LINER LT3690 42v, 2.5a synchronous step-down regulator Datasheet

Electrical Specifications Subject to Change
LT8610
42V, 2.5A Synchronous
Step-Down Regulator
with 2.5µA Quiescent
Current
DESCRIPTION
FEATURES
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Wide Input Voltage Range: 3.4V to 42V
Ultralow Quiescent Current Burst Mode® Operation:
2.5μA IQ Regulating 12VIN to 3.3VOUT
Output Ripple < 10mVP-P
High Efficiency Synchronous Operation:
96% Efficiency at 1A, 5VOUT from 12VIN
94% Efficiency at 1A, 3.3VOUT from 12VIN
Fast Minimum Switch-On Time: 50ns
Low Dropout Under All Conditions: 200mV at 1A
Allows Use Of Small Inductors
Low EMI
Adjustable and Synchronizable: 200kHz to 2.2MHz
Current Mode Operation
Accurate 1V Enable Pin Threshold
Internal Compensation
Output Soft-Start and Tracking
Small Thermally Enhanced 16-Lead MSOP Package
APPLICATIONS
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Automotive and Industrial Supplies
General Purpose Step-Down
GSM Power Supplies
The LT®8610 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.
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 LT8610 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 LT8610 is available in a small
16-lead MSOP 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 2.5A Step-Down Converter
100
VIN
4.7μF
BST
0.1μF
4.7μH
EN/UV
SW
PG
SYNC
10nF
LT8610
BIAS
1M
TR/SS
1μF
FB
10pF
INTVCC
RT PGND GND
60.4k
95
VOUT
5V
47μF 2.5A
90
EFFICIENCY (%)
VIN
5.5V TO 42V
12VIN to 5VOUT Efficiency
85
80
75
70
65
55
50
fSW = 700kHz
fSW = 700kHz
VIN = 12V
VIN = 24V
60
243k
8610 TA01a
0
0.5
1.5
1
LOAD CURRENT (A)
2
2.5
8610 G01
8610p
1
LT8610
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1)
VIN, EN/UV, PG..........................................................42V
BIAS ..........................................................................30V
BST Pin Above SW Pin................................................4V
FB, TR/SS, RT, INTVCC ...............................................4V
SYNC Voltage .............................................................6V
Operating Junction Temperature Range (Note 2)
LT8610E ................................................. –40 to 125°C
LT8610I.................................................. –40 to 125°C
Storage Temperature Range ......................–65 to 150°C
TOP VIEW
SYNC
TR/SS
RT
EN/UV
VIN
VIN
PGND
PGND
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
17
GND
FB
PG
BIAS
INTVCC
BST
SW
SW
SW
MSE PACKAGE
16-LEAD PLASTIC MSOP
θJA = 40°C/W, θJC(PAD) = 10°C/W
EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT8610EMSE#PBF
LT8610EMSE#TRPBF
8610
16-Lead Plastic MSOP
–40°C to 125°C
LT8610IMSE#PBF
LT8610IMSE#TRPBF
8610
16-Lead Plastic MSOP
–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
Minimum Input Voltage
VIN Quiescent Current
VEN/UV = 0V, VSYNC = 0V
VEN/UV = 2V, Not Switching, VSYNC = 0V
TYP
MAX
l
MIN
2.9
3.4
V
l
1.0
1.0
3
8
μA
μA
l
1.7
1.7
4
10
μA
μA
0.24
0.5
mA
24
210
50
350
μA
μA
0.970
0.970
0.973
0.982
V
V
0.004
0.02
%/V
VEN/UV = 2V, Not Switching, VSYNC = 2V
VIN Current in Regulation
VOUT = 0.97V, VIN = 6V, Output Load = 100μA
VOUT = 0.97V, VIN = 6V, Output Load = 1mA
l
l
Feedback Reference Voltage
VIN = 6V, ILOAD = 0.5A
VIN = 6V, ILOAD = 0.5A
l
VIN = 4.0V to 42V, ILOAD = 0.5A
l
Feedback Voltage Line Regulation
0.967
0.958
UNITS
Feedback Pin Input Current
VFB = 1V
–20
20
nA
INTVCC Voltage
ILOAD = 0mA, VBIAS = 0V
ILOAD = 0mA, VBIAS = 3.3V
3.23
3.25
3.4
3.29
3.57
3.35
V
V
2.5
2.6
2.7
V
INTVCC Undervoltage Lockout
BIAS Pin Current Consumption
VBIAS = 3.3V, ILOAD = 1A, 2MHz
Minimum On-Time
ILOAD = 1A, SYNC = 0V
ILOAD = 1A, SYNC = 3.3V
Minimum Off-Time
8.5
l
l
mA
30
30
50
45
70
65
ns
ns
50
80
110
ns
8610p
2
LT8610
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C.
PARAMETER
CONDITIONS
Oscillator Frequency
RT = 221k, ILOAD = 1A
RT = 60.4k, ILOAD = 1A
RT = 18.2k, ILOAD = 1A
Top Power NMOS On-Resistance
ISW = 1A
Top Power NMOS Current Limit
Bottom Power NMOS On-Resistance
VINTVCC = 3.4V, ISW = 1A
Bottom Power NMOS Current Limit
VINTVCC = 3.4V
SW Leakage Current
VIN = 42V, VSW = 0V, 42V
EN/UV Pin Threshold
EN/UV Rising
MIN
TYP
MAX
UNITS
l
l
l
180
665
1.85
210
700
2.00
240
735
2.15
kHz
kHz
MHz
l
3.5
4.8
2.5
3.3
120
mΩ
5.8
65
–1.5
l
0.94
EN/UV Pin Hysteresis
1.0
mΩ
4.8
A
1.5
μA
1.06
40
–20
A
V
mV
EN/UV Pin Current
VEN/UV = 2V
20
nA
PG Upper Threshold Offset from VFB
VFB Falling
l
6
9.0
12
%
PG Lower Threshold Offset from VFB
VFB Rising
l
–6
–9.0
–12
%
40
nA
680
2000
Ω
1.1
2.0
1.4
2.4
V
V
40
nA
2.2
3.2
μA
PG Hysteresis
1.3
PG Leakage
VPG = 3.3V
PG Pull-Down Resistance
VPG = 0.1V
SYNC Threshold
SYNC Falling
SYNC Rising
SYNC Pin Current
VSYNC = 2V
l
0.8
1.6
–40
l
TR/SS Source Current
TR/SS Pull-Down Resistance
–40
Fault Condition, TR/SS = 0.1V
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 LT8610E 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
LT8610I 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.
1.2
%
230
Ω
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.
