LT8336
40V, 2.5A, Low IQ Synchronous
Step-Up Silent Switcher with PassThru
FEATURES
DESCRIPTION
Silent Switcher® Architecture
n Ultralow EMI Emissions
n Optional Spread Spectrum Frequency Modulation
n Integrated 40V, 2.5A Power Switches
n Wide Input/Output Voltage Range: 2.7V to 40V
n Low V Pin Quiescent Current:
IN
n 0.3µA in Shutdown
n 4µA in Burst Mode® Operation
n 15µA in PassThru™ Operation
n 100% Duty Cycle Capability for Synchronous MOSFET
n Adjustable and Synchronizable: 300kHz to 3MHz
n Pulse-Skipping or Burst Mode Operation at Light Load
n Output Soft-Start and Power Good Monitor
n Internal Compensation
n Accurate 1V Enable Pin Threshold
n Small 16-Lead (3mm × 3mm) LQFN Package
n AEC-Q100 Qualified for Automotive Applications
The LT®8336 is a low IQ, synchronous step-up DC/DC
converter. It features Silent Switcher architecture and
optional spread spectrum frequency modulation to minimize EMI emissions while delivering high efficiencies at
high switching frequencies.
APPLICATIONS
The LT8336 features output soft-start, an output power
good flag and output overvoltage lockout.
n
n
n
Automotive and Industrial Power Supplies
General Purpose Step-Up
The wide input/output voltage range, low VIN pin quiescent current in Burst Mode operation, and 100% duty
cycle capability for the synchronous MOSFET in PassThru
operation (VIN ≥ VOUT), make the LT8336 ideally suited
for general purpose step-up and automotive preboost
applications.
The LT8336 integrates 40V, 2.5A power switches, operating at a fixed switching frequency programmable between
300kHz and 3MHz and synchronizable to an external clock.
Pulse-skipping or Burst Mode operation can be selected,
with or without spread-spectrum frequency modulation,
to optimize efficiency and EMI performance.
All registered trademarks and trademarks are the property of their respective owners. Protected
by U.S patents, including 10686381.
TYPICAL APPLICATION
High Efficiency 8V to 16V Input, 2MHz, 24V Output Boost Converter
90
0.1µF
10µF
SW
VIN
80
BST
VOUT
24V
0.6A AT 8V VIN
1.2A AT 16V VIN
VOUT
LT8336
1M
INTVCC
RT
1µF
10µF
×2
FB
SYNC/MODE
GND
1k
70
60
100
50
40
20
VIN = 16V
VIN = 8V
Burst Mode OPERATION
10
43.2k
0
0.1
47.5k
2MHz
1
10
100
1k
OUTPUT CURRENT (mA)
POWER LOSS (mW)
EN/UVLO
PG
10k
100
EFFICIENCY (%)
VIN
8V TO 16V
Efficiency
6.8µH
10
1
10k
8336 TA01b
8336 TA01a
Rev. A
Document Feedback
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1
LT8336
ABSOLUTE MAXIMUM RATINGS
PIN CONFIGURATION
(Note 1)
VIN
EN/UVLO
NC
INTVCC
PG
TOP VIEW
VIN, VOUT, EN/UVLO...................................................40V
SYNC/MODE, FB..........................................................6V
PG..............................................................................10V
Operating Junction Temperature Range (Notes 2, 3)
LT8336E............................................. –40°C to 125°C
LT8336J............................................. –40°C to 150°C
LT8336H............................................. –40°C to 150°C
Storage Temperature Range................... –65°C to 150°C
Maximum Reflow (Package Body)
Temperature....................................................... 260°C
NC
16 15 14 13
12 BST
SYNC/MODE 1
RT 2
11 SW
17
GND
GND 3
10 SW
FB 4
7
8
GND
GND
6
VOUT
5
NC
VOUT
9 SW
NC
LQFN PACKAGE
16-LEAD (3mm × 3mm) LQFN
θJA = 42.8°C/W; θJCtop = 45.2°C/W;
θJCbottom = 8.2°C/W (Note 4)
EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
PART MARKING
PART NUMBER
PACKAGE*
TYPE
MSL
RATING
Au (RoHS)
LQFN (Laminate
Package with QFN
Footprint)
3
Au (RoHS)
LQFN (Laminate
Package with QFN
Footprint)
3
DEVICE
FINISH CODE
PAD FINISH
LHHP
e4
LHHP
e4
LT8336EV#PBF
LT8336JV#PBF
LT8336HV#PBF
TEMPERATURE RANGE
(SEE NOTE 2)
–40°C to 125°C
–40°C to 150°C
AUTOMOTIVE PRODUCTS**
LT8336EV#WPBF
LT8336JV#WPBF
LT8336HV#WPBF
• Contact the factory for parts specified with wider operating temperature
ranges. Pad or ball finish code is per IPC/JEDEC J-STD-609.
