LT8640/LT8640-1
42V, 5A Synchronous
Step-Down Silent Switcher
with 2.5µA Quiescent Current
DESCRIPTION
FEATURES
Silent Switcher® Architecture
n Ultralow EMI Emissions
n Spread Spectrum Frequency 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 5A Maximum Continuous Output, 7A Peak
Transient Output
n Ultralow Quiescent Current Burst Mode® Operation
n 2.5µA I Regulating 12V to 3.3V
Q
IN
OUT
n Output Ripple < 10mV
P-P
n Fast Minimum Switch On-Time: 30ns
n Low Dropout Under All Conditions: 100mV at 1A
n Forced Continuous Mode (LT8640-1 Only)
n Safely Tolerates Inductor Saturation in Overload
n Adjustable and Synchronizable: 200kHz to 3MHz
n Peak Current Mode Operation
n Output Soft-Start and Tracking
n Small 18-Lead 3mm × 4mm QFN and Side Wettable QFN
n AEC-Q100 Qualified for Automotive Applications
The LT®8640/LT8640-1 step-down regulator features Silent
Switcher architecture designed to minimize EMI emissions
while delivering high efficiency at frequencies up to 3MHz.
An ultralow 2.5µA quiescent current—with the output in
full regulation—enables applications requiring highest
efficiency at very small load currents.
n
The LT8640/LT8640-1 allows high VIN to low VOUT conversion
at high frequency with a fast minimum top switch on-time of
30ns. The SYNC/MODE pin selects between Burst Mode
operation, spread spectrum mode, synchronization to
an external clock, and either pulse-skipping (LT8640) or
forced continuous mode (LT8640-1).
SYNC/
150°C
INTERNAL
PACKAGE MODE ≠ 0 VC COMP GRADE CLKOUT CAPS
APPLICATIONS
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.
Automotive and Industrial Supplies
General Purpose Step-Down
n GSM Power Supplies
n
n
TYPICAL APPLICATION
12VIN to 5VOUT Efficiency
5V 5A Step-Down Converter
4.7µF
EN/UV
VIN1
GND1
PG
10nF
VIN2
GND2
LT8640/
LT8640-1 BST
SYNC/MODE
TR/SS
41.2k
fSW = 1MHz
0.1µF 3.3µH
4.7pF
INTVCC
RT
VOUT
5V
5A
47µF
243k
1.88
80
1.50
1.13
75
POWER LOSS
65
60
0.5
8640 TA01a
2.25
EFFICIENCY
85
70
1M
FB
GND
2.63
90
1µF
SW
BIAS
1µF
95
1
POWER LOSS (W)
1µF
3.00
EFFICIENCY (%)
VIN
5.5V TO 42V
100
0.75
1MHz, L = 3.3µH
2MHz, L = 2.2µH 0.38
3MHz, L = 1µH
0
1.5 2 2.5 3 3.5 4 4.5 5
LOAD CURRENT (A)
8640 TA01b
Rev. D
Document Feedback
For more information www.analog.com
1
LT8640/LT8640-1
PIN CONFIGURATION
VIN, EN/UV, PG...........................................................42V
BIAS...........................................................................25V