8610p
3
LT8610
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency at 5VOUT
Efficiency at 3.3VOUT
Efficiency at 5VOUT
95
95
90
90
90
80
85
85
70
80
75
70
65
80
75
70
fSW = 700kHz
VIN = 12V
VIN = 24V
55
0
0.5
1.5
1
LOAD CURRENT (A)
2
55
50
0.5
0
1.5
1
LOAD CURRENT (A)
2
8610 G01
Efficiency at 3.3VOUT
90
8610 G03
VOUT = 3.3V
0.982
REFERENCE VOLTAGE (V)
EFFICIENCY (%)
EFFICIENCY (%)
40
30
90
88
86
0.1
10
LOAD CURRENT (mA)
84
VIN = 12V
VIN = 24V
82
0.25
0.976
0.973
0.970
0.967
0.964
1000
0.75
0.958
1.25
1.75
SWITCHING FREQUENCY (MHz)
8610 G04
2.25
0.955
–55
Load Regulation
1.03
0.20
1.02
0.15
CHANGE IN VOUT (%)
0.25
EN RISING
1.00
0.99
Line Regulation
VOUT = 3.3V
VIN = 12V
0.06
0.10
0.05
0
0.04
0.02
0
–0.02
–0.04
–0.15
–0.06
0.96
–0.20
–0.08
0.95
–55
–0.25
–25
5
35
65
95
TEMPERATURE (°C)
125
155
8610 G07
VOUT = 3.3V
ILOAD = 0.5A
0.08
–0.10
EN FALLING
155
0.10
–0.05
0.98
125
8610 G06
CHANGE IN VOUT (%)
EN Pin Thresholds
1.01
65
35
5
95
TEMPERATURE (°C)
–25
8610 G05
1.04
0.97
0.979
0.961
fSW = 700kHz
VIN = 12V
VIN = 24V
0
0.001
1000
Reference Voltage
92
70
50
0.1
10
LOAD CURRENT (mA)
0.985
80
EN THRESHOLD (V)
0
0.001
2.5
94
60
fSW = 700kHz
VIN = 12V
VIN = 24V
10
Efficiency vs Frequency
96
10
40
8610 G02
100
20
50
20
fSW = 700kHz
VIN = 12V
VIN = 24V
60
2.5
60
30
65
60
50
EFFICIENCY (%)
100
EFFICIENCY (%)
100
EFFICIENCY (%)
100
–0.10
0
0.5
1.5
2
1
LOAD CURRENT (A)
2.5
3
8610 G08
0
5
10
15 20 25 30 35
INPUT VOLTAGE (V)
40
45
8610 G09
8610p
4
LT8610
TYPICAL PERFORMANCE CHARACTERISTICS
No Load Supply Current
No Load Supply Current
VOUT = 3.3V
IN REGULATION
4.5
4.0
20
INPUT CURRENT (μA)
INPUT CURRENT (μA)
Top FET Current Limit vs Duty Cycle
25
3.5
3.0
2.5
2.0
1.5
1.0
6.0
VOUT = 3.3V
VIN = 12V
IN REGULATION
5.5
5.0
CURRENT LIMIT (A)
5.0
15
10
3.5
2.5
0
0
5
10
15 20 25 30 35
INPUT VOLTAGE (V)
40
0
–55
45
65
5
95
35
TEMPERATURE (°C)
–25
125
8610 G10
2.0
155
Top FET Current Limit
250
3.4
70% DC
3.5
3.0
3.2
3.0
2.8
5
35
65
TEMPERATURE (°C)
95
2.4
–55
125
–25
5
35
65
TEMPERATURE (°C)
Switch Drop
80
400
75
100
BOT SW
0
–55
125
MINIMUM ON-TIME (ns)
300
250
TOP SW
200
BOT SW
100
1
1.5
2
SWITCH CURRENT (A)
2.5
3
65
60
55
50
45
8610 G41
30
–55
125
155
8610 G40
95
VIN = 3.3V
ILOAD = 0.5A
90
85
80
75
70
65
35
0
65
5
95
35
TEMPERATURE (°C)
Minimum Off-Time
40
50
–25
100
ILOAD = 1A, VSYNC = 0V
ILOAD = 1A, VSYNC = 3V
ILOAD = 2.5A, VSYNC = 0V
ILOAD = 2.5A, VSYNC = 3V
70
350
0.5
TOP SW
Minimum On-Time
450
0
150
8610 G15
8610 G14
150
95
MINIMUM OFF-TIME (ns)
–25
SWITCH CURRENT = 1A
50
2.6
2.5
–55
1.0
200
SWITCH DROP (mV)
CURRENT LIMIT (A)
30% DC
0.8
Switch Drop
Bottom FET Current Limit
4.0
0.4
0.6
DUTY CYCLE
8610 G13
3.6
4.5
0.2
0
8610 G11
5.0
CURRENT LIMIT (A)
4.0
3.0
5
0.5
SWITCH DROP (mV)
4.5
–25
65
35
5
95
TEMPERATURE (°C)
125
155
8610 G17
60
–50 –25
95
65
35
TEMPERATURE (°C)
5
125
155
8610 G18
8610p
5
LT8610
TYPICAL PERFORMANCE CHARACTERISTICS
Switching Frequency
700
730
600
500
400
300
200
RT = 60.4k
710
700
690
680
670
0
1
0.5
1.5
2
2.5
LOAD CURRENT (A)
95
65
35
TEMPERATURE (°C)
5
125
8610 G19
800
VOUT = 5V
fSW = 700kHz
SWITCHING FREQUENCY (kHz)
40
20
600
1.0
400
300
0
45
0
0
0.2
0.4
0.6
FB VOLTAGE (V)
0
1
10.5
FB RISING
10.0
2.0
1.9
1.8
1.7
125
155
8610 G24
FB FALLING
9.5
9.0
1.4
–7.5
–8.0
–8.5
–9.0
FB RISING
–9.5
FB FALLING
–10.0
8.5
–10.5
8.0
–11.0
7.5
7.0
–55
1.2
PG Low Thresholds
11.0
2.1
1.0
0.4 0.6 0.8
TR/SS VOLTAGE (V)
–7.0
11.5
2.2
0.2
8610 G23
PG THRESHOLD OFFSET FROM VREF (%)
VSS = 0.5V
PG THRESHOLD OFFSET FROM VREF (%)
SS PIN CURRENT (μA)
0.8
PG High Thresholds
2.3
95
65
35
TEMPERATURE (°C)
0.4
0.2
12.0
5
0.6
8610 G22
Soft-Start Current
1.6
–50 –25
0.8
200
8610 G39
2.4
200
Soft-Start Tracking
500
0
40
100
50
150
LOAD CURRENT (mA)
0
1.2
100
25 30 35
INPUT VOLTAGE (V)
200
8610 G21
FB VOLTAGE (V)
LOAD CURRENT (mA)
60
20
300
0
155
VOUT = 3.3V
VIN = 12V
VSYNC = 0V
RT = 60.4k
700
80
15
400
Frequency Foldback
100
10
500
8610 G20
Minimum Load to Full Frequency
(SYNC DC High)
5
600
100
660
–55 –25
3
VIN = 12V
VOUT = 3.3V
700
720
100
0
Burst Frequency
800
SWITCHING FREQUENCY (kHz)
740
SWITCHING FREQUENCY (kHz)
DROPOUT VOLTAGE (mV)
Dropout Voltage
800
–11.5
–25
65
35
5
95
TEMPERATURE (°C)
125
155
8610 G25
–12.0
–55
–25
65
35
5
95
TEMPERATURE (°C)
125
155
8610 G26
8610p
6
LT8610
TYPICAL PERFORMANCE CHARACTERISTICS
RT Programmed Switching
Frequency
VIN UVLO
5.00
225
3.4
4.75
BIAS PIN CURRENT (mA)
3.6
200
3.2
INPUT VOLTAGE (V)
RT PIN RESISTOR (kΩ)
Bias Pin Current
250
175
150
125
100
75
3.0
2.8
2.6
2.4
VBIAS = 5V
VOUT = 5V
ILOAD = 1A
fSW = 700kHz
4.50
4.25
4.00
3.75
3.50
50
2.2
25
0
0.2
0.6
1.4
1.8
1
SWITCHING FREQUENCY (kHz)
2.2
3.25
2.0
–55 –25
3.00
95
65
35
TEMPERATURE (°C)
5
125
155
5
10
15
20 25 30 35
INPUT VOLTAGE (V)
Switching Waveforms
Bias Pin Current
45
8610 G29
8610 G28
8610 G27
40
Switching Waveforms
12
VBIAS = 5V
VOUT = 5V
VIN = 12V
ILOAD = 1A