–40°C to 125°C
–40°C to 150°C
• Recommended LGA and BGA PCB Assembly and Manufacturing
Procedures
*The LT8336 package has the same dimensions as a standard 3mm × 3mm QFN. • LGA and BGA Package and Tray Drawings
**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. VIN = 5V, EN/UVLO = 2V, unless otherwise noted.
PARAMETER
CONDITIONS
VIN Operation Voltage
VIN Quiescent Current
TYP
UNITS
40
V
1
10
µA
µA
4
8
µA
SYNC/MODE = Open, Not Switching
0.9
1.5
mA
VIN = 10.1V, VOUT = 10V, FB = 1.05V (In PassThru Mode)
15
25
µA
l
2.7
MAX
0.3
0.3
l
EN/UVLO = 0.15V
EN/UVLO = 0.15V
SYNC/MODE = 0V, Not Switching
2
MIN
Rev. A
For more information www.analog.com
LT8336
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 5V, EN/UVLO = 2V, unless otherwise noted.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
E-Grade/H-Grade
J-Grade
l
l
0.994
0.985
0.980
1.000
1.000
1.000
1.006
1.010
1.012
V
V
V
FB Line Regulation
2.7V < VIN < 40V
l
0.005
0.02
%/V
FB Pin Input Current
FB = 1.0V
20
nA
Switching Frequency
RT = 357kΩ
RT = 102kΩ
RT = 47.5kΩ
RT = 30.1kΩ
FB Regulation Voltage
–20
l
1.85
Spread Spectrum Modulation Frequency as
Percentage of fSW
Spread Spectrum Modulation Frequency
Range as Percentage of fSW
Synchronizable Frequency
SYNC/MODE = External Clock
l
0.3
SYNC/MODE Pin Input Logic Level for
Frequency Synchronization
SYNC Logic Low
SYNC Logic High
l
l
1.7
Soft-Start Time
RT = 47.5kΩ
EN/UVLO Threshold Voltage
Falling
Hysteresis
EN/UVLO Input Bias Current
EN/UVLO = 2V
300
1
2
3
2.15
0.45
%
20
%
3
0.4
1.4
l
0.94
kHz
MHz
MHz
MHz
MHz
V
V
ms
1.0
100
1.06
V
mV
40
nA
PG Upper Threshold Offset from Regulated FB FB Falling
Hysteresis
l
5
8
1
12
%
%
PG Lower Threshold Offset from Regulated FB FB Rising
Hysteresis
l
–12
–8
1
–5
%
%
40
nA
700
2000
Ω
PG Leakage Current
PG = 3.5V
PG Pull-Down Resistance
PG = 0.1V
Bottom Switch On-Resistance
ISW = 1A
–40
–40
l
70
Bottom Switch Current Limit
l
Bottom Switch Minimum Off-time
2.5
3
20
Bottom Switch Minimum On-time
VIN = 9.5V, VOUT = 10V
Top Switch On-Resistance
ISW = 1A
20
SW Leakage Current
VOUT = 40V, SW = 0V, 40V
VOUT Pin Current
SYNC/MODE = 0V, VOUT = 10V, Not Switching
VIN = 10.1V, VOUT = 10V, FB = 1.05V (In PassThru Mode)
PassThru Mode VIN to VOUT Threshold
(VIN – VOUT)
PassThru Mode Top Switch Reverse
Current Limit
mΩ
3.3
A
50
ns
80
75
–1.5
ns
mΩ
1.5
μA
1
30
μA
μA
FB = 1.05V, VIN Rising
FB = 1.05V, VIN Falling
0
–0.6
V
V
VIN = 9.9V, VOUT = 10V, FB = 1.05V (Top Switch Turns Off)
750
mA
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 LT8336E is guaranteed to meet performance specifications
from the 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 LT8336J/ LT8336H are guaranteed to meet performance specifications
over the –40°C to 150°C operating junction temperature ranges. High
junction temperatures degrade operating lifetimes; operating lifetime is
de-rated for junction temperatures greater than 125°C.
Note 3: These ICs include overtemperature protection that is intended to
protect the device during momentary overload conditions. The maximum
rated junction temperature will be exceeded when this protection is active.
Continuous operation above the specified absolute maximum operating
junction temperature may impair device reliability or permanently damage
the device.
Note 4: θ values are determined by simulation per JESD51 conditions.
