LT8611 Datasheet PDF - Linear Technology

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LT8611
Linear Technology

Part Number LT8611
Description 2.5A Synchronous Step-Down Regulator
Page 24 Pages


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FEATURES
n Rail-to-Rail Current Sense Amplifier with Monitor
n Wide Input Voltage Range: 3.4V to 42V
n Ultralow Quiescent Current Burst Mode® Operation:
2.5μA IQ Regulating 12VIN to 3.3VOUT
Output Ripple < 10mVP-P
n High Efficiency Synchronous Operation:
96% Efficiency at 1A, 5VOUT from 12VIN
94% Efficiency at 1A, 3.3VOUT from 12VIN
n Fast Minimum Switch-On Time: 50ns
n Low Dropout Under All Conditions: 200mV at 1A
n Allows Use Of Small Inductors
n Low EMI
n Adjustable and Synchronizable: 200kHz to 2.2MHz
n Current Mode Operation
n Accurate 1V Enable Pin Threshold
n Internal Compensation
n Output Soft-Start and Tracking
n Small Thermally Enhanced 3mm × 5mm 24-Lead
QFN Package
APPLICATIONS
n Automotive and Industrial Supplies
n General Purpose Step-Down
n CCCV Power Supplies
Electrical Specifications Subject to Change
LT8611
42V, 2.5A Synchronous
Step-Down Regulator with
Current Sense and 2.5µA
Quiescent Current
DESCRIPTION
The LT®8611 is a compact, high efficiency, high speed
synchronous monolithic step-down switching regulator
that consumes only 2.5μA of quiescent current. Top and
bottom power switches are included with all necessary
circuitry to minimize the need for external components.
The built-in current sense amplifier with monitor and
control pins allows accurate input or output current
regulation and limiting. Low ripple Burst Mode operation
enables high efficiency down to very low output currents
while keeping the output ripple below 10mVP-P. A SYNC
pin allows synchronization to an external clock. Internal
compensation with peak current mode topology allows
the use of small inductors and results in fast transient
response and good loop stability. The EN/UV pin has an
accurate 1V threshold and can be used to program VIN
undervoltage lockout or to shut down the LT8611 reduc-
http://www.DataSheet4U.com/
ing the input supply current to 1μA. A capacitor on the
TR/SS pin programs the output voltage ramp rate during
start-up. The PG flag signals when VOUT is within ±9% of
the programmed output voltage as well as fault conditions.
The LT8611 is available in a small 24-lead 3mm × 5mm
QFN package with exposed pad for low thermal resistance.
L, LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners.
TYPICAL APPLICATION
5V Step-Down Converter with 2.5A Output Current Limit
VIN
5.5V TO 42V
4.7μF ON OFF
VIN
EN/UV
BST
SYNC
LT8611
SW
IMON
ICTRL
ISP
ISN
BIAS
INTVCC
PG
TR/SS
0.1μF
RT
FB
PGND GND
1μF 52.3k
0.1μF
4.7μH
0.02Ω
1μF
VOUT
5V
2.5A
10pF
1M
243k
47μF
fSW = 800kHz
8611 TA01a
12VIN to 5VOUT Efficiency
100
95
90
85
80
75
70
65
60
55
50
0
fSW = 700kHz
VIN = 12V
VIN = 24V
0.5 1 1.5 2 2.5
LOAD CURRENT (A)
8611 TA01b
8611p
1



