LT8640S-2/LT8643S-2
42V, 6A Synchronous Step-Down Silent
Switcher with 2.5µA Quiescent Current
FEATURES
DESCRIPTION
Silent Switcher ® Architecture
n Ultralow EMI Emissions
n Optional Spread Spectrum Modulation
n High Efficiency at High Frequency
n Up to 96% Efficiency at 1MHz, 12V to 5V
IN
OUT
n Up to 95% Efficiency at 2MHz, 12V to 5V
IN
OUT
n Wide Input Voltage Range: 3.4V to 42V
n 6A Maximum Continuous, 7A Peak Output
n Ultralow Quiescent Current Burst Mode® Operation
n 2.5µA I Regulating 12V to 3.3V
Q
IN
OUT (LT8640S-2)
n Output Ripple < 10mV
P-P
n External Compensation: Fast Transient Response
and Current Sharing (LT8643S-2)
n Fast Minimum Switch On-Time: 30ns
n Low Dropout Under All Conditions: 100mV at 1A
n Forced Continuous Mode
n Adjustable and Synchronizable: 200kHz to 3MHz
n Output Soft-Start and Tracking
n Small 24-Lead 4mm × 4mm LQFN Package
n AEC-Q100 Qualified for Automotive Applications
The LT®8640S-2/LT8643S-2 synchronous step-down
regulator features Silent Switcher architecture designed
to minimize EMI emissions while delivering high efficiency
at high switching frequencies. Peak current mode control
with a 30ns minimum on-time allows high step-down
ratios even at high switching frequencies.The LT8643S-2
has external compensation to enable current sharing and
fast transient response at high switching frequencies.
APPLICATIONS
n
n
n
Burst Mode operation enables ultralow standby current
consumption, forced continuous mode can control
frequency harmonics across the entire output load range,
or spread spectrum operation can further reduce EMI
emissions.
SYNC/
150°C
INTERNAL
PACKAGE MODE ≠ 0 VC COMP GRADE CLKOUT CAPS
Automotive and Industrial Supplies
General Purpose Step-Down
PulseInternal
Skipping
Yes
No
No
Internal
Yes
No
No
FCM
Internal
No
Yes
Yes
LQFN
FCM
External
No
Yes
Yes
LQFN
FCM
Internal
Yes
Yes
No
LQFN
FCM
External
Yes
Yes
No
LT8640
QFN
LT8640-1
QFN
FCM
LT8640S
LQFN
LT8643S
LT8640S-2
LT8643S-2
All registered trademarks and trademarks are the property of their respective owners. Protected
by U.S. patents, including 8823345.
TYPICAL APPLICATION
12VIN to 5VOUT Efficiency
5V, 6A Step-Down Converter
VIN
5.7V TO 42V
GND
VIN
BST
0.1µF
SW
3.3µH
VOUT
5V
6A
BIAS
1µF
41.2k
fSW = 1MHz
INTVCC
10pF
RT
1M
100µF
FB
GND
95
2.8
90
1µF
GND
LT8640S-2
3.2
243k
2.4
EFFICIENCY
85
2.0
80
1.6
1.2
75
POWER LOSS
POWER LOSS (W)
1µF
EN/UV
VIN
EFFICIENCY (%)
4.7µF
100
0.8
1MHz, L = 3.3µH
65
2MHz, L = 2.2µH 0.4
3MHz, L = 1µH
0
60
0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6
LOAD CURRENT (A)
70
8640s2 TA01b
8640s2 TA01a
Rev. A
Document Feedback
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1
LT8640S-2/LT8643S-2
ABSOLUTE MAXIMUM RATINGS
(Note 1)
VIN, EN/UV, PG...........................................................42V
BIAS...........................................................................25V
FB, TR/SS ...................................................................4V
SYNC/MODE Voltage ..................................................6V
Operating Junction Temperature Range (Note 2)
LT8640S-2E/LT8643S-2E................... –40°C to 125°C
LT8640S-2I/LT8643S-2I..................... –40°C to 125°C
LT8640S-2H/LT8643S-2H.................. –40°C to 150°C
Storage Temperature Range................... –65°C to 150°C
