LT8618/LT8618-3.3/LT8618C
High Efficiency 65V/100mA
Synchronous Bucks
DESCRIPTION
FEATURES
High Efficiency Synchronous Operation
n > 90% Efficiency at 30mA, 12V to 3.3V
IN
OUT
n Pin Selectable Forced Continuous or Burst Mode®
Operation (LT8618C Only)
n Ultralow Quiescent Current Burst Mode Operation
n < 2.5µA I Regulating 48V to 3.3V
Q
IN
OUT
n Output Ripple < 10mV
P-P
n 3.4V to 60V Input Operation Range (65V Max)
n Fast Minimum Switch-On Time: 35ns
n Adjustable (All) And Synchronizable (LT8618C
Only) Switching Frequency: 200kHz to 2.2MHz
n Fixed 3.3V Output Voltage Version (LT8618-3.3)
n Accurate 1V Enable Pin Threshold (All) with
Adjustable Hysteresis (LT8618C Only)
n Internal Compensation
n Output Soft-Start and Tracking
n Small 12-Lead 2mm × 2mm LQFN (LT8618C) and
10-Lead 3mm × 2mm DFN Packages
n AEC-Q100 Qualified for Automotive Applications
(LT8618/LT8618-3.3)
The LT®8618 family are compact, high speed synchronous monolithic step-down switching regulators that
deliver up to 100mA to the output with high efficiency at
a constant frequency, even up to 2.2MHz. They accept a
wide input voltage range up to 65V (transients only, 60V
for continuous operation), and consume only 2.5µA of
quiescent current when operating in Burst Mode. Top and
bottom power switches are included with all necessary
circuitry to minimize the need for external components.
n
The LT8618C includes BST and INTVCC ceramic capacitors for a more compact solution while having SYNC/
MODE and HYST pins. The SYNC/MODE pin selects the
regulator’s operation between forced continuous mode,
for predictive interference in sampling systems, Burst
Mode, for increased efficiency at light loads or spread
spectrum for Low EMI. It also allows synchronization to
an external clock to further increase signal to noise ratio
in high-resolution acquisition systems.
A PG flag signals when VOUT is within ±7.5% of the programmed output voltage and when in fault conditions.
Thermal shutdown provides additional protection.
APPLICATIONS
Industrial Sensors
n Industrial Internet of Things
n 4mA to 20mA Current Loops
n Flow Meters
n Automotive Housekeeping Supplies
n
PACKAGE
SYNC/
HYST
150°C
GRADE
INTERNAL
CAPS
FB
RESISTORS
DFN
No
Yes
No
External
LT8618
LT8618-3.3
DFN
No
Yes
No
Internal
LT8618C
LQFN
Yes
No
Yes
External
All registered trademarks and trademarks are the property of their respective owners.
TYPICAL APPLICATION
Efficiency at VOUT = 3.3V
100
3.3V, Step-Down Converter
OFF ON
VIN
1µF
1µF
10nF
95
BST
47nF
120µH
LT8618-3.3
EN/UV
SW
INTVCC
BIAS
TR/SS
110k
VOUT
3.3V
100mA
PG
RT
OUT
VIN = 24V
85
VIN = 48V
80
75
70
65
60
22µF
GND
VIN = 12V
90
EFFICIENCY (%)
VIN
4.2V TO 60V
8618 TA1a
55
50
fSW = 400kHz
fSW = 400kHz
0
10 20 30 40 50 60 70 80 90 100
OUTPUT CURRENT (mA)
8618 TA1b
Rev. A
Document Feedback
For more information www.analog.com
1
LT8618/LT8618-3.3/LT8618C
ABSOLUTE MAXIMUM RATINGS
(Note 1)
VIN, EN/UV Voltage (Note 4)....................... –0.3V to 65V
PG Voltage.................................................. –0.3V to 42V
BIAS Voltage............................................... –0.3V to 25V
HYST Voltage (LT8618C Only).....................–0.3V to 12V
FB (LT8618/LT8618C), TR/SS Voltages......... –0.3V to 4V
OUT (LT8618-3.3)......................................... –0.3V to 6V
SYNC/MODE Voltage (LT8618C Only)........... –0.3V to 6V
Operating Junction Temperature Range (Note 2)
LT8618E/LT8618E-3.3/LT8618CA........... –40°C to 125°C
LT8618I/LT8618I-3.3............................... –40°C to 125°C
LT8618J/LT8618J-3.3............................. –40°C to 150°C
Storage Temperature Range................... –65°C to 150°C
PIN CONFIGURATION
LT8618C
1
SW
2
BIAS
3
INTVCC
4
RT
5
10 VIN
11
GND
9
EN/UV
8
PG
7
TR/SS
6
FB/OUT*
DDB PACKAGE
10-LEAD (3mm × 2mm) PLASTIC DFN
θJA = 76°C/W, θJC = 13.5°C/W
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
* FB FOR LT8618, OUT FOR LT8618-3.3
VIN
1
EN/UV
2
HYST
3
PG
4
DNC
BST
12
11
13
GND
5
6
TR/SS
TOP VIEW
GND
TOP VIEW
FB
LT8618/LT8618-3.3
10 SW
9
BIAS
8
RT
7
SYNC/MODE
LQFN PACKAGE
12-LEAD (2mm × 2mm × 0.74mm)
TJMAX = 125°C, θJA = 51°C/W
EXPOSED PAD (PIN 13) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
TAPE AND REEL (MINI)
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT8618EDDB#TRMPBF
LT8618EDDB#TRPBF
LHHF
10-Lead (3mm × 2mm) Plastic DFN
–40°C to 125°C
LT8618IDDB#TRMPBF
LT8618IDDB#TRPBF
LHHF
10-Lead (3mm × 2mm) Plastic DFN
–40°C to 125°C
LT8618JDDB#TRMPBF
LT8618JDDB#TRPBF
LHHF
10-Lead (3mm × 2mm) Plastic DFN
–40°C to 150°C
LT8618EDDB-3.3#TRMPBF
LT8618EDDB-3.3#TRPBF
LHHW
10-Lead (3mm × 2mm) Plastic DFN
–40°C to 125°C
LT8618IDDB-3.3#TRMPBF
LT8618IDDB-3.3#TRPBF
LHHW
10-Lead (3mm × 2mm) Plastic DFN
–40°C to 125°C
LT8618JDDB-3.3#TRMPBF
LT8618JDDB-3.3#TRPBF
LHHW
10-Lead (3mm × 2mm) Plastic DFN
–40°C to 150°C
LT8618CAV#TRMPBF
LT8618CAV#TRPBF
LHNG
12-Lead (2mm × 2mm) LQFN (Laminate –40°C to 125°C
Package with QFN footprint)
2
Rev. A
For more information www.analog.com
LT8618/LT8618-3.3/LT8618C
ORDER INFORMATION
TAPE AND REEL (MINI)
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT8618EDDB#WTRMPBF
LT8618EDDB#WTRPBF
LHHF
10-Lead (3mm × 2mm) Plastic DFN
–40°C to 125°C
LT8618IDDB#WTRMPBF
LT8618IDDB#WTRPBF
LHHF
10-Lead (3mm × 2mm) Plastic DFN
–40°C to 125°C
LT8618JDDB#WTRMPBF
LT8618JDDB#WTRPBF
LHHF
10-Lead (3mm × 2mm) Plastic DFN
–40°C to 150°C
LT8618EDDB-3.3#WTRMPBF
LT8618EDDB-3.3#WTRPBF
LHHW
10-Lead (3mm × 2mm) Plastic DFN
–40°C to 125°C
LT8618IDDB-3.3#WTRMPBF
LT8618IDDB-3.3#WTRPBF
LHHW
10-Lead (3mm × 2mm) Plastic DFN
–40°C to 125°C
LT8618JDDB-3.3#WTRMPBF
LT8618JDDB-3.3#WTRPBF
LHHW
10-Lead (3mm × 2mm) Plastic DFN
–40°C to 150°C
AUTOMOTIVE PRODUCTS**
Contact the factory for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
Tape and reel specifications. Some packages are available in 500 unit reels through designated sales channels with #TRMPBF suffix.
**Versions of this part are available with controlled manufacturing to support the quality and reliability requirements of automotive applications. These
models are designated with a #W suffix. Only the automotive grade products shown are available for use in automotive applications. Contact your
local Analog Devices account representative for specific product ordering information and to obtain the specific Automotive Reliability reports for
these models.
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C.