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LT8611
ABSOLUTE MAXIMUM RATINGS
(Note 1)
VIN, EN/UV, PG, ISP, ISN...........................................42V
BIAS..........................................................................30V
BST Pin Above SW Pin................................................4V
FB, TR/SS, RT, INTVCC, IMON, ICTRL.........................4V
SYNC Voltage .............................................................6V
Operating Junction Temperature Range (Note 2)
LT8611E ................................................. –40 to 125°C
LT8611I .................................................. –40 to 125°C
Storage Temperature Range ......................–65 to 150°C
PIN CONFIGURATION
TOP VIEW
SYNC 1
TR/SS 2
RT 3
EN/UV 4
VIN 5
VIN 6
PGND 7
PGND 8
24 23 22 21
25
GND
9 10 11 12
20 FB
19 PG
18 BIAS
17 INTVCC
16 BST
15 SW
14 SW
13 SW
UDD PACKAGE
24-LEAD (3mm w 5mm) PLASTIC QFN
θJA = 38°C/W, θJC(PAD) = 10°C/W
EXPOSED PAD (PIN 25) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT8611EUDD#PBF
LT8611IUDD#PBF
LT8611EUDD#TRPBF
LT8611IUDD#TRPBF
8611
8611
24-Lead (3mm × 5mm) Plastic QFN
http://www.DataSheet4U.com/
24-Lead (3mm × 5mm) Plastic QFN
–40°C to 125°C
–40°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.
Consult LTC Marketing for information on non-standard lead based finish parts.
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/
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C.
PARAMETER
CONDITIONS
MIN TYP MAX
UNITS
Minimum Input Voltage
l
2.9 3.4
V
VIN Quiescent Current
VEN/UV = 0V, VSYNC = 0V
1.0 3
μA
l
1.0 8
μA
VEN/UV = 2V, Not Switching, VSYNC = 0V
1.7 4
μA
l
1.7 10
μA
VIN Current in Regulation
Feedback Reference Voltage
Feedback Voltage Line Regulation
Feedback Pin Input Current
INTVCC Voltage
VEN/UV = 2V, Not Switching, VSYNC = 2V
VOUT = 0.97V, VIN = 6V, Output Load = 100μA
VOUT = 0.97V, VIN = 6V, Output Load = 1mA
VIN = 6V, ILOAD = 0.5A
VIN = 6V, ILOAD = 0.5A
VIN = 4.0V to 42V, ILOAD = 0.5A
VFB = 1V
ILOAD = 0mA, VBIAS = 0V
ILOAD = 0mA, VBIAS = 3.3V
l
l
0.967
l 0.956
l
–20
3.23
3.25
0.46
24
210
0.970
0.970
0.004
3.4
3.29
1
50
350
0.973
0.984
0.02
20
3.57
3.35
mA
μA
μA
V
V
%/V
nA
V
V
8611p
2



