LINER LT1176CN8-5 Step-down switching regulator Datasheet

LT1176/LT1176-5
Step-Down
Switching Regulator
FEATURES
■
■
■
■
■
■
■
■
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 converter, and as a flyback converter. The switch output is
specified to swing below ground.
1.2A On-Board Switch
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. This makes the device respond nearly instantaneously
to input voltage fluctuations and makes loop gain independent of input voltage. As a result, dynamic behavior of the
regulator is significantly improved over previous designs.
UO
APPLICATI
■
■
■
■
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 selfboot 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
U
DESCRIPTIO
The LT1176 is a 1A monolithic bipolar switching regulator
which requires only a few external parts for normal opera-
The LT1176 is available in a low cost 8-lead DIP package
with frequency preset at 100kHz and current limit at 1.7A An
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.
UO
TYPICAL APPLICATI
5V Buck Converter Efficiency
Basic 5V Positive Buck Converter
90
L1*
100µH
LT1176-5
GND
+
VIN = 10V
1N5819
SENSE
VC
R3
2.7k
C3
100µF
L = 100µH ON MAGNETICS INC.
SIZE T-50 KOOL Mµ CORE
5V, 0.8A
VSW
VIN
+
C1
470µF
25V
EFFICIENCY (%)
10V T0 35V
80
VIN = 20V
70
C2
0.01µF
*COILTRONICS #100-1-52
LT1176/76-5 • TA01
PULSE ENGINEERING, INC. #PE-92102
HURRICANE #HL-AG210LL
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.
60
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
LOAD CURRENT (A)
LT1176/76-5 • TA02
1
LT1176/LT1176-5
U
U
RATI GS
W
W W
W
AXI U
U
ABSOLUTE
PACKAGE/ORDER 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
8
VSW
ILIM 2
7
VC
GND 3
6
STATUS
FB/SENSE 4
5
SHUTDOWN
LT1176CN8
LT1176CN8-5
N8 PACKAGE
8-LEAD PLASTIC DIP
TJ MAX = 125°C, θJA = 90°C/ W*
TOP VIEW
VIN 1
20 VSW
NC 2
19 NC
ILIM 3
18 VC
GND 4
17 GND
GND 5
16 GND
GND 6
15 GND
GND 7
14 GND
NC 8
*These thermal resistance numbers are for typical mounting technique. Lower thermal resistance
can be obtained with large copper lands, thermal glues or heatsinks.
ORDER PART
NUMBER
VIN 1
ORDER PART
NUMBER
LT1176CS
LT1176CS-5
13 STATUS
FB/SENSE 9
12 SHUTDOWN
NC 10
11 NC
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
Switch “ON” Voltage (Note 1)
ISW = 0.2A
ISW = 1A
Switch “OFF” Leakage
VIN = 25V, VSW = 0
VIN = VMAX, VSW = 0 (Note 7)
Supply Current (Note 2)
VFB = 2.5V, VIN ≤ 35V
VSHDN = 0.1V (Device Shutdown) (Note 8)
●
●
Minimum Supply Voltage
Normal Mode
Startup Mode (Note 3)
●
●
Switch Current Limit (Note 4)
ILIM Open
RLIM = 10k (Note 5)
RLIM = 7k (Note 5)
●
Maximum Duty Cycle
MIN
8V ≤ VIN ≤ VMAX (Note 7)
1V ≤ VC ≤ 4V
Error Amplifier Transconductance (Note 9)
Error Amplifier Source and Sink Current
2
Source (VFB = 2V or VSENSE = 4V)
Sink (VFB = 2.5V or VSENSE = 5.5V)
UNITS
V
V
150
250
µA
µA
7.5
140.0
10
300
mA
µA
7.3
3.5
8.0
4.8
V
V
1.2
1.7
1.2
0.8
2.2
A
A
A
●
85
90
90
85
100
●
VFB = 0V Through 2k (Note 4) (LT1176)
VSENSE = 0V (Note 4) (LT1176-5)
Error Amplifier Voltage Gain (Note 9)
MAX
1.1
1.4
Switching Frequency
Switching Frequency Line Regulation
TYP
●
●
%
110
120
kHz
kHz
kHz
kHz
0.1
%/ V
20
20
0.03
●
2000
V/ V
3700
5000
8000
µmho
100.0
0.7
140.0
1.0
225.0
1.6
µA
mA
LT1176/LT1176-5
ELECTRICAL CHARACTERISTICS
TJ = 25°C, VIN = 25V, unless otherwise noted
PARAMETER
CONDITIONS
Feedback Pin Bias Current (LT1176)
VFB = VREF
●
MIN
Reference Voltage (LT1176)
VC = 2V
●
Reference Voltage Tolerance (LT1176)
VREF (Nominal) = 2.21V
All Conditions of Input Voltage, Output
Voltage, Temperature and Load Current
●
Sense Voltage (LT1176-5)
VC = 2V
●
Sense Voltage Tolerance (LT1176-5)
VOUT (Nominal) = 5V
All Conditions of Input Voltage,
Temperature and Load Current
●
Output Voltage Line Regulation
2
UNITS
µA
2.21
2.265
V
±1.5
±2.5
%
%
5
5.15
V
±0.5
±1.0
±2
±3
%
%
5
8
kΩ
●
0.005
0.02
%/ V
Over Temperature
●
1.5
– 4.0
VSHDN = 5V ●
5
10
50
20
µA
µA
●
●
2.2
0.1
2.45
0.30
2.7
0.5
V
V
±4
±5
±6
%
4.5
5.0
V
0.25
0.4
V
4.85
3
8V ≤ VIN ≤ VMAX (Note 7)
VC Voltage at 0% Duty Cycle
Multiplier Reference Voltage
Shutdown Pin Current
VSHDN ≤ VTHRESHOLD (≅ 2.5V)
MAX
0.5
±0.5
±1.0
Sense Pin Divider Resistance (LT1176-5)
2.155
TYP
V
mV/°C
24
●
Shutdown Thresholds
Switch Duty Cycle = 0
Fully Shut Down
Status Window
As a Percent of Output Voltage
Status High Level
ISTATUS = 10µA Sourcing
●
Status Low Level
ISTATUS = 1.6mA Sinking
●
3.5
V
Status Delay Time
9
µs
Status Minimum Width
30
µs
The ● denotes specifications which apply over the full operating temperature 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 (VFB) of 2.5V forces the VC 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
VSENSE = 5.5V.
