FeaTures
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LT8616
Dual 42V Synchronous
Monolithic Step-Down Regulator
with 6.5µA Quiescent Current
DescripTion
The
LT
®
8616
is a high efficiency, high speed, dual synchro-
nous monolithic step-down switching regulator that con-
sumes only 6.5µA of quiescent current with both channels
enabled. Both channels contain all switches and necessary
circuitry to minimize the need for external components.
Low ripple Burst Mode operation enables high efficiency
down to very low output currents while minimizing output
ripple. 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-
able pins have accurate 1V thresholds and can be used to
program undervoltage lockout. Capacitors on the TR/SS
pins programs the output voltage ramp rate during start-
up while the PG pins signal when each output is within
10% of the programmed output voltage. The LT8616 is
available in a TSSOP package for high reliability.
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.
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Wide Input Voltage Range: 3.4V to 42V
2.5A and 1.5A Buck Regulators with Separate Inputs
Fast Minimum Switch On-Time: 35ns
Ultralow Quiescent Current Burst Mode
®
Operation:
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6.5µA I Regulating 12V to 5V
Q
IN
OUT
and 3.3V
OUT
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Output Ripple < 15mV
180° Out of Phase Switching
Adjustable and Synchronizable: 200kHz to 3MHz
Accurate 1V Enable Pin Thresholds
Internal Compensation
Output Soft-Start and Tracking
TSSOP Package: Output Stays at or Below Regulation
Voltage During Adjacent Pin Short or When a Pin Is
Left Floating
Thermally Enhanced 28-Lead TSSOP Package
applicaTions
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Automotive and Industrial Supplies
General Purpose Step-Down
Typical applicaTion
5V, 3.3V, 700kHz Step-Down Converter
V
IN
12V
4.7µF
V
IN1
EN/UV1
V
IN2
EN/UV2
LT8616
1M
10nF
1µF
PG1
PG2
SYNC/MODE
TR/SS1
TR/SS2
INTV
CC
RT
GND
SW1
1M
FB1
187k
5.6pF
BOOST1
0.1µF
10µH
V
OUT1
5V, 1.5A
47µF
100
90
80
EFFICIENCY (%)
70
60
50
0.1µF
4.7µH
SW2
1M
FB2
316k
8616 TA01a
Efficiency
4.7µF
V
IN1
= V
IN2
= 12V
f
SW
= 700kHz
BIAS
BOOST2
V
OUT2
3.3V, 2.5A
40
30
0.01
0.1
1
10
LOAD (mA)
CH1, 5V
OUT
CH2, 3.3V
OUT
100
1000
8616 TA01b
56.2k
10pF
2 x 47µF
For more information
www.linear.com/LT8616
1
8616f
LT8616
absoluTe MaxiMuM raTings
(Note 1)
pin conFiguraTion
TOP VIEW
EN/UV2
PG2
SW2
SW2
SW2
BOOST2
NC
BOOST1
SW1
1
2
3
4
5
6
7
8
9
29
GND
28 TR/SS2
27 FB2
26 FB2
25 NC
24 V
IN2
23 NC
22 BIAS
21 INTV
CC
20 NC
19 V
IN1
18 NC
17 SYNC/MODE
16 EN/UV1
15 RT
V
IN1
, V
IN2
, EN/UV1, EN/UV2, PG1, PG2.....................42V
BIAS ..........................................................................30V
BST1 Above SW1, BST2 Above SW2, FB1, FB2,
TR/SS1, TR/SS2 .....................................................4V
SYNC/MODE ...............................................................6V
Operating Junction Temperature Range (Note 2)
LT8616E ............................................. –40°C to 125°C
LT8616I.............................................. –40°C to 125°C
LT8616H ............................................ –40°C to 150°C
Storage Temperature Range .................. –60°C to 150°C
SW1 10
PG1 11
TR/SS1 12
FB1 13
FB1 14
FE PACKAGE
28-LEAD PLASTIC TSSOP
T
JMAX
= 150°C,
θ
JA
= 30°C/W,
θ
JC
= 10°C/W
EXPOSED PAD (PIN 29) IS GND, MUST BE SOLDERED TO PCB
orDer inForMaTion
LEAD FREE FINISH
LT8616EFE#PBF
LT8616IFE#PBF
LT8616HFE#PBF
TAPE AND REEL
LT8616EFE#TRPBF
LT8616IFE#TRPBF
LT8616HFE#TRPBF
PART MARKING*
LT8616FE
LT8616FE
LT8616FE
PACKAGE DESCRIPTION
28-Lead Plastic TSSOP
28-Lead Plastic TSSOP
28-Lead Plastic TSSOP
TEMPERATURE RANGE
–40 to 125°C
–40 to 125°C
–40 to 150°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 nonstandard 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/
2
8616f
For more information
www.linear.com/LT8616
LT8616
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C.