Rev. A
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3
LT8336
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency and Power Loss
vs Output Current
100
10k
100
100
50
40
30
10
VIN = 16V
VIN = 8V
FRONT PAGE CIRCUIT
Burst Mode OPERATION
20
10
0
0.1
1
10
100
1k
OUTPUT CURRENT (mA)
EFFICIENCY (%)
60
70
PULSE–SKIPPING
LOSS
60
50
40
0
10
PULSE–SKIPPING
EFFICIENCY
30
1.08
80
1.07
EFFICIENCY (%)
30
20
10
0
0.1
1
10
100
LOAD CURRENT (mA)
1
10
100
OUTPUT CURRENT (mA)
1k
1.04
1.03
1.02
1.01
EN/UVLO FALLING
0.99
–50 –25
OSCILLATOR FREQUENCY (MHz)
OSCILLATOR FREQUENCY (MHz)
2.02
2
1.98
1.96
1.94
1.92
0
25 50 75 100 125 150
TEMPERATURE (°C)
0
1.004
1.002
1
0.998
0.996
0.994
0.992
25 50 75 100 125 150
TEMPERATURE (°C)
RT = 47.5kΩ
SYNC/MODE = INTVCC
2.4
0.99
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
3976 G06
Switching Waveforms, Soft-Start
VOUT
10V/DIV
2.3
24V
IL
1A/DIV
2.2
EN/UVLO
2V/DIV
2.1
1ms/DIV
2.0
1.9
8336 G09
VIN = 12V
FRONT PAGE CIRCUIT
0
50
100
150 200
TIME (μs)
250
300
8336 G07
4
15
1.006
8336 G05
2.5
2.04
6
9
12
INDUCTOR VALUE (μH)
8336 G03
Oscillator Frequency with Spread
Spectrum Modulation
2.06
3
1.008
1.05
RT = 47.5kΩ
SYNC/MODE = OPEN
1.9
–50 –25
65
FB Regulation Voltage vs
Temperature
1.06
Oscillator Frequency vs
Temperature
2.08
0.1
EN/UVLO RISING
8336 G04
2.1
75
1.01
1
1000
ILOAD = 5mA
3.3μH: COILCRAFT XFL4020-332ME
4.7μH: COILCRAFT XFL4020-472ME
6.8μH: COILCRAFT XEL4030-682ME
10μH: COILCRAFT XAL5050-103ME
15μH: COILCRAFT XAL5050-153ME
FRONT PAGE CIRCUIT
80
70
FB REGULATION VOLTAGE (V)
90
EN/UVLO THRESHOLD (V)
1.09
VIN = 12V
300kHz, L = 47μH
1MHz, L = 15μH
2MHz, L = 6.8μH
3MHz, L = 4.7μH
FRONT PAGE CIRCUIT
Burst Mode OPERATION
VIN = 8V
85
EN/UVLO Thresholds vs
Temperature
100
40
90
8336 G02
Efficiency vs Output Current at
Different Switching Frequencies
50
VIN = 16V
FRONT PAGE CIRCUIT
8336 G01
60
1
VIN = 12V
10
70
100
BURST LOSS
20
1
10k
95
POWER LOSS (mW)
70
100
1k
80
1k
POWER LOSS (mW)
EFFICIENCY (%)
80
10k
BURST EFFICIENCY
90
90
Burst Mode Efficiency
vs Inductor Value
EFFICIENCY (%)
Efficiency and Power Loss
vs Output Current
TA ≈ TJ = 25°C, unless otherwise noted.
8336 G08
Rev. A
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LT8336
TYPICAL PERFORMANCE CHARACTERISTICS
TA ≈ TJ = 25°C, unless otherwise noted.
Bottom Switch Current Limit vs
Temperature
Switching Waveforms, Soft-Start
at Different VIN Voltages
Max Programmable Switching
Frequency vs Input Voltage
3.5
MAX SWITCHING FREQUENCY (MHz)
3.2
VOUT AT VIN = 16V
VOUT AT VIN = 12V
VOUT AT VIN = 8V
0V
EN/UVLO
2V/DIV
500μs/DIV
8336 G10
FRONT PAGE CIRCUIT
CURRENT LIMIT (A)
3.1
VOUT
10V/DIV
3.0
2.9
2.8
2.7
2.6
2.5
–50 –25
0
3.0
2.5
2.0
1.5
1.0
0.5
0
2.70
25 50 75 100 125 150
TEMPERATURE (°C)
2.75
2.80
2.85 2.90
VIN (V)
2.95
8336 G12
8336 G11
Switching Waveforms, Current
Limit at 85% Duty Cycle
IL
1A/DIV
IL
1A/DIV
0A
0A
VSW
10V/DIV
VSW
10V/DIV
500ns/DIV
300
250
500ns/DIV
8336 G13
VIN = 4.15V
FRONT PAGE CIRCUIT
Power Switch Voltage Drop vs
Switch Current
SWITCH DROP (mV)
Switching Waveforms, Current
Limit at 15% Duty Cycle
3.00
8336 G14
VIN = 21.5V
FRONT PAGE CIRCUIT
200
TOP SWITCH
150
100
BOTTOM SWITCH
50
0
0
0.5
1
1.5
2
SWITCH CURRENT (A)
2.5
3
8336 G15
Power Switch Voltage Drop vs
Temperature
160
SWITCH DROM (mV)
140
Switching Waveforms, Load Step
in Pulse-Skipping Mode Operation
SWITCH CURRENT = 1A
IOUT
0.5A/DIV
IL
1A/DIV
0A
120
100
TOP SWITCH
IOUT
0.5A/DIV
IL
1A/DIV
0A
BOTTOM SWITCH
200μs/DIV
40
0.5A
VOUT
0.5V/DIV
(AC)
VOUT
0.5V/DIV
(AC)
80
60
0.5A
Switching Waveforms, Load Step
in Burst