LT1176CSW#TR [Linear]
LT1176/LT1176-5 - Step-Down Switching Regulator; Package: SO; Pins: 20; Temperature Range: 0°C to 70°C;型号: | LT1176CSW#TR |
厂家: | Linear |
描述: | LT1176/LT1176-5 - Step-Down Switching Regulator; Package: SO; Pins: 20; Temperature Range: 0°C to 70°C 稳压器 开关 |
文件: | 总4页 (文件大小:181K) |
中文: | 中文翻译 | 下载: | 下载PDF数据表文档文件 |
LT1176/LT1176-5
Step-Down
Switching Regulator
tion. The power switch, all oscillator and control circuitry,
and all current limit components are included on the chip.
The topology is a classic positive “buck” configuration but
several design innovations allows this device to be used as
a positive-to-negative converter, a negative boost con-
verter, and as a flyback converter. The switch output is
specified to swing below ground.
EATURE
1.2A On-Board Switch
S
F
■
■
■
■
■
■
■
■
100kHz Switching Frequency
Excellent Dynamic Behavior
DIP and Surface Mount Packages
Only 8mA Quiescent Current
Preset 5V Output Available
Operates Up to 35V Input
Micropower Shutdown Mode
The LT1176 uses a true analog multiplier in the feedback
loop.Thismakesthedevicerespondnearlyinstantaneously
to input voltage fluctuations and makes loop gain indepen-
dent of input voltage. As a result, dynamic behavior of the
regulator is significantly improved over previous designs.
O U
PPLICATI
A
S
■
On-chip pulse by pulse current limiting makes the LT1176
nearly bust-proof for output overloads or shorts. The input
voltage range as a buck converter is 8V to 35V, but a self-
boot feature allows input voltages as low as 5V in the
inverting and boost configurations.
Buck Converter with Output Voltage Range of
2.5V to 30V
Positive-to-Negative Converter
Negative Boost Converter
■
■
■
Mulitple Output Buck Converter
The LT1176 is available in a low cost 8-lead DIP package
withfrequencypresetat100kHzandcurrentlimitat1.7AAn
adjustable output is offered as well as a preset 5V version.
For further design details and application help, see the
LT1074/LT1076 data sheet and Application Note 44.
U
DESCRIPTIO
The LT1176 is a 1A monolithic bipolar switching regulator
which requires only a few external parts for normal opera-
U
O
TYPICAL APPLICATI
5V Buck Converter Efficiency
Basic 5V Positive Buck Converter
90
L1*
100µH
L = 100µH ON MAGNETICS INC.
SIZE T-50 KOOL Mµ CORE
5V, 0.8A
10V T0 35V
V
IN
V
SW
V
= 10V
LT1176-5
SENSE
IN
1N5819
80
70
60
V
IN
= 20V
GND
V
C
+
C1
470µF
R3
2.7k
25V
+
C3
100µF
C2
0.01µF
*COILTRONICS #100-1-52
PULSE ENGINEERING, INC. #PE-92102
HURRICANE #HL-AG210LL
LT1176/76-5 • TA01
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
LOAD CURRENT (A)
THESE ARE LOW COST POWDERED IRON CORES. OPTIMUM EFFICIENCY
AND SMALLEST SIZE IS OBTAINED BY USING A LOW LOSS CORE SUCH
AS MAGNETICS INC. KOOL Mµ. SEE EFFICIENCY GRAPH.
LT1176/76-5 • TA02
1
LT1176/LT1176-5
W W W
U
ABSOLUTE AXI U RATI GS
/O
PACKAGE RDER I FOR ATIO
Input Voltage .......................................................... 38V
Switch Voltage With Respect to Input Voltage........ 50V
Switch Voltage With Respect to Ground Pin
(VSW Negative) (Note 6) ......................................... 20V
Feedback Pin Voltage.......................................–2V, 10V
Shutdown Pin Voltage (Not to Exceed VIN) ............. 35V
Status Pin Voltage
(Current Must Be Limited to 5mA When Status Pin
Switches “ON”) ................................................... 30V
ILIM 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
TOP VIEW
ORDER PART
V
1
2
3
4
8
7
6
5
V
V
IN
SW
NUMBER
I
LIM
C
GND
STATUS
LT1176CN8
LT1176CN8-5
FB/SENSE
SHUTDOWN
N8 PACKAGE
8-LEAD PLASTIC DIP
TJ MAX = 125°C, θJA = 90°C/ W*
TOP VIEW
ORDER PART
NUMBER
V
1
2
3
4
5
6
7
8
9
20
19 NC
18
V
IN
SW
NC
I
V
LIM
C
LT1176CS
LT1176CS-5
GND
GND
17 GND
16 GND
GND
15 GND
GND
14 GND
NC
13 STATUS
12 SHUTDOWN
11 NC
*These thermal resistance numbers are for typical mounting technique. Lower thermal resistance
can be obtained with large copper lands, thermal glues or heatsinks.