FB, TR/SS ...................................................................4V
SYNC/MODE Voltage ..................................................6V
Operating Junction Temperature Range (Note 2)
LT8640E/LT8640-1E........................... –40°C to 125°C
LT8640I/LT8640-1I............................. –40°C to 125°C
LT8640J/LT8640-1J............................ –40°C to 150°C
LT8640H/LT8640-1H.......................... –40°C to 150°C
Storage Temperature Range.......................–65 to 150°C
SYNC/MODE
17
PG
20 19 18
FB
GND
TOP VIEW
16 TR/SS
BIAS 1
INTVCC 2
15 RT
BST 3
21
SW
13 VIN2
11 GND2
7
8
9
10
GND2
GND1 6
14 EN/UV
SW
VIN1 4
22
SW
SW
(Note 1)
GND1
ABSOLUTE MAXIMUM RATINGS
UDC AND UDCF PACKAGES
18-LEAD (3mm × 4mm) PLASTIC QFN
θJA = 40°C/W, θJC(PAD) = 12°C/W (Note 3)
EXPOSED PAD (PINS 21, 22) ARE SW, SHOULD BE SOLDERED TO PCB
NOTE: PINS 5 AND 12 ARE REMOVED. CONFIGURATION DOES NOT MATCH
JEDEC 20-LEAD PACKAGE OUTLINE
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING* PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT8640EUDC#PBF
LT8640EUDC#TRPBF
LGNJ
18-Lead (3mm × 4mm) Plastic QFN
–40°C to 125°C
LT8640IUDC#PBF
LT8640IUDC#TRPBF
LGNJ
18-Lead (3mm × 4mm) Plastic QFN
–40°C to 125°C
LT8640HUDC#PBF
LT8640HUDC#TRPBF
LGNJ
18-Lead (3mm × 4mm) Plastic QFN
–40°C to 150°C
LT8640EUDC-1#PBF
LT8640EUDC-1#TRPBF
LGVT
18-Lead (3mm × 4mm) Plastic QFN
–40°C to 125°C
LT8640IUDC-1#PBF
LT8640IUDC-1#TRPBF
LGVT
18-Lead (3mm × 4mm) Plastic QFN
–40°C to 125°C
LT8640HUDC-1#PBF
LT8640HUDC-1#TRPBF
LGVT
18-Lead (3mm × 4mm) Plastic QFN
–40°C to 150°C
LT8640EUDCF#PBF
LT8640EUDCF#TRPBF
LHJK
18-Lead (3mm × 4mm) Plastic Side Wettable QFN
–40°C to 125°C
LT8640IUDCF#PBF
LT8640IUDCF#TRPBF
LHJK
18-Lead (3mm × 4mm) Plastic Side Wettable QFN
–40°C to 125°C
LT8640JUDCF#PBF
LT8640JUDCF#TRPBF
LHJK
18-Lead (3mm × 4mm) Plastic Side Wettable QFN
–40°C to 150°C
LT8640EUDCF-1#PBF
LT8640EUDCF-1#TRPBF
LHGX
18-Lead (3mm × 4mm) Plastic Side Wettable QFN
–40°C to 125°C
LT8640IUDCF-1#PBF
LT8640IUDCF-1#TRPBF
LHGX
18-Lead (3mm × 4mm) Plastic Side Wettable QFN
–40°C to 125°C
LT8640JUDCF-1#PBF
LT8640JUDCF-1#TRPBF
LHGX
18-Lead (3mm × 4mm) Plastic Side Wettable QFN
–40°C to 150°C
AUTOMOTIVE PRODUCTS**
LT8640JUDCF#WPBF
LT8640JUDCF#WTRPBF
LHJK
18-Lead (3mm × 4mm) Plastic Side Wettable QFN
–40°C to 150°C
LT8640JUDCF-1#WPBF
LT8640JUDCF-1#WTRPBF
LHGX
18-Lead (3mm × 4mm) Plastic Side Wettable QFN
–40°C to 150°C
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.