BIAS PIN CURRENT (mA)
10
IL
200mA/DIV
IL
1A/DIV
8
VSW
5V/DIV
6
4
VSW
5V/DIV
500ns/DIV
12VIN TO 5VOUT AT 1A
8610 G31
500μs/DIV
12VIN TO 5VOUT AT 10mA
VSYNC = 0V
2
8610 G32
0
0
0.5
1
1.5
2
SWITCHING FREQUENCY (MHz)
2.5
8610 G30
Transient Response
Switching Waveforms
IL
1A/DIV
Transient Response
ILOAD
1A/DIV
ILOAD
1A/DIV
VOUT
100mV/DIV
VSW
10V/DIV
500ns/DIV
36VIN TO 5VOUT AT 1A
8610 G33
VOUT
200mV/DIV
50μs/DIV
0.5A TO 1.5A TRANSIENT
12VIN, 5VOUT
COUT = 47μF
8610 G34
50μs/DIV
0.5A TO 2.5A TRANSIENT
12VIN, 5VOUT
COUT = 47μF
8610 G35
8610p
7
LT8610
TYPICAL PERFORMANCE CHARACTERISTICS
Transient Response
Start-Up Dropout Performance
ILOAD
1A/DIV
Start-Up Dropout Performance
VIN
VIN
VIN
2V/DIV
VOUT
200mV/DIV
VIN
2V/DIV
VOUT
VOUT
2V/DIV
50μs/DIV
50mA TO 1A TRANSIENT
12VIN, 5VOUT
COUT = 47μF
8610 G36
100ms/DIV
2.5Ω LOAD
(2A IN REGULATION)
VOUT
2V/DIV
8610 G37
VOUT
100ms/DIV
20Ω LOAD
(250mA IN REGULATION)
8610 G38
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 INTVCC for pulse-skipping mode. When in pulseskipping mode, the IQ 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 LT8610
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 INTVCC
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 LT8610 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 VIN if the shutdown feature is not used. An
external resistor divider from VIN can be used to program
a VIN threshold below which the LT8610 will shut down.
VIN (Pins 5, 6): The VIN pins supply current to the LT8610
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 capacitor as close as possible to the VIN pins, and the negative
capacitor terminal as close as possible to the PGND pins.
PGND (Pins 7, 8): Power Switch Ground. These pins are
the return path of the internal bottom-side power switch
and must be tied together. Place the negative terminal of
the input capacitor as close to the PGND pins as possible.
SW (Pins 9, 10, 11): The SW pins are the outputs of the
internal power switches. Tie these pins together and connect 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.
INTVCC (Pin 13): Internal 3.4V Regulator Bypass Pin.
The internal power drivers and control circuits are powered from this voltage. INTVCC maximum output current is 20mA. Do not load the INTVCC pin with external
circuitry. INTVCC current will be supplied from BIAS if
VBIAS > 3.1V, otherwise current will be drawn from VIN.
Voltage on INTVCC will vary between 2.8V and 3.4V when
VBIAS 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.
8610p
8
LT8610
PIN FUNCTIONS
BIAS (Pin 14): The internal regulator will draw current from
BIAS instead of VIN 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 VOUT. If this pin is tied to a supply other
than VOUT 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 VIN is above 3.4V,
regardless of EN/UV pin state.
FB (Pin 16): The LT8610 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 VOUT.
Typically, this capacitor is 4.7pF to 10pF.
GND (Exposed Pad Pin 17): Ground. The exposed pad
must be connected to the negative terminal of the input
capacitor and soldered to the PCB in order to lower the
thermal resistance.
BLOCK DIAGRAM
VIN
VIN
5, 6
CIN
–
+
INTERNAL 0.97V REF
R3
OPT
1V
4
EN/UV
+
–
SHDN
SLOPE COMP
R4
OPT
15
PG
±9%
C1
R1
R2
16
FB
CSS
OPT
3
1
TR/SS
INTVCC
VC
14
13
CVCC
OSCILLATOR
200kHz TO 2.2MHz
BST
BURST
DETECT
SHDN
TSD
INTVCC UVLO
VIN UVLO
2.2μA
2
RT
ERROR
AMP
+
+
–
VOUT
BIAS
3.4V
REG
SWITCH
LOGIC
AND
ANTISHOOT
THROUGH
12
CBST
M1
L
SW
VOUT
9-11
COUT
M2
PGND
SHDN
TSD
VIN UVLO
7, 8
RT
SYNC
GND
17
8610 BD
8610p
9
LT8610
OPERATION
The LT8610 is a monolithic, constant frequency, current
mode step-down DC/DC converter. An oscillator, with
frequency set using a resistor on the RT pin, turns on
the internal top power switch at the beginning of each
clock cycle. Current in the inductor then increases until
the top switch current comparator trips and turns off the
top power switch. The peak inductor current at which
the top switch turns off is controlled by the voltage on
the internal VC node. The error amplifier servos the VC
node by comparing the voltage on the VFB pin with an
internal 0.97V reference. When the load current increases
it causes a reduction in the feedback voltage relative to
the reference leading the error amplifier to raise the VC
voltage until the average inductor current matches the new
load current. When the top power switch turns off, the
synchronous power switch turns on until the next clock
cycle begins or inductor current falls to zero. If overload
conditions result in more than 3.3A flowing through the
bottom switch, the next clock cycle will be delayed until
switch current returns to a safe level.
If the EN/UV pin is low, the LT8610 is shut down and
draws 1μA from the input. When the EN/UV pin is above
1V, the switching regulator will become active.
