LT8640S/LT8643S
42V, 6A Synchronous Step-Down Silent Switcher 2
with 2.5µA Quiescent Current
FEATURES
DESCRIPTION
Silent Switcher 2 Architecture
n Ultralow EMI Emissions on Any PCB
n Eliminates PCB Layout Sensitivity
n Internal Bypass Capacitors Reduce Radiated EMI
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)
n Output Ripple < 10mV
P-P
n External Compensation: Fast Transient Response
and Current Sharing (LT8643S)
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
®
n
The LT®8640S/LT8643S synchronous step-down regulator
features second generation Silent Switcher architecture
designed to minimize EMI emissions while delivering high
efficiency at high switching frequencies. This includes
the integration of bypass capacitors to optimize all the
fast current loops inside and make it easy to achieve
advertised EMI performance by reducing layout sensitivity.
This performance makes the LT8640S/LT8643S ideal for
noise-sensitive applications and environments.
Peak current mode control with a 30ns minimum on-time
allows high step-down ratios even at high switching
frequencies. The LT8643S has external compensation to
enable current sharing and fast transient response at high
switching frequencies.
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.
PACKAGE SYNC/MODE ≠ 0 VC COMP 150°C GRADE CLKOUT INTERNAL CAPS
LT8640
QFN
Pulse-Skipping
Internal
Yes
No
No
LT8640-1
QFN
FCM
Internal
Yes
No
No
LT8640S
LQFN
FCM
Internal
No
Yes
Yes
APPLICATIONS
LT8643S
LQFN
FCM
External
No
Yes
Yes
LT8640S-2
LQFN
FCM
Internal
Yes
Yes
No
Automotive and Industrial Supplies
n General Purpose Step-Down
LT8643S-2
LQFN
FCM
External
Yes
Yes
No
n
All registered trademarks and trademarks are the property of their respective owners. Protected
by U.S. patents, including 8823345.
TYPICAL APPLICATION
100
4.7µF
SW
EN/UV
BIAS
10pF
LT8640S
RT
41.2k
fSW = 1MHz
1M
100µF
FB
GND
243k
8640S TA01a
2.4
EFFICIENCY
85
2.0
80
1.6
1.2
75
POWER LOSS
POWER LOSS (W)
VIN
VOUT
5V
6A
EFFICIENCY (%)
90
3.3µH
3.2
2.8
95
5V 6A Step-Down Converter
VIN
5.7V TO 42V
12V
5VEfficiency
12VIN
toIN5VtoOUT
OUT Efficiency
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
8640S TA01b
Rev. C
Document Feedback
For more information www.analog.com
1
LT8640S/LT8643S
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)
LT8640SE/LT8643SE.......................... –40°C to 125°C
LT8640SI/LT8643SI........................... –40°C to 125°C
Storage Temperature Range................... –65°C to 150°C
Maximum Reflow (Package Body) Temperature...... 260°C
PIN CONFIGURATION
6
2
GND
3
15 NC
NC
4
14 VIN
VIN
5
13 VIN
VIN
6
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 25–28) ARE GND, SHOULD BE SOLDERED TO PCB
SYNC/MODE
CLKOUT
CLKOUT
8
TR/SS
SYNC/MODE
7
VC
TR/SS
28
GND
PG
GND
16 GND
FB
PG
27
GND
INTVCC
17 EN/UV
24
23
22
21
20
19
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
VIN
26
GND
1
SW
5
25
GND
BIAS
SW
VIN
18 RT
SW
4
19
TOP VIEW
SW
NC
20
SW
3
21
SW
GND
22
SW
2
23
SW
INTVCC
24
SW
1
BST
BIAS
LT8643S
FB
TOP VIEW
BST
LT8640S
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 25–28) ARE GND, SHOULD BE SOLDERED TO PCB
ORDER INFORMATION
PART NUMBER
TAPE AND REEL
LT8640SEV#PBF
LT8640SEV#TRPBF
LT8640SIV#PBF
LT8640SIV#TRPBF
LT8643SEV#PBF
LT8643SEV#TRPBF
LT8643SIV#PBF
LT8643SIV#TRPBF
PAD
FINISH
PART MARKING*
DEVICE
8640S
Au(RoHS)
PACKAGE
TYPE**
FINISH CODE
MSL
RATING TEMPERATURE RANGE
e4
LQFN (Laminate Package
with QFN Footprint)
3
–40°C to 125°C
e4
LQFN (Laminate Package
with QFN Footprint)
3
–40°C to 125°C
8643S
AUTOMOTIVE PRODUCTS***
LT8640SEV#WPBF
LT8640SEV#WTRPBF
LT8640SIV#WPBF
LT8640SIV#WTRPBF
LT8643SEV#WPBF
LT8643SEV#WTRPBF
LT8643SIV#WPBF
LT8643SIV#WTRPBF
8640S
Au(RoHS)
8643S
• Contact the factory for parts specified with wider operating temperature ranges. *Pad or
ball finish code is per IPC/JEDEC J-STD-609.