Maximum Reflow (Package Body) Temperature...... 260°C
PIN CONFIGURATION
LT8640S-2
LT8643S-2
PG
GND
TR/SS
SYNC/MODE
CLKOUT
FB
PG
VC
TR/SS
SYNC/MODE
CLKOUT
21
20
19
27
GND
28
GND
BIAS
1
INTVCC
2
GND
3
NC
4
14 VIN
VIN
5
13 VIN
VIN
6
17 EN/UV
16 GND
15 NC
7
8
9
10
11
12
LQFN PACKAGE
24-LEAD (4mm × 4mm × 0.94mm)
JEDEC BOARD: θJA = 38°C/W, θJC(PAD) = 7°C/W (NOTE 3)
DEMO BOARD: θJA = 24°C/W
EXPOSED PAD (PINS 25 TO 28) ARE GND, SHOULD BE SOLDERED TO PCB
2
18 RT
25
GND
26
GND
27
GND
28
GND
17 EN/UV
16 GND
15 NC
14 VIN
13 VIN
7
8
9
10
11
12
SW
26
GND
SW
18 RT
25
GND
SW
6
22
SW
5
23
SW
VIN
VIN
24
BST
4
19
SW
NC
20
SW
3
21
SW
GND
22
SW
2
23
SW
1
24
BST
BIAS
INTVCC
TOP VIEW
FB
TOP VIEW
LQFN PACKAGE
24-LEAD (4mm × 4mm × 0.94mm)
JEDEC BOARD: θJA = 38°C/W, θJC(PAD) = 7°C/W (NOTE 3)
DEMO BOARD: θJA = 24°C/W
EXPOSED PAD (PINS 25 TO 28) ARE GND, SHOULD BE SOLDERED TO PCB
Rev. A
For more information www.analog.com
LT8640S-2/LT8643S-2
ORDER INFORMATION
PART NUMBER
PART MARKING*
FINISH CODE
PACKAGE
TYPE**
PAD FINISH
MSL
RATING
TEMPERATURE RANGE
–40°C to 125°C
LT8640SEV-2#PBF
LT8640SIV-2#PBF
e4
LT8643SEV-2#PBF
LT8643SIV-2#PBF
–40°C to 125°C
86402
LT8640SHV-2#PBF
LQFN (Laminate Package
with QFN Footprint)
Au (RoHS)
–40°C to 150°C
3
–40°C to 125°C
86432
–40°C to 125°C
LT8643SHV-2#PBF
–40°C to 150°C
AUTOMOTIVE PRODUCTS***
LT8640SIV-2#WPBF
LT8640SHV-2#WPBF
LT8643SIV-2#WPBF
LT8643SHV-2#WPBF
–40°C to 125°C
86402
e4
LQFN (Laminate Package
with QFN Footprint)
Au (RoHS)
86432
–40°C to 150°C
3
–40°C to 125°C
–40°C to 150°C
• Contact the factory for parts specified with wider operating temperature ranges. *Pad
or ball finish code is per IPC/JEDEC J-STD-609.
• Recommended LGA and BGA PCB Assembly and Manufacturing
Procedures
• Device temperature grade is indicated by a label on the shipping container.
• LGA and BGA Package and Tray Drawings
Parts ending with PBF are RoHS and WEEE compliant. **The LT8640S-2/LT8643S-2 package has the same dimensions as a standard 4mm × 4mm QFN package.
***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
Minimum Input Voltage
VIN Quiescent Current in Shutdown
VEN/UV = 0V
LT8640S-2 VIN Quiescent Current in Sleep
(Internal Compensation)
VEN/UV = 2V, VFB > 0.97V, VSYNC = 0V
LT8643S-2 VIN Quiescent Current in Sleep
(External Compensation)
VEN/UV = 2V, VFB > 0.97V, VSYNC = 0V, VBIAS = 0V
MIN
TYP
MAX
UNITS
l
3.0
3.4
V
l
0.75
0.75
3
10
µA
µA
l
1.7
1.7
4
10
µA
µA
l
230
230
290
340
µA
µA
VEN/UV = 2V, VFB > 0.97V, VSYNC = 0V, VBIAS = 5V
19
25
µA
LT8643S-2 BIAS Quiescent Current in Sleep
VEN/UV = 2V, VFB > 0.97V, VSYNC = 0V, VBIAS = 5V
200
260
µA
LT8640S-2 VIN Current in Regulation
VOUT = 0.97V, VIN = 6V, ILOAD = 100µA, VSYNC = 0
VOUT = 0.97V, VIN = 6V, ILOAD = 1mA, VSYNC = 0
l
l
21
220
60
390
µA
µA
Feedback Reference Voltage
VIN = 6V
VIN = 6V
l
0.970
0.970
0.976
0.982
V
V
VIN = 4.0V to 36V
l
0.004
0.02
%/V
Feedback Voltage Line Regulation
Feedback Pin Input Current
VFB = 1V
LT8643S-2 Error Amp Transconductance
VC = 1.25V
0.964
0.958
–20
20
1.7
LT8643S-2 Error Amp Gain
nA
mS
260
LT8643S-2 VC Source Current
VFB = 0.77V, VC = 1.25V
350
µA
LT8643S-2 VC Sink Current
VFB = 1.17V, VC = 1.25V
350
µA
5
A/V
LT8643S-2 VC Pin to Switch Current Gain
Rev. A
For more information www.analog.com
3
LT8640S-2/LT8643S-2
ELECTRICAL
CHARACTERISTICS
The
l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C.
