FEATURES
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LT8610AX
42V, 3.5A Synchronous
Step-Down Regulator with
Operation to 175°C
DESCRIPTION
The
LT
®
8610AX
is a compact, high efficiency, high speed
synchronous monolithic step-down switching regulator
rated to 175°C junction temperature. The LT8610AX is
100% tested a 175°C. 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 across a wide range of
output currents while keeping the output ripple low. 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 V
IN
undervoltage lockout or to shut down the LT8610AX. A
capacitor on the TR/SS pin programs the output voltage
ramp rate during startup while the PG flag signals when
V
OUT
is within ±9% of the programmed output voltage
as well as fault conditions. The LT8610AX is available in
small 16-lead MSOP package with exposed pad for low
thermal resistance.
L,
LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners.
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100% Tested at 175°C
±2% Reference Accuracy Over –40°C to 175°C Range
Wide Input Voltage Range: 3.7V to 42V
Ultralow Quiescent Current Burst Mode
®
Operation
High Efficiency Synchronous Operation
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91% Eff. at 0.5A, at 175°C, 3.3V
OUT
from 12V
IN
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92% Eff. at 0.5A, at 175°C, 5V
OUT
from 12V
IN
Adjustable and Synchronizable Frequency: 200kHz
to 2.2MHz
No Thermal Shutdown
Internal Compensation
Output Soft-Start and Tracking
Power Good Flag
Small Thermally-Enhanced 16-Lead MSOP Package
APPLICATIONS
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Oil and Gas Exploration
TYPICAL APPLICATION
3.3V Step-Down Converter
100
V
IN
3.7V TO 42V
V
IN
4.7µF
100nF
TR/SS
1µF
INTV
CC
RT
GND
60.4k
f
SW
= 700kHz
8610AX TA01a
Efficiency at
Efficiency at 175°C
175°C
90
BST
0.1µF 4.7µH
LT8610AX
SW
BIAS
PG
FB
SYNC
41.2k
49.9k
100k
10pF
47µF
×2
1210
X7R
V
OUT
3.3V
3.5A
EN/UV
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
1
T
A
= 175°C
12V
IN
10
100
1k
LOAD CURRENT (mA)
10k
8610AX TA01b
8610axf
For more information
www.linear.com/LT8610AX
1
LT8610AX
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW
SYNC
TR/SS
RT
EN/UV
V
IN
V
IN
NC
GND
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
FB
PG
BIAS
INTV
CC
BST
SW
SW
SW
V
IN
, EN/UV, PG..........................................................42V
BIAS ..........................................................................30V
FB, TR/SS Voltage ......................................................4V
SYNC Voltage .............................................................6V
Operating Junction Temperature Range (Note 2)
LT8610AX .............................................. –40 to 175°C
Storage Temperature Range ......................–65 to 150°C
17
GND
MSE PACKAGE
16-LEAD PLASTIC MSOP
θ
JA
= 40°C/W,
θ
JC(PAD)
= 10°C/W
EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LT8610AXMSE#PBF
TAPE AND REEL
(http://www.linear.com/product/LT8610AX#orderinfo)
PART MARKING
8610AX
PACKAGE DESCRIPTION
16-Lead Plastic MSOP
TEMPERATURE RANGE
–40°C to 175°C
LT8610AXMSE#TRPBF
Consult LTC Marketing for parts specified with wider operating temperature ranges.
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/.
Some packages are available in 500 unit reels through
designated sales channels with #TRMPBF suffix.
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C.
PARAMETER
Minimum Input Voltage
V
IN
Current in Regulation
Feedback Reference Voltage
Oscillator Frequency
PG Upper Threshold Offset from V
FB
PG Lower Threshold Offset from V
FB
V
OUT
= 0.97V, V
IN
= 6V, Output Load = 100μA
V
OUT
= 0.97V, V
IN
= 6V, Output Load = 1mA
V
IN
= 12V
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ELECTRICAL CHARACTERISTICS
CONDITIONS
MIN
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TYP
3.2
26
230
MAX
3.7
100
400
0.978
0.990
735
12
–6
UNITS
V
μA
μA
V
V
kHz
%
%
0.966
0.950
665
6
–12
0.972
0.970
700
9
–9
R
T
= 60.4k
V
FB
Falling
V
FB
Rising
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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:
Devices are 100% tested at 175°C to the limits shown. For normal
operating temperature range specifications, please see the LT8610A/
LT8610AB data sheet. The LT8610AX performance is based on the
LT8610AB.
Note 3.
The LT8610AX is guaranteed over the full –40°C to 175°C
operating junction temperature range. High junction temperatures degrade
operating lifetimes. Operating lifetime is derated at junction temperatures
greater than 125°C. The LT8610AX has no thermal shutdown.