• Device temperature grade is indicated by a label on the shipping container.
• Recommended LGA and BGA PCB Assembly and
Manufacturing Procedures
• LGA and BGA Package and Tray Drawings
Parts ending with PBF are RoHS and WEEE compliant. **The LT8640S/LT8643S 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.
Rev. C
2
For more information www.analog.com
LT8640S/LT8643S
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
TYP
MAX
l
MIN
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
19
25
µA
200
260
µA
21
220
60
390
µA
µA
0.970
0.970
0.976
0.982
V
V
0.004
0.02
%/V
20
nA
VEN/UV = 0V
LT8640S VIN Quiescent Current in Sleep
(Internal Compensation)
VEN/UV = 2V, VFB > 0.97V, VSYNC = 0V
LT8643S VIN Quiescent Current in Sleep
(External Compensation)
VEN/UV = 2V, VFB > 0.97V, VSYNC = 0V, VBIAS = 0V
VEN/UV = 2V, VFB > 0.97V, VSYNC = 0V, VBIAS = 5V
UNITS
LT8643S BIAS Quiescent Current in Sleep
VEN/UV = 2V, VFB > 0.97V, VSYNC = 0V, VBIAS = 5V
LT8640S VIN Current in Regulation
VOUT = 0.97V, VIN = 6V, ILOAD = 100µA, VSYNC = 0
VOUT = 0.97V, VIN = 6V, ILOAD = 1mA, VSYNC = 0
l
l
Feedback Reference Voltage
VIN = 6V
VIN = 6V
l
Feedback Voltage Line Regulation
VIN = 4.0V to 36V
l
Feedback Pin Input Current
VFB = 1V
LT8643S Error Amp Transconductance
VC = 1.25V
1.7
LT8643S VC Source Current
VFB = 0.77V, VC = 1.25V
350
µA
LT8643S VC Sink Current
VFB = 1.17V, VC = 1.25V
350
µA
5
A/V
0.964
0.958
–20
LT8643S Error Amp Gain
260
LT8643S VC Pin to Switch Current Gain
LT8643S VC Clamp Voltage
2.6
BIAS Pin Current Consumption
VBIAS = 3.3V, fSW = 2MHz
Minimum On-Time
ILOAD = 1.5A, SYNC = 0V
ILOAD = 1.5A, SYNC = 2V
Oscillator Frequency
RT = 221k
RT = 60.4k
RT = 18.2k
Top Power NMOS On-Resistance
ISW = 1A
V
14
l
l
Minimum Off-Time
l
l
l
180
665
1.8
l
7.5
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
Bottom Power NMOS On-Resistance
mS
VINTVCC = 3.4V, ISW = 1A
SW Leakage Current
VIN = 42V, VSW = 0V, 42V
EN/UV Pin Threshold
EN/UV Rising
10
mΩ
12.5
27
–1.5
l
0.94
EN/UV Pin Hysteresis
1.0
mΩ
1.5
µA
1.06
V
40
EN/UV Pin Current
VEN/UV = 2V
–20
PG Upper Threshold Offset from VFB
VFB Falling
l
5
PG Lower Threshold Offset from VFB
VFB Rising
l
–5.25
PG Hysteresis
mV
20
nA
7.5
10.25
%
–8
–10.75
%
0.2
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
–40
0.7
2.2
A
%
40
nA
700
2000
Ω
0.9
1.2
2.55
1.4
2.9
V
V
V
Rev. C
For more information www.analog.com
3
LT8640S/LT8643S
ELECTRICAL
CHARACTERISTICS
The
l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C.
PARAMETER
CONDITIONS
Spread Spectrum Modulation
Frequency Range
RT = 60.4k, VSYNC = 3.3V
Spread Spectrum Modulation Frequency
VSYNC = 3.3V
MIN
MAX
22
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
1.2
1.9
UNITS
%
3
TR/SS Source Current
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 LT8640SE/LT8643SE 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 LT8640SI/LT8643SI is guaranteed over the full –40°C to 125°C
operating junction temperature range. The junction 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.