To optimize efficiency at light loads, the LT8610 operates
in Burst Mode operation in light load situations. Between
bursts, all circuitry associated with controlling the output
switch is shut down, reducing the input supply current to
1.7μA. In a typical application, 2.5μA will be consumed
from the input supply when regulating with no load. The
SYNC pin is tied low to use Burst Mode operation and can
be tied to a logic high to use pulse-skipping mode. If a
clock is applied to the SYNC pin the part will synchronize to
an external clock frequency and operate in pulse-skipping
mode. While in pulse-skipping mode the oscillator operates
continuously and positive SW transitions are aligned to
the clock. During light loads, switch pulses are skipped
to regulate the output and the quiescent current will be
several hundred μA.
To improve efficiency across all loads, supply current to
internal circuitry can be sourced from the BIAS pin when
biased at 3.3V or above. Else, the internal circuitry will draw
current from VIN. The BIAS pin should be connected to
VOUT if the LT8610 output is programmed at 3.3V or above.
Comparators monitoring the FB pin voltage will pull the
PG pin low if the output voltage varies more than ±9%
(typical) from the set point, or if a fault condition is present.
The oscillator reduces the LT8610’s operating frequency
when the voltage at the FB pin is low. This frequency
foldback helps to control the inductor current when the
output voltage is lower than the programmed value which
occurs during start-up or overcurrent conditions. When
a clock is applied to the SYNC pin or the SYNC pin is
held DC high, the frequency foldback is disabled and the
switching frequency will slow down only during overcurrent conditions.
8610p
10
LT8610
APPLICATIONS INFORMATION
Achieving Ultralow Quiescent Current
To enhance efficiency at light loads, the LT8610 operates
in low ripple Burst Mode operation, which keeps the output capacitor charged to the desired output voltage while
minimizing the input quiescent current and minimizing
output voltage ripple. In Burst Mode operation the LT8610
delivers single small pulses of current to the output capacitor followed by sleep periods where the output power is
supplied by the output capacitor. While in sleep mode the
LT8610 consumes 1.7μA.
As the output load decreases, the frequency of single current pulses decreases (see Figure 1a) and the percentage
of time the LT8610 is in sleep mode increases, resulting in
Burst Frequency
800
VIN = 12V
VOUT = 3.3V
SWITCHING FREQUENCY (kHz)
700
600
500
400
300
200
100
0
100
50
150
LOAD CURRENT (mA)
0
(1a)
200
8610 F01a
Minimum Load to Full Frequency (SYNC DC High)
100
much higher light load efficiency than for typical converters. By maximizing the time between pulses, the converter
quiescent current approaches 2.5μA for a typical application
when there is no output load. Therefore, to optimize the
quiescent current performance at light loads, the current
in the feedback resistor divider must be minimized as it
appears to the output as load current.
While in Burst Mode operation the current limit of the top
switch is approximately 400mA resulting in output voltage
ripple shown in Figure 2. Increasing the output capacitance
will decrease the output ripple proportionally. As load ramps
upward from zero the switching frequency will increase
but only up to the switching frequency programmed by
the resistor at the RT pin as shown in Figure 1a. The output load at which the LT8610 reaches the programmed
frequency varies based on input voltage, output voltage,
and inductor choice.
For some applications it is desirable for the LT8610 to
operate in pulse-skipping mode, offering two major differences from Burst Mode operation. First is the clock stays
awake at all times and all switching cycles are aligned to
the clock. In this mode much of the internal circuitry is
awake at all times, increasing quiescent current to several
hundred μA. Second is that full switching frequency is
reached at lower output load than in Burst Mode operation
(see Figure 1b). To enable pulse-skipping mode, the SYNC
pin is tied high either to a logic output or to the INTVCC
pin. When a clock is applied to the SYNC pin the LT8610
will also operate in pulse-skipping mode.
5VOUT
700kHz
LOAD CURRENT (mA)
80
IL
200mA/DIV
60
40
VOUT
10mV/DIV
20
VSYNC = 0V
0
5
10
15
20
25 30 35
INPUT VOLTAGE (V)
(1b)
40
45
5μs/DIV
8610 F02
Figure 2. Burst Mode Operation
8610 F01b
Figure 1. SW Frequency vs Load Information in
Burst Mode Operation (1a) and Pulse-Skipping Mode (1b)
8610p
11
LT8610
APPLICATIONS INFORMATION
FB Resistor Network
The output voltage is programmed with a resistor divider
between the output and the FB pin. Choose the resistor
values according to:
⎛ V
⎞
R1= R2 ⎜ OUT – 1⎟
⎝ 0.970V ⎠
(1)
where RT is in kΩ and fSW is the desired switching frequency in MHz.
Table 1. SW Frequency vs RT Value
fSW (MHz)
RT (kΩ)
0.2
232
0.3
150
0.4
110
Reference designators refer to the Block Diagram. 1%
resistors are recommended to maintain output voltage
accuracy.
0.5
88.7
0.6
71.5
0.7
60.4
If low input quiescent current and good light-load efficiency
are desired, use large resistor values for the FB resistor
divider. The current flowing in the divider acts as a load
current, and will increase the no-load input current to the
converter, which is approximately:
0.8
52.3
1.0
41.2
1.2
33.2
14
28.0
1.6
23.7
1.8
20.5
2.0
18.2
2.2
15.8
⎛ V
⎞ ⎛ V ⎞ ⎛ 1⎞
IQ = 1.7µA + ⎜ OUT ⎟ ⎜ OUT ⎟ ⎜ ⎟
⎝ R1+R2 ⎠ ⎝ VIN ⎠ ⎝ n ⎠
(2)
where 1.7μA is the quiescent current of the LT8610 and
the second term is the current in the feedback divider
reflected to the input of the buck operating at its light
load efficiency n. For a 3.3V application with R1 = 1M and
R2 = 412k, the feedback divider draws 2.3μA. With VIN =
12V and n = 80%, this adds 0.8μA to the 1.7μA quiescent
current resulting in 2.5μA no-load current from the 12V
supply. Note that this equation implies that the no-load
current is a function of VIN; this is plotted in the Typical
Performance Characteristics section.
When using large FB resistors, a 4.7pF to 10pF phase-lead
capacitor should be connected from VOUT to FB.
Setting the Switching Frequency
The LT8610 uses a constant frequency PWM architecture
that can be programmed to switch from 200kHz to 2.2MHz
by using a resistor tied from the RT pin to ground. A table
showing the necessary RT value for a desired switching
frequency is in Table 1.
The RT resistor required for a desired switching frequency
can be calculated using:
RT =
46.5
– 5.2
fSW
(3)
Operating Frequency Selection and Trade-Offs
Selection of the operating frequency is a trade-off between
efficiency, component size, and input voltage range. The
advantage of high frequency operation is that smaller inductor and capacitor values may be used. The disadvantages
are lower efficiency and a smaller input voltage range.