2
Rev. D
For more information www.analog.com
LT8640/LT8640-1
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
TYP
MAX
l
MIN
2.9
3.4
V
l
0.75
0.75
3
10
µA
µA
l
1.7
1.7
4
10
µA
µA
0.3
0.5
mA
21
220
50
350
µA
µA
0.970
0.970
0.976
0.982
V
V
0.004
0.02
%/V
VEN/UV = 0V
VEN/UV = 2V, Not Switching, VSYNC = 0V
VEN/UV = 2V, Not Switching, VSYNC = 2V (LT8640 Only)
VIN Current in Regulation
VOUT = 0.97V, VIN = 6V, Output Load = 100µA
VOUT = 0.97V, VIN = 6V, Output Load = 1mA
l
l
Feedback Reference Voltage
VIN = 6V, ILOAD = 0.5A
VIN = 6V, ILOAD = 0.5A
l
VIN = 4.0V to 42V
l
Feedback Voltage Line Regulation
Feedback Pin Input Current
VFB = 1V
BIAS Pin Current Consumption
VBIAS = 3.3V, fSW = 2MHz
Minimum On-Time
ILOAD = 1.5A, SYNC = 0V
ILOAD = 1.5A, SYNC = 3.3V
0.964
0.958
–20
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
1.85
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
35
30
50
50
ns
ns
80
110
ns
210
700
2.00
240
735
2.15
kHz
kHz
MHz
10
mΩ
12.5
28
–15
l
0.94
EN/UV Pin Hysteresis
1.0
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
mΩ
µA
1.06
V
mV
20
nA
7.5
10.25
%
–8
–10.75
%
0.2
PG Leakage
VPG = 3.3V
PG Pull-Down Resistance
VPG = 0.1V
–40
SYNC/MODE Threshold
SYNC/MODE DC and Clock Low Level Voltage
SYNC/MODE Clock High Level Voltage
SYNC/MODE DC High Level Voltage
Spread Spectrum Modulation
Frequency Range
RT = 60.4k, VSYNC = 3.3V
Spread Spectrum Modulation Frequency
VSYNC = 3.3V
l
TR/SS Source Current
0.7
1.0
2.3
Fault Condition, TR/SS = 0.1V
%
40
nA
700
2000
Ω
0.9
1.2
2.6
1.1
1.4
2.9
V
V
V
22
%
3
l
1.2
A
15
40
EN/UV Pin Current
nA
mA
67
Top Power NMOS Current Limit
TR/SS Pull-Down Resistance
20
11
UNITS
1.9
200
kHz
2.6
µA
Ω
Rev. D
For more information www.analog.com
3
LT8640/LT8640-1
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
TYP
MAX
LT8640-1 Output Sink Current in Forced
Continuous Mode
VFB = 1.01V, L = 6.8µH, RT = 60.4k
0.25
0.6
1
A
LT8640-1 VIN to Disable Forced Continuous
Mode
VIN Rising
35
37
39
V
LT8640-1 VFB Offset from Feedback
Reference Voltage to Disable Forced
Continuous Mode
VFB Rising
7
9.5
12
%
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 LT8640E/LT8640-1E 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 LT8640I/LT8640-1I is guaranteed over the full –40°C to 125°C
operating junction temperature range. The LT8640J/LT8640-1J and the
LT8640H/LT8640-1H 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 temperature (TJ, in °C) is calculated from the
4
UNITS
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 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. D
For more information www.analog.com
LT8640/LT8640-1
TYPICAL PERFORMANCE CHARACTERISTICS
12VIN to 3.3VOUT Efficiency
vs Frequency
EFFICIENCY
95
2.25
90