2
8610axf
For more information
www.linear.com/LT8610AX
LT8610AX
TYPICAL PERFORMANCE CHARACTERISTICS
Reference Voltage
Reference Voltage
1000
990
REFERENCE VOLTAGE (mV)
980
NUMBER OF PARTS
970
960
950
940
930
920
25
50
75 100 125 150
TEMPERATURE (°C)
175
200
0
950 955 960 965 970 975 980 985 990
REFERENCE VOLTAGE (mV)
8610AX G02
Reference Voltage at 175°C
Reference Voltage at 175C
45
N = 347
µ = 968.5
σ
= 3.33
EFFICIENCY (%)
100
90
80
70
60
50
40
30
20
10
Efficiency at 175°C, V
OUT
= 3.3V
Efficiency at 175°C, V
= 3.3V
OUT
T
A
= 175°C
f
SW
= 700kHz
12V
IN
24V
IN
36V
IN
LOAD = 0.5A
30
15
0
0.01
0.1
1
10
100
LOAD CURRENT (mA)
1k
10k
8610AX G01
8610AX G03
Efficiency at 175°C, V
OUT
= 3.3V
100
95
90
EFFICIENCY (%)
85
80
75
70
65
60
100 200 300 400 500 600 700 800 900 1000
LOAD CURRENT (mA)
8610AX G04
OUT
Efficiency at 175°C, V
OUT
= 5V
Efficiency at 175°C, V
= 5V
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0.01
0.1
1
10
100
LOAD CURRENT (mA)
1k
10k
OUT
Efficiency at 175°C, V
OUT
= 5V
100
95
90
EFFICIENCY (%)
85
80
75
70
65
60
100 200 300 400 500 600 700 800 900 1000
LOAD CURRENT (mA)
8610AX G06
OUT
T
A
= 175°C
f
SW
= 700kHz
12V
IN
24V
IN
36V
IN
T
A
= 175°C
f
SW
= 700kHz
12V
IN
24V
IN
36V
IN
12V
IN
24V
IN
36V
IN
T
A
= 175°C
f
SW
= 700kHz
8610AX G05
No Load Input Current at 175°C
200
180
160
INPUT CURRENT (uA)
140
120
100
80
60
40
20
0
5
10
15
20
25
30
INPUT VOLTAGE (V)
35
40
T
A
= 175°C
FRONT PAGE APP
3.3V
OUT
IN REGULATION
EN Cycling at 175°C
T
A
= 175°C
EN
5V/DIV
V
OUT
2V/DIV
PG
2V/DIV
SS
2V/DIV
10ms/DIV
8610AX G08
Power Up at 175°C
V
IN
10V/DIV
V
OUT
2V/DIV
PG
2V/DIV
SS
2V/DIV
10ms/DIV
T
A
= 175°C
8610AX G09
8610AX G07
8610axf
For more information
www.linear.com/LT8610AX
3
LT8610AX
PIN FUNCTIONS
SYNC (Pin 1):
External Clock Synchronization Input.
Ground this pin for low ripple Burst Mode operation at low
output loads. Tie to a clock source for synchronization to
an external frequency. Apply a DC voltage of 3V or higher
or tie to INTV
CC
for pulse-skipping mode. When in pulse-
skipping mode, the I
Q
will increase to several hundred µA.
Do not float this pin.
TR/SS (Pin 2):
Output Tracking and Soft-Start Pin. This
pin allows user control of output voltage ramp rate during
start-up. A TR/SS voltage below 0.97V forces the LT8610AX
to regulate the FB pin to equal the TR/SS pin voltage. When
TR/SS is above 0.97V, the tracking function is disabled
and the internal reference resumes control of the error
amplifier. An internal 2.2μA pull-up current from INTV
CC
on
this pin allows a capacitor to program output voltage slew
rate. This pin is pulled to ground with an internal 230Ω
MOSFET during shutdown and fault conditions; use a series
resistor if driving from a low impedance output. This pin
may be left floating if the tracking function is not needed.
RT (Pin 3):
A resistor is tied between RT and ground to
set the switching frequency.
EN/UV (Pin 4):
The LT8610AX is shut down when this
pin is low and active when this pin is high. The hysteretic
threshold voltage is 1.00V going up and 0.96V going
down. Tie to V
IN
if the shutdown feature is not used. An
external resistor divider from V
IN
can be used to program
a V
IN
threshold below which the LT8610AX will shut down.
V
IN
(Pins 5, 6):
The V
IN
pins supply current to the LT8610AX
internal circuitry and to the internal topside power switch.
These pins must be tied together and be locally bypassed.
Be sure to place the positive terminal of the input capaci-
tor as close as possible to the V
IN
pins, and the negative
capacitor terminal as close as possible to the GND pins.
NC (Pin 7):
No Connect. This pin is not connected to
internal circuitry.