PARAMETER
Common
Quiescent Current
EN/UV1 = EN/UV2 = 0V, Current from V
IN1
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elecTrical characTerisTics
CONDITIONS
MIN
TYP
1.7
1.7
3.0
3.0
0.5
MAX
4.0
8.0
5.0
12.0
1.0
798
802
20
UNITS
µA
µA
µA
µA
mA
mV
mV
%/V
nA
V
mV
nA
%
%
%
nA
Ω
µA
Ω
mA
EN/UV1 = EN/UV2 = 2V, SYNC = 0V (Burst Mode), Not Switching,
Current from V
IN1
EN/UV1 = EN/UV2 = 2V, SYNC = 3V (Pulse-Skipping Mode), Not
Switching, Current from BIAS or V
IN1
FB Voltage
FB Voltage Line Regulation
FB Pin Input Current
EN/UV Pin Threshold
EN/UV Pin Hysteresis
EN/UV Pin Current
PG Upper Threshold from V
FB
PG Lower Threshold from V
FB
PG Hysteresis
PG Leakage
PG Pull-Down Resistance
TR/SS Source Current
TR/SS Pull-Down Resistance
BIAS Pin Current Consumption
Oscillator Frequency
TR/SS = 0.1V
V
OUT1
= 3.3V, Load1 = 0.5A, V
OUT2
= 3.3V, Load2 = 0.5A, f
SW
= 1MHz
R
T
= 14.7kΩ
R
T
= 37.4kΩ
R
T
= 221kΩ
SYNC Falling
SYNC Rising
SYNC = 3V
PG = 3.3V
PG = 0.1V
EN/UV = 2V
FB Rising
FB Falling
V
IN
= 6V, Load = 0.5A
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782
778
–20
790
790
0.005
V
IN
= 4V to 25V, Load = 0.5A
FB = 0.79V
Rising
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0.97
–20
1.03
50
1.09
20
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6
–6
–100
10
–10
1
13
–13
100
350
1
2
250
7
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l
3
1.85
900
160
0.4
–100
2.05
1000
200
2.25
1100
240
2.4
100
MHz
kHz
kHz
V
V
nA
V
µA
µA
ns
mΩ
A
mΩ
A
µA
SYNC Threshold
SYNC Pin Current
Channel 1
Minimum V
IN1
Voltage
Supply Current in Regulation
SW1 Minimum On-Time
SW1 Top NMOS On-Resistance
SW1 Peak Current Limit
SW1 Bottom NMOS On-Resistance
SW1 Valley Current Limit
SW1 Leakage Current
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3.0
80
620
3.4
110
910
55
5.2
3.0
2
V
IN
= 6V, V
OUT1
= 3.3V, Load = 100µA
V
IN
= 6V, V
OUT1
= 3.3V Load = 1mA
Load = 0.25A, Pulse-Skipping Mode
(Note 3)
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20
3.2
1.5
–2
35
310
4.2
190
2.0
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V
IN1
= 42V, V
SW1
= 0V, 42V
For more information
www.linear.com/LT8616
3
8616f
LT8616
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C.
PARAMETER
Channel 2
Minimum V
IN1
Voltage to Use
Channel2
Supply Current in Regulation
SW2 Minimum On-Time
SW2 Top NMOS On-Resistance
SW2 Peak Current Limit
SW2 Bottom NMOS On-Resistance
SW2 Valley Current Limit
SW2 Leakage Current
V
IN2
= 42V, V
SW2
= 0V, 42V
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 LT8616E 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
LT8616I is guaranteed over the full –40°C to 125°C operating junction
temperature range. The LT8616H is guaranteed over the full –40°C to
150°C operating junction temperature range.