1.13
75
POWER LOSS
70
65
60
0.5
1
1.75
85
1.40
80
1.05
75
POWER LOSS
65
60
0.5
1
90
L = WE–LHMI1040 0.70
1MHz, L = 2.2μH
2MHz, L = 1μH 0.35
3MHz, L = 1μH
0
1.5 2 2.5 3 3.5 4 4.5 5
LOAD CURRENT (A)
8640 G01
1.8
75
70
60
55
0
0.5
Efficiency at 3.3VOUT
Efficiency at 5VOUT
90
90
80
80
2.1
70
70
1.8
75
1.5
65
60
55
50
0
0.5
1
1.2
VIN = 12V 0.9
VIN = 24V
0.6
VIN = 36V
fSW = 1MHz 0.3
L = IHLP3232DZ-01, 2.2μH
0
1.5 2 2.5 3 3.5 4 4.5 5
LOAD CURRENT (A)
100
60
50
40
fSW = 1MHz
L = IHLP3232DZ-01, 4.7μH
VIN = 12V
VIN = 24V
VIN = 36V
30
20
10
0
0.01
0.1
1
10
100
0.1
1
10
100
LOAD CURRENT (mA)
8640 G06
Reference Voltage
VIN = 12V
0.977
EFFICIENCY (%)
88
86
VIN = 12V
VOUT = 3.3V
ILOAD = 2A
L = IHLP3232DZ-01, 4.7μH
VIN = 24V
85
80
75
VOUT = 5V
ILOAD = 10mA
L = IHLP3232DZ-01
70
3
REFERENCE VOLAGE (V)
90
90
65
1000
0.979
92
EFFICIENCY (%)
0
0.01
Burst Mode Operation Efficiency
vs Inductor Value
94
2
1.5
2.5
0.5
1
SWITCHING FREQUENCY (MHz)
fSW = 1MHz
L = IHLP3232DZ-01, 4.7μH
VIN = 12V
VIN = 24V
VIN = 36V
30
10
95
0
40
8640 G05
96
82
50
LOAD CURRENT (mA)
Efficiency vs Frequency
84
60
20
1000
8640 G04
80
EFFICIENCY (%)
80
EFFICIENCY (%)
2.7
2.4
POWER LOSS (W)
95
70
1
8640 G03
90
POWER LOSS
1.2
VIN = 12V 0.9
VIN = 24V
0.6
VIN = 36V
fSW = 1MHz 0.3
L = IHLP3232DZ-01, 3.3μH
0
1.5 2 2.5 3 3.5 4 4.5 5
LOAD CURRENT (A)
65
50
1.5
POWER LOSS
100
EFFICIENCY
2.1
80
3.0
85
2.4
EFFICIENCY
85
8640 G02
Efficiency at 3.3VOUT
100
EFFICIENCY (%)
2.7
2.10
EFFICIENCY
70
L = WE–LHMI1040 0.75
1MHz, L = 3.3µH
2MHz, L = 2.2µH 0.38
3MHz, L = 1µH
0
1.5 2 2.5 3 3.5 4 4.5 5
LOAD CURRENT (A)
3.0
95
POWER LOSS (W)
1.50
80
100
2.45
POWER LOSS (W)
1.88
85
POWER LOSS (W)
EFFICIENCY (%)
90
2.63
EFFICIENCY (%)
95
Efficiency at 5VOUT
2.80
100
3.00
100
EFFICIENCY (%)
12VIN to 5VOUT Efficiency
vs Frequency
1
2
3
4
5
6
INDUCTOR VALUE (µH)
7
0.973
0.971
0.969
0.967
0.965
0.963
8
8640 G08
8640 G07
0.975
0.961
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
8640 G09
Rev. D
For more information www.analog.com
5
LT8640/LT8640-1
TYPICAL PERFORMANCE CHARACTERISTICS
EN Pin Thresholds
0.12
0.10
1.02
0.10
1.00
0.99
0.98
0.08
CHANGE IN VOUT (%)
EN RISING
1.01
CHANGE IN VOUT (%)
EN THRESHOLD (V)
Line Regulation
Load Regulation
0.15
1.03
0.05
0
–0.05
0.97
EN FALLING
0.95
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
–0.15
0.02
0
–0.04
VOUT = 5V
VIN = 12V
R1/R2 = 100k/24.3k
0
0.5
1.5 2 2.5 3 3.5
LOAD CURRENT (A)
1
4
4.5
5
–0.08
5
10
15
20 25 30 35
INPUT VOLTAGE (V)
40
45
8640 G12
Top FET Current Limit vs Duty Cycle
No-Load Supply Current
4.0
Top FET Current Limit
10.0
12.0
9.5
3.5
2.5
2.0
CURRENT LIMIT (A)
CURRENT LIMIT (A)
9.0
3.0
8.5
8.0
7.5
11.0
VOUT = 3.3V
L = 4.7µH
IN REGULATION
0
5
10
15 20 25 30 35
INPUT VOLTAGE (V)
40