PARAMETER
CONDITIONS
MIN
LT8643S-2 VC Clamp Voltage
BIAS Pin Current Consumption
VBIAS = 3.3V, fSW = 2MHz
Minimum On-Time
ILOAD = 1.5A, SYNC = 0V
ILOAD = 1.5A, SYNC = 2V
l
l
Minimum Off-Time
Oscillator Frequency
RT = 221k
RT = 60.4k
RT = 18.2k
Top Power NMOS On-Resistance
ISW = 1A
l
l
l
180
665
1.8
TYP
MAX
2.6
V
14
mA
30
30
50
45
ns
ns
80
110
ns
210
700
1.95
240
735
2.1
kHz
kHz
MHz
66
Top Power NMOS Current Limit
l
Bottom Power NMOS On-Resistance
VINTVCC = 3.4V, ISW = 1A
SW Leakage Current
VIN = 42V, VSW = 0V, 42V
EN/UV Pin Threshold
EN/UV Rising
7.5
10
mΩ
12.5
27
–1.5
l
0.94
EN/UV Pin Hysteresis
1.0
VEN/UV = 2V
PG Upper Threshold Offset from VFB
PG Lower Threshold Offset from VFB
–20
A
mΩ
1.5
1.06
40
EN/UV Pin Current
UNITS
µA
V
mV
20
nA
VFB Falling
l
5
7.5
10.25
%
VFB Rising
l
–5.25
–8
–10.75
%
40
nA
700
2000
Ω
0.9
1.2
2.55
1.4
2.9
V
V
V
PG Hysteresis
0.2
–40
%
PG Leakage
VPG = 3.3V
PG Pull-Down Resistance
VPG = 0.1V
l
SYNC/MODE Threshold
SYNC/MODE DC and Clock Low Level Voltage
SYNC/MODE Clock High Level Voltage
SYNC/MODE DC High Level Voltage
l
l
l
Spread Spectrum Modulation
Frequency Range
RT = 60.4k, VSYNC = 3.3V
22
%
Spread Spectrum Modulation Frequency
VSYNC = 3.3V
3
kHz
TR/SS Source Current
l
TR/SS Pull-Down Resistance
Fault Condition, TR/SS = 0.1V
Output Sink Current in Forced Continuous
Mode
VFB = 1.01V, L = 6.8µH, RT = 60.4k
VIN to Disable Forced Continuous Mode
VIN Rising
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 LT8640-2E/LT8643E 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 LT8640-2I/LT8643I is guaranteed over the full –40°C to
125°C operating junction temperature range. The LT8640-2H/LT8643H is
guaranteed over the full –40°C to 150°C operating junction temperature
range. High junction temperatures degrade operating lifetimes. Operating
lifetime is derated at junction temperatures greater than 125°C. The junction
4
0.7
2.2
1.2
1.9
2.6
200
µA
Ω
0.25
0.6
1.1
A
35
37
39
V
temperature (TJ, in °C) is calculated from the ambient temperature (TA in
°C) and power dissipation (PD, in Watts) according to the formula:
TJ = TA + (PD • θJA)
where θJA (in °C/W) is the package thermal impedance.
Note 3: θ values determined per JEDEC 51-7, 51-12. See the Applications
Information section for information on improving the thermal resistance
and for actual temperature measurements of a demo board in typical
operating conditions.
