LT8612 Datasheet PDF - Linear Technology

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LT8612
Linear Technology

Part Number LT8612
Description 6A Synchronous Step-Down Regulator
Page 20 Pages


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Features
n Wide Input Voltage Range: 3.4V to 42V
n Ultralow Quiescent Current Burst Mode® Operation:
3μA IQ Regulating 12VIN to 3.3VOUT
Output Ripple < 10mVP-P
n High Efficiency Synchronous Operation:
95% Efficiency at 3A, 5VOUT from 12VIN
94% Efficiency at 3A, 3.3VOUT from 12VIN
n Fast Minimum Switch-On-Time: 40ns
n Low Dropout Under All Conditions: 250mV at 3A
n Allows Use Of Small Inductors
n Safely Tolerates Inductor Saturation in Overload
Conditions
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 × 6mm 28-Lead
QFN Package
Applications
n Automotive and Industrial Supplies
n General Purpose Step-Down
n GSM Power Supplies
LT8612
42V, 6A Synchronous
Step-Down Regulator
with 3µA Quiescent
Current
Description
The LT®8612 is a compact, high efficiency, high speed
synchronous monolithic step-down switching regulator
that consumes only 3µA of quiescent current. Top and
bottom power switches are included with all necessary
circuitry to minimize the need for external components.
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 cur-
rent 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 LT8612 reducing 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 LT8612 is available in a small
3mm × 6mm 28-lead 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 6A Step-Down Converter
VIN
5.6V TO 42V
10µF
10nF
1µF
VIN
EN/UV
PG
LT8612
SYNC
BST
SW
BIAS
TR/SS
FB
INTVCC
RT PGND GND
60.4k
0.1µF
3.9µH
1M
10pF
243k
fSW = 700kHz
L: EPCOS B82559
8612 TA01a
VOUT
5V
100µF 6A
1210
Efficiency at 5VOUT
100 VIN = 12V
95
90 VIN = 24V
85
80
75
70
65 fSW = 700kHz
L = 3.9µH
60
01 2 3 4
LOAD CURRENT (A)
56
8612 TA01b
For more information www.linear.com/LT8612
8612f
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LT8612
Absolute Maximum Ratings
(Note 1)
VIN, EN/UV, PG...........................................................42V
BIAS...........................................................................25V
BST Pin Above SW Pin................................................4V
FB, TR/SS, RT, INTVCC ................................................4V
SYNC Voltage ..............................................................6V
Operating Junction Temperature Range (Note 2)
LT8612E.................................................. –40 to 125°C
LT8612I................................................... –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
VIN 7
PGND 8
PGND 9
PGND 10
28 27 26 25
29
GND
11 12 13 14
24 FB
23 PG
22 BIAS
21 INTVCC
20 BST
19 SW
18 SW
17 SW
16 SW
15 SW
UDE PACKAGE
28-LEAD (3mm × 6mm) PLASTIC QFN
θJA = 40°C/W, θJC(PAD) = 5°C/W
EXPOSED PAD (PIN 29) IS GND, MUST BE SOLDERED TO PCB
Order Information
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT8612EUDE#PBF
LT8612EUDE#TRPBF
LGHW
28-Lead (3mm × 6mm) Plastic QFN
–40°C to 125°C
LT8612IUDE#PBF
LT8612IUDE#TRPBF
LGHW
28-Lead (3mm × 6mm) Plastic QFN
–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/
E lectrical 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
Minimum Input Voltage
l 2.9 3.4
VIN Quiescent Current
VEN/UV = 0V, VSYNC = 0V
1.0 5
l 1.0 20
VEN/UV = 2V, Not Switching, VSYNC = 0V
1.7 6
l 1.7 20
VIN Current in Regulation
Feedback Reference Voltage
Feedback Voltage Line Regulation
Feedback Pin Input Current
VEN/UV = 2V, Not Switching, VSYNC = 2V
VOUT = 0.97V, VIN = 6V, Output Load = 100µA
VOUT = 0.97V, VIN = 6V, Output Load = 1mA
VIN = 12V, ILOAD = 500mA
VIN = 12V, ILOAD = 500mA
VIN = 4.0V to 25V, ILOAD = 0.5A
VFB = 1V
l
l
0.964
l 0.958
l
–20
0.3
24
230
0.970
0.970
0.004
0.5
0.6
60
370
0.976
0.982
0.025
20
2 For more information www.linear.com/LT8612
UNITS
V
µA
µA
µA
µA
mA
µA
µA
V
V
%/V
nA
8612f