5% DC
10.0
9.0
7.0
1.5
1.0
VOUT = 5V
ILOAD = 1A
R1/R2 = 100k/24.3k
–0.06
8640 G11
8640 G10
INPUT CURRENT (µA)
0.04
–0.02
–0.10
0.96
0.06
6.5
6.0
45
0
0.2
0.4
0.6
DUTY CYCLE
8640 G13
0.8
8.0
–50 –25
1
0
25 50 75 100 125 150
TEMPERATURE (°C)
8640 G14
8640 G15
Switch Drop
SWITCH CURRENT = 1A
100
TOP SWITCH
75
50
BOTTOM SWITCH
25
0
25 50 75 100 125 150
TEMPERATURE (°C)
350
300
TOP SWITCH
250
200
150
100
34
31
BOTTOM SWITCH
0
1
4
2
3
SWITCH CURRENT (A)
8640 G16
6
37
28
50
0
VSYNC = FLOAT
VSYNC = 0V
40
400
SWITCH DROP (mV)
SWITCH DROP (mV)
43
450
125
0
–50 –25
Minimum On-Time
Switch Drop
500
MINIMUM ON-TIME (ns)
150
5
25
–50
ILOAD = 2A
–25
0
25
50
75
TEMPERATURE (°C)
100
125
8640 G18
8640 G17
Rev. D
For more information www.analog.com
LT8640/LT8640-1
TYPICAL PERFORMANCE CHARACTERISTICS
Switching Frequency
Dropout Voltage
740
600
VIN = 5V
VOUT SET TO REGULATE AT 5V
L = IHLP3232DZ-01, 1µH
FRONT PAGE APPLICATION
VIN = 12V
1000 VOUT = 5V
300
200
100
SWITCHING FREQUENCY (kHz)
400
0
RT = 60.4k
730
SWITCHING FREQUENCY (kHz)
DROPOUT VOLTAGE (mV)
500
Burst Frequency
1200
720
710
700
690
680
670
0
0.5
1.5 2 2.5 3 3.5
LOAD CURRENT (A)
1
4
4.5
660
–50 –25
5
0
20
600
1.0
500
400
300
20 25
30 35
INPUT VOLTAGE (V)
40
0
45
0
0.2
0.4
0.6
FB VOLTAGE (V)
0.8
PG THRESHOLD OFFSET FROM VREF (%)
SS PIN CURRENT (µA)
1.9
1.8
1.7
1.6
1.5
25 50 75 100 125 150
TEMPERATURE (°C)
0
0.2
1.0
0.4 0.6 0.8
TR/SS VOLTAGE (V)
1.4
PG Low Thresholds
–6.0
9.5
9.0
8.5
8.0
7.5
1.2
8640 G24
PG High Thresholds
2.0
0
0
1
10.0
VSS = 0.5V
1.4
–50 –25
0.4
8640 G23
Soft-Start Current
2.1
0.6
0.2
8640 G22
2.2
0.8
200
PG THRESHOLD OFFSET FROM VREF (%)
15
400
Soft-Start Tracking
100
10
100
200
300
LOAD CURRENT (mA)
1.2
FB VOLTAGE (V)
40
0
8640 G21
VOUT = 3.3V
VIN = 12V
VSYNC = 0V
RT = 60.4k
700
SWITCHING FREQUENCY (kHz)
LOAD CURRENT (mA)
800
FRONT PAGE APPLICATION
VOUT = 5V
fSW = 1MHz
5
200
Frequency Foldback
60
0
400
8640 G20
Minimum Load to Full Frequency
(Pulse-Skipping Mode)
80
600
0
25 50 75 100 125 150
TEMPERATURE (°C)
8640 G19
100
800
FB RISING
FB FALLING
7.0
6.5
6.0
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
8640 G26
8640 G25
–6.5
–7.0
–7.5
FB RISING
–8.0
–8.5
FB FALLING
–9.0
–9.5
–10.0
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
8640 G27
Rev. D
For more information www.analog.com
7
LT8640/LT8640-1
TYPICAL PERFORMANCE CHARACTERISTICS
RT Programmed Switching
Frequency
3.6
225
8.5
3.4
200
125
100
75
BIAS PIN CURRENT (mA)
150
3.0
2.8
2.6
2.4
50
0
0.2
0.6
1.4 1.8 2.2 2.6
1
SWITCHING FREQUENCY (MHz)
2.0
–55 –25
3
95
65
35
TEMPERATURE (°C)
5
125
Bias Pin Current
80
10
5
2.6
1.4 1.8
2.2
0.6
1
SWITCHING FREQUENCY (MHz)
3
90
DC2202A DEMO BOARD
VIN = 12V, fSW = 1MHz
VIN = 24V, fSW = 1MHz
VIN = 12V, fSW = 2MHz