FB/SENSE
NC 10
S PACKAGE
20-LEAD PLASTIC SOL
TJMAX = 125 °C, θJA = 50°C/ W*
ELECTRICAL CHARACTERISTICS TJ = 25°C, VIN = 25V, unless otherwise noted
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Switch “ON” Voltage (Note 1)
I
= 0.2A
= 1A
●
●
1.1
1.4
V
V
SW
SW
I
Switch “OFF” Leakage
V
V
= 25V, V = 0
150
250
µA
µA
IN
IN
SW
= V
, V = 0 (Note 7)
MAX SW
Supply Current (Note 2)
Minimum Supply Voltage
Switch Current Limit (Note 4)
V
V
= 2.5V, V ≤ 35V
SHDN
●
●
7.5
10
mA
FB
IN
= 0.1V (Device Shutdown) (Note 8)
140.0
300
µA
Normal Mode
Startup Mode (Note 3)
●
●
7.3
3.5
8.0
4.8
V
V
I
Open
●
1.2
85
1.7
1.2
0.8
2.2
A
A
A
LIM
R
R
= 10k (Note 5)
= 7k (Note 5)
LIM
LIM
Maximum Duty Cycle
Switching Frequency
●
●
90
%
90
85
100
110
120
kHz
kHz
kHz
kHz
V
V
= 0V Through 2k (Note 4) (LT1176)
20
20
FB
= 0V (Note 4) (LT1176-5)
SENSE
Switching Frequency Line Regulation
Error Amplifier Voltage Gain (Note 9)
Error Amplifier Transconductance (Note 9)
Error Amplifier Source and Sink Current
8V ≤ V ≤ V
(Note 7)
●
0.03
2000
5000
0.1
%/V
V/V
IN
MAX
1V ≤ V ≤ 4V
C
3700
8000
µmho
Source (V = 2V or V
= 4V)
= 5.5V)
100.0
0.7
140.0
1.0
225.0
1.6
µA
mA
FB
SENSE
SENSE
Sink (V = 2.5V or V
FB
2
LT1176/LT1176-5
ELECTRICAL CHARACTERISTICS
TJ = 25°C, VIN = 25V, unless otherwise noted
PARAMETER
CONDITIONS
MIN
TYP
0.5
MAX
2
UNITS
µA
Feedback Pin Bias Current (LT1176)
Reference Voltage (LT1176)
Reference Voltage Tolerance (LT1176)
V
= V
●
●
FB
REF
V = 2V
C
2.155
4.85
3
2.21
2.265
V
V
(Nominal) = 2.21V
±0.5
±1.0
±1.5
±2.5
%
%
REF
All Conditions of Input Voltage, Output
Voltage, Temperature and Load Current
●
●
●
Sense Voltage (LT1176-5)
V = 2V
C
5
5.15
V
Sense Voltage Tolerance (LT1176-5)
V
(Nominal) = 5V
±0.5
±1.0
±2
±3
%
%
OUT
All Conditions of Input Voltage,
Temperature and Load Current
Sense Pin Divider Resistance (LT1176-5)
Output Voltage Line Regulation
5
8
kΩ
8V ≤ V ≤ V
(Note 7)
MAX
●
●
0.005
0.02
%/V
IN
V Voltage at 0% Duty Cycle
C
1.5
–4.0
V
Over Temperature
mV/°C
Multiplier Reference Voltage
Shutdown Pin Current
24
V
V
= 5V
●
5
10
50
20
µA
µA
SHDN
V
≤ V
( 2.5V)
THRESHOLD
●
SHDN
Shutdown Thresholds
Switch Duty Cycle = 0
Fully Shut Down
●
●
2.2
0.1
2.45
0.30
2.7
0.5
V
V
Status Window
As a Percent of Output Voltage
±4
±5
4.5
0.25
9
±6
5.0
0.4
%
V
Status High Level
Status Low Level
Status Delay Time
Status Minimum Width
I
I
= 10µA Sourcing
●
●
3.5
STATUS
STATUS
= 1.6mA Sinking
V
µs
µs
30
The
ture range.
●
denotes specifications which apply over the full operating tempera-
voltage is less than 1.3V to avoid extremely short switch-on times. During
testing, V or V is adjusted to give a minimum switch-on time of 1µs.
FB
SENSE
Note 1: To calculate maximum switch “ON” voltage at current between low
Note 5: I = (R – 1k)/7.65k
LM LIM
and high conditions, a linear interpolation may be used.
