Pin Voltage (Forced) .........................................5.5V
Maximum Operating Ambient Temperature Range
LT1176C/LT1176C-5 ................................. 0°C to 70°C
Maximum Operating Junction Temperature Range
LT1176C/LT1176C-5 ............................... 0°C to 125°C
Storage Temperature Range .................. –65°C to 150°C
Lead Temperature (Soldering, 10 sec)................... 300°C
*These thermal resistance numbers are for typical mounting technique. Lower thermal
resistance can be obtained with large copper lands, thermal glues or heat sinks.
PIN CONFIGURATION
TOP VIEW
V
IN
1
TOP VIEW
V
IN
1
I
LIM
2
GND 3
FB/SENSE 4
8
7
6
5
V
SW
V
C
STATUS
SHUTDOWN
NC 2
I
LIM
3
GND 4
GND 5
GND 6
GND 7
NC 8
FB/SENSE 9
NC 10
20 V
SW
19 NC
18 V
C
17 GND
16 GND
15 GND
14 GND
13 STATUS
12 SHUTDOWN
11 NC
SW PACKAGE
20-LEAD PLASTIC SOL
T
JMAX
= 125°C,
θ
JA
= 50°C/W
N8 PACKAGE
8-LEAD PLASTIC DIP
T
JMAX
= 125°C,
θ
JA
= 90°C/W
ORDER INFORMATION
LEAD FREE FINISH
LT1176CN8#PBF
LT1176CN8-5#PBF
LT1176CSW#PBF
LT1176CSW-5#PBF
LT1176CSW#TRPBF
LT1176CSW-5#TRPBF
TAPE AND REEL
PART MARKING*
LT1176CN8
LT1176CN8-5
LT1176CSW
LT1176CSW-5
PACKAGE DESCRIPTION
8-Lead Plastic DIP
8-Lead Plastic DIP
20-Lead Plastic SOL
20-Lead Plastic SOL
TEMPERATURE RANGE
0°C to 125°C
0°C to 125°C
0°C to 125°C
0°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/
11765fb
2
LT1176/LT1176-5
ELECTRICAL CHARACTERISTICS
PARAMETER
Switch ON Voltage (Note 2)
Switch OFF Leakage
Supply Current (Note 3)
Minimum Supply Voltage
Switch Current Limit (Note 5)
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. T
J
= 25°C, V
IN
25V, unless otherwise noted.
CONDITIONS
I
SW
= 0.2A
I
SW
= 1A
V
IN
= 25V, V
SW
= 0
V
IN
= V
MAX
, V
SW
= 0 (Note 8)
V
FB
= 2.5V, V
IN
≤ 35V
V
SHDN
= 0.1V (Device Shutdown) (Note 9)
Normal Mode
Startup Mode (Note 4)
I
LIM
Open
R
LIM
= 10k (Note 6)
R
LIM
= 7k (Note 6)
l
l
l
l
l
l
l
MIN
TYP
MAX
1.1
1.4
150
250
UNITS
V
V
µA
µA
mA
µA
V
V
A
A
A
%
kHz
kHz
kHz
kHz
%/V
V/V
µmho
µA
mA
µA
V
%
%
V
%
%
kΩ
%/V
V
mV/°C
V
7.5
140.0
7.3
3.5
1.2
1.7
1.2
0.8
90
100
20
20
0.03
2000
3700
5000
140
1.0
0.5
2.155
2.21
±0.5
±1.0
4.85
5
±0.5
±0.1
3
5
0.005
1.5
–4.0
24
5
2.2
0.1
±4
3.5
10
2.45
0.30
±5
4.5
10
300
8.0
4.8
2.2
Maximum Duty Cycle
Switching Frequency
l
l
85
90
85
V
FB
= 0V Through 2k (Note 5) (LT1176)
V
SENSE
= 0V (Note 5) (LT1176-5)
Switching Frequency Line Regulation
Error Amplifier Voltage Gain (Note 10)
Error Amplifier Transconductance (Note 10)
Error Amplifier Source and Sink Current
Feedback Pin Bias Current (LT1176)
Reference Voltage (LT1176)
Reference Voltage Tolerance (LT1176)
Source (V
FB
= 2V or V
SENSE
= 4V)
Sink (V
FB
= 2.5V or V
SENSE
= 5.5V)
V
FB
= V
REF
V
C
= 2V
V
REF
(Nominal) = 2.21V
All Conditions of Input Voltage, Output Voltage,
Temperature and Load Current
V
C
= 2V
V
OUT
(Nominal) = 5V
All Conditions of Input Voltage,
Temperature and Load Current
8V ≤ V
IN
≤ V
MAX
(Note 8)
Overtemperature
V
SHDN
= 5V
V
SHDN
≤ V
THRESHOLD
(@ 2.5V)
Switch Duty Cycle = 0
Fully Shutdown
As a Percent of Output Voltage
I
STATUS
= 10µA Sourcing
l
l
l
l
l
l
110
120
8V ≤ V
IN
≤ V
MAX
(Note 8)
1V ≤ V
C
≤ 4V
l
0.1
8000
225.0
1.6
2
2.265
±2
±3
5.15
±2
±3
8
0.02
100.0
0.7
Sense Voltage (LT1176-5)
Sense Voltage Tolerance (LT1176-5)
Sense Pin Divider Resistance (LT1176-5)
Output Voltage Line Regulation