VIN = 24V, fSW = 2MHz
70
60
40
30
20
0
0
1
2
3
LOAD CURRENT (A)
4
5
70
60
40
45
50
40
30
20
0
0
0.2
0.4
0.6
DUTY CYCLE OF 7A LOAD
0.8
8640 G33
8640 G32
Switching Waveforms, Burst
Mode Operation
Switching Waveforms
IL
1A/DIV
VSW
10V/DIV
VSW
5V/DIV
8
20 25 30 35
INPUT VOLTAGE (V)
10
IL
500mA/DIV
8640 G34
15
DC2202A DEMO BOARD
VIN = 12V
VOUT = 5V
fSW = 2MHz
STANDBY LOAD = 0.25A
1KHz PULSED LOAD = 7A
80
50
Switching Waveforms, Full
Frequency Continuous Operation
VSW
5V/DIV
10
Case Temperature Rise vs 7A
Pulsed Load
8640 G31
IL
1A/DIV
5
8640 G30
10
500ns/DIV
FRONT PAGE APPLICATION
12VIN TO 5VOUT AT 1A
5.5
155
CASE TEMPERATURE RISE (°C)
VBIAS = 5V
VOUT = 5V
VIN = 12V
ILOAD = 1A
0
0.2
6.5
Case Temperature Rise
CASE TEMPERATURE RISE (°C)
BIAS PIN CURRENT (mA)
15
7.0
8640 G29
8640 G28
20
7.5
6.0
2.2
25
VBIAS = 5V
VOUT = 5V
ILOAD = 1A
fSW = 1MHz
8.0
3.2
175
INPUT VOLTAGE (V)
RT PIN RESISTOR (kΩ)
Bias Pin Current
VIN UVLO
250
5µs/DIV
FRONT PAGE APPLICATION
12VIN TO 5VOUT AT 10mA
VSYNC = 0V
8640 G35
500ns/DIV
FRONT PAGE APPLICATION
36VIN TO 5VOUT AT 1A
8640 G36
Rev. D
For more information www.analog.com
LT8640/LT8640-1
TYPICAL PERFORMANCE CHARACTERISTICS
Transient Response; Load Current
Stepped from 100mA (Burst Mode
Operation) to 1.1A
Transient Response; Load Current
Stepped from 1A to 2A
IL
1A/DIV
IL
1A/DIV
VOUT
100mV/DIV
VOUT
200mV/DIV
50µs/DIV
FRONT PAGE APPLICATION
1A TO 2A TRANSIENT
12VIN, 5VOUT
COUT = 47µF
50µs/DIV
FRONT PAGE APPLICATION
100mA (Burst Mode OPERATION) TO
1.1A TRANSIENT
12VIN, 5VOUT
COUT = 47µF
8640 G37
Start-Up Dropout Performance
Start-Up Dropout Performance
VIN
VIN
2V/DIV
VIN
VIN
2V/DIV
VOUT
VOUT
2V/DIV
VOUT
VOUT
2V/DIV
100ms/DIV
2.5Ω LOAD
(2A IN REGULATION)
8640 G38
100ms/DIV
20Ω LOAD
(250mA IN REGULATION)
8640 G39
8640 G40
Conducted EMI Performance
60
50
AMPLITUDE (dBµV)
40
30
20
10
0
-10
-20
FIXED FREQUENCY MODE
SPREAD SPECTRUM MODE
-30
-40
0
3
6
9
12
15
18
21
FREQUENCY (MHz)
24
27
30
8640 G41
DC2202A DEMO BOARD
(WITH EMI FILTER INSTALLED)
14V INPUT TO 5V OUTPUT AT 4A, fSW = 2MHz
Rev. D
For more information www.analog.com
9
LT8640/LT8640-1
TYPICAL PERFORMANCE CHARACTERISTICS
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
FIXED FREQUENCY MODE
SPREAD SPECTRUM MODE
0
-5
0
100
200
300
400
500
600
700
800
900
1000
FREQUENCY (MHz)
50
HORIZONTAL POLARIZATION
PEAK DETECTOR
45
AMPLITUDE (dBµV/m)
40
35
30
25
20
15
10
5
CLASS 5 PEAK LIMIT
FIXED FREQUENCY MODE
SPREAD SPECTRUM MODE
0
-5
0
100
200
300
400
500
600
700
800
900
1000
FREQUENCY (MHz)
DC2202A DEMO BOARD
(WITH EMI FILTER INSTALLED)
14V INPUT TO 5V OUTPUT AT 4A, fSW = 2MHz
10
8640 G42
Rev. D
For more information www.analog.com
LT8640/LT8640-1
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.
