
60
80
V
V
SAT
Output Switch
LT1170
q
0.15
0.24
"On" Resistance (Note 3)
LT1171
q
0.30
0.50
LT1172
q
0.60
1.00
Control Voltage to Switch
LT1170
8
A/V
Current Transconductance
LT1171
4
A/V
LT1172
2
A/V
I
LIM
Switch Current Limit
(LT1170)
Duty Cycle = 50%
T
J
25
C
q
5
10
A
Duty Cycle = 50%
T
J
<
25
C
q
5
11
A
Duty Cycle = 80% (Note 4)
q
4
10
A
(LT1171)
Duty Cycle = 50%
T
J
25
C
q
2.5
5.0
A
Duty Cycle = 50%
T
J
<
25
C
q
2.5
5.5
A
Duty Cycle = 80% (Note 4)
q
2.0
5.0
A
(LT1172)
Duty Cycle = 50%
T
J
25
C
q
1.25
3.0
A
Duty Cycle = 50%
T
J
<
25
C
q
1.25
3.5
A
Duty Cycle = 80% (Note 4)
q
1.00
2.5
A
The
q
denotes the specifications which apply over the full operating tem-
perature range, otherwise specifications are at T
A
= 25
C. V
IN
= 15V, V
C
= 0.5V, V
FB
= V
REF
, output pin open, unless otherwise noted.
ELECTRICAL CHARACTERISTICS
4
LT1170/LT1171/LT1172
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
I
IN
Supply Current Increase
25
35
mA/A
I
SW
During Switch On-Time
f
Switching Frequency
88
100
112
kHz
q
85
115
kHz
DC
MAX
Maximum Switch Duty Cycle
q
85
92
97
%
Shutdown Mode
3V
V
IN
V
MAX
100
250
A
Supply Current
V
C
= 0.05V
Shutdown Mode
3V
V
IN
V
MAX
100
150
250
mV
Threshold Voltage
q
50
300
mV
Flyback Sense Delay Time (Note 5)
1.5
s
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
C
in hi clamp, V
FB
= 0.8V. I
SW
= 4A for LT1170,
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
LIM
= 3.33 (2 DC) for the LT1170,
I
LIM
= 1.67 (2 DC) for the LT1171, and I
LIM
= 0.833 (2 DC) for the
LT1172.
Note 5: Minimum input voltage for isolated flyback mode is 7V. V
MAX
=
55V for HV grade in fully isolated mode to avoid switch breakdown.
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
IN
(max, output shorted) = 15V +
buck and inverting mode
R = Inductor DC resistance
I
L
= 10A for LT1170, 5A for LT1171, and 2.5A for LT1172
Vf = Output catch diode forward voltage at I
L
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.
Switch Current Limit vs Duty Cycle*
TEMPERATURE (
C)
75
MINIMUM INPUT VOLTAGE (V)
25
25
50
150
1170/1/2 G02
50
0
75 100 125
2.9
2.8
2.7
2.6
2.5
2.4
2.3
SWITCH CURRENT = 0A
SWITCH CURRENT = I
MAX
Minimum Input Voltage
Switch Saturation Voltage
DUTY CYCLE (%)
0
SWITCH CURRENT (A)
16
12
8
4
0
40
1170/1/2 G01
20 30
50
60 70 80
90 100
25
C
125
C
55
C
10
* DIVIDE VERTICAL SCALE BY TWO FOR
LT1171, BY FOUR FOR LT1172.
SWITCH CURRENT (A)*
0
SWITCH SATURATION VOLTAGE (V)
8
1170/1/2 G03
1
2
3
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
4
5
6
7
25
C
150
C
55
C
100
C
* DIVIDE CURRENT BY TWO FOR
LT1171, BY FOUR FOR LT1172.
(R)(I
L
) + Vf
(t)(f)
The
q
denotes the specifications which apply over the full operating tem-
perature range, otherwise specifications are at T
A
= 25
C. V
IN
= 15V, V
C
= 0.5V, V
FB
= V
REF
, output pin open, unless otherwise noted.
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
ELECTRICAL CHARACTERISTICS
5
LT1170/LT1171/LT1172
INPUT VOLTAGE (V)
0
SUPPLY CURRENT (mA)
10
20
30
40
1170/1/2 G09
50
15
14
13
12
11
10
9
8
7
6
5
60
T
J
= 25
C
NOTE THAT THIS CURRENT DOES NOT
INCLUDE DRIVER CURRENT, WHICH IS
A FUNCTION OF LOAD CURRENT AND
DUTY CYCLE.
90% DUTY CYCLE
50% DUTY CYCLE
10% DUTY CYCLE
0% DUTY CYCLE
* UNDER VERY LOW OUTPUT CURRENT CONDITIONS,
DUTY CYCLE FOR MOST CIRCUITS WILL APPROACH
10% OR LESS.
Supply Current vs Input Voltage*
V
C
PIN VOLTAGE (mV)
0
SUPPLY CURRENT (
A)
200
180
160
140
120
100
80
60
40
20
0
40
1170/1/2 G10
10
20 30
50 60 70 80 90 100
T
J
= 150
C
55
C
T
J
125
C
Shutdown Mode Supply Current
TEMPERATURE (
C)
TRANSCONDUCTANCE (
mho)
5000
4500
4000
3500
3000
2500
2000
1500
1000
500
0
1170/1/2 G11
75
25
25
50
150
50
0
75 100 125
g
m
=
I (V
C
PIN)
V (FB PIN)
Error Amplifier Transconductance
V
C
Pin Characteristics
SUPPLY VOLTAGE (V)
0
SUPPLY CURRENT (
A)
10
20
30
40
160
140
120
100
80
60
40
20
0
50
60
1170/1/2 G07
V
C
= 50mV
V
C
= 0V
T
J
= 25
C
Supply Current vs Supply Voltage
(Shutdown Mode)
Driver Current* vs Switch Current
SWITCH CURRENT (A)
0
DRIVER CURRENT (mA)
1
2
3
160
140
120
100
80
60
40
20
0
4
5
1170/1/2 G08
T
J
= 55
C
T
J
=
25
C
* AVERAGE LT1170 POWER SUPPLY CURRENT IS
FOUND BY MULTIPLYING DRIVER CURRENT BY
DUTY CYCLE, THEN ADDING QUIESCENT CURRENT.
V
C
PIN VOLTAGE (V)
300
200
100
0
100
200
300
400
1170/1/2 G12
V
C
PIN CURRENT (
A)
0
2.0
0.5
1.0
1.5
2.5
V
FB
= 1.5V (CURRENT INTO V
C
PIN)
V
FB
= 0.8V (CURRENT OUT OF V
C
PIN)
T
J
= 25
C
Reference Voltage vs Temperature
INPUT VOLTAGE (V)
0
REFERENCE VOLTAGE CHANGE (mV)
10
20
30
40
1170/1/2 G04
50
5
4
3
2
1
0
1
2
3
4
5
60
T
J
= 150
C
T
J
= 55
C
T
J
= 25
C
Line Regulation
TEMPERATURE (
C)
REFERENCE VOLTAGE (V)
1170/1/2 G05
1.250
1.248
1.246
1.244
1.242
1.240
1.238
1.236
1.234
75
25
25
50
150
50
0
75 100 125
TEMPERATURE (
C)
FEEDBACK BIAS CURRENT (nA)
1170/1/2 G06
800
700
600
500
400
300
200
100
0
75
25
25
50
150
50
0
75 100 125
Feedback Bias Current vs
Temperature
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
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