The highest switching frequency (fSW(MAX)) for a given
application can be calculated as follows:
fSW(MAX) =
(
VOUT + VSW(BOT)
tON(MIN) VIN – VSW(TOP) + VSW(BOT)
)
(4)
where VIN is the typical input voltage, VOUT is the output
voltage, VSW(TOP) and VSW(BOT) are the internal switch
drops (~0.3V, ~0.15V, respectively at maximum load)
and tON(MIN) is the minimum top switch on-time (see the
Electrical Characteristics). This equation shows that a
slower switching frequency is necessary to accommodate
a high VIN/VOUT ratio.
For transient operation, VIN may go as high as the absolute maximum rating of 42V regardless of the RT value,
however the LT8610 will reduce switching frequency as
necessary to maintain control of inductor current to assure safe operation.
8610p
12
LT8610
APPLICATIONS INFORMATION
The LT8610 is capable of a maximum duty cycle of greater
than 99%, and the VIN-to-VOUT dropout is limited by the
RDS(ON) of the top switch. In this mode the LT8610 skips
switch cycles, resulting in a lower switching frequency
than programmed by RT.
For applications that cannot allow deviation from the programmed switching frequency at low VIN/VOUT ratios use
the following formula to set switching frequency:
VIN(MIN) =
VOUT + VSW(BOT)
1– fSW • tOFF(MIN)
– VSW(BOT) + VSW(TOP) (5)
where VIN(MIN) is the minimum input voltage without
skipped cycles, VOUT is the output voltage, VSW(TOP) and
VSW(BOT) are the internal switch drops (~0.3V, ~0.15V,
respectively at maximum load), fSW is the switching frequency (set by RT), and tOFF(MIN) is the minimum switch
off-time. Note that higher switching frequency will increase
the minimum input voltage below which cycles will be
dropped to achieve higher duty cycle.
Inductor Selection and Maximum Output Current
The LT8610 is designed to minimize solution size by
allowing the inductor to be chosen based on the output
load requirements of the application. During overload or
short-circuit conditions the LT8610 safely tolerates operation with a saturated inductor through the use of a high
speed peak-current mode architecture.
A good first choice for the inductor value is:
L=
VOUT + VSW(BOT)
fSW
(6)
where fSW is the switching frequency in MHz, VOUT is
the output voltage, VSW(BOT) is the bottom switch drop
(~0.15V) and L is the inductor value in μH.
To avoid overheating and poor efficiency, an inductor must
be chosen with an RMS current rating that is greater than
the maximum expected output load of the application. In
addition, the saturation current (typically labeled ISAT)
rating of the inductor must be higher than the load current
plus 1/2 of in inductor ripple current:
1
IL(PEAK) =ILOAD(MAX) + ∆IL
2
where ∆IL is the inductor ripple current as calculated in
Equation 9 and ILOAD(MAX) is the maximum output load
for a given application.
As a quick example, an application requiring 1A output
should use an inductor with an RMS rating of greater than
1A and an ISAT of greater than 1.3A. During long duration
overload or short-circuit conditons, the inductor RMS
routing requirement is greater to avoid overheating of the
inductor. To keep the efficiency high, the series resistance
(DCR) should be less than 0.04Ω, and the core material
should be intended for high frequency applications.
The LT8610 limits the peak switch current in order to
protect the switches and the system from overload faults.
The top switch current limit (ILIM) is at least 3.5A at low
duty cycles and decreases linearly to 2.8A at DC = 0.8. The
inductor value must then be sufficient to supply the desired
maximum output current (IOUT(MAX)), which is a function
of the switch current limit (ILIM) and the ripple current.
IOUT(MAX) =ILIM –
∆IL
2
(8)
The peak-to-peak ripple current in the inductor can be
calculated as follows:
∆IL =
⎛
VOUT ⎞
• ⎜ 1–
⎟
L • fSW ⎝
VIN(MAX) ⎠
VOUT
(9)
where fSW is the switching frequency of the LT8610, and
L is the value of the inductor. Therefore, the maximum
output current that the LT8610 will deliver depends on
the switch current limit, the inductor value, and the input
and output voltages. The inductor value may have to be
increased if the inductor ripple current does not allow
sufficient maximum output current (IOUT(MAX)) given the
switching frequency, and maximum input voltage used in
the desired application.
The optimum inductor for a given application may differ
from the one indicated by this design guide. A larger value
inductor provides a higher maximum load current and
reduces the output voltage ripple. For applications requiring smaller load currents, the value of the inductor may
be lower and the LT8610 may operate with higher ripple
(7)
8610p
13
LT8610
APPLICATIONS INFORMATION
current. This allows use of a physically smaller inductor,
or one with a lower DCR resulting in higher efficiency. Be
aware that low inductance may result in discontinuous
mode operation, which further reduces maximum load
current.
For more information about maximum output current
and discontinuous operation, see Linear Technology’s
Application Note 44.
Finally, for duty cycles greater than 50% (VOUT/VIN > 0.5),
a minimum inductance is required to avoid sub-harmonic
oscillation. See Application Note 19.
Input Capacitor
Bypass the input of the LT8610 circuit with a ceramic capacitor of X7R or X5R type placed as close as possible to
the VIN and PGND pins. Y5V types have poor performance
over temperature and applied voltage, and should not be
used. A 4.7μF to 10μF ceramic capacitor is adequate to
bypass the LT8610 and will easily handle the ripple current.
Note that larger input capacitance is required when a lower
switching frequency is used. If the input power source has
high impedance, or there is significant inductance due to
long wires or cables, additional bulk capacitance may be
necessary. This can be provided with a low performance
electrolytic capacitor.
Step-down regulators draw current from the input supply in pulses with very fast rise and fall times. The input
capacitor is required to reduce the resulting voltage
ripple at the LT8610 and to force this very high frequency
switching current into a tight local loop, minimizing EMI.
A 4.7μF capacitor is capable of this task, but only if it is
placed close to the LT8610 (see the PCB Layout section).
A second precaution regarding the ceramic input capacitor
concerns the maximum input voltage rating of the LT8610.
A ceramic input capacitor combined with trace or cable
inductance forms a high quality (under damped) tank circuit. If the LT8610 circuit is plugged into a live supply, the
input voltage can ring to twice its nominal value, possibly
exceeding the LT8610’s voltage rating. This situation is
easily avoided (see Linear Technology Application Note 88).
Output Capacitor and Output Ripple
The output capacitor has two essential functions. Along
with the inductor, it filters the square wave generated
by the LT8610 to produce the DC output. In this role it
determines the output ripple, thus low impedance at the
switching frequency is important. The second function
is to store energy in order to satisfy transient loads and
stabilize the LT8610’s control loop. Ceramic capacitors
have very low equivalent series resistance (ESR) and
provide the best ripple performance. For good starting
values, see the Typical Applications section.
Use X5R or X7R types. This choice will provide low output
ripple and good transient response. Transient performance
can be improved with a higher value output capacitor and
the addition of a feedforward capacitor placed between
VOUT and FB. Increasing the output capacitance will also
decrease the output voltage ripple. A lower value of output
capacitor can be used to save space and cost but transient
performance will suffer and may cause loop instability. See
the Typical Applications in this data sheet for suggested
capacitor values.