Note 4: 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.
Rev. A
For more information www.analog.com
LT8640S-2/LT8643S-2
TYPICAL PERFORMANCE CHARACTERISTICS
12VIN to 3.3VOUT Efficiency
vs Frequency
3.2
2.4
90
80
1.6
75
1.2
POWER LOSS
1.6
75
1.2
POWER LOSS
70
3.0
2.7
90
2.4
EFFICIENCY
85
2.1
80
1.8
75
1.5
70
65
60
55
50
1.2
POWER LOSS
0
1
VIN = 12V 0.9
VIN = 24V
0.6
VIN = 36V
fSW = 1MHz 0.3
L = IHLP3232DZ-01, 2.2µH
0
2
3
4
5
6
LOAD CURRENT (A)
100
50
VIN = 12V
VIN = 24V
VIN = 36V
40
30
20
0.01
30
20
0.01
fSW = 1MHz
L = IHLP3232DZ-01, 4.7µH
0.1
1
10
100
LOAD CURRENT (mA)
1000
8640s2 G07
EFFICIENCY (%)
EFFICIENCY (%)
100
80
40
1
8640s2 G03
100
LT8643S-2 Low Load Efficiency
at 5VOUT
1
10
100
LOAD CURRENT (mA)
60
50
40
VIN = 12V
VIN = 24V
VIN = 36V
30
20
fSW = 1MHz
L = IHLP3232DZ-01, 4.7µH
0.1
70
10
0.1
1000
fSW = 1MHz
L = IHLP3232DZ–01, 4.7µH
1
10
100
LOAD CURRENT (mA)
1000
8640s2 G05
80
VIN = 12V
VIN = 24V
VIN = 36V
0
1.2
VIN = 12V 0.9
VIN = 24V
0.6
VIN = 36V
fSW = 1MHz 0.3
L = IHLP3232DZ-01, 3.3µH
0
2
3
4
5
6
LOAD CURRENT (A)
65
80
60
90
50
1.5
POWER LOSS
70
90
70
90
60
75
50
80
LT8640S-2 Low Load Efficiency at
3.3V
Efficiency
OUT at 3.3V OUT
70
1.8
55
LT8640S-2 Low Load Efficiency
at 5VOUT
OUT
8640s2 G04
100
2.1
80
60
90
EFFICIENCY (%)
95
2.4
EFFICIENCY
85
8640s2 G02
POWER LOSS (W)
EFFICIENCY (%)
100
2.0
80
8640s2 G01
Efficiency at 3.3VOUT
90
L = WE-LHMI1040 0.8
1MHz, L = 2.2µH
0.4
65
2MHz, L = 1µH
3MHz, L = 1µH
0
60
0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6
LOAD CURRENT (A)
L = WE-LHMI1040 0.8
1MHz, L = 3.3µH
65
2MHz, L = 2.2µH 0.4
3MHz, L = 1µH
0
60
0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6
LOAD CURRENT (A)
70
2.7
2.4
EFFICIENCY
85
2.8
POWER LOSS (W)
2.0
3.0
95
POWER LOSS (W)
85
100
EFFICIENCY (%)
EFFICIENCY
95
POWER LOSS (W)
EFFICIENCY (%)
90
2.8
Efficiency at 5VOUT
3.2
8640s2 G06
LT8643S-2 Low Load Efficiency at
3.3VOUT
94
92
70
60
50
40
VIN = 12V
VIN = 24V
VIN = 36V
30
fSW = 1MHz
L = IHLP3232DZ–01, 4.7µH
20
10
0.1
Efficiency vs Frequency
96
1
10
100
LOAD CURRENT (mA)
1000
8640s2 G08
EFFICIENCY (%)
95
100
EFFICIENCY (%)
100
EFFICIENCY (%)
12VIN to 5VOUT Efficiency
vs Frequency
Frequency
vs
90
88
86
84
VIN = 12V
VOUT = 3.3V
ILOAD = 2A
L = IHLP3232DZ-01, 4.7µH
82
80
0
0.5
1
1.5
2
2.5
SWITCHING FREQUENCY (MHz)
3
8640s2 G09
Rev. A
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5
LT8640S-2/LT8643S-2
TYPICAL PERFORMANCE CHARACTERISTICS
Burst Mode Operation Efficiency
vs Inductor Value (LT8640S-2)
Reference Voltage
100
VIN = 12V
VIN = 24V
85
80
75
VOUT = 5V
ILOAD = 10mA
L = IHLP3232DZ-01
70
65
1
2
3
4
5
6
INDUCTOR VALUE (µH)
977
1.02
973
971
969
967
–25
0
25
50
75
TEMPERATURE (°C)
8640s2 G10