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elecTrical characTerisTics
CONDITIONS
MIN
TYP
3.0
80
620
MAX
3.4
110
910
55
6.5
4.5
2
UNITS
V
µA
µA
ns
mΩ
A
mΩ
A
µA
V
IN
= 6V, V
OUT2
= 3.3V, Load2 = 100µA
V
IN
= 6V, V
OUT2
= 3.3V Load2 = 1mA
Load = 0.25A, Pulse-Skipping Mode
(Note 3)
l
20
4.5
2.5
–2
35
145
5.5
120
3.5
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Note 3:
Current limit guaranteed by design and/or correlation to static test.
Slope compensation reduces current limit at higher duty cycle.
Note 4:
This IC includes overtemperature protection that is intended
to protect the device during momentary overload conditions. Junction
temperature will exceed the maximum operating junction temperature
when overtemperature protection is active. Continuous operation above
the specified maximum operating junction temperature may impair device
reliability. See High Temperature Considerations section.
4
8616f
For more information
www.linear.com/LT8616
LT8616
Typical perForMance characTerisTics
Efficiency at 5V
OUT
100
98
96
EFFICIENCY (%)
EFFICIENCY (%)
94
92
90
88
86
84
82
80
CH1, 12V
IN
CH1, 24V
IN
CH2, 12V
IN
CH2, 24V
IN
0 0.25 0.5 0.75 1.0 1.25 1.5 1.75 2.0 2.25 2.5
LOAD (A)
8616 G01
f
SW
= 700kHz
100
f = 700kHz
95
SW
90
85
80
75
70
65
60
55
50
45
40
35
30
0.01
10
0.1
1
LOAD (mA)
Efficiency at 5V
OUT
Efficiency vs Frequency
95
94
93
92
EFFICIENCY (%)
91
90
89
88
87
86
85
0.2
0.6
CH1, 5V, 1A
CH2, 3.3V, 1.5A
1.0 1.4 1.8 2.2
FREQUENCY (MHz)
2.6
3.0
V
IN1
= V
IN2
= 12V
CH1, 12V
IN
CH1, 24V
IN
CH2, 12V
IN
CH2, 24V
IN
100
1000
8616 G02
8616 G03
100
98
96
94
EFFICIENCY (%)
92
90
88
86
84
82
80
Efficiency at 3.3V
OUT
f
SW
= 700kHz
CH1, 12V
IN
CH1, 24V
IN
CH2, 12V
IN
CH2, 24V
IN
0 0.25 0.5 0.75 1.0 1.25 1.5 1.75 2.0 2.25 2.5
LOAD (A)
8616 G04
100
95 f
SW
= 700kHz
90
85
80
75
70
65
60
55
50
45
40
35
30
0.01
0.1
1
10
LOAD (mA)
Efficiency at 3.3V
OUT
No Load Supply Current
10
9
8
INPUT CURRENT (µA)
7
6
5
4
3
2
1
0
0
5
10
15
20 25
V
IN
(V)
V
OUT1
= 3.3V
V
OUT2
= 5V
30
35
40
EFFICIENCY (%)
CH1, 12V
IN
CH1, 24V
IN
CH2, 12V
IN
CH2, 24V
IN
100
1000
8616 G05
8616 G06
No Load Supply Current
30
V
IN1
= V
IN2
= 12V
V
OUT1
= 5V
25 V
OUT2
= 3.3V
IN REGULATION
BIAS CURRENT (mA)
20
15
10
5
0
–50 –25
18
16
14
12
10
8
6
4
2
0
25 50 75 100 125 150
TEMPERATURE (°C)
8616 G07
BIAS Current
vs Switching Frequency
1.1
1.08
1.06
EN THRESHOLD (V)
1.04
1.02
1.0
0.98
0.96
0.94
EN/UV Threshold
SUPPLY CURRENT (µA)
0
V
IN1
= V
IN2
= 12V
V
OUT1
= 5V
LOAD1 = 1A
V
OUT2
= 3.3V
LOAD2 = 1A
0
0.5
1.0
1.5
2.0
FREQUENCY (MHz)
2.5
3.0
8616 G08
0.92
–50 –25
EN RISING
EN FALLING
0
25 50 75 100 125 150
TEMPERATURE (°C)
8616 G09
For more information
www.linear.com/LT8616
5
8616f
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