TYP
kHz
2.6
200
µA
Ω
0.25
0.6
1.1
A
35
37
39
V
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. C
4
For more information www.analog.com
LT8640S/LT8643S
TYPICAL PERFORMANCE CHARACTERISTICS
12VIN to 5VOUT Efficiency
vs Frequency
12VIN to 3.3VOUT Efficiency
vs Frequency
2.4
90
80
1.6
1.2
POWER LOSS
80
75
1.2
POWER LOSS
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
1.6
70
8640S G01
3.0
2.7
90
2.4
EFFICIENCY
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
30
20
0.01
fSW = 1MHz
L = IHLP3232DZ-01, 4.7µH
0.1
1
10
100
LOAD CURRENT (mA)
1000
8640S G07
100
EFFICIENCY (%)
EFFICIENCY (%)
0
1
100
LT8643S Low Load Efficiency at
5VOUT
60
50
VIN = 12V
VIN = 24V
VIN = 36V
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)
LT8643S Low Load Efficiency at
3.3VOUT
Efficiency vs Frequency
96
94
92
70
60
50
40
VIN = 12V
VIN = 24V
VIN = 36V
30
fSW = 1MHz
L = IHLP3232DZ–01, 4.7µH
20
10
0.1
1000
8640 G06
8640 G05
80
40
55
8640S G03
70
20
0.01
80
VIN = 12V
VIN = 24V
VIN = 36V
60
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)
80
30
90
50
65
90
40
90
60
70
50
1.5
POWER LOSS
80
LT8640S Low Load Efficiency at
Efficiency
3.3V
OUT at 3.3V OUT
70
75
LT8640S Low Load Efficiency at
5VOUT
OUT
8640S G04
100
1.8
90
EFFICIENCY (%)
95
85
2.1
80
8640S G02
POWER LOSS (W)
EFFICIENCY (%)
100
Efficiency at 3.3VOUT
2.4
EFFICIENCY
85
EFFICIENCY (%)
75
2.0
3.0
2.7
90
2.4
EFFICIENCY
85
2.8
95
Efficiency at 5VOUT
POWER LOSS (W)
2.0
100
POWER LOSS (W)
85
3.2
1
10
100
LOAD CURRENT (mA)
1000
8640S G08
EFFICIENCY (%)
EFFICIENCY
95
POWER LOSS (W)
EFFICIENCY (%)
90
2.8
EFFICIENCY (%)
95
100
EFFICIENCY (%)
3.2
100
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
8640S G09
Rev. C
For more information www.analog.com
5
LT8640S/LT8643S
TYPICAL PERFORMANCE CHARACTERISTICS
Burst Mode Operation Efficiency
vs Inductor Value (LT8640S)
Reference Voltage
REFERENCE VOLTAGE (mV)
VIN = 12V
95
EFFICIENCY (%)
90
VIN = 24V
85
80
75
VOUT = 5V
ILOAD = 10mA
L = IHLP3232DZ-01
70
65
1
2
3
4
5
6
INDUCTOR VALUE (µH)
7
1.03
977
1.02
975
973
971
969
967
963
0.96
–25
0
25
50
75
TEMPERATURE (°C)
100
0.05
1
2
3
4
LOAD CURRENT (A)
5
6
0.12
0.30
0.10
0.10
0.00
–0.10
–0.20
0.06
0.04
0.02
0.00
–0.02
0
1
LT8643S Line Regulation
2
3
4
LOAD CURRENT (A)
5
6
–0.08
LT8640S No-Load Supply Current
–0.09
VOUT = 5V
ILOAD = 1A
–0.12
–0.15
5
10
15
20 25 30 35
INPUT VOLTAGE (V)
40
45
8640S G16
20 25 30 35
INPUT VOLTAGE (V)
3.0
2.5
2.0
1.5
1.0
40
45
VOUT = 5V
L = 4.7µH
IN REGULATION
200
INPUT CURRENT (µA)
INPUT CURRENT (µA)
CHANGE IN VOUT (%)
0.09
–0.06
15
LT8643S No-Load Supply Current
3.5
0
10
225
0.12
–0.03
5
8640S G15
4.0
0.03
VOUT = 5V
ILOAD = 1A
–0.06
8640S G14
0.15
125
–0.04
VOUT = 5V
VIN = 12V
8640S G13
0.06
100
0.08
0.20
–0.40
0
25
50
75
TEMPERATURE (°C)
LT8640S Line Regulation
0.40
–0.30
VOUT = 5V
VIN = 12V
–25
8640S G12
CHANGE IN VOUT (%)
CHANGE IN VOUT (%)
CHANGE IN VOUT (%)
0
EN FALLING
0.95
–50
125
LT8643S Load Regulation
0.10
0
0.98
0.97
LT8640S Load Regulation
–0.15
0.99
8640S G11
0.15
–0.10
1.00
965
8640S G10
0.05
EN RISING
1.01
961
–50
8