LT8640S-2 Load Regulation
0
0.05
VOUT = 5V
VIN = 12V
VSYNC = 0V
1
2
3
4
LOAD CURRENT (A)
6
0.30
0.10
0.10
0.00
–0.10
–0.20
–0.40
1
0.02
0.00
–0.02
–0.04
VOUT = 5V
VIN = 12V
VSYNC = 0V
0
0.04
2
3
4
LOAD CURRENT (A)
5
6
–0.08
VOUT = 5V
ILOAD = 1A
–0.15
5
10
15
20 25 30 35
INPUT VOLTAGE (V)
40
45
3.0
2.5
2.0
1.5
1.0
VOUT = 3.3V
L = 4.7µH
IN REGULATION
0
5
10
15 20 25 30 35
INPUT VOLTAGE (V)
8640s2 G16
6
20 25 30 35
INPUT VOLTAGE (V)
40
45
VOUT = 5V
L = 4.7µH
IN REGULATION
200
INPUT CURRENT (µA)
INPUT CURRENT (µA)
CHANGE IN VOUT (%)
0.09
–0.12
15
225
3.5
–0.09
10
LT8643S-2 No-Load Supply
Current
4.0
–0.06
5
8640s2 G15
0.12
0
VOUT = 5V
ILOAD = 1A
–0.06
8640s2 G14
0.15
125
0.06
LT8640S-2 No-Load Supply
Current
–0.03
100
0.08
0.20
LT8643S-2 Line Regulation
0.03
0
25
50
75
TEMPERATURE (°C)
LT8640S-2 Line Regulation
0.12
8640s2 G13
0.06
–25
8640s2 G12
0.40
–0.30
5
EN FALLING
0.95
–50
125
CHANGE IN VOUT (%)
CHANGE IN VOUT (%)
CHANGE IN VOUT (%)
0.05
0
100
LT8643S-2 Load Regulation
0.10
–0.15
0.98
8640s2 G11
0.15
–0.10
0.99
0.96
961
–50
8
1.00
0.97
965
963
7
EN RISING
1.01
EN THRESHOLD (V)
EFFICIENCY (%)
90
1.03
975
REFERENCE VOLTAGE (mV)
95
EN Pin Thresholds
979
40
175
150
125
100
75
50
45
8640s2 G17
25
5
10
15
20 25 30 35
INPUT VOLTAGE (V)
40
45
8640s2 G18
Rev. A
For more information www.analog.com
LT8640S-2/LT8643S-2
TYPICAL PERFORMANCE CHARACTERISTICS
Top FET Current Limit vs Duty Cycle
Top FET Current Limit
Switch Drop vs Temperature
12
11.0
150
SWITCH CURRENT = 1A
10.5
125
9.0
8.5
8.0
7.5
10
SWITCH DROP (mV)
11
9.5
CURRENT LIMIT (A)
CURRENT LIMIT (A)
10.0
5% DC
9
7.0
100
TOP SWITCH
75
50
25
BOTTOM SWITCH
6.5
6.0
0.1
0.3
0.5
DUTY CYCLE
0.7
8
–50
0.9
–25
0
25
50
75
TEMPERATURE (°C)
100
600
DROPOUT VOLTAGE (mV)
SWITCH DROP (mV)
350
300
TOP SWITCH
200
150
100
0
400
300
200
BOTTOM SWITCH
0
1
2
3
4
SWITCH CURRENT (A)
0
5
0
0.5
1
1.5 2 2.5 3 3.5
LOAD CURRENT (A)
Switching Frequency
720
710
700
690
680
670
–25
0
25
50
75
TEMPERATURE (°C)
4
4.5
20
–50
5
100
125
8640s2 G25
ILOAD = 2A
VOUT = 0.97V
fSW = 3MHz
–25
0
25
50
75
TEMPERATURE (°C)
1.2
1000
1.0
800
0.8
600
400
0
FRONT PAGE APPLICATION
VIN = 12V
VOUT = 5V
0
100
200
300
400
LOAD CURRENT (mA)
125
LT8640S-2 Soft-Start Tracking
1200
200
100
8640s2 G24
FB VOLTAGE (V)
RT = 60.4k
660
–50
28
Burst Frequency
SWITCHING FREQUENCY (kHz)
SWITCHING FREQUENCY (kHz)
730
32
8640s2 G23
8640s2 G22
740
36
24
100
50
125
Burst Mode OPERATION
FORCED CONTINUOUS MODE
40
MINIMUM ON–TIME (ns)
500
100
Minimum On-Time
44
VIN = 5V
VOUT SET TO REGULATE AT 5V
L = IHLP3232DZ-01, 1µH
450
0
25
50
75
TEMPERATURE (°C)
8640s2 G21
Dropout Voltage
Switch Drop vs Switch Current
500
400
–25
8640s2 G20
8640s2 G19
250
0
–50
125
500
600
8640s2 G26
0.6