PARAMETER
CONDITIONS
Operating Input Voltage
Minimum Input Voltage
(Note 5)
VIN Quiescent Current
VEN/UV = 0V
VEN/UV = 2V, Not Switching
VIN Current in Regulation
MIN
l
TYP
3.4
MAX
60
UNITS
V
l
2.9
3.4
V
l
1
1.7
4
12
µA
µA
VIN = 12V, VOUT = 3.3V, ILOAD = 100µA
VIN = 12V, VOUT = 3.3V, ILOAD = 1mA
56
400
µA
µA
LT8618/LT8618C Feedback Reference Voltage
VIN = 12V, ILOAD = 100µA
l
0.762
0.778
0.798
V
LT8618-3.3 Output Voltage
VIN = 12V, ILOAD = 100µA
l
3.2
3.3
3.4
V
FB/OUT Voltage Line Regulation
VIN = 4V to 60V
l
±0.02
±0.06
LT8618/LT8618C FB Pin Input Current
VFB = 0.8V
l
BIAS Pin Current Consumption
VBIAS = 3.3V, ILOAD = 30mA, 700kHz
±20
0.8
%/V
nA
mA
Minimum On-Time
l
35
65
ns
Minimum Off-Time
l
90
120
ns
200
2.00
260
2.15
kHz
MHz
Oscillator Frequency
RT = 221k
RT = 18.2k
l
l
140
1.85
Top Power NMOS On-Resistance
3
Top Power NMOS Current Limit
l
150
Bottom Power NMOS On-Resistance
200
Ω
250
1.3
SW Leakage Current
VIN = 48V
l
EN/UV Pin Threshold
Pin Voltage Rising
l
Ω
15
0.98
EN/UV Pin Hysteresis
1.05
1.11
50
EN/UV Pin Current
VEN/UV = 2V
HYST Pull-Down Resistance
VHYST = 0.1V, VEN/UV < 0.9V, LT8618C Only
HYST Pin Leakage Current
VHYST = 1V, VEN/UV > 1.2V, LT8618C Only
PG Upper Threshold Offset from VFB/OUT
VFB/OUT Rising, LT8618/LT8618-3.3
VFB/OUT Rising, LT8618C
280
l
l
5.0
4.5
7.5
7.5
mA
µA
V
mV
±50
nA
500
Ω
±200
nA
10.0
10.0
%
%
Rev. A
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3
LT8618/LT8618-3.3/LT8618C
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C.
PARAMETER
CONDITIONS
PG Lower Threshold Offset from VFB/OUT
VFB/OUT Falling
l
MIN
TYP
MAX
UNITS
–10.0
–7.5
–5.0
%
PG Hysteresis
0.5
PG Leakage
VPG = 42V
PG Pull-Down Resistance
VPG = 0.1V
SYNC/MODE Threshold Voltage
LT8618C Only
TR/SS Source Current
VTR/SS = 0.1V, E- and I-Grades
VTR/SS = 0.1V, J- and A-Grades
±200
nA
550
1200
Ω
l
TR/SS Pull-Down Resistance
Fault Condition, VTR/SS = 0.1V
VIN to Disable Forced Continuous Mode
VIN Rising, LT8618C Only
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 LT8618E/LT8618E-3.3 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 LT8618I/LT8618I-3.3 is guaranteed over the full –40°C to 125°C
operating junction temperature range. The LT8618J/LT8618J-3.3 is
guaranteed over the full –40°C to 150°C operating junction temperature
range. The LT8618CA is specified over the –40°C to 125°C operating
junction temperature range. High junction temperatures degrade operating
lifetimes. Operating lifetime is derated at junction temperatures greater
%
0.4
0.9
1.5
V
l
l
1
1
2
2
3.5
4
µA
µA
300
900
Ω
l
30
32
34
V
than 125°C. Note the maximum ambient temperature consistent with
these specifications is determined by specific operating conditions in
conjunction with board layout, the rated package thermal impedance and
other environmental factors.
Note 3: This IC includes overtemperature protection that is intended to
protect the device during overload conditions. Junction temperature will
exceed 125°C when overtemperature protection is active. Continuous
operation above the specified maximum operating junction temperature
will reduce lifetime
Note 4: Absolute maximum voltage at the VIN and EN/UV pins is 65V for
transients, and 60V for continuous operation.
Note 5: For the LT8618-3.3, minimum input voltage will be limited by
output voltage.
TYPICAL PERFORMANCE CHARACTERISTICS
LT8618:
Burst Mode Efficiency (5V Output)
LT8618:
Burst Mode Efficiency (5V Output)
VIN = 12V
VIN = 24V
80
VIN = 48V
70
60
4
100
90
90
80
80
70
VIN = 12V
60
VIN = 24V
50
VIN = 48V
40
30
L = 33µH
fSW = 2MHz
0
10 20 30 40 50 60 70 80 90 100
OUTPUT CURRENT (mA)
8618 G01
VIN = 12V
VIN = 24V
VIN = 48V
70
60
50
40
30
20
20
50
40
EFFICIENCY (%)
EFFICIENCY (%)
90
100
EFFICIENCY (%)
100
LT8618C: Forced Continuous
Mode Efficiency (5V Output)
L = 33µH
fSW = 2MHz
10
0
1μ
10μ
100μ
1m
10m
OUTPUT CURRENT (A)
100m
8618 G02
L = 47µH
fSW = 2MHz
10
0
0
10 20 30 40 50 60 70 80 90 100
OUTPUT CURRENT (mA)
8618 G31
Rev. A
For more information www.analog.com
LT8618/LT8618-3.3/LT8618C
TYPICAL PERFORMANCE CHARACTERISTICS
LT8618C:
Burst Mode Efficiency (5V Output)
LT8618C:
Burst Mode Efficiency (5V Output)
100
100
70
60
60
70
50
40
30
60
50
40
30
20
50
40
70
L = 47µH
fSW = 2MHz
0
20
L = 47µH
fSW = 2MHz
10
0
1μ
10 20 30 40 50 60 70 80 90 100
OUTPUT CURRENT (mA)
10μ
8618 G32
LT8618/LT8618C:
FB Voltage
100μ
1m
10m
OUTPUT CURRENT (A)
VIN = 48V
10
0
1μ
100m
10μ
8618 G33
VIN = 24V
100μ
1m
10m
OUTPUT CURRENT (A)
3.310
5.0
VO UT = 3.3V
R1 = 309kΩ
R2 = 1MΩ
778
777
776
3.305
4.2
INPUT CURRENT (µA)
OUT REGULATION VOLTAGE (V)
FB REGULATION VOLTAGE (mV)
4.6
779
3.300
3.295
3.290
3.8
3.4
3.0
2.6
LT8618
2.2
LT8618-3.3
1.8
3.285
LT8618C
1.4
0
3.280
−50 −25
25 50 75 100 125 150
TEMPERATURE (°C)
8618 G05
LT8618/LT8618-3.3:
Burst Mode Efficiency (3.3V Output)
VIN = 24V
70
EFFICIENCY (%)
EFFICIENCY (%)
VIN = 12V
80
VIN = 48V
60
40
100
90
90
80
80
70
70
VIN = 12V
60
VIN = 24V
50
VIN = 48V
40
30
L = 33µH
fSW = 2MHz
0
10 20 30 40 50 60 70 80 90 100
OUTPUT CURRENT (mA)
8618 G03
0
10
20
30
40
INPUT VOLTAGE (V)
50
60
8618 G09
LT8618C: Forced Continuous
Mode Efficiency (3.3V Output)
100
VIN = 12V
VIN = 24V
VIN = 48V
60
50
40
30
20
20
50
1.0
25 50 75 100 125 150
TEMPERATURE (°C)
8618 G06
LT8618/LT8618-3.3:
Burst Mode Efficiency (3.3V Output)
100
90
0
EFFICIENCY (%)
775
−50 −25
100m
8618 G34
No-Load Supply Current
In Burst Mode (3.3V Output)
LT8618-3.3:
OUT Voltage
780
VIN = 12V
80
VIN = 48V
EFFICIENCY (%)
EFFICIENCY (%)
EFFICIENCY (%)
VIN = 48V
80
L = 47µH
90 fSW = 2MHz
VIN = 24V
80
VIN = 24V
100
VIN = 12V
90
VIN = 12V
90
LT8618C: Forced Continuous
Mode Efficiency (5V Output)
L = 33µH
fSW = 2MHz
10
0
1μ
10μ
100μ
1m
10m
OUTPUT CURRENT (A)
100m
8618 G04
L = 33µH
fSW = 2MHz
10
0
0