EN Pin Thresholds
979
EN THRESHOLD (V)
100
VOUT = 3.3V
L = 4.7µH
IN REGULATION
0
5
10
15 20 25 30 35
INPUT VOLTAGE (V)
40
175
150
125
100
75
50
45
8640S G17
25
5
10
15
20 25 30 35
INPUT VOLTAGE (V)
40
45
8640S G18
Rev. C
6
For more information www.analog.com
LT8640S/LT8643S
TYPICAL PERFORMANCE CHARACTERISTICS
Top FET Current Limit vs Duty Cycle
Top FET Current Limit
11.0
Switch Drop vs Temperature
150
12
SWITCH CURRENT = 1A
10.5
125
9.5
9.0
8.5
8.0
7.5
10
SWITCH DROP (mV)
11
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)
8640S G19
600
DROPOUT VOLTAGE (mV)
SWITCH DROP (mV)
TOP SWITCH
150
100
0
400
300
200
1
2
3
4
SWITCH CURRENT (A)
0
5
0
0.5
1
8640S G22
720
710
700
690
680
670
–25
0
25
50
75
TEMPERATURE (°C)
4
4.5
20
–50
5
ILOAD = 2A
VOUT = 0.97V
fSW = 3MHz
100
125
8640S G25
–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 Soft-Start Tracking
1200
200
100
8640S G24
FB VOLTAGE (V)
RT = 60.4k
660
–50
1.5 2 2.5 3 3.5
LOAD CURRENT (A)
Burst Frequency
SWITCHING FREQUENCY (kHz)
SWITCHING FREQUENCY (kHz)
730
28
8640S G23
Switching Frequency
740
32
BOTTOM SWITCH
0
125
36
24
100
50
100
Burst Mode OPERATION
FORCED CONTINUOUS MODE
40
MINIMUM ON–TIME (ns)
500
400
300
0
25
50
75
TEMPERATURE (°C)
Minimum On-Time
44
VIN = 5V
VOUT SET TO REGULATE AT 5V
L = IHLP3232DZ-01, 1µH
450
350
–25
8640S G21
Dropout Voltage
Switch Drop vs Switch Current
200
0
–50
125
8640S G20
500
250
100
500
600
8640S 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
8640S G27
Rev. C
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7
LT8640S/LT8643S
TYPICAL PERFORMANCE CHARACTERISTICS
LT8643S Soft-Start Tracking
2.2
1.2
0.6
0.4
0.2
0.2
0.4
0.6 0.8 1 1.2
TR/SS VOLTAGE (V)
1.4
1.6
2.0
1.9
1.8
1.7
1.6
PG THRESHOLD OFFSET FROM VREF (%)
PG THRESHOLD OFFSET FROM VREF (%)
9.0
FB RISING
7.5
FB FALLING
6.5
–25
–250
–500
–200
–25
0
25
50
75
TEMPERATURE (°C)
100
125
0
25
50
75
TEMPERATURE (°C)
100
125
VC = 1.25V
–100
0
100
FB PIN ERROR VOLTAGE (mV)
200
8640S G30
RT Programmed Switching
Frequency
PG Low Thresholds
9.5
6.0
–50
–125
8640S G29
10.0
7.0
0
1.4
–50
PG High Thresholds
8.0
125
–375
8640S G28
8.5
250
1.5
–6.0
250
–6.5
225
200
–7.0
–7.5
RT PIN RESISTOR (kΩ)
0
375
VC PIN CURRENT (µA)
TR/SS PIN CURRENT (µA)
FB VOLTAGE (V)
0.8
500
VSS = 0.5V
2.1
1.0
0
LT8643S Error Amp Output
Current
Soft-Start Current
FB RISING
–8.0
FB FALLING
–8.5
–9.0
175
150
125
100
75
50
–9.5
25
–10.0
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
0
0.2
125
8640S G32
8640S G31
0.6
1.4 1.8 2.2 2.6
1
SWITCHING FREQUENCY (MHz)
3
8640S G33
Bias Pin Current
3.4
8.0
3.2
3.0
2.8
2.4
–50
7.5
7.0
6.5
VBIAS = 5V
VOUT = 5V
ILOAD = 1A
fSW = 1MHz
6.0
2.6
–25
0
25
50
75
TEMPERATURE (°C)
100
125
8640S G34
Bias Pin Current
25
BIAS PIN CURRENT (mA)
8.5
BIAS PIN CURRENT (mA)
INPUT VOLTAGE (V)
Minimum Input Voltage
3.6
5.5
5
10
15
20 25 30 35
INPUT VOLTAGE (V)
40
45
8640S 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
8640S G36
Rev. C
8
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LT8640S/LT8643S
TYPICAL PERFORMANCE CHARACTERISTICS
Case Temperature Rise vs 7A