0.4
0.2
0
0
0.2
1.0
0.4 0.6 0.8
TR/SS VOLTAGE (V)
1.2
1.4
8640s2 G27
Rev. A
For more information www.analog.com
7
LT8640S-2/LT8643S-2
TYPICAL PERFORMANCE CHARACTERISTICS
LT8643S-2 Soft-Start Tracking
2.2
1.2
0.4
1.9
1.8
1.7
1.6
0.2
0.4
0.6 0.8 1 1.2
TR/SS VOLTAGE (V)
1.4
1.6
1.4
–50
–500
–200
–25
0
25
50
75
TEMPERATURE (°C)
100
PG THRESHOLD OFFSET FROM VREF (%)
PG THRESHOLD OFFSET FROM VREF (%)
9.0
FB RISING
7.5
FB FALLING
6.5
–25
0
25
50
75
TEMPERATURE (°C)
100
125
250
–6.5
225
–7.5
FB RISING
–8.0
FB FALLING
–8.5
–9.0
75
25
–25
0
25
50
75
TEMPERATURE (°C)
100
0
0.2
125
125
8640s2 G34
3
Bias Pin Current
25
7.5
7.0
6.5
VBIAS = 5V
VOUT = 5V
ILOAD = 1A
fSW = 1MHz
6.0
100
0.6
1.4 1.8 2.2 2.6
1
SWITCHING FREQUENCY (MHz)
8640s2 G33
BIAS PIN CURRENT (mA)
INPUT VOLTAGE (V)
100
Bias Pin Current
2.6
8
125
8640s2 G32
8.0
0
25
50
75
TEMPERATURE (°C)
150
50
–10.0
–50
3.4
–25
175
–9.5
8.5
2.8
200
200
–7.0
Minimum Input Voltage
3.0
–100
0
100
FB PIN ERROR VOLTAGE (mV)
8640s2 G30
–6.0
3.6
3.2
VC = 1.25V
RT Programmed Switching
Frequency
8640s2 G31
2.4
–50
125
PG Low Thresholds
9.5
6.0
–50
–250
8640s2 G29
10.0
7.0
–125
–375
PG High Thresholds
8.0
0
1.5
8640s2 G28
8.5
125
RT PIN RESISTOR (kΩ)
0.2
250
BIAS PIN CURRENT (mA)
0
VC PIN CURRENT (µA)
0.6
375
2.0
TR/SS PIN CURRENT (µA)
FB VOLTAGE (V)
0.8
500
VSS = 0.5V
2.1
1.0
0
LT8643S-2 Error Amp Output
Current
Soft-Start Current
5.5
5
10
15
20 25 30 35
INPUT VOLTAGE (V)
40
45
8640s2 G35
20
VBIAS = 5V
VOUT = 5V
VIN = 12V
ILOAD = 1A
15
10
5
0
0.2
0.6
1
1.4 1.8 2.2 2.6
SWITCHING FREQUENCY (MHz)
3.0
8640s2 G36
Rev. A
For more information www.analog.com
LT8640S-2/LT8643S-2
TYPICAL PERFORMANCE CHARACTERISTICS
Case Temperature Rise vs 7A
Pulsed Load
Case Temperature Rise
80
90
DC2530A DEMO BOARD
VIN = 12V, fSW = 1MHz
VIN = 24V, fSW = 1MHz
VIN = 12V, fSW = 2MHz
VIN = 24V, fSW = 2MHz
60
50
40
30
20
10
0
DC2530A DEMO BOARD
VIN = 12V
VOUT = 5V
fSW = 2MHz
STANDBY LOAD = 0.25A
1kHz PULSED LOAD = 7A
80
CASE TEMPERATURE RISE (°C)
CASE TEMPERATURE RISE (°C)
70
Switching Rising Edge
70
60
VSW
2V/DIV
50
40
30
20
10
0
1
2
3
4
LOAD CURRENT (A)
5
6
0
0
0.2
0.4
0.6
0.8
DUTY CYCLE OF 7A LOAD
8640s2 G37
1
Switching Waveforms, Burst
Mode Operation
Switching Waveforms
IL
1A/DIV
IL
500mA/DIV
VSW
5V/DIV
VSW
10V/DIV
VSW
5V/DIV
500ns/DIV
8640s2 G40
8640s2 G41
5µs/DIV
FRONT PAGE APPLICATION
12VIN TO 5VOUT AT 10mA
VSYNC = 0V
FRONT PAGE APPLICATION
12VIN TO 5VOUT AT 1A
ILOAD
2A/DIV
ILOAD
2A/DIV
VOUT
100mV/DIV
VOUT
100mV/DIV
FRONT PAGE APPLICATION
2A TO 4A TRANSIENT
12VIN, 5VOUT
fSW = 2MHz
COUT = 100µF, CLEAD = 10pF
500ns/DIV
FRONT PAGE APPLICATION
36VIN TO 5VOUT AT 1A
8640s2 G42
LT8643S-2 Transient Response;
External Compensation