10 20 30 40 50 60 70 80 90 100
OUTPUT CURRENT (mA)
8618 G35
Rev. A
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5
LT8618/LT8618-3.3/LT8618C
TYPICAL PERFORMANCE CHARACTERISTICS
LT8618C:
Burst Mode Efficiency (3.3V Output)
LT8618C:
Burst Mode Efficiency (3.3V Output)
100
100
100
80
VIN = 24V
70
VIN = 48V
70
60
VIN = 24V
60
50
40
30
20
50
L = 33µH
fSW = 2MHz
0
0
1μ
L = 33µH
fSW = 2MHz
10μ
8618 G36
Load Regulation
0.20
0.4
0.15
0.1
0
−0.1
−0.2
−0.3
−0.4
40
60
80
OUTPUT CURRENT (mA)
100
VIN = 24V
10μ
100μ
1m
10m
OUTPUT CURRENT (A)
2.25
L = 33µH
fSW = 2MHz
2.00
−0.05
−0.10
1.75
1.50
1.25
(FORCED
CONTINUOUS
MODE)
1.00
0.75
0.50
L = 120µH
fSW = 400kHz
0.25
0
10
100m
8618 G38
2.50
0
−0.20
VIN = 48V
LT8618C: No-Load Supply Current
In Forced Continuous Mode
(3.3V Output)
VOUT = 3.3V
IOUT = 100mA
8618 G07
20
30
40
INPUT VOLTAGE (V)
50
0
60
0
10
(PULSE SKIPPING)
20
30
40
INPUT VOLTAGE (V)
8618 G08
Top FET Current Limit
vs Duty Cycle
50
60
8618 G39
Top FET Current Limit
vs Temperature
220
200
VIN = 12V
VOUT = 5V
1.6 ILOAD = 100mA
215
1.4
1.2
1.0
VBIAS = 3.3V
VBIAS = 5V
0.6
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2
SWITCHING FREQUENCY (MHz)
8618 G40
190
SWITCH CURRENT (mA)
TOP FET CURRENT LIMIT (mA)
BIAS PIN CURRENT (mA)
30
8618 G37
0.05
1.8
6
40
0
1μ
100m
0.10
BIAS Current
0.8
100μ
1m
10m
OUTPUT CURRENT (A)
−0.15
20
50
10
INPUT CURRENT (mA)
0.2
CHANGE IN VOUT (%)
CHANGE IN VOUT (%)
0.3
0
60
Line Regulation
0.5
−0.5
70
20
10
10 20 30 40 50 60 70 80 90 100
OUTPUT CURRENT (mA)
VIN = 12V
80
VIN = 48V
EFFICIENCY (%)
EFFICIENCY (%)
80
VIN = 12V
EFFICIENCY (%)
90
L = 33µH
90 fSW = 2MHz
VIN = 12V
90
40
LT8618C: Forced Continuous
Mode Efficiency (3.3V Output)
180
170
210
205
200
195
190
185
160
0
20
40
60
DUTY CYCLE (%)
80
100
8618 G10
180
−50 −25
0
25 50 75 100 125 150
TEMPERATURE (°C)
8618 G11
Rev. A
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LT8618/LT8618-3.3/LT8618C
TYPICAL PERFORMANCE CHARACTERISTICS
600
Minimum On-Time
vs Temperature
Switch Drop vs Switch Current
Switch Drop vs Temperature
400
SWITCH CURRENT = 100mA
40
39
400
TOP SW
300
200
BOT SW
100
38
300
MINIMUM ON-TIME (ns)
SWITCH DROP (mV)
SWITCH DROP (mV)
500
200
TOP SW
100
37
36
35
34
33
32
BOT SW
31
0
−50 −25
0
0
25 50 75 100 125 150
TEMPERATURE (°C)
8618 G12
Minimum Off-Time
vs Temperature
30
−50 −25
100
95
90
85
2030
2020
300
250
200
150
100
0
25 50 75 100 125 150
TEMPERATURE (°C)
8618 G15
Burst Frequency vs Load Current
L = 33µH
VIN = 12V
VOUT = 3.3V
1750
1500
1250
1000
750
500
LT8618C
(SYNC = 0)
250
0
L = 47µH
VIN = 12V
VOUT = 5V
SWITCHING FREQUENCY (kHz)
LT8618/LT8618-3.3
2000
0
10 20 30 40 50 60 70 80 90 100
LOAD CURRENT (mA)
8618 G16
8618 G18
1980
1970
1950
−50 −25
1.0
2250
0.9
2000
0.8
1750
0.7
1500
1250
1000
0.5
0.4
0.3
500
0.2
0.1
RT = 18.2kΩ
0
0.1
0.2
25 50 75 100 125 150
TEMPERATURE (°C)
8618 G17
0.6
750
0
RT = 18.2kΩ
0
Soft-Start Tracking
2500
250
10 20 30 40 50 60 70 80 90 100
LOAD CURRENT (mA)
1990
Frequency Foldback
2500
2250
2000
FB VOLTAGE (V)
0
2010
1960
50
80
−50 −25
25 50 75 100 125 150
TEMPERATURE (°C)
8618 G14
Switching Frequency
vs Temperature
SWITCHING FREQUENCY (kHz)
100
0
8618 G13
L=MOS6020-333ML
350 VOUT = 3.3V
DROPOUT VOLTAGE (mV)
MINIMUM OFF-TIME (ns)
40
60
80
SWITCH CURRENT (mA)
400
105
SWITCHING FREQUENCY (kHz)
20
Dropout Voltage vs Load Current
110
0
0
0.3 0.4 0.5 0.6
FB VOLTAGE (V)
0.7
0.8
8618 G19
0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2
TR/SS VOLTAGE (V)
8618 G20
Rev. A
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7
LT8618/LT8618-3.3/LT8618C
TYPICAL PERFORMANCE CHARACTERISTICS
Soft-Start Current vs Temperature
VIN UVLO
3.2
3.1
2.4
3.0
VIN UVLO (V)
SOFT-START CURRENT (μA)
2.5
2.3
2.2
2.9
2.8
2.7
2.1
2.6
2.0
−50 −25
0
2.5
−50 −25
25 50 75 100 125 150
TEMPERATURE (°C)
8618 G21
6
6
6
5
5
5
5
4
VIN
3
3
2
2
VOUT
0
0
1
2
3
4
5
INPUT VOLTAGE (V)
6
7
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
6
4
7
RLOAD = 50Ω
4
4
VIN
3
3
2
1
1
0
0
2
VOUT
0
8618 G23
1
2
3
4
5
INPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
7
OUTPUT VOLTAGE (V)
7
RLOAD = 500Ω
1
8
25 50 75 100 125 150
TEMPERATURE (°C)
8618 G22
Start-Up Dropout
Start-Up Dropout
7
0
1
6
7
0
8618 G24
Rev. A
For more information www.analog.com
LT8618/LT8618-3.3/LT8618C
TYPICAL PERFORMANCE CHARACTERISTICS
LT8618/LT8618-3.3:
Switching Waveforms
LT8618/LT8618-3.3:
Switching Waveforms
LT8618C: Forced Continuous
Mode Switching Waveforms
IL
20mA/DIV
IL
25mA/DIV
IL
10mA/DIV
SW
5V/DIV
SW
16V/DIV
SW
5V/DIV
12VIN TO 3.3VOUT AT 50mA
1µs/DIV
L = 100µH
48VIN TO 3.3VOUT AT 50mA
1µs/DIV
8618 G25
LT8618/LT8618-3.3:
Switching Waveforms
12VIN TO 5VOUT AT 5mA
L = 100µH
200ns/DIV
8618 G26
LT8618/LT8618-3.3:
Switching Waveforms
IL
20mA/DIV
IL
100mA/DIV
SW
4V/DIV
SW
16V/DIV
SW
4V/DIV
5µs/DIV
L = 100µH
48VIN TO 3.3VOUT AT 4mA
Transient Response
L = 47µH
500ns/DIV
8618 G28
8618 G42
LT8618C: Transition Between Burst
Mode And Forced Continuous Mode
Transient Response
100mA
ILOAD
25mA/DIV
12VIN TO 5VOUT AT 20mA
L = 100µH
5µs/DIV
8618 G27
8618 G41
LT8618C: Burst Mode
Switching Waveforms
IL
20mA/DIV
12VIN TO 3.3VOUT AT 3mA
L = 47µH
100mA
ILOAD
25mA/DIV
50mA
VSYNC
2V/DIV
50mA
ILOAD = 2mA
VOUT
20mV/DIV
ILOAD = 50mA
VOUT
20mV/DIV
VOUT
20mV/DIV
VOUT
20mV/DIV
VIN = 12V
COUT = 22µF
fSW = 400kHz
100µs/DIV
8618 G29
VIN = 48V
COUT = 22µF
fSW = 400kHz
100µs/DIV
8618 G30
ILOAD = 100mA
VOUT
20mV/DIV
VOUT = 3.3V, L = 120µH, COUT = 2 × 47µF
500µs/DIV
Rev. A
For more information www.analog.com
9
LT8618/LT8618-3.3/LT8618C
PIN FUNCTIONS
LT8618/LT8618-3.3
BST (Pin 1): This pin is used to provide a drive voltage higher than the input voltage, to the topside power
switch. Place a 47nF boost capacitor as close as possible
to the IC. Do not put resistance in series with this pin.