V
C
Voltage at 0% Duty Cycle
Multiplier Reference Voltage
Shutdown Pin Current
Shutdown Thresholds
Status Window
Status High Level
l
l
l
l
l
l
20
50
2.7
0.5
±6
5.0
µA
µA
V
V
%
V
11765fb
3
LT1176/LT1176-5
ELECTRICAL CHARACTERISTICS
PARAMETER
Status Low Level
Status Delay Time
Status Minimum Width
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:
To calculate maximum switch ON voltage at current between low
and high conditions, a linear interpolation may be used.
Note 3:
A feedback pin voltage (V
FB
) of 2.5V forces the V
C
pin to its low
clamp level and the switch duty cycle to zero. This approximates the
zero load condition where duty cycle approaches zero. The LT1176-5 has
V
SENSE
= 5.5V.
Note 4:
Total voltage from V
IN
pin to ground pin must be ≥ 8V after
start-up for proper regulation.
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. T
J
= 25°C, V
IN
25V, unless otherwise noted.
CONDITIONS
I
STATUS
= 1.6mA Sinking
l
MIN
TYP
0.25
9
30
MAX
0.4
UNITS
V
µs
µs
Note 5:
Switch frequency is internally scaled down when the feedback pin
voltage is less than 1.3V to avoid extremely short switch-on times. During
testing, V
FB
or V
SENSE
is adjusted to give a minimum switch-on time of
1µs.
Note 6:
I
LM
= (R
LIM
– 1k)/7.65k
Note 7:
Switch to input voltage limitation must also be observed.
Note 8:
V
MAX
= 35V
Note 9:
Does not include switch leakage.
Note 10:
Error amplifier voltage gain and transconductance are
specified relative to the internal feedback node. To calculate gain and
transconductance from the sense pin (Output) to the V
C
pin on the
LT1176-5, multiply by 0.44.
Application Hints
Although the LT1176 has a peak switch rating of 1.2A and a maximum duty
cycle of 85%, it must be used cautiously in applications which require high
switch current and high duty cycle simultaneously, to avoid excessive chip
temperature. Thermal resistance is 90°C/W for the 8-pin DIP package and
50°C/W for the 20-pin SO. This limits continuous chip power dissipation to
the 0.5W to 1W range. These numbers assume typical mounting techniques.
Extra or thick copper connected to the leads can reduce thermal resistance.
Bonding the package to the board or using a clip style heat sink can also help.
The following formulas will give chip power dissipation and peak switch current
for the standard buck converter. Note that surges less than 30 seconds do not
need to be considered from a thermal standpoint, but for proper regulation,
they must not result in peak switch currents exceeding the 1.2A limit.
Power = I
LOAD
(V
OUT
/V
IN
) + V
IN
[7mA + 3mA (V
OUT
/V
IN
) + 0.012 (I
LOAD
)]
I
PEAK
= I
LOAD(PEAK)
+ [V
OUT
(V
IN
– V
OUT
)]/2E
5
(V
IN
)(L)
Example: V
IN
= 15V, V
OUT
= 5V, I
LOAD
= 0.5A Continuous, 0.8A Peak,
L = 100µH
Power (I
LOAD
= 0.5A) = 0.38W
I
PEAK
(I
LOAD
= 0.8A) = 0.97A
Where component size or height is critical, we suggest using solid tantalum
capacitors (singly or in parallel), but be sure to use units rated for switching
applications. Coiltronics is a good source for low profile surface mount
inductors and AVX makes high quality surface mount tantalum capacitors. For
further help, use Application Notes 19 and 44,LTC’s SwitcherCAD
®
computer
design program, and our knowledgeable application department.
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