When choosing a capacitor, special attention should be
given to the data sheet to calculate the effective capacitance
under the relevant operating conditions of voltage bias and
temperature. A physically larger capacitor or one with a
higher voltage rating may be required.
Ceramic Capacitors
Ceramic capacitors are small, robust and have very low
ESR. However, ceramic capacitors can cause problems
when used with the LT8610 due to their piezoelectric nature.
When in Burst Mode operation, the LT8610’s switching
frequency depends on the load current, and at very light
loads the LT8610 can excite the ceramic capacitor at audio
frequencies, generating audible noise. Since the LT8610
operates at a lower current limit during Burst Mode operation, the noise is typically very quiet to a casual ear. If
this is unacceptable, use a high performance tantalum or
electrolytic capacitor at the output. Low noise ceramic
capacitors are also available.
8610p
14
LT8610
APPLICATIONS INFORMATION
A final precaution regarding ceramic capacitors concerns
the maximum input voltage rating of the LT8610. As
previously mentioned, a ceramic input capacitor combined
with trace or cable inductance forms a high quality (underdamped) tank circuit. If the LT8610 circuit is plugged
into a live supply, the input voltage can ring to twice its
nominal value, possibly exceeding the LT8610’s rating.
This situation is easily avoided (see Linear Technology
Application Note 88).
Enable Pin
The LT8610 is in shutdown when the EN pin is low and
active when the pin is high. The rising threshold of the EN
comparator is 1.0V, with 40mV of hysteresis. The EN pin
can be tied to VIN if the shutdown feature is not used, or
tied to a logic level if shutdown control is required.
Adding a resistor divider from VIN to EN programs the
LT8610 to regulate the output only when VIN is above a
desired voltage (see the Block Diagram). Typically, this
threshold, VIN(EN), is used in situations where the input
supply is current limited, or has a relatively high source
resistance. A switching regulator draws constant power
from the source, so source current increases as source
voltage drops. This looks like a negative resistance load
to the source and can cause the source to current limit or
latch low under low source voltage conditions. The VIN(EN)
threshold prevents the regulator from operating at source
voltages where the problems might occur. This threshold
can be adjusted by setting the values R3 and R4 such that
they satisfy the following equation:
⎛ R3 ⎞
VIN(EN) = ⎜ +1⎟ •1.0V
⎝ R4 ⎠
(10)
where the LT8610 will remain off until VIN is above VIN(EN).
Due to the comparator’s hysteresis, switching will not stop
until the input falls slightly below VIN(EN).
When operating in Burst Mode operation for light load
currents, the current through the VIN(EN) resistor network
can easily be greater than the supply current consumed
by the LT8610. Therefore, the VIN(EN) resistors should be
large to minimize their effect on efficiency at low loads.
INTVCC Regulator
An internal low dropout (LDO) regulator produces the 3.4V
supply from VIN that powers the drivers and the internal
bias circuitry. The INTVCC can supply enough current for
the LT8610’s circuitry and must be bypassed to ground
with a minimum of 1μF ceramic capacitor. Good bypassing
is necessary to supply the high transient currents required
by the power MOSFET gate drivers. To improve efficiency
the internal LDO can also draw current from the BIAS
pin when the BIAS pin is at 3.1V or higher. Typically the
BIAS pin can be tied to the output of the LT8610, or can
be tied to an external supply of 3.3V or above. If BIAS is
connected to a supply other than VOUT, be sure to bypass
with a local ceramic capacitor. If the BIAS pin is below
3.0V, the internal LDO will consume current from VIN.
Applications with high input voltage and high switching
frequency where the internal LDO pulls current from VIN
will increase die temperature because of the higher power
dissipation across the LDO. Do not connect an external
load to the INTVCC pin.
Output Voltage Tracking and Soft-Start
The LT8610 allows the user to program its output voltage
ramp rate by means of the TR/SS pin. An internal 2.2μA
pulls up the TR/SS pin to INTVCC. Putting an external
capacitor on TR/SS enables soft starting the output to prevent current surge on the input supply. During the soft-start
ramp the output voltage will proportionally track the TR/SS
pin voltage. For output tracking applications, TR/SS can
be externally driven by another voltage source. From 0V to
0.97V, the TR/SS voltage will override the internal 0.97V
reference input to the error amplifier, thus regulating the
FB pin voltage to that of TR/SS pin. When TR/SS is above
0.97V, tracking is disabled and the feedback voltage will
regulate to the internal reference voltage. The TR/SS pin
may be left floating if the function is not needed.
An active pull-down circuit is connected to the TR/SS pin
which will discharge the external soft-start capacitor in
the case of fault conditions and restart the ramp when the
faults are cleared. Fault conditions that clear the soft-start
capacitor are the EN/UV pin transitioning low, VIN voltage
falling too low, or thermal shutdown.
8610p
15
LT8610
APPLICATIONS INFORMATION
Output Power Good
When the LT8610’s output voltage is within the ±9%
window of the regulation point, which is a VFB voltage in
the range of 0.883V to 1.057V (typical), the output voltage
is considered good and the open-drain PG pin goes high
impedance and is typically pulled high with an external
resistor. Otherwise, the internal pull-down device will pull
the PG pin low. To prevent glitching both the upper and
lower thresholds include 1.3% of hysteresis.
The PG pin is also actively pulled low during several fault
conditions: EN/UV pin is below 1V, INTVCC has fallen too
low, VIN is too low, or thermal shutdown.
Synchronization
To select low ripple Burst Mode operation, tie the SYNC pin
below 0.4V (this can be ground or a logic low output). To
synchronize the LT8610 oscillator to an external frequency
connect a square wave (with 20% to 80% duty cycle) to
the SYNC pin. The square wave amplitude should have valleys that are below 0.4V and peaks above 2.4V (up to 6V).
The LT8610 will not enter Burst Mode operation at low
output loads while synchronized to an external clock, but
instead will pulse skip to maintain regulation. The LT8610
may be synchronized over a 200kHz to 2.2MHz range. The
RT resistor should be chosen to set the LT8610 switching
frequency equal to or below the lowest synchronization
input. For example, if the synchronization signal will be
500kHz and higher, the RT should be selected for 500kHz.
The slope compensation is set by the RT value, while the
minimum slope compensation required to avoid subharmonic oscillations is established by the inductor size,
input voltage, and output voltage. Since the synchronization frequency will not change the slopes of the inductor
current waveform, if the inductor is large enough to avoid
subharmonic oscillations at the frequency set by RT, then
the slope compensation will be sufficient for all synchronization frequencies.
For some applications it is desirable for the LT8610 to
operate in pulse-skipping mode, offering two major differences from Burst Mode operation. First is the clock stays
awake at all times and all switching cycles are aligned to
the clock. Second is that full switching frequency is reached
at lower output load than in Burst Mode operation. These
16
two differences come at the expense of increased quiescent
current. To enable pulse-skipping mode, the SYNC pin is
tied high either to a logic output or to the INTVCC pin.