Note 6: Switch to input voltage limitation must also be observed.
Note 7: V = 35V
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-
Note 2: A feedback pin voltage (V ) of 2.5V forces the V pin to its low
FB
C
MAX
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
= 5.5V.
SENSE
Note 3: Total voltage from V pin to ground pin must be ≥8V after start-
IN
tance from the sense pin (Output) to the V pin on the LT1176-5, multiply
C
up for proper regulation.
Note 4: Switch frequency is internally scaled down when the feedback pin
by 0.44.
Power = I
(V /V ) + V [7mA + 3mA (V /V ) + 0.012 (I
)]
LOAD
Application Hints
LOAD OUT IN
IN
OUT IN
5
I
= I
+ [V
(V – V )]/2E (V )(L)
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.
PEAK
LOAD(PEAK)
OUT IN OUT IN
Example: V = 15V, V
= 5V, I
= 0.5A Continuous, 0.8A Peak,
IN
OUT
LOAD
L = 100µH
Power (I
I
= 0.5A) = 0.38W
= 0.8A) = 0.97A
LOAD
(I
PEAK LOAD
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.
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-
tationthattheinterconnectionofitscircuitsasdescribedhereinwillnotinfringeonexistingpatentrights.
3
LT1176/LT1176-5
W
BLOCK DIAGRA
INPUT SUPPLY
0.3V
10µA
320µA
+
6V
µPOWER
6V TO ALL
CIRCUITRY
REGULATOR
AND BIAS
SHUTDOWN
500Ω
–
2.35V
CURRENT LIMIT
SHUTDOWN
CURRENT LIMIT
COMP
0.16Ω
+
–
+
–
C2
I
LIM
4.5V
10k
SHUTDOWN
FREQ SHIFT
R
R/S
LATCH
R
G1
100kHz
OSCILLATOR
S
Q
SYNC
OUTPUT
VOLTAGE
MONITOR
3V
P-P
V
IN
400Ω
+
–
Z
+
C1
ANALOG
X MULTIPLIER
XYZ
A1
STATUS
ERROR
AMP
PULSE WIDTH
COMPARATOR
SWITCH
OUTPUT
(V
2.21V
–
Y
)
SW
LT1176/76-5 • BD
2.8k
2.2k*
V
C
24V (EQUIVALENT)
FB/SENSE
*CONNECTED ON 5V VERSION ONLY
U
PACKAGE DESCRIPTIO
Dimensions in inches (milimeters) unless otherwise noted.
N Package 8-Lead Plastic DIP
0.400
(10.160)
MAX
0.130 ± 0.005
0.300 – 0.320
0.045 – 0.065
(3.302 ± 0.127)
(1.143 – 1.651)
(7.620 – 8.128)
8
1
7
6
5
4
0.065
(1.651)
TYP
0.250 ± 0.010
(6.350 ± 0.254)
0.009 – 0.015
(0.229 – 0.381)
0.125
0.020
(0.508)
MIN
(3.175)
MIN
+0.025
–0.015
2
3
0.045 ± 0.015
(1.143 ± 0.381)
0.325
+0.635
8.255
(
)
–0.381
0.100 ± 0.010
(2.540 ± 0.254)
0.018 ± 0.003
(0.457 ± 0.076)
S Package 20-Lead Plastic SOL
0.496 – 0.512
(12.598 – 13.005)
0.291 – 0.299
(7.391 – 7.595)
0.037 – 0.045
(0.940 – 1.143)
0.093 – 0.104
(2.362 – 2.642)
19 18
16
14 13 12 11
20
17
15
0.005
(0.127)
RAD MIN
0.010 – 0.029
(0.254 – 0.737)
× 45°
0° – 8° TYP
0.050
(1.270)
TYP
0.394 – 0.419
(10.007 – 10.643)
SEE
NOTE
0.004 – 0.012
(0.102 – 0.305)
0.009 – 0.013
(0.229 – 0.330)
SEE NOTE
0.014 – 0.019
0.016 – 0.050
(0.406 – 1.270)
(0.356 – 0.482)
TYP
NOTE:
PIN 1 IDENT, NOTCH ON TOP AND CAVITIES ON THE BOTTOM OF PACKAGES ARE THE MANUFACTURING OPTIONS.
THE PART MAY BE SUPPLIED WITH OR WITHOUT ANY OF THE OPTIONS.
2
3
5
7
8
9
10
1
4
6
LT/GP 0393 10K REV 0
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7487
4
●
●
LINEAR TECHNOLOGY CORPORATION 1993
(408) 432-1900 FAX: (408) 434-0507 TELEX: 499-3977
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