LT1176 Linear Technology, LT1176 Datasheet - Page 3

• Manufacturer Part Number: LT1176
• Description: Step-Down Switching Regulator
• Manufacturer: Linear Technology

The
ture range.
Note 1: To calculate maximum switch “ON” voltage at current between low
and high conditions, a linear interpolation may be used.
Note 2: A feedback pin voltage (V
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
Note 3: Total voltage from V
up for proper regulation.
Note 4: Switch frequency is internally scaled down when the feedback pin
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 heatsink 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.
ELECTRICAL C
PARAMETER
Feedback Pin Bias Current (LT1176)
Reference Voltage (LT1176)
Reference Voltage Tolerance (LT1176)
Sense Voltage (LT1176-5)
Sense Voltage Tolerance (LT1176-5)
Sense Pin Divider Resistance (LT1176-5)
Output Voltage Line Regulation
V
Multiplier Reference Voltage
Shutdown Pin Current
V
Shutdown Thresholds
Status Window
Status High Level
Status Low Level
Status Delay Time
Status Minimum Width
SENSE
C
SHDN
Voltage at 0% Duty Cycle
denotes specifications which apply over the full operating tempera-
= 5.5V.
V
THRESHOLD
( 2.5V)
IN
HARA TERISTICS
pin to ground pin must be 8V after start-
FB
) of 2.5V forces the V
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
C
CONDITIONS
V
V
V
All Conditions of Input Voltage, Output
Voltage, Temperature and Load Current
V
V
All Conditions of Input Voltage,
Temperature and Load Current
8V V
Over Temperature
V
Switch Duty Cycle = 0
Fully Shut Down
As a Percent of Output Voltage
I
I
STATUS
STATUS
FB
C
REF
C
OUT
SHDN
= 2V
= 2V
= V
(Nominal) = 2.21V
(Nominal) = 5V
IN
= 5V
REF
= 10 A Sourcing
= 1.6mA Sinking
C
V
pin to its low
MAX
(Note 7)
T
J
= 25 C, V
Power = I
I
Example: V
Power (I
I
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.
voltage is less than 1.3V to avoid extremely short switch-on times. During
testing, V
Note 5: I
Note 6: Switch to input voltage limitation must also be observed.
Note 7: V
Note 8: Does not include switch leakage.
Note 9: Error amplifier voltage gain and transconductance are specified
relative to the internal feedback node. To calculate gain and transconduc-
tance from the sense pin (Output) to the V
by 0.44.
PEAK
PEAK
IN
= 25V, unless otherwise noted
= I
(I
LOAD
LOAD(PEAK)
LOAD
LM
FB
MAX
LOAD
L = 100 H
IN
= (R
or V
= 0.8A) = 0.97A
= 15V, V
= 0.5A) = 0.38W
= 35V
(V
SENSE
LIM
OUT
+ [V
– 1k)/ 7.65k
/V
OUT
is adjusted to give a minimum switch-on time of 1 s.
IN
OUT
) + V
= 5V, I
(V
5
IN
IN
[7mA + 3mA (V
– V
LOAD
2.155
LT1176/LT1176-5
MIN
4.85
OUT
2.2
0.1
3.5
10
50
3
4
= 0.5A Continuous, 0.8A Peak,
)]/2E
C
pin on the LT1176-5, multiply
5
0.005
– 4.0
(V
TYP
2.21
0.25
0.5
4.5
1.5
24
20
2.45
0.30
30
OUT
0.5
1.0
1.0
5
0.5
5
9
IN
A
5
)(L)
/V
IN
) + 0.012 (I
2.265
MAX
5.15
0.02
2.7
0.5
5.0
0.4
2
1.5
2.5
8
A
2
3
6
LOAD
UNITS
mV/ C
3
%/ V
)]
k
%
%
%
%
%
A
V
V
V
V
V
V
V
V
s
s