LT1076-5
5V Step-Down
Switching Regulator
FEATURES
s
s
s
s
s
s
s
s
DESCRIPTIO
Fixed 5V Output
2A On-Board Switch
100kHz Switching Frequency
2% Output Voltage Tolerance Over Temperature
Greatly Improved Dynamic Behavior
Available in Low Cost 5-Lead Package
Only 9.5mA Quiescent Current
Operates Up to 60V Input
APPLICATI
s
s
S
s
5V Output Buck Converter
Tapped Inductor Buck Converter with 4A Output
at 5V
Positive-to-Negative Converter
The LT1076-5 is a 2A fixed 5V output monolithic bipolar
switching regulator which requires only a few external
parts for normal operation. The power switch, all oscillator
and control circuitry, all current limit components, and an
output monitor are included on the chip. The topology is
a classic positive “buck” configuration but several design
innovations allow 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
40V below ground, allowing the LT1076-5 to drive a
tapped inductor in the buck mode with output currents up
to 4A.
The LT1076-5 uses a true analog multiplier in the feedback
loop. This makes the device respond nearly instanta-
neously to input voltage fluctuations and makes loop gain
independent of input voltage. As a result, dynamic behav-
ior of the regulator is significantly improved over previous
designs.
On-chip pulse by pulse current limiting makes the LT1076-
5 nearly bust-proof for output overloads or shorts. The
input voltage range as a buck converter is 8V to 60V, but
a self-boot feature allows input voltages as low as 5V in the
inverting and boost configurations.
The LT1076-5 is available in a low cost 5-lead TO-220
package with frequency pre-set at 100kHz and current
limit at 2.6A. See Application Note 44 for design details.
TYPICAL APPLICATI
8V TO 40V
Basic Positive Buck Converter
100µH**
†
V
IN
LT1076-5
SENSE
GND
V
C
R3
1.5k
V
SW
MBR340*
5V
≤1.8A
* MBR330P MAY BE USED
FOR V
IN
≤
25V
** COILTRONICS #100-1-52
HURRICANE #HL-AG210LL
†
+
C3
200µF
C2
0.033µF
+
C1
500µF
25V
LT1076-5 TA01
U
VALUE MAY BE REDUCED TO 50µH
FOR OUTPUT LOADS BELOW 1.5A
UO
UO
1
LT1076-5
ABSOLUTE
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
FRONT VIEW
7
6
5
4
3
2
1
R PACKAGE
7-LEAD PLASTIC DD
SHDN
V
C
SENSE
GND
I
LIM
V
SW
V
IN
Input Voltage
LT1076-5............................................................ 45V
LT1076HV-5 ....................................................... 64V
Switch Voltage with Respect to Input Voltage
LT1076-5............................................................ 64V
LT1076HV-5 ....................................................... 75V
Switch Voltage with Respect to Ground Pin
(V
SW
Negative)
LT1076-5 (Note 5).............................................. 35V
LT1076HV-5 (Note 5) ......................................... 45V
Sense Pin Voltage ........................................... – 2V, 10V
Maximum Operating Ambient Temperature Range
LT1076C-5, LT1076HVC-5 ..................... 0°C to 70°C
LT1076I-5, LT1076HVI-5 .................. – 40°C to 85°C
Maximum Operating Junction Temperature Range
LT1076C-5, LT1076HVC-5 ................... 0°C to 125°C
LT1076I-5, LT1076HVI-5 ................ – 40°C to 125°C
Maximum Storage Temperature .......... –65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER PART