Note 3: Total voltage from VIN pin to ground pin must be ≥8V after startup for proper regulation.
Note 4: 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, VFB or VSENSE is adjusted to give a minimum switch-on time of 1µs.
Note 5: ILM = (RLIM – 1k)/ 7.65k
Note 6: Switch to input voltage limitation must also be observed.
Note 7: VMAX = 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 transconductance from the sense pin (Output) to the VC pin on the LT1176-5, multiply
by 0.44.
Application Hints
Power = ILOAD (VOUT/VIN) + VIN [7mA + 3mA (VOUT/VIN) + 0.012 (ILOAD)]
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.
IPEAK = ILOAD(PEAK) + [VOUT (VIN – VOUT)]/2E5(VIN)(L)
Example: VIN = 15V, VOUT = 5V, ILOAD = 0.5A Continuous, 0.8A Peak,
L = 100µH
Power (ILOAD = 0.5A) = 0.38W
IPEAK (ILOAD = 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.
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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
3
LT1176/LT1176-5
W
BLOCK DIAGRA
INPUT SUPPLY
10µA
0.3V
320µA
+
6V
REGULATOR
AND BIAS
µPOWER
SHUTDOWN
–
2.35V
6V TO ALL
CIRCUITRY
500Ω
CURRENT LIMIT
SHUTDOWN
+
CURRENT LIMIT
COMP
0.16Ω
+
C2
–
–
ILIM
4.5V
SHUTDOWN
10k
FREQ SHIFT
100kHz
OSCILLATOR
SYNC
OUTPUT
VOLTAGE
MONITOR
S
R
R/S
Q
LATCH
R
G1
3VP-P
VIN
+
STATUS
2.21V
–
2.8k
C1
ANALOG
X MULTIPLIER
XYZ
A1
ERROR
AMP
400Ω
+
Z
–
PULSE WIDTH
COMPARATOR
SWITCH
OUTPUT
(VSW)
Y
LT1176/76-5 • BD
2.2k*
VC
FB/SENSE
24V (EQUIVALENT)
*CONNECTED ON 5V VERSION ONLY
U
PACKAGE DESCRIPTIO
Dimensions in inches (milimeters) unless otherwise noted.
N Package 8-Lead Plastic DIP
0.300 – 0.320
(7.620 – 8.128)
(
+0.635
8.255
–0.381
)
0.130 ± 0.005
(3.302 ± 0.127)
0.045 – 0.065
(1.143 – 1.651)
8
7
6
5
0.065
(1.651)
TYP
0.009 – 0.015
(0.229 – 0.381)
+0.025
0.325 –0.015
0.400
(10.160)
MAX
0.250 ± 0.010
(6.350 ± 0.254)
0.125
(3.175)
MIN
0.045 ± 0.015
(1.143 ± 0.381)
0.100 ± 0.010
(2.540 ± 0.254)
0.020
(0.508)
MIN
1
2
4
3
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)
0.005
(0.127)
RAD MIN
0.010 – 0.029 × 45°
(0.254 – 0.737)
0.093 – 0.104
(2.362 – 2.642)
0.037 – 0.045
(0.940 – 1.143)
20
19
18
17
16
15
14
13
12
11
0° – 8° TYP
0.009 – 0.013
(0.229 – 0.330)
SEE NOTE
0.016 – 0.050
(0.406 – 1.270)
0.050
(1.270)
TYP
0.394 – 0.419
(10.007 – 10.643)
SEE
0.004 – 0.012 NOTE
(0.102 – 0.305)
0.014 – 0.019
(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.
1
4
Linear Technology Corporation
2
3
4
5
6
7
8
9
10
LT/GP 0393 10K REV 0
1630 McCarthy Blvd., Milpitas, CA 95035-7487
(408) 432-1900 ● FAX: (408) 434-0507 ● TELEX: 499-3977
 LINEAR TECHNOLOGY CORPORATION 1993
Similar pages