SW (Pins 9, 10, 11):
The SW pins are the outputs of the
internal power switches. Tie these pins together and con-
nect them to the inductor and boost capacitor. This node
should be kept small on the PCB for good performance.
BST (Pin 12):
This pin is used to provide a drive voltage,
higher than the input voltage, to the topside power switch.
Place a 0.1µF boost capacitor as close as possible to the IC.
INTV
CC
(Pin 13):
Internal 3.4V Regulator Bypass Pin.
The internal power drivers and control circuits are pow-
ered from this voltage. INTV
CC
maximum output cur-
rent is 20mA. Do not load the INTV
CC
pin with external
circuitry. INTV
CC
current will be supplied from BIAS if
V
BIAS
> 3.1V, otherwise current will be drawn from V
IN
.
Voltage on INTV
CC
will vary between 2.8V and 3.4V when
V
BIAS
is between 3.0V and 3.6V. Decouple this pin to power
ground with at least a 1μF low ESR ceramic capacitor
placed close to the IC.
BIAS (Pin 14):
The internal regulator will draw current from
BIAS instead of V
IN
when BIAS is tied to a voltage higher
than 3.1V. For output voltages of 3.3V and above this pin
should be tied to V
OUT
. If this pin is tied to a supply other
than V
OUT
use a 1µF local bypass capacitor on this pin.
PG (Pin 15):
The PG pin is the open-drain output of an
internal comparator. PG remains low until the FB pin is
within ±9% of the final regulation voltage, and there are
no fault conditions. PG is valid when V
IN
is above 3.4V,
regardless of EN/UV pin state.
FB (Pin 16):
The LT8610AX regulates the FB pin to 0.970V.
Connect the feedback resistor divider tap to this pin. Also,
connect a phase lead capacitor between FB and V
OUT
.
Typically, this capacitor is 4.7pF to 10pF.
GND (Pin 8, Exposed Pad Pin 17):
Ground. These pins
are the return path of the internal bottom-side switch and
must be tied together. Place the negative terminal of the
input capacitor as close to the GND pin and exposed pad
as possible. The exposed pad must be soldered to the PCB
in order to lower the thermal resistance.
4
8610axf
For more information
www.linear.com/LT8610AX
LT8610AX
APPLICATIONS INFORMATION
For Application Information, Block Diagram, and Typical Performance Curves from –40°C to 150°C range, please see
the
LT8610A/LT8610AB
Series data sheet. The LT8610AX will perform similarly to the LT8610AB. The LT8610AX
has no thermal shutdown.
PACKAGE DESCRIPTION
Please refer to
http://www.linear.com/product/LT8610AX#packaging
for the most recent package drawings.
MSE Package
16-Lead Plastic MSOP, Exposed Die Pad
(Reference LTC DWG # 05-08-1667 Rev F)
BOTTOM VIEW OF
EXPOSED PAD OPTION
2.845
±0.102
(.112
±.004)
0.889
±0.127
(.035
±.005)
2.845
±0.102
(.112
±.004)
1
8
0.35
REF
5.10
(.201)
MIN
1.651
±0.102
3.20 – 3.45
(.065
±.004)
(.126 – .136)
0.305
±0.038
(.0120
±.0015)
TYP
0.50
(.0197)
BSC
16
4.039
±0.102
(.159
±.004)
(NOTE 3)
DETAIL “B”
CORNER TAIL IS PART OF
DETAIL “B” THE LEADFRAME FEATURE.
FOR REFERENCE ONLY
9
NO MEASUREMENT PURPOSE
0.280
±0.076
(.011
±.003)
REF
1.651
±0.102
(.065
±.004)
0.12 REF
RECOMMENDED SOLDER PAD LAYOUT
DETAIL “A”
0° – 6° TYP
16151413121110 9
0.254
(.010)
GAUGE PLANE
4.90
±0.152
(.193
±.006)
3.00
±0.102
(.118
±.004)
(NOTE 4)
0.53
±0.152
(.021
±.006)
DETAIL “A”
0.18
(.007)
1.10
(.043)
MAX
1234567 8
0.86
(.034)
REF
SEATING
PLANE
0.50
NOTE:
(.0197)
1. DIMENSIONS IN MILLIMETER/(INCH)
BSC
2. DRAWING NOT TO SCALE
3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.
MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
6. EXPOSED PAD DIMENSION DOES INCLUDE MOLD FLASH. MOLD FLASH ON E-PAD SHALL
NOT EXCEED 0.254mm (.010") PER SIDE.
0.17 – 0.27
(.007 – .011)
TYP
0.1016
±0.0508
(.004
±.002)
MSOP (MSE16) 0213 REV F
8610axf
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 representa-
tion that the interconnection of its
information
www.linear.com/LT8610AX
existing patent rights.
For more
circuits as described herein will not infringe on
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