NUMBER
LT1076CR-5
T
JMAX
= 110°C
θ
WILL VARY FROM APPROXIMATELY 30°C/W WITH
2.8IN
2
OF 1 OZ COPPER TO 70°C/W WITH 0.20IN
2
OF
1 OZ COPPER.
FRONT VIEW
5
4
3
2
1
T PACKAGE
5-LEAD TO-220
V
IN
V
SW
GND
V
C
SENSE
LT1076CT-5
LT1076HVCT-5
LT1076IT-5
LT1076HVIT-5
FOR STRAIGHT LEADS, ORDER FLOW 06
T
JMAX
= 110°C,
θ
JA
= 130°C/W
FRONT VIEW
7
6
5
4
3
2
1
Y PACKAGE
7-LEAD TO-220
SHDN
V
C
SENSE
GND
I
LIM
V
SW
V
IN
LT1076CY-5
T
JMAX
= 110°C,
θ
JA
= 130°C/W
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
PARAMETER
Switch “On” Voltage (Note 1)
Switch “Off” Leakage
Supply Current (Note 2)
CONDITIONS
I
SW
= 0.5A
I
SW
= 2A
T
J
= 25°C, V
IN
= 25V, unless otherwise noted.
MIN
q
q
TYP
MAX
1.2
1.7
150
250
UNITS
V
V
µA
µA
mA
mA
µA
V
V
A
A
A
%
V
IN
= 25V, V
SW
= 0
V
IN
= V
MAX
, V
SW
= 0 (Note 6)
V
OUT
= 5.5V, V
IN
≤
40V
40V < V
IN
< 60V
V
SHDN
= 0.1V (Device Shutdown) (Note 8)
Normal Mode
Start-Up Mode (Note 3)
I
LIM
= Open
R
LIM
= 10k (Note 9)
R
LIM
= 7k (Note 9)
q
q
q
q
q
8.5
9.0
140
7.3
3.5
2
2.6
1.8
1.2
90
11
12
300
8.0
4.8
3.2
Minimum Supply Voltage
Switch Current Limit (Note 4)
Maximum Duty Cycle
q
85
2
U
W
U
U
W W
W
LT1076-5
ELECTRICAL CHARACTERISTICS
PARAMETER
Switching Frequency
CONDITIONS
T
J
= 25°C, V
IN
= 25V, unless otherwise noted.
MIN
q
q
TYP
100
20
0.03
2000
MAX
110
120
0.1
UNITS
kHz
kHz
kHz
%/ V
V/ V
µmho
µA
mA
kΩ
V
%
%
%/ V
V
mV/°C
V
µA
µA
V
V
°C/
W
T
J
≤
125°C
V
OUT
= V
SENSE
= 0V (Note 4)
8V
≤
V
IN
≤
V
MAX
(Note 7)
1V
≤
V
C
≤
4V
90
85
Switching Frequency Line Regulation
Error Amplifier Voltage Gain (Note 7)
Error Amplifier Transconductance (Note 7)
Error Amplifier Source and Sink Current
Sense Pin Divider Resistance
Sense Voltage
Output Voltage Tolerance
3700
Source (V
SENSE
= 4.5V)
Sink (V
SENSE
= 5.5V)
100
0.7
3
V
C
= 2V
V
OUT
(Nominal) = 5V
All Conditions of Input Voltage, Output Voltage,
Temperature and Load Current
8V
≤
V
IN
≤
V
MAX
(Note 6)
Over Temperature
q
q
q
q
5000
140
1.0
5
5
±0.5
±1.0
0.005
1.5
–4.0
24
8000
225
1.6
8
5.15
±2
±3
0.02
4.85
Output Voltage Line Regulation
V
C
Voltage at 0% Duty Cycle
Multiplier Reference Voltage
Shutdown Pin Current
Shutdown Thresholds
Thermal Resistance Junction to Case
V
SHDN
= 5V
V
SHDN
≤
V
THRESHOLD
(≅ 2.5V)
Switch Duty Cycle = 0
Fully Shut Down
5
2.2
0.1
10
2.45
0.30
20
50
2.7
0.5
4
The
q
denotes specifications which apply over the full operating
temperature range.
Note 1:
To calculate maximum switch “on” voltage at currents between
low and high conditions, a linear interpolation may be used.
Note 2:
A sense pin voltage (V
SENSE
) of 5.5V 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.