SW (Pin 2): The SW pin is the output of the internal power
switches. Connect this pin to the inductor. This node
should be kept small on the PCB for good performance.
BIAS (Pin 3): The internal regulator will draw current from
BIAS instead of VIN when BIAS is tied to a voltage higher
than 3.2V. For output voltages of 3.3V to 25V 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.
If no supply is available, tie this pin to GND.
INTVCC (Pin 4): Internal 3.4V Regulator Bypass Pin. The
internal power drivers and control circuits are powered
from this voltage. INTVCC maximum output current is
2mA. Do not load the INTVCC pin with external circuitry.
INTVCC current will be supplied from BIAS if BIAS >
3.2V, 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 a low ESR ceramic capacitor of at least 1μF
placed close to the IC.
RT (Pin 5): Tie a resistor between RT and ground to set
the switching frequency.
FB (Pin 6, LT8618 Only): The LT8618 regulates the FB
pin to 0.778V. Connect the feedback resistor divider tap
to this pin.
OUT (Pin 6, LT8618-3.3 Only): The LT8618-3.3 regulates
the OUT pin to 3.3V. This pin connects to the internal
feedback divider that programs the fixed output voltage.
Tie the output to this pin.
10
TR/SS (Pin 7): Output Tracking and Soft-Start Pin. This
pin allows user control of output voltage ramp rate during start-up. A TR/SS voltage below 0.778V forces the
LT8618 to regulate the FB pin to equal the TR/SS pin voltage. When TR/SS is above 0.778V, the tracking function is
disabled and the internal reference resumes control of the
error amplifier. An internal 2µA pull-up current on this pin
allows a capacitor to program output voltage slew rate.
This pin is pulled to ground with a 300Ω MOSFET during
shutdown and fault conditions; use a series resistor if
driving from a low impedance output.
PG (Pin 8): The PG pin is the open-drain output of an
internal comparator. PG remains low until the FB pin is
within ±7.5% 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.
EN/UV (Pin 9): The LT8618 is shut down when this pin is
low and active when high. The hysteretic threshold voltage is 1.05V rising and 1.00V falling. 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 LT8618 will shut down.
VIN (Pin 10): The VIN pin supplies current to the LT8618
internal circuitry and to the internal top side power switch.
This pin must be locally bypassed. Be sure to place the
positive terminal of the input capacitor as close as possible to the VIN pin, and the negative capacitor terminal
as close as possible to the GND pin.
GND (Exposed Pad Pin 11): 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.
Rev. A
For more information www.analog.com
LT8618/LT8618-3.3/LT8618C
PIN FUNCTIONS
LT8618C
VIN (Pin 1): The VIN pin supplies current to the LT8618C
internal circuitry and the internal top side power switch.
This pin must be locally bypassed. Place the positive terminal of the input capacitor as close as possible to the
VIN pin, and the negative capacitor terminal as close as
possible to the GND pin.
EN/UV (Pin 2): The LT8618C is shut down when this pin
is low and active when high. The hysteretic threshold
voltage is 1.05V rising and 1.00V falling. Tie to VIN if the
shutdown feature is not used. An external resistor divider
from VIN can program a VIN threshold below which the
LT8618C will shut down.
HYST (Pin 3): EN/UV Hysteresis Open-Drain Logic Output.
This pin is pulled to ground when EN/UV (Pin 2) is below
1V. This pin can be used to adjust the EN/UV pin hysteresis. See applications information.
PG (Pin 4): The PG pin is the open-drain output of an
internal comparator. PG remains low until the FB pin is
within ±7.5% 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 5): The LT8618C regulates the FB pin to 0.778V.
Connect the feedback resistor divider tap to this pin.
TR/SS (Pin 6): Output Tracking and Soft-Start Pin. This
pin allows user control of output voltage ramp rate during start-up. A TR/SS voltage below 0.778V forces the
LT8618C to regulate the FB pin to equal the TR/SS pin
voltage. When TR/SS is above 0.778V, the tracking function is disabled, and the internal reference resumes control of the error amplifier. An internal 2µA pull-up current
on this pin allows a capacitor to program output voltage slew rate. This pin is pulled to ground with a 300Ω
MOSFET during shutdown and fault conditions; use a
series resistor if driving from a low impedance output.
SYNC/MODE (Pin 7): This pin programs four different operating modes: 1) Burst Mode operation. Tie this
pin to ground for Burst Mode operation at low output
loads—this will result in ultralow quiescent current. 2)
Forced Continuous mode (FCM). This mode offers fast
transient response and full frequency operation over a
wide load range. Float this pin for FCM. When floating, the
pin leakage current should be 3V for forced continuous mode with spread-spectrum modulation. 4)
Synchronization mode. Drive this pin with a clock source
to synchronize to an external frequency. During synchronization, the part will operate in forced continuous mode.
RT (Pin 8): Tie a resistor between RT and ground to set
the switching frequency.
BIAS (Pin 9): The internal regulator will draw current from
BIAS instead of VIN when BIAS is tied to a voltage higher
than 3.2V. For output voltages of 3.3V to 25V, 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.
If no supply is available, tie to GND.
SW (Pin 10): The SW pin is the output of the internal
power switches. Connect this pin to the inductor. This node
should be kept small on the PCB for good performance.
DNC (Pin 11): Do not connect pin. This pin should be
left floating.
GND (Pin 12, Exposed Pad Pin 13): Ground. The exposed
pad must be connected to the input capacitor’s negative
terminal and soldered to the PCB to lower the thermal
resistance.
Rev. A
For more information www.analog.com
11
LT8618/LT8618-3.3/LT8618C
BLOCK DIAGRAM
VIN
10
VIN
BIAS
CIN
R3
9
INTERNAL 0.778V REF
+
–
1V
EN/UV
–
+
SHDN
3
3.4V
REG
INTVCC
SLOPE COMP
4
R4
CINTVCC
RT
5
8
RT
ERROR
AMP
±7.5%
PG
+
+
–
CSS
VC
2µA
R1
LT8618
ONLY
CBST
SW
L
VOUT
2
COUT
M2
GND
SHDN
TSD
V IN UVLO
R2
1
M1
SWITCH
LOGIC
AND
ANTISHOOT
THROUGH
BURST
DETECT
SHDN
TSD
INTVCC UVLO
VIN UVLO
TR/SS
7
BST
OSCILLATOR
200kHz TO 2.2MHz
11
LT8618-3.3
OUT
ONLY*
FB
6
6
R2
R1
8618 BDa
* R1 = 1.5M, R2 = 4.6875M
LT8618/LT8618-3.3
VIN
1
CIN
R3
(OPT)
2
R4
(OPT)
VIN
BIAS
EN/UV
1V
3
–
+
–
+
INTERNAL 0.778V REF
OSCILLATOR
200kHz TO 2.2MHz
ERROR
AMP
PG
±7.5%
+
–
VC
SHDN
TSD
INTVCC UVLO
VIN UVLO
BST
BURST
DETECT
INTVCC
2µA
CSS
6
7
RT
INTVCC
SLOPE COMP
R5
(OPT)
4
3.5V
REG
SHDN
HYST
8
9
M1
SWITCH
LOGIC
AND
ANTISHOOT
THROUGH
SW
M2
GND
TR/SS
SHDN
TSD
VIN UVLO
RT
VOUT
COUT
60k
SYNC/MODE
L
10
GND
12
13
600k
FB
R2
5
R1
LT8618C
12
Rev. A
For more information www.analog.com
LT8618/LT8618-3.3/LT8618C
OPERATION
The LT8618 family is monolithic constant frequency current mode step-down DC/DC converters. Operation is best
understood by referring to the Block Diagrams. An internal oscillator turns on the integrated 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
FB pin with an internal 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 the inductor current falls to zero.