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LT8612
E lectrical Characteristics The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C.
PARAMETER
INTVCC Voltage
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
CONDITIONS
ILOAD = 0mA, VBIAS = 0V
ILOAD = 0mA, VBIAS = 3.3V
VBIAS = 3.3V, ILOAD = 1A, 2MHz
ILOAD = 2A, SYNC = 0V
ILOAD = 2A, SYNC = 3.3V
RT = 221k, ILOAD = 1A
RT = 60.4k, ILOAD = 1A
RT = 18.2k, ILOAD = 1A
ISW = 1A
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
MIN
3.23
3.25
2.4
l 20
l 20
50
l 180
l 665
l 1.85
l 7.5
l6
–6
l 0.94
–20
l 6.5
l –6.5
–40
l
0.7
1.0
–40
l 1.4
TYP MAX
3.4 3.57
3.29 3.35
2.6 2.8
14
40 60
35 55
85 120
210 240
700 735
2.00 2.15
65
9.7 12.0
29
10 12
0.1 6
1.0 1.06
40
1 20
9.0 11.5
–9.0 –11.5
1.3
40
680 2000
1.0 1.4
1.3 1.55
40
2.1 2.7
230
UNITS
V
V
V
mA
ns
ns
ns
kHz
kHz
MHz
A
A
µA
V
mV
nA
%
%
%
nA
Ω
V
V
nA
µA
Ω
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 LT8612E 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
LT8612I 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.
For more information www.linear.com/LT8612
8612f
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LT8612
Typical Performance Characteristics
Efficiency at 5VOUT
100 VIN = 12V
95
90 VIN = 24V
85
80
75
70
65 fSW = 700kHz
L = 3.9µH, EPCOS B82559
60
01 2 3
4
LOAD CURRENT (A)
56
8612 G01
Efficiency at 3.3VOUT
100
VIN = 12V
90
80
VIN = 24V
70
60
50
40
0.00001 0.0001 0.001 0.01
fSW = 700kHz
L = 3.9µH
0.1 1 10
LOAD CURRENT (A)
8612 G04
EN/UV Pin Thresholds
1.02
1.01
EN/UV RISING
1.00
0.99
0.98
0.97 EN/UV FALLING
0.96
0.95
–55 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
8612 G07
Efficiency at 3.3VOUT
100
95 VIN = 12V
90
85 VIN = 24V
80
75
70
65 fSW = 700kHz
L = 3.9µH, EPCOS B82559
60
01 2 3
4
LOAD CURRENT (A)
Efficiency vs Frequency
100
56
8612 G02
95
90
85
80
75
VOUT = 3.3V
VIN = 12V
L = 3.9µH
70 LOAD = 2A
0 500
1000
1500
FREQUENCY (kHz)
2000
2500
8612 G05
Load Regulation
0.5
0.4
0.3
0.2
0.1
0
–0.1
–0.2
–0.3
–0.4
–0.5
01 2 3 4
OUTPUT LOAD (A)
56
8612 G08
Efficiency at 5VOUT
100
VIN = 12V
90
80
VIN = 24V
70
60
50
40
0.00001 0.0001 0.001 0.01
fSW = 700kHz
L = 3.9µH
0.1 1 10
LOAD CURRENT (A)
8612 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
8612 G06
Line Regulation
0.10
0.08
VOUT = 5V
LOAD = 1A
0.06
0.04
0.02
0
–0.02
–0.04
–0.06
–0.08
–0.10
0
10 20 30 40
INPUT VOLTAGE (V)
50
8612 G09
4 For more information www.linear.com/LT8612
8612f



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