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LT8611
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C.
PARAMETER
INTVCC Undervoltage Lockout
BIAS Pin Current Consumption
Minimum On-Time
Minimum Off-Time
Oscillator Frequency
Top Power NMOS On-Resistance
Top Power NMOS Current Limit
Bottom Power NMOS On-Resistance
Bottom Power NMOS Current Limit
SW Leakage Current
EN/UV Pin Threshold
EN/UV Pin Hysteresis
EN/UV Pin Current
PG Upper Threshold Offset from VFB
PG Lower Threshold Offset from VFB
PG Hysteresis
PG Leakage
PG Pull-Down Resistance
SYNC Threshold
SYNC Pin Current
TR/SS Source Current
TR/SS Pull-Down Resistance
Current Sense Voltage (VISP-ISN)
IMON Monitor Pin Voltage
ISP, ISN Pin Bias Current
CONDITIONS
VBIAS = 3.3V, ILOAD = 1A, 2MHz
ILOAD = 1A, SYNC = 0V
ILOAD = 1A, SYNC = 3.3V
RT = 221k, ILOAD = 1A
RT = 60.4k, ILOAD = 1A
RT = 18.2k, ILOAD = 1A
VINTVCC = 3.4V, ISW = 1A
VINTVCC = 3.4V
VINTVCC = 3.4V, ISW = 1A
VINTVCC = 3.4V
VIN = 42V, VSW = 0V, 42V
EN/UV Rising
VEN/UV = 2V
VFB Falling
VFB Rising
VPG = 3.3V
VPG = 0.1V
SYNC Falling
SYNC Rising
VSYNC = 2V
Fault Condition, TR/SS = 0.1V
VICTRL = 1.5V, VISN = 3.3V
VICTRL = 1.5V, VISN = 0V
VICTRL = 800mV, VISN = 3.3V
VICTRL = 800mV, VISN = 0V
VICTRL = 200mV, VISN = 3.3V
VICTRL = 200mV, VISN = 0V
VISP-ISN = 50mV, VISN = 3.3V
VISP-ISN = 50mV, VISN = 0V
VISP-ISN = 10mV, VISN = 3.3V
VISP-ISN = 10mV, VISN = 0V
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MIN TYP MAX
2.5 2.6 2.7
8.5
l 30 50 70
l 30 45 65
50 80 110
l 180 210 240
l 665 700 735
l 1.85 2.00 2.15
120
l 3.5 4.8 5.8
65
2.5 3.3 4.8
–1.5 1.5
l 0.94 1.0 1.06
40
–20 20
l6
9.0 12
l –6
–9.0 –12
1.3
–40 40
l 680 2000
0.8 1.1 1.4
1.6 2.0 2.4
–40 40
l 1.2 2.2 3.2
230
l 48 50 52
l 46.5 50.5 55.5
l 39 41 15
l 38 42 46
l6
10 14
l5
10.5 16
l 0.965 1.00 1.035
l 0.900 0.99 1.080
l 150 220 290
l 130 205 280
l –20
20
UNITS
V
mA
ns
ns
ns
kHz
kHz
MHz
A
A
μA
V
mV
nA
%
%
%
nA
Ω
V
V
nA
μA
Ω
mV
mV
mV
mV
mV
mV
V
V
mV
mV
μA
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: The LT8611E is guaranteed to meet performance specifications
from 0°C to 125°C junction temperature. Specifications over the –40°C
to 125°C operating junction temperature range are assured by design,
characterization, and correlation with statistical process controls. The
LT8611I is guaranteed over the full –40°C to 125°C operating junction
temperature range. High junction temperatures degrade operating
lifetimes. Operating lifetime is derated at junction temperatures greater
than 125°C.
Note 3: This IC includes overtemperature protection that is intended to
protect the device during overload conditions. Junction temperature will
exceed 150°C when overtemperature protection is active. Continuous
operation above the specified maximum operating junction temperature
will reduce lifetime.
8611p
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LT8611
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency at 5VOUT
100
95
90
85
80
75
70
65
60 fSW = 700kHz
55
VIN = 12V
VIN = 24V
50
0 0.5 1 1.5 2 2.5
LOAD CURRENT (A)
8611 G01
Efficiency at 3.3VOUT
100
90
80
70
60
50
40
30
20
10
0
0.001
fSW = 700kHz
VIN = 12V
VIN = 24V
0.1 10 1000
LOAD CURRENT (mA)
8611 G04
EN Pin Thresholds
1.04
1.03
1.02
1.01
EN RISING
1.00
0.99
0.98
0.97 EN FALLING
0.96
0.95
–55 –25
5 35 65 95
TEMPERATURE (°C)
125 155
8611 G07
Efficiency at 3.3VOUT
100
95
90
85
80
75
70
65
60 fSW = 700kHz
55
VIN = 12V
VIN = 24V
50
0 0.5 1 1.5 2 2.5
LOAD CURRENT (A)
8611 G02
Efficiency vs Frequency
96
VOUT = 3.3V
94
92
90
88
86
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84
82
0.25
VIN = 12V
VIN = 24V
0.75 1.25 1.75
SWITCHING FREQUENCY (MHz)
2.25
8611 G05
Load Regulation
0.25
VOUT = 3.3V
0.20 VIN = 12V
0.15
0.10
0.05
0
–0.05
–0.10
–0.15
–0.20
–0.25
0
0.5 1 1.5 2
LOAD CURRENT (A)
2.5 3
8611 G08
Efficiency at 5VOUT
100
90
80
70
60
50
40
30
20
10
0
0.001
fSW = 700kHz
VIN = 12V
VIN = 24V
0.1 10 1000
LOAD CURRENT (mA)
8611 G03
Reference Voltage
0.985
0.982
0.979
0.976
0.973
0.970
0.967
0.964
0.961
0.958
0.955
–55 –25
5 35 65 95
TEMPERATURE (°C)
125 155
8611 G06
Line Regulation
0.10
0.08
VOUT = 3.3V
ILOAD = 0.5A
0.06
0.04
0.02
0
–0.02
–0.04
–0.06
–0.08
–0.10
0
5 10 15 20 25 30 35 40 45
INPUT VOLTAGE (V)
8611 G09
8611p
4



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