The LT8610 does not operate in forced continuous mode
regardless of SYNC signal. Never leave the SYNC pin
floating.
Shorted and Reversed Input Protection
The LT8610 will tolerate a shorted output. Several features
are used for protection during output short-circuit and
brownout conditions. The first is the switching frequency
will be folded back while the output is lower than the set
point to maintain inductor current control. Second, the
bottom switch current is monitored such that if inductor
current is beyond safe levels switching of the top switch
will be delayed until such time as the inductor current
falls to safe levels.
Frequency foldback behavior depends on the state of the
SYNC pin: If the SYNC pin is low the switching frequency
will slow while the output voltage is lower than the programmed level. If the SYNC pin is connected to a clock
source or tied high, the LT8610 will stay at the programmed
frequency without foldback and only slow switching if the
inductor current exceeds safe levels.
There is another situation to consider in systems where
the output will be held high when the input to the LT8610
is absent. This may occur in battery charging applications
or in battery-backup systems where a battery or some
other supply is diode ORed with the LT8610’s output. If
the VIN pin is allowed to float and the EN pin is held high
(either by a logic signal or because it is tied to VIN), then
the LT8610’s internal circuitry will pull its quiescent current
through its SW pin. This is acceptable if the system can
tolerate several μA in this state. If the EN pin is grounded
the SW pin current will drop to near 1μA. However, if the
VIN pin is grounded while the output is held high, regardless of EN, parasitic body diodes inside the LT8610 can
pull current from the output through the SW pin and
the VIN pin. Figure 3 shows a connection of the VIN and
EN/UV pins that will allow the LT8610 to run only when
the input voltage is present and that protects against a
shorted or reversed input.
8610p
LT8610
APPLICATIONS INFORMATION
D1
VIN
VIN
LT8610
GND
EN/UV
GND
VOUT
8610 F03
1
16
TR/SS
2
15
RT
3
14 BIAS
4
13 INTVCC
5
12
6
11
7
10
8
9
SYNC
FB
PG
Figure 3. Reverse VIN Protection
PCB Layout
For proper operation and minimum EMI, care must be taken
during printed circuit board layout. Figure 4 shows the
recommended component placement with trace, ground
plane and via locations. Note that large, switched currents
flow in the LT8610’s VIN pins, PGND pins, and the input capacitor (C1). The loop formed by the input capacitor should
be as small as possible by placing the capacitor adjacent
to the VIN and PGND pins. When using a physically large
input capacitor the resulting loop may become too large
in which case using a small case/value capacitor placed
close to the VIN and PGND pins plus a larger capacitor
further away is preferred. These components, along with
the inductor and output capacitor, should be placed on the
same side of the circuit board, and their connections should
be made on that layer. Place a local, unbroken ground
plane under the application circuit on the layer closest to
the surface layer. The SW and BOOST nodes should be
as small as possible. Finally, keep the FB and RT nodes
small so that the ground traces will shield them from the
SW and BOOST nodes. The exposed pad on the bottom of
the package must be soldered to ground so that the pad
is connected to ground electrically and also acts as a heat
sink thermally. To keep thermal resistance low, extend the
ground plane as much as possible, and add thermal vias
under and near the LT8610 to additional ground planes
within the circuit board and on the bottom side.
High Temperature Considerations
For higher ambient temperatures, care should be taken in
the layout of the PCB to ensure good heat sinking of the
LT8610. The exposed pad on the bottom of the package
EN/UV
BST
VIN
SW
GND
VOUT
8610 F04
VOUT LINE TO BIAS
VIAS TO GROUND PLANE
OUTLINE OF LOCAL
GROUND PLANE
Figure 4. Recommended PCB Layout for the LT8610
must be soldered to a ground plane. This ground should
be tied to large copper layers below with thermal vias;
these layers will spread heat dissipated by the LT8610.
Placing additional vias can reduce thermal resistance
further. The maximum load current should be derated
as the ambient temperature approaches the maximum
junction rating. Power dissipation within the LT8610 can
be estimated by calculating the total power loss from an
efficiency measurement and subtracting the inductor loss.
The die temperature is calculated by multiplying the LT8610
power dissipation by the thermal resistance from junction
to ambient. The LT8610 will stop switching and indicate
a fault condition if safe junction temperature is exceeded.
8610p
17
LT8610
TYPICAL APPLICATIONS
5V Step-Down Converter
VIN
5.5V TO 42V
VIN
4.7μF
12V Step-Down Converter
BST
0.1μF
2.5μH
EN/UV
SW
LT8610
SYNC
BIAS
TR/SS
PG
10nF
VIN
12.5V TO 42V
VIN
4.7μF
VOUT
5V
47μF 2.5A
0.1μF
10μH
SW
BIAS
SYNC
10nF
VIN
3.4V TO 15V
(42V TRANSIENT)
VOUT
5V
68μF 2.5A
TR/SS
VIN
1M
INTVCC
RT PGND GND
PG
POWER GOOD
VIN
PG
SW
BIAS
SYNC
VOUT
3.3V
2.5A
47μF
INTVCC
RT PGND GND
18.2k
PG
LT8610
1μF
1M
4.7pF
110k
4.7pF
1M
8610 TA07
8610 TA04
Ultralow EMI 5V 2.5A Step-Down Converter
FB1
BEAD
BST
0.1μF
8.2μH
EN/UV
LT8610
SW
BIAS
VOUT
3.3V
68μF 2.5A
VIN
5.5V TO 42V
4.7μH
VIN
4.7μF
4.7μF
4.7μF
SYNC
TR/SS
1μF
FB
INTVCC
RT PGND GND
BST
0.1μF
4.7μH
EN/UV
SW
PG
10nF
fSW = 400kHz
866k
FB
INTVCC
RT PGND GND
fSW = 400kHz
VIN
VOUT
1.8V
120μF 2.5A
SW
BIAS
SYNC
3.3V Step-Down Converter
110k
0.1μF
4.7μH
10nF
412k
fSW = 2MHz
SYNC
BST
EN/UV
TR/SS
FB
PG
8610 TA06
VIN
4.7μF
TR/SS
1μF
4.7μF
1M
1.8V Step-Down Converter
10nF
VIN
3.8V TO 42V
4.7pF
fSW = 2MHz
VIN
3.4V TO 42V
0.1μF
1.8μH
LT8610
866k
FB
18.2k
BST
EN/UV
BIAS
INTVCC
RT PGND GND
8610 TA03
4.7μF
VOUT
1.8V
68μF 2.5A
SW
TR/SS
3.3V Step-Down Converter
VIN
3.8V TO 27V
(42V TRANSIENT)
LT8610
1μF
243k
fSW = 400kHz
0.1μF
1μH
SYNC
10pF
110k
BST
EN/UV
10nF
PG
FB
88.7k
8610 TA09
4.7μF
100k
1μF
10pF
1.8V 2MHz Step-Down Converter
BST
EN/UV
POWER GOOD
1M
fSW = 1MHz
5V Step-Down Converter
LT8610
PG
41.2k
8610 TA02
VIN
TR/SS
INTVCC
RT PGND GND
243k
fSW = 2MHz
4.7μF
BIAS
FB
10pF
18.2k
VOUT
12V
47μF 2.5A
100k
POWER GOOD
1μF
INTVCC
RT PGND GND
VIN
5.5V TO 42V
SYNC
10nF
1M
FB
0.1μF
10μH
SW
LT8610
100k
1μF
BST
EN/UV
10nF
1M
LT8610
BIAS
1M
TR/SS
1μF
4.7pF
FB
10pF
INTVCC
RT PGND GND
412k
52.3k
8610 TA05
VOUT
5V
47μF 2.5A
243k
FB1: TDK MPZ2012S221A
fSW = 800kHz
8610 TA11
8610p
18
LT8610
PACKAGE DESCRIPTION
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
MSE Package
16-Lead Plastic MSOP, Exposed Die Pad
(Reference LTC DWG # 05-08-1667 Rev E)
BOTTOM VIEW OF
EXPOSED PAD OPTION
2.845 t 0.102
(.112 t .004)
5.23
(.206)
MIN
2.845 t 0.102
(.112 t .004)
0.889 t 0.127
(.035 t .005)
8
1
1.651 t 0.102
(.065 t .004)
1.651 t 0.102 3.20 – 3.45
(.065 t .004) (.126 – .136)
0.305 t 0.038
(.0120 t .0015)
TYP
16
0.50
(.0197)
BSC
4.039 t 0.102
(.159 t .004)
(NOTE 3)
RECOMMENDED SOLDER PAD LAYOUT
0.254
(.010)
0.35
REF
0.12 REF
DETAIL “B”
CORNER TAIL IS PART OF
DETAIL “B” THE LEADFRAME FEATURE.