Note 3:
Total voltage from V
IN
pin to ground pin must be
≥
8V after start-
up for proper regulation. For T
A
< 25°C, limit = 5V.
Note 4:
Switch frequency is internally scaled down when the sense pin
voltage is less than 2.6V to avoid extremely short switch on times. During
current limit testing, V
SENSE
is adjusted to give a minimum switch on time
of 1µs.
Note 5:
Switch to input voltage limitation must also be observed.
Note 6:
V
MAX
= 40V for the LT1076-5 and 60V for the LT1076HV-5.
Note 7:
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, multiply by
0.44.
Note 8:
Does not include switch leakage.
Note 9:
I
LIM
≈
R
LIM
– 1k
5k
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.
3
LT1076-5
PACKAGE DESCRIPTIO
0.060
(1.524)
(
+0.012
0.331 –0.020
+0.305
8.407 –0.508
)
0.050 ± 0.010
(1.270 ± 0.254)
0.030 ± 0.008
(0.762 ± 0.203)
(
+0.012
0.143 –0.020
+0.305
3.632 –0.508
)
0.390 – 0.415
(9.906 – 10.541)
0.460 – 0.500
(11.684 – 12.700)
0.057 – 0.077
(1.448 – 1.956)
0.390 – 0.410
(9.91 – 10.41)
0.103 – 0.113
(2.62 – 2.87)
0.026 – 0.036
(0.66 – 0.91)
0.045 – 0.055
(1.14 – 1.40)
4
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7487
(408) 432-1900
q
FAX
: (408) 434-0507
q
TELEX
: 499-3977
U
Dimensions in inches (millimeters) unless otherwise noted.
R Package, 7-Lead Plastic DD
0.401 ± 0.015
(10.185 ± 0.381)
0.175 ± 0.008
(4.445 ± 0.203)
15° TYP
0.050 ± 0.008
(1.270 ± 0.203)
0.059
(1.499)
TYP
(
+0.008
0.004 –0.004
+0.203
0.102 –0.102
)
0.105 ± 0.008
(2.667 ± 0.203)
0.022 ± 0.005
(0.559 ± 0.127)
0.050 ± 0.012
(1.270 ± 0.305)
DD7 0693
T Package, 5-Lead TO-220
0.147 – 0.155
(3.734 – 3.937)
DIA
0.230 – 0.270
(5.842 – 6.858)
0.570 – 0.620
(14.478 – 15.748)
0.330 – 0.370
(8.382 – 9.398)
0.620
(15.75)
TYP
0.700 – 0.728
(17.780 – 18.491)
0.165 – 0.180
(4.293 – 4.572)
0.045 – 0.055
(1.143 – 1.397)
0.152 – 0.202
0.260 – 0.320 (3.860 – 5.130)
(6.604 – 8.128)
0.095 – 0.115
(2.413 – 2.921)
0.013 – 0.023
(0.330 – 0.584)
0.028 – 0.038
(0.711 – 0.965)
0.135 – 0.165
(3.429 – 4.191)
0.155 – 0.195
(3.937 – 4.953)
T5 (FORMED) 0694
Y Package, 7-Lead TO-220
0.147 – 0.155
(3.73 – 3.94)
DIA
0.169 – 0.185
(4.29 – 4.70)
0.045 – 0.055
(1.14 – 1.40)
0.235 – 0.258
(5.97 – 6.55)
0.560 – 0.590
(14.22 – 14.99)
0.620
(15.75)
TYP
0.700 – 0.728
(17.78 – 18.49)
0.152 – 0.202
(3.86 – 5.13)
0.260 – 0.320
(6.60 – 8.13)
0.016 – 0.022
(0.41 – 0.56)
0.135 – 0.165
(3.43 – 4.19)
0.095 – 0.115
(2.41 – 2.92)
0.155 – 0.195
(3.94 – 4.95)
Y7 0893
LT/GP 0794 5K REV A • PRINTE IN USA
©
LINEAR TECHNOLOGY CORPORATION 1994
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