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. Decouple this pin to power ground with at least
a 1µF low ESR ceramic capacitor placed close to the IC.
BST (Pin 3): 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.
VIN1 (Pin 4): The LT8640/LT8640-1 requires two 1µF
small input bypass capacitors. One 1µF capacitor should
be placed between VIN1 and GND1. A second 1µF capacitor
should be placed between VIN2 and GND2. These capacitors must be placed as close as possible to the LT8640/
LT8640-1. A third larger capacitor of 2.2µF or more should
be placed close to the LT8640/LT8640-1 with the positive
terminal connected to VIN1 and VIN2, and the negative
terminal connected to ground. See applications section
for sample layout.
GND1 (6, 7): Power Switch Ground. These pins are the
return path of the internal bottom side power switch and
must be tied together. Place the negative terminal of the
input capacitor as close to the GND1 pins as possible. Also
be sure to tie GND1 to the ground plane. See the Applications Information section for sample layout.
SW (Pins 8, 9): The SW pins are the outputs of the internal
power switches. Tie these pins together and connect them
to the inductor and boost capacitor. This node should be
kept small on the PCB for good performance and low EMI.
GND2 (10, 11): Power Switch Ground. These pins are the
return path of the internal bottom side power switch and
must be tied together. Place the negative terminal of the
input capacitor as close to the GND2 pins as possible. Also
be sure to tie GND2 to the ground plane. See the Applications Information section for sample layout.
VIN2 (Pin 13): The LT8640/LT8640-1 requires two 1µF
small input bypass capacitors. One 1µF capacitor should
be placed between VIN1 and GND1. A second 1µF capacitor
should be placed between VIN2 and GND2. These capacitors must be placed as close as possible to the LT8640/
LT8640-1. A third larger capacitor of 2.2µF or more should
be placed close to the LT8640/LT8640-1 with the positive terminal connected to VIN1 and VIN2, and the negative terminal connected to ground. See the Applications
Information section for sample layout.
EN/UV (Pin 14): The LT8640/LT8640-1 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 LT8640/LT8640-1
will shut down.
RT (Pin 15): A resistor is tied between RT and ground to
set the switching frequency.
TR/SS (Pin 16): Output Tracking and Soft-Start Pin. This
pin allows user control of output voltage ramp rate during start-up. A TR/SS voltage below 0.97V forces the
LT8640/LT8640-1 to regulate the FB pin to equal the TR/
SS pin voltage. When TR/SS is above 0.97V, the tracking
function is disabled and the internal reference resumes
control of the error amplifier. An internal 1.9µA pull-up
current from INTVCC on this pin allows a capacitor to
program output voltage slew rate. This pin is pulled to
ground with an internal 200Ω MOSFET during shutdown
and fault conditions; use a series resistor if driving from
a low impedance output. This pin may be left floating if
the tracking function is not needed.
SYNC/MODE (Pin 17, LT8640 Only): 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) Pulse-skipping mode. This mode offers full frequency
operation down to low output loads before pulse skipping
occurs. Float this pin for pulse-skipping mode. When
floating, pin leakage currents should be
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