LT8640S-2 Transient Response;
Internal Compensation
20µs/DIV
8640s2 G39
8640s2 G38
Switching Waveforms, Full
Frequency Continuous Operation
IL
1A/DIV
2ns/DIV
VIN = 12V
ILOAD = 2A
8640s2 G43
20µs/DIV
8640s2 G44
FRONT PAGE APPLICATION
2A TO 4A TRANSIENT
12VIN, 5VOUT
fSW = 2MHz
CC = 330pF, RC = 8.45k
COUT = 100µF, CLEAD = 4.7pF
Rev. A
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9
LT8640S-2/LT8643S-2
TYPICAL PERFORMANCE CHARACTERISTICS
LT8640S-2 Transient Response;
100mA to 1.1A Transient
LT8643S-2 Transient Response;
100mA to 1.1A Transient
ILOAD
1A/DIV
ILOAD
1A/DIV
Burst Mode OPERATION
Burst Mode OPERATION
VOUT
100mV/DIV
VOUT
100mV/DIV
FCM
FCM
8640s2 G45
50µs/DIV
VIN
2V/DIV
VOUT
2V/DIV
FRONT PAGE APPLICATION
100mA TO 1.1A TRANSIENT
12VIN, 5VOUT, fSW = 1MHz
COUT = 100µF
Start-Up Dropout Performance
Start-Up Dropout Performance
VIN
VIN
VIN
2V/DIV
VOUT
100ms/DIV
2.5Ω LOAD
(2A IN REGULATION)
10
8640s2 G46
50µs/DIV
CC = 330pF, RC = 6.49k, CLEAD = 4.7pF
100mA TO 1.1A TRANSIENT
12VIN, 5VOUT, fSW = 1MHz
COUT = 100µF
VOUT
VOUT
2V/DIV
8640s2 G47
100ms/DIV
20Ω LOAD
(250mA IN REGULATION)
8640s2 G48
Rev. A
For more information www.analog.com
LT8640S-2/LT8643S-2
TYPICAL PERFORMANCE CHARACTERISTICS
Conducted
EMI Performance
Conducted EMI
Performance
60
50
AMPLITUDE (dBµV)
40
30
20
10
0
–10
–20
SPREAD SPECTRUM MODE
FIXED FREQUENCY MODE
–30
–40
0
3
6
9
12
15
18
FREQUENCY (MHz)
DC2530A DEMO BOARD USING LT8640S
(WITH EMI FILTER INSTALLED)
14V INPUT TO 5V OUTPUT AT 4A, fSW = 2MHz
21
24
27
30
8640s2 G49
Radiated EMI Performance
(CISPR25 Radiated Emission Test with Class 5 Peak Limits)
50
VERTICAL POLARIZATION
PEAK DETECTOR
45
AMPLITUDE (dBµV/m)
40
35
30
25
20
15
10
5
CLASS 5 PEAK LIMIT
SPREAD SPECTRUM MODE
FIXED FREQUENCY MODE
0
–5
0
100
200
300
400
500
600
FREQUENCY (MHz)
700
800
900
1000
8640s2 G50a
50
HORIZONTAL POLARIZATION
PEAK DETECTOR
45
AMPLITUDE (dBµV/m)
40
35
30
25
20
15
10
5
CLASS 5 PEAK LIMIT
SPREAD SPECTRUM MODE
FIXED FREQUENCY MODE
0
–5
0
100
200
300
400
500
600
FREQUENCY (MHz)
DC2530A DEMO BOARD USING LT8640S
(WITH EMI FILTER INSTALLED)
14V INPUT TO 5V OUTPUT AT 4A, fSW = 2MHz
700
800
900
1000
8640s2 G50b
Rev. A
For more information www.analog.com
11
LT8640S-2/LT8643S-2
PIN FUNCTIONS
BIAS (Pin 1): 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 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. However, especially
for high input or high frequency applications, BIAS should
be tied to output or an external supply of 3.3V or above.
INTVCC (Pin 2): 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 BIAS > 3.1V,
otherwise current will be drawn from VIN. Voltage on
INTVCC will vary between 2.8V and 3.4V when BIAS is