Pulsed Load
Case Temperature Rise
80
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
Switch Rising Edge
DC2530A DEMO BOARD
VIN = 12V
VOUT = 5V
fSW = 2MHz
STANDBY LOAD = 0.25A
1kHz PULSED LOAD = 7A
80
CASE TEMPERATURE RISE (°C)
70
CASE TEMPERATURE RISE (°C)
90
70
60
VSW
2V/DIV
50
40
30
20
10
0
1
2
3
4
LOAD CURRENT (A)
5
0
6
0
8640S G37
0.2
0.4
0.6
0.8
DUTY CYCLE OF 7A LOAD
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
8640S G40
FRONT PAGE APPLICATION
12VIN TO 5VOUT AT 1A
5µs/DIV
FRONT PAGE APPLICATION
12VIN TO 5VOUT AT 10mA
VSYNC = 0V
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
8640S G41
500ns/DIV
FRONT PAGE APPLICATION
36VIN TO 5VOUT AT 1A
8640S G42
LT8643S Transient Response;
External Compensation
LT8640S Transient Response;
Internal Compensation
20µs/DIV
8640S G39
8640S G38
Switching Waveforms, Full
Frequency Continuous Operation
IL
1A/DIV
2ns/DIV
VIN = 12V
ILOAD = 2A
8640S G43
20µs/DIV
8640S G44
2A TO 4A TRANSIENT
12VIN, 5VOUT
fSW = 2MHz
CC = 330pF, RC = 8.45k
COUT = 100µF, CLEAD = 4.7pF
Rev. C
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9
LT8640S/LT8643S
TYPICAL PERFORMANCE CHARACTERISTICS
LT8640S Transient Response;
100mA to 1.1A Transient
LT8643S 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
50µs/DIV
VIN
2V/DIV
VOUT
2V/DIV
8640S G45
8640S G46
FRONT PAGE APPLICATION
100mA TO 1.1A TRANSIENT
12VIN, 5VOUT, fSW = 1MHz
COUT = 100µF
50µs/DIV
CC = 330pF, RC = 6.49k, CLEAD = 4.7pF
100mA TO 1.1A TRANSIENT
12VIN, 5VOUT, fSW = 1MHz
COUT = 100µF
Start-Up Dropout Performance
Start-Up Dropout Performance
VIN
VOUT
100ms/DIV
2.5Ω LOAD
(2A IN REGULATION)
VIN
VIN
2V/DIV
VOUT
VOUT
2V/DIV
8640S G47
100ms/DIV
20Ω LOAD
(250mA IN REGULATION)
8640S G48
Rev. C
10
For more information www.analog.com
LT8640S/LT8643S
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)
21
24
27
DC2530A DEMO BOARD
(WITH EMI FILTER INSTALLED)
14V INPUT TO 5V OUTPUT AT 4A, fSW = 2MHz
30
8640S 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
8640S 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)
700
DC2530A DEMO BOARD
(WITH EMI FILTER INSTALLED)
14V INPUT TO 5V OUTPUT AT 4A, fSW = 2MHz
800
900
1000
8640S G50b
Rev. C
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11
LT8640S/LT8643S
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. This pin should be floated.
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/LT8643S internal circuitry and to the internal
topside power switch. These pins must be tied together
and be locally bypassed with a capacitor of 2.2µF or more.
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 GND pins.
BST (Pin 7): This pin is used to provide a drive voltage,
higher than the input voltage, to the topside power switch.
This pin should be floated.
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/LT8643S 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/
LT8643S 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/LT8643S,
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
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