If overload conditions result in excess current flowing
through the bottom switch, the next clock cycle will be
delayed until switch current returns to a safe level.
To optimize efficiency, the LT8618 enters Burst Mode
operation during 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 with a 48V input, 2.5µA will be
consumed from the input supply when regulating with
no load. The LT8618/LT8618-3.3 does not have a SYNC/
MODE pin and always operates in Burst Mode. The SYNC/
MODE pin (LT8618C only) is tied low to use Burst Mode
operation with a fixed burst current limit of 180mA for
improved efficiency at very light loads and can be floated
to use forced continuous mode (FCM). If a clock is applied
to the SYNC/MODE pin, the part will synchronize to an
external clock frequency and operate in FCM. The SYNC/
MODE pin may be tied high for spread spectrum modulation mode, and the LT8618C will operate like FCM but vary
the clock frequency to reduce EMI.
The LT8618C can operate in forced continuous mode
(FCM) for fast transient response and full frequency
operation over a wide load range. When in FCM, the
oscillator operates continuously, and positive SW transitions are aligned to the clock. Negative inductor current
is allowed. The LT8618C can sink current from the output
and return it to the input in this mode, improving load step
transient response.
To improve efficiency across all loads, supply current to
internal circuitry is drawn from the BIAS pin when biased
at 3.2V or above. Else, the internal circuitry will draw current from VIN. The BIAS pin should be connected to VOUT
if the output is programmed to a voltage between 3.3V
and 25V.
Comparators monitoring the FB (LT8618/LT8618C) or
OUT (LT8618-3.3) pin voltage will pull the PG pin low if
the output voltage varies more than ±7.5% (typical) from
the set point or if a fault condition is present.
In the LT8618 family, the oscillator reduces its operating
frequency when the voltage at the FB (LT8618/LT8618C)
or OUT (LT8618-3.3) 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/MODE pin (LT8618C only), the
SYNC/MODE pin is floated or held DC high, the frequency
foldback is disabled, and the switching frequency will
slow down only during overcurrent conditions.
If the EN/UV pin is low, the LT8618 family is shut down
and draws 1µA from the input. When the EN/UV pin is
above 1.05V, the switching regulator becomes active.
The HYST pin (LT8618C only) provides an added degree
of flexibility for the EN/UV pin operation. This open-drain
output is pulled to ground whenever the EN/UV comparator is not tripped, signaling that the LT8618C is not in
normal operation. In applications where the EN/UV pin
is used to monitor the VIN voltage through an external
resistive divider, the HYST pin can be used to increase
the effective EN/UV comparator hysteresis.
Rev. A
For more information www.analog.com
13
LT8618/LT8618-3.3/LT8618C
APPLICATIONS INFORMATION
Achieving Ultralow Quiescent Current
To enhance efficiency at light loads, the LT8618 family
enters into 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. This is the default operation of
LT8618/LT8618-3.3. For the LT8618C, the SYNC/MODE
pin must be tied to ground. In Burst Mode operation, the
LT8618 family 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 LT8618 family consumes 1.7μA.
As the output load decreases, the frequency of single current pulses decreases (see Figure 1) and the percentage of
time the LT8618 family is in sleep mode increases, resulting in 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.
VOUT
5mV/DIV
SW
5V/DIV
IL
20mA/DIV
500µs/DIV
Figure 2. Burst Mode Operation (LT8618/LT8618-3.3)
VOUT
5mV/DIV
SW
5V/DIV
IL
100mA/DIV
500µs/DIV
2500
SWITCHING FREQUENCY (kHz)
2250
L = 33µH
VIN = 12V
VOUT = 3.3V
1750
1500
load at which the LT8618 family reaches the programmed
frequency varies based on input voltage, output voltage,
and inductor choice.
1250
1000
750
500
LT8618C
(SYNC = 0)
250
0
0
L = 47µH
VIN = 12V
VOUT = 5V
10 20 30 40 50 60 70 80 90 100
LOAD CURRENT (mA)
8618 F01
Figure 1. SW Burst Mode Frequency vs Load
While in Burst Mode operation, the current limit of the top
switch is approximately 40mA in the LT8618/LT8618-3.3
and 180mA in the LT8618C, resulting in output voltage
ripple shown in Figure 2 and Figure 3. As the 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 1. The output
14
8618 F03
Figure 3. Burst Mode Operation (LT8618C)
LT8618/LT8618-3.3
2000
8618 F02
Since the higher Burst Mode current limit of the LT8618C
leads to a higher inductor current ripple, its switching
frequency is reduced accordingly and will usually never
reach the frequency programmed by the resistor at the
RT pin over the entire load range. Use forced continuous
mode (see next section) for full frequency operation. The
LT8618C applies slope compensation even in Burst Mode
to ensure stable operation at higher load currents.
Forced Continuous Mode (LT8618C Only)
The LT8618C can operate in forced continuous mode
(FCM) for fast transient response and full frequency operation over a wide load range. When in FCM, the oscillator
operates continuously, and positive SW transitions are
aligned to the clock. Negative inductor current is allowed
Rev. A
For more information www.analog.com
LT8618/LT8618-3.3/LT8618C
APPLICATIONS INFORMATION
at light loads or under large transient conditions. The
LT8618C can sink current from the output and return it
to the input in this mode, improving load step transient
response. At light loads, FCM operation is less efficient
than Burst Mode operation or pulse-skipping mode. Still,
it may be desirable in applications where it is necessary
to keep switching harmonics out of the signal band. FCM
must be used if the output is required to sink current. To
enable FCM (LT8618C only), float the SYNC/MODE pin.
Leakage current on this pin should be 3V. In this mode, triangular frequency modulation
is used to vary the switching frequency between 100%
and approximately 120% of the value programmed by
RT. The modulation frequency is approximately 3kHz. For
example, when the LT8618C is programmed to 2MHz,
the frequency will vary from 2MHz to 2.4MHz at a 3kHz
rate. When spread-spectrum operation is selected, Burst
Mode operation is disabled, and the part will run in forced
continuous mode.
Synchronization (LT8618C only)
To synchronize the LT8618C oscillator to an external frequency, connect a square wave (with 20% to 80% duty
The LT8618C achieves very high efficiency at very light
loads when operating in Burst Mode due to its fixed top
switch current limit of 180mA in this mode. The internal VC node does not control peak inductor current but
instead the period between current pulses. Thus it does
not need to vary much to keep the output in regulation
over the entire load current range. In Forced Continuous
Mode, on the other hand, the VC node controls the peak
inductor current and thus varies widely with load current.
For a given load current, the VC node voltage required to
keep the output in regulation may differ between Burst
Mode and FCM. The error amplifier adjusts the VC node
to the new required level when switching between these
modes of operation. During this transition, the output may
experience a load current dependent transient with worstcase amplitude happening at full load. Applications that
transition between Burst Mode and FCM require a larger
output capacitor to keep output voltage transients below
acceptable limits at full load current.
Rev. A
For more information www.analog.com
15
LT8618/LT8618-3.3/LT8618C
APPLICATIONS INFORMATION
FB Resistor Network (LT8618)
The output voltage is programmed with a resistor divider
between the output and the FB pin. Choose the resistor
values according to:
⎛ V
⎞
R2 = R1⎜ OUT – 1⎟
⎝ 0.778V ⎠
1% resistors are recommended to maintain output voltage accuracy.
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)
t ON(MIN) VIN – VSW(TOP) + VSW(BOT)
)
Setting the Switching Frequency
where VIN is the typical input voltage, VOUT is the output
voltage, VSW(TOP) and VSW(BOT) are the internal switch
drops (~0.3V, ~0.13V, respectively at max load) and
tON(MIN) is the minimum top switch on-time (see Electrical
Characteristics). This equation shows that slower switching frequency is necessary to accommodate a high VIN/
VOUT ratio.
The LT8618 family 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. Table 1 shows the necessary RT value for
a desired switching frequency.
For transient operation VIN may go as high as the Abs Max
rating regardless of the RT value, however the LT8618
family will reduce switching frequency as necessary
to maintain control of inductor current to assure safe
operation.
Table 1. SW Frequency vs RT Value
The LT8618 family is capable of maximum duty cycle
approaching 100%, and the VIN to VOUT dropout is limited
by the RDS(ON) of the top switch. In this mode the LT8618
family skips switch cycles, resulting in a lower switching
frequency than programmed by RT.
The total resistance of the FB resistor divider should be
selected to be as large as possible when good low load
efficiency is desired: The resistor divider generates a
small load on the output, which should be minimized to
optimize the quiescent current at low loads.
fSW (MHz)
RT (kΩ)
0.2
221
0.3
143
0.4
110
0.5
86.6
0.6
71.5
0.7
60.4
0.8
52.3
0.9
46.4
1.0
40.2
1.2
33.2
1.4
27.4
1.6
23.7
1.8
20.5
2.0
18.2
2.2
16.2
For applications that cannot allow deviation from the programmed switching frequency at low VIN/VOUT ratios, use
the following formula to set switching frequency:
Operating Frequency Selection and Trade-Offs
Selection of the operating frequency is a trade-off
between efficiency, component size, and input voltage
16
VIN(MIN) =
VOUT + VSW(BOT)
1– fSW • t OFF(MIN)
– VSW(BOT) + VSW(TOP)
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, ~0.13V,
respectively at max load), fSW is the switching frequency
(set by RT), and tOFF(MIN) is the minimum switch offtime. Note that higher switching frequency will increase
the minimum input voltage below which cycles will be
dropped to achieve higher duty cycle.
Rev. A
For more information www.analog.com
LT8618/LT8618-3.3/LT8618C
APPLICATIONS INFORMATION
Inductor Selection and Maximum Output Current
The LT8618 family 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 LT8618 family safely tolerates
operation with a saturated inductor through the use of a
high speed peak-current mode architecture.
is a function of the switch current limit (ILIM) and the
ripple current:
VOUT + VSW(BOT)
fSW
• 19
where fSW is the switching frequency in MHz, VOUT is
the output voltage, VSW(BOT) is the bottom switch drop
(~0.13V) and L is the inductor value in μH. Using an
inductor value more than two times this calculated size
is not recommended.
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 the inductor ripple current:
∆IL
2
The peak-to-peak ripple current in the inductor can be
calculated as follows:
A good first choice for the inductor value is:
L=
IOUT(MAX) = ILIM –
ΔIL =
⎞
VOUT ⎛
V
1– OUT ⎟
⎜
L • fSW ⎝ VIN(MAX) ⎠
where fSW is the switching frequency, and L is the value
of the inductor. Therefore, the maximum output current
that the LT8618 family 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.
For more information about maximum output current and
discontinuous operation, see Analog Devices Application
Note 44.
Finally, for duty cycles greater than 50%, a minimum
inductance is required to avoid sub-harmonic oscillation:
1
IL(PEAK) = ILOAD(MAX) + ∆ L
2
where ∆IL is the inductor ripple current as calculated several paragraphs below and ILOAD(MAX) is the maximum
output load for a given application.
As a quick example, an application requiring 100mA output should use an inductor with an RMS rating of greater
than 100mA and an ISAT of greater than 160mA. To keep
the efficiency high, the series resistance (DCR) should be
less than 1Ω, and the core material should be intended
for high frequency applications.
The LT8618 family 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 150mA
at low duty cycles and decreases linearly to 120mA at D =
0.8. The inductor value must then be sufficient to supply
the desired maximum output current (IOUT(MAX)), which
L MIN =
VOUT + VSW(BOT)
0.08 • fSW
where fSW is the switching frequency, VOUT is the output
voltage, VSW(BOT) is the bottom switch drop (~0.13V) and
LMIN is the inductor value.
Input Capacitor
Bypass the input of the LT8618 family circuit with a
ceramic capacitor of X7R or X5R type. Y5V types have
poor performance over temperature and applied voltage,
and should not be used. A 1μF to 2.2μF ceramic capacitor
is adequate to bypass the LT8618 family and will easily
handle the ripple current. 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.
Rev. A
For more information www.analog.com
17
LT8618/LT8618-3.3/LT8618C
APPLICATIONS INFORMATION
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 LT8618 family and to force this very high frequency
switching current into a tight local loop, minimizing EMI.
A 1μF capacitor is capable of this task, but only if it is
placed close to the LT8618 family (see the PCB Layout
section). A second precaution regarding the ceramic input
capacitor concerns the maximum input voltage rating
of the LT8618 family. A ceramic input capacitor combined with trace or cable inductance forms a high quality
(under damped) tank circuit. If the LT8618 family circuit
is plugged into a live supply, the input voltage can ring to
twice its nominal value, possibly exceeding the LT8618
family’s voltage rating. This situation is easily avoided
(see Analog Devices 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 LT8618 family 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 LT8618 family’s control loop. Ceramic
capacitors have very low equivalent series resistance
(ESR) and provide the best ripple performance. A good
starting value is:
C OUT =
50
VOUT • fSW
where fSW is the switching frequency in MHz, VOUT is
the output voltage, and COUT is the recommended output
capacitance in μF. 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. Due to its larger burst mode current limit, the
LT8618C requires a larger COUT for low output voltage ripple. A lower value of output capacitor can be used to save
space and cost but transient performance will suffer and
18
may cause loop instability. See the Typical Applications
in this data sheet for suggested capacitor values. The
LT8618‑3.3 has an internal feedforward capacitor and
therefore requires a minimum COUT of 22μF.
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 LT8618 family due to their piezoelectric nature. When in Burst Mode operation, the
LT8618 family’s switching frequency depends on the
load current, and at very light loads the LT8618 family can excite the ceramic capacitor at audio frequencies, generating audible noise. Since the LT8618 family operates at a lower current limit during Burst Mode
operation, the noise is typically very quiet. If this is unacceptable, use a high performance tantalum or electrolytic
capacitor at the output.
A final precaution regarding ceramic capacitors concerns
the maximum input voltage rating of the LT8618 family.
As previously mentioned, a ceramic input capacitor combined with trace or cable inductance forms a high quality
(under damped) tank circuit. If the LT8618 family circuit
is plugged into a live supply, the input voltage can ring to
twice its nominal value, possibly exceeding the LT8618
family’s rating. This situation is easily avoided (see Analog
Devices Application Note 88).
EN/UV Pin and Programmable Hysteresis of LT8618C
The LT8618 family is in shutdown when the EN/UV pin is
low and active when the pin is high. The rising threshold
of the EN/UV comparator is 1.05V, with 50mV of hysteresis. The EN/UV 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/UV programs
the LT8618 family to regulate the output only when VIN
Rev. A
For more information www.analog.com
LT8618/LT8618-3.3/LT8618C
APPLICATIONS INFORMATION
is above a desired voltage (see Block Diagram). Typically,
this threshold, VIN(EN/UV), 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/UV) 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:
⎛ VIN(EN/UV) ⎞
R3 = ⎜
– 1⎟ •R4
⎝ 1.05V
⎠
where the LT8618 family will remain off until VIN is above
VIN(EN/UV). Due to the comparator’s hysteresis, switching
will not stop until the input falls slightly below VIN(EN/UV).
Additional hysteresis may be added with the use of the
HYST pin (LT8618C only). The HYST pin is an open-drain
output that is pulled to ground whenever the EN/UV pin
voltage is below the threshold that keeps the part in shutdown. As shown in the Block Diagram, a simple resistive
divider can be used to meet specific operating VIN voltage
requirements.
Specific values for these UVLO thresholds can be computed from the following equations:
⎛ R3 ⎞
VIN(EN/UV)↑ =1.05V ⎜ 1+ ⎟
⎝ R4 ⎠
R3 ⎞
⎛
VIN(EN/UV)↓ =1V ⎜ 1+
⎝ R4+R5 ⎟⎠
where VIN(EN/UV)↑ is the rising VIN UVLO threshold and
VIN(EN/UV)↓ is the falling VIN UVLO threshold. The hysteresis VIN(EN/UV)H = VIN(EN/UV)↑ – VIN(EN/UV)↓ is set by R5:
R5=
R3
VIN(EN/UV)H
R3
1.05 +0.05 –
R4
1V
– R4
The minimum value of these UVLO thresholds is limited to
the internal minimum VIN Voltage shown in the Electrical
Characteristics table. Be aware that the HYST pin cannot
be allowed to exceed its absolute maximum rating of 12V.
To keep the voltage on the HYST pin from exceeding 12V,
the following relation should be satisfied:
R5
⎛
⎞
VIN(MAX) • ⎜
≤ 12V
⎝ R3+R4+R5 ⎟⎠
When in Burst Mode operation for light-load currents,
the current through the VIN(EN/UV) resistor network can
easily be greater than the supply current consumed by the
LT8618 family. Therefore, the VIN(EN/UV) 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. INTVCC can supply enough current
for the LT8618 family’s circuitry. Good bypassing is necessary to supply the high transient currents required by
the power MOSFET gate drivers. Therefore, the INTVCC pin
of the LT8618/LT8618-3.3 must be bypassed to ground
with a ceramic capacitor of at least 1μF. The LT8618C
does not have an INTVCC pin but provides an on-package
capacitor as an internal bypass. To improve efficiency,
the internal LDO can also draw current from the BIAS
pin when the BIAS pin is at 3.2V or higher. Typically, the
BIAS pin can be tied to the output of the LT8618 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 LT8618 family allows the user to program its output
voltage ramp rate by means of the TR/SS pin. An internal
Rev. A
For more information www.analog.com
19
LT8618/LT8618-3.3/LT8618C
APPLICATIONS INFORMATION
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 0.778V, the TR/SS voltage will override the
internal 0.778V reference input to the error amplifier, thus
regulating the FB pin voltage to that of TR/SS pin. When
TR/SS is above 0.778V, tracking is disabled and the feedback voltage will regulate to the internal reference voltage.
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.
the LT8618 family to individual applications and limiting
thermal dissipation during short circuit conditions.
There is another situation to consider in systems where
the output will be held high when the input to the LT8618
family 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 LT8618 family’s
output. If the VIN pin is allowed to float and the EN/UV pin
is held high (either by a logic signal or because it is tied to
VIN), then the LT8618 family’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/UV pin is grounded the SW pin current will drop to
near 0.7µA. However, if the VIN pin is grounded while the
D1
VIN
LT8618
EN/UV
Output Power Good
GND
8618 F04
When the LT8618 family’s output voltage is within the
±7.5% window of the regulation point, which is a VFB
voltage in the range of 0.720V to 0.836V (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 drain pulldown device will pull the PG pin low. To prevent glitching both the upper and lower thresholds include 0.5% 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, or thermal shutdown.
Shorted and Reversed Input Protection
The LT8618 family 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. This allows for tailoring
20
VIN
Figure 4. Reverse VIN Protection
output is held high, regardless of EN/UV, parasitic body
diodes inside the LT8618 family can pull current from the
output through the SW pin and the VIN pin. Figure 4 shows
a connection of the VIN and EN/UV pins that will allow the
LT8618 family to run only when the input voltage is present and that protects against a shorted or reversed input.
PCB Layout
For proper operation and minimum EMI, care must be
taken during printed circuit board layout. Figure 5 shows
the recommended component placement with trace,
ground plane and via locations. Note that large, switched
currents flow in the LT8618 family’s VIN pins, GND pins,
and the input capacitor (CIN). The loop formed by the
input capacitor should be as small as possible by placing
the capacitor adjacent to the VIN and GND 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 GND pins plus
a larger capacitor further away is preferred. These components, along with the inductor and output capacitor,
Rev. A
For more information www.analog.com
LT8618/LT8618-3.3/LT8618C
APPLICATIONS INFORMATION
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. In addition, keep the FB and RT nodes small so that the ground
traces will shield them from the SW and BOOST nodes.
Finally, route the LT8618C’s SYNC node below the ground
plane in order to minimize capacitive coupling to the FB
and TR/SS 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 near the LT8618 family to additional ground planes
within the circuit board and on the bottom side. Figure 5
and Figure 6 show basic guidelines for layout examples
that can pass the CISPR25 radiated emission test with
class 5 limits.
COUT
VOUT
GND
COUT
VIN
VOUT
CIN
CBST
L
CIN
L
2
BIAS
3
INTVCC
10
9
EN/UV
8
PG
4
7
TR/SS
RT 5
6
FB
11
VIN
1
EN/UV 2
R1
8 RT
5
6
TR/SS
GND
10 SW
9 BIAS
13
HYST 3
PG 4
LT8618C
12 11
FB
GND
CINTVCC
1
GND
BST
SW
LT8618
7 SYNC
RT
R2
CPL
VOUT
VIAS
C PL
Figure 5. LT8618/LT8618-3.3, Recommended PCB Layout
R1
RT
GND
VOUT
8618 F05
R2
8618 F06
VIAS
Figure 6. LT8618C, Recommended PCB Layout
Rev. A
For more information www.analog.com
21
LT8618/LT8618-3.3/LT8618C
TYPICAL APPLICATIONS
Typical Performance Minimum
Load to Full Frequency
3.3V Step-Down Converter
60
C1
47nF
VIN
C2
1µF
BST
EN/UV
50
L1
120µH
SW
R2
100k
LT8618-3.3
INTVCC
C3
1µF
C4
10nF
VOUT
3.3V
100mA
POWER
GOOD
PG
TR/SS
BIAS
RT
OUT
INPUT VOLTAGE (V)
VIN
4.2V TO 60V
40
30
FULL FREQUENCY
20
10
C5
22µF
X7R
1206
16V
GND
R1
110k
8618 TA03a
fSW = 400kHz
0
8618 TA03b
Typical Performance Minimum
Load to Full Frequency
60
C1
47nF
VIN
BST
EN/UV
SW
INTVCC
C4
10nF
VOUT
3.3V
100mA
R2
100k
LT8618-3.3
C3
1µF
50
L1
33µH
POWER
GOOD
PG
TR/SS
BIAS
INPUT VOLTAGE (V)
C2
1µF
10 20 30 40 50 60 70 80 90 100
LOAD CURRENT (mA)
L1: LPS5030-124MR
3.3V, 2MHz Step-Down Converter
VIN
4.2V TO 60V
0
40
30
FULL FREQUENCY
20
10
RT
OUT
C5
22µF
X7R
1206
16V
GND
R1
18.2k
8618 TA04a
fSW = 2MHz
0
0
10 20 30 40 50 60 70 80 90 100
LOAD CURRENT (mA)
8618 TA04b
L1: WE-LQS 3012
Typical Performance Minimum
Load to Full Frequency
5V, 2MHz Step-Down Converter
60
C1
47nF
C2
1µF
VIN
BST
EN/UV
SW
50
L1
47µH
R2
100k
LT8618
INTVCC
C3
1µF
C4
10nF
PG
TR/SS
fSW = 2MHz
22
POWER
GOOD
40
30
FULL FREQUENCY
20
BIAS
RT
R1
18.2k
VOUT
5V
100mA
INPUT VOLTAGE (V)
VIN
5.8V TO 60V
FB
GND
8618 TA05a
10
R3
1MΩ
C5
4.7µF
X7R
1210
16V
R4
187k
0
0