FOR REFERENCE ONLY
9
NO MEASUREMENT PURPOSE
0.280 t 0.076
(.011 t .003)
REF
16151413121110 9
DETAIL “A”
0s – 6s TYP
3.00 t 0.102
(.118 t .004)
(NOTE 4)
4.90 t 0.152
(.193 t .006)
GAUGE PLANE
0.53 t 0.152
(.021 t .006)
1234567 8
DETAIL “A”
1.10
(.043)
MAX
0.18
(.007)
SEATING
PLANE
0.17 – 0.27
(.007 – .011)
TYP
0.50
(.0197)
BSC
NOTE:
1. DIMENSIONS IN MILLIMETER/(INCH)
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.
0.86
(.034)
REF
0.1016 t 0.0508
(.004 t .002)
MSOP (MSE16) 0911 REV E
8610p
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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
19
LT8610
TYPICAL APPLICATION
3.3V and 1.8V with Ratio Tracking
VIN
3.8V TO 42V
VIN
4.7μF
VIN
3.8V TO 27V
BST
0.1μF
5.6μH
EN/UV
PG
Ultralow IQ 2.5V, 3.3V Step-Down with LDO
LT8610
VIN
4.7μF
VOUT1
3.3V
47μF 2.5A
SW
SYNC
10nF
BST
0.1μF
1.8μH
EN/UV
PG
LT8610
SYNC
VOUT1
3.3V
47μF 2.5A
SW
BIAS
10nF
BIAS
TR/SS
1μF
FB
INTVCC
RT PGND GND
TR/SS
232k
1μF
FB
4.7pF
88.7k
INTVCC
RT PGND GND
97.6k
18.2k
fSW = 500kHz
fSW = 2MHz
1M
4.7pF
IN
412k
OUT
LT3008-2.5
VOUT2
2.5V
2.2μF 20mA
SHDN SENSE
8610 TA10
VIN
4.7μF
BST
0.1μF
3.3μH
EN/UV
PG
LT8610
VOUT2
1.8V
2.5A
68μF
SW
SYNC
24.3k
TR/SS
BIAS
FB
10k
1μF
INTVCC
RT PGND GND
88.7k
fSW = 500kHz
80.6k
4.7pF
93.1k
8610 TA08
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LT8611
42V, 2.5A, 96% Efficiency, 2.2MHz Synchronous Micropower Step-Down
DC/DC Converter with IQ = 2.5μA and Input/Output Current Limit/Monitor
VIN: 3.4V to 42V, VOUT(MIN) = 0.97V, IQ = 2.5μA,
ISD < 1μA, 3mm × 5mm QFN-24 Package
LT3690
36V with 60V Transient Protection, 4A, 92% Efficiency, 1.5MHz
Synchronous Micropower Step-Down DC/DC Converter with IQ = 70μA
VIN: 3.9V to 36V, VOUT(MIN) = 0.985V, IQ = 70μA,
ISD < 1μA, 4mm × 6mm QFN-26 Package
LT3971
38V, 1.2A, 2.2MHz High Efficiency Micropower Step-Down DC/DC
Converter with IQ = 2.8μA
VIN: 4.2V to 38V, VOUT(MIN) = 1.21V, IQ = 2.8μA,
ISD < 1μA, 3mm × 3mm DFN-10 and MSOP-10E Packages
LT3991
55V, 1.2A, 2.2MHz High Efficiency Micropower Step-Down DC/DC
Converter with IQ = 2.8μA
VIN: 4.2V to 55V, VOUT(MIN) = 1.21V, IQ = 2.8μA,
ISD < 1μA, 3mm × 3mm DFN-10 and MSOP-10E Packages
LT3970
40V, 350mA, 2.2MHz High Efficiency Micropower Step-Down DC/DC
Converter with IQ = 2.5μA
VIN: 4.2V to 40V, VOUT(MIN) = 1.21V, IQ = 2.5μA,
ISD < 1μA, 3mm × 2mm DFN-10 and MSOP-10 Packages
LT3990
62V, 350mA, 2.2MHz High Efficiency MicroPower Step-Down DC/DC
Converter with IQ = 2.5μA
VIN: 4.2V to 62V, VOUT(MIN) = 1.21V, IQ = 2.5μA,
ISD < 1μA, 3mm × 3mm DFN-10 and MSOP-6E Packages
LT3480
36V with Transient Protection to 60V, 2A (IOUT), 2.4MHz, High Efficiency
Step-Down DC/DC Converter with Burst Mode Operation
VIN: 3.6V to 36V, Transient to 60V, VOUT(MIN) = 0.78V,
IQ = 70μA, ISD < 1μA, 3mm × 3mm DFN-10 and
MSOP-10E Packages
LT3980
58V with Transient Protection to 80V, 2A (IOUT), 2.4MHz, High Efficiency
Step-Down DC/DC Converter with Burst Mode Operation
VIN: 3.6V to 58V, Transient to 80V, VOUT(MIN) = 0.78V,
IQ = 85μA, ISD < 1μA, 3mm × 4mm DFN-16 and
MSOP-16E Packages
8610p
20 Linear Technology Corporation
LT 0512 • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
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© LINEAR TECHNOLOGY CORPORATION 2012