between 3.0V and 3.6V. Place a low ESR ceramic capacitor of at least 1µF from this pin to ground close to the IC.
GND (Pins 3, 16, Exposed Pad Pins 25–28): Ground.
Place the negative terminal of the input capacitor as close
to the GND pins as possible. The exposed pads should
be soldered to the PCB for good thermal performance. If
necessary due to manufacturing limitations Pins 25 to 28
may be left disconnected, however thermal performance
will be degraded.
NC (Pins 4, 15): No Connect. This pin is not connected
to internal circuitry and can be tied anywhere on the PCB,
typically ground.
VIN (Pins 5, 6, 13, 14): The VIN pins supply current to
the LT8640S-2/LT8643S-2 internal circuitry and to the
internal topside power switch. The LT8640S-2/LT8643S-2
requires the use of multiple VIN bypass capacitors. Two
small 1µF capacitors should be placed as close as possible to the LT8640S-2/LT8643S-2, one capacitor on each
side of the device (CIN1, CIN2). A third capacitor with a
larger value, 2.2µF or higher, should be placed near CIN1
or CIN2. See Applications Information section for sample
layout.
BST (Pin 7): 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.
12
SW (Pins 8–12): The SW pins are the outputs of the internal power switches. Tie these pins together and connect
them to the inductor. This node should be kept small on
the PCB for good performance and low EMI.
EN/UV (Pin 17): The LT8640S-2/LT8643S-2 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 LT8640S-2/
LT8643S-2 will shut down.
RT (Pin 18): A resistor is tied between RT and ground to
set the switching frequency.
CLKOUT (Pin 19): In forced continuous mode, spread
spectrum, and synchronization modes, the CLKOUT pin
will provide a ~200ns wide pulse at the switch frequency.
The low and high levels of the CLKOUT pin are ground and
INTVCC respectively, and the drive strength of the CLKOUT
pin is several hundred ohms. In Burst Mode operation,
the CLKOUT pin will be low. Float this pin if the CLKOUT
function is not used.
SYNC/MODE (Pin 20): For the LT8640S-2/LT8643S-2, 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,
pin leakage currents should be 3.1V
OR GND
VOUT
1.8V
6A
10pF
866k
FB
1M
GND
100µF
1210
X5R/X7R
8640s2 TA02
fSW = 2MHz
L: XEL6030
PINS NOT USED IN THIS CIRCUIT:
CLKOUT, PG, SYNC/MODE
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DESCRIPTION
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LT8610A/
LT8610AB
42V, 3.5A, 96% Efficiency, 2.2MHz Synchronous MicroPower StepDown DC/DC Converter with IQ = 2.5µA
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LT8610
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30
Rev. A
05/21
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