10 20 30 40 50 60 70 80 90 100
LOAD CURRENT (mA)
8618 TA05b
L1: LPS5030-473MR
Rev. A
For more information www.analog.com
LT8618/LT8618-3.3/LT8618C
TYPICAL APPLICATIONS
Typical Performance Minimum
Load to Full Frequency
1.8V Step-Down Converter
60
C1
47nF
VIN
C2
1µF
BST
EN/UV
50
L1
47µH
SW
R2
100k
LT8618
INTVCC
C3
1µF
PG
TR/SS
C4
10nF
R3
1MΩ
FB
VOUT
1.8V
100mA
INPUT VOLTAGE (V)
VIN
3.4V TO 60V
POWER
GOOD
40
30
FULL FREQUENCY
20
10
RT
R4
768k
BIAS
GND
R1
60.4k
C5
22µF
X7R
1210
16V
8618 TA06a
fSW = 700kHz
0
L1: WE-LQS 3012
Typical Performance Minimum
Load to Full Frequency
60
C1
47nF
R5
11MΩ
VIN
BST
EN/UV
SW
50
L1
220µH
R2
100k
LT8618
INTVCC
C3
1µF
C4
10nF
R6
500k
PG
TR/SS
POWER
GOOD
BIAS
RT
R1
40.2k
VOUT
12V
100mA
INPUT VOLTAGE (V)
C2
1µF
FB
GND
C5
2.2µF
X7R
1206
50V
R4
102k
8618 TA07a
40
30
FULL FREQUENCY
20
10
R3
1.47MΩ
fSW = 1MHz
0
60
C1
47nF
BST
EN/UV
SW
R2
100k
LT8618
INTVCC
C3
1µF
C4
10nF
PG
TR/SS
C6, 330pF
VOUT
1.8V
100mA
POWER
GOOD
FB
BIAS
GND
C5
200µF
X7R
1206
6.3V
R4
768k
8618 TA08a
fSW = 400kHz
40
30
FULL FREQUENCY
20
10
R3, 1MΩ
RT
R1
110k
50
L1
47µH
INPUT VOLTAGE (V)
VIN
10 20 30 40 50 60 70 80 90 100
LOAD CURRENT (mA)
Typical Performance Minimum
Load to Full Frequency
1.8V Step-Down Converter with Large Output Capacitor
C2
1µF
R5 SHORTED
0
8618 TA07b
L1: WE-LQS 4025
VIN
3.4V TO 60V
10 20 30 40 50 60 70 80 90 100
LOAD CURRENT (mA)
8618 TA06b
12V Step-Down Converter with Undervoltage Lockout
VIN
23V
TO 60V
0
0
0
10 20 30 40 50 60 70 80 90 100
LOAD CURRENT (mA)
8618 TA08b
L1: WE-LQS 3012
Rev. A
For more information www.analog.com
23
LT8618/LT8618-3.3/LT8618C
TYPICAL APPLICATIONS
5V, 2MHz Step-Down Converter
VIN
5.8V TO 60V
L1
47µH
VIN
C1
1µF
R2
100k
EN/UV
SYNC
SYNC
POWER
GOOD
PG
LT8618C
TR/SS
C2
10nF
VOUT
5V
100mA
SW
BIAS
RT
R3
1M
FB
GND
R1
18.2k
C3
22µF
X7R
16V
R4
187k
fSW = 2MHz
L1: LPS5030-473MR
8618 TA09
3.3V, 400kHz Step-Down Converter
L1
120µH
VIN
4.2V TO 60V
VIN
C1
1µF
SW
R2
100k
EN/UV
SYNC
SYNC
TR/SS
C2
10nF
POWER
GOOD
PG
LT8618C
C3
1nF
BIAS
RT
FB
GND
R1
110k
VOUT
3.3V
100mA
R4
392k
R3
1.27M
fSW = 400kHz
C4
47µF
X5R
16V
L1: LPS5030-124MR
C5
47µF
X5R
16V
8618 TA10
24V, 2.2MHz Step-Down Converter
VIN
4.2V TO 60V
L1
220µH
D1
VIN
C1
1µF
EN/UV
SYNC
SYNC
C2
10nF
LT8618C
TR/SS
PG
C3
33pF
BIAS
RT
R1
16.2k
FB
GND
R4
187k
R3
5.62M
fSW = 2.2MHz
C4
10µF
50V
2220/X7R
C5
10µF
50V
2220/X7R
C6
10µF
50V
2220/X7R
(EFFECTIVE CAPACITANCE OF 22µF)
D1: OPTIONAL PROTECTION
AGAINST VIN TRANSIENTS
24
VOUT
24V
100mA
SW
L1: WE-LQFS 4828
8618 TA11
Rev. A
For more information www.analog.com
LT8618/LT8618-3.3/LT8618C
PACKAGE DESCRIPTION
DDB Package
10-Lead Plastic DFN (3mm × 2mm)
(Reference LTC DWG # 05-08-1722 Rev Ø)
0.64 ±0.05
(2 SIDES)
0.70 ±0.05
2.55 ±0.05
1.15 ±0.05
PACKAGE
OUTLINE
0.25 ±0.05
0.50 BSC
2.39 ±0.05
(2 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
3.00 ±0.10
(2 SIDES)
R = 0.05
TYP
R = 0.115
TYP
6
0.40 ±0.10
10
2.00 ±0.10
(2 SIDES)
PIN 1 BAR
TOP MARK
(SEE NOTE 6)
0.200 REF
0.75 ±0.05
0 – 0.05
0.64 ±0.05
(2 SIDES)
5
0.25 ±0.05
PIN 1
R = 0.20 OR
0.25 × 45°
CHAMFER
1
(DDB10) DFN 0905 REV Ø
0.50 BSC
2.39 ±0.05
(2 SIDES)
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING CONFORMS TO VERSION (WECD-1) IN JEDEC PACKAGE OUTLINE M0-229
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE
Rev. A
For more information www.analog.com
25
For more information www.analog.com
0.70 ±0.05
2.50 ±0.05
0.25 ±0.05
5
0.70
SUGGESTED PCB LAYOUT
TOP VIEW
2.50 ±0.05
0.70
0.0000
aaa Z
2×
D
PACKAGE TOP VIEW
0.2500
PIN 1
CORNER
0.2500
X
aaa Z
// bbb Z
0.7500
0.2500
0.0000
0.2500
0.7500
PACKAGE
OUTLINE
Y
E
2×
Z
H1
MIN
0.65
0.01
0.30
0.22
DETAIL C
SUBSTRATE
SYMBOL
A
A1
L
b
D
E
D1
E1
e
H1
H2
aaa
bbb
ccc
ddd
eee
fff
DETAIL B
H2
MOLD
CAP
NOM
0.74
0.02
0.40
0.25
2.00
2.00
0.70
0.70
0.50
0.24 REF
0.50 REF
DIMENSIONS
12b
eee M Z X Y
fff M Z
DETAIL C
A1
12×
0.10
0.10
0.10
0.10
0.15
0.08
MAX
0.83
0.03
0.50
0.28
e/2
e
L
SUBSTRATE THK
MOLD CAP HT
NOTES
DETAIL A
DETAIL B
A
(Reference LTC DWG # 05-08-1530 Rev B)
ddd Z
Z
26
e
7
6
D1
e
0.250
5
DETAIL A
PACKAGE BOTTOM VIEW
6
11
b
12
4
1
PIN 1 NOTCH
0.14 × 45°
4
SEE NOTES
DETAILS OF PIN 1 IDENTIFIER ARE OPTIONAL, BUT MUST BE
LOCATED WITHIN THE ZONE INDICATED. THE PIN 1 IDENTIFIER
MAY BE EITHER A MOLD OR MARKED FEATURE
THE EXPOSED HEAT FEATURE MAY HAVE OPTIONAL CORNER RADII
5
6
LQFN 12 0618 REV B
METAL FEATURES UNDER THE SOLDER MASK OPENING NOT SHOWN
SO AS NOT TO OBSCURE THESE TERMINALS AND HEAT FEATURES
4
3. PRIMARY DATUM -Z- IS SEATING PLANE
2. ALL DIMENSIONS ARE IN MILLIMETERS
NOTES:
1. DIMENSIONING AND TOLERANCING PER ASME Y14.5M-1994
E1
b 10
ccc M Z X Y
ccc M Z X Y
LQFN Package
12-Lead (2mm × 2mm × 0.74mm)
LT8618/LT8618-3.3/LT8618C
PACKAGE DESCRIPTION
Rev. A
LT8618/LT8618-3.3/LT8618C
REVISION HISTORY
REV
DATE
DESCRIPTION
A
11/21
Update to Features and Description.
1
Addition of LQFN package option and grade option for DFN package.
2
Addition of electrical characteristics for LQFN package.
PAGE NUMBER
4
Addition of performance characteristics for LQFN package.
4-9
Addition of block diagram for LQFN package.
12
Addition of PCB layout for LQFN package.
21
Addition of typical applications for LQFN package.
Updates to text.
24
10, 13-22
Rev. A
Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog
Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications
subject to change without notice. No license For
is granted
implication or
otherwise under any patent or patent rights of Analog Devices.
more by
information
www.analog.com
27
LT8618/LT8618-3.3/LT8618C
TYPICAL APPLICATION
2.5V Step-Down Converter
Typical Performance Minimum
Load to Full Frequency
C1
47nF
C2
1µF
VIN
BST
EN/UV
SW
60
L1
100µH
R2
100k
LT8618
C3
1µF
C4
10nF
INTVCC
PG
TR/SS
FB
RT
R1
110k
VOUT
2.5V
100mA
BIAS
POWER
GOOD
R3
1.47MΩ
R4
665k
GND
8618 TA02
C5
22µF
X7R
1210
16V
50
INPUT VOLTAGE (V)
VIN
3.4V TO 60V
40
30
FULL FREQUENCY
20
10
0
fSW = 400kHz
0
10 20 30 40 50 60 70 80 90 100
LOAD CURRENT (mA)
8618 TA02b
L1: WE-LQS 4025
RELATED PARTS
PART NUMBER DESCRIPTION
COMMENTS
LT8604/
LT8604C
42V, 120mA, 90% Efficiency, 2.2MHz Synchronous MicroPower
Step-Down DC/DC Converter with IQ = 2.5µA.
VIN = 3.2V to 42V, VOUT(MIN) = 0.778V, IQ = 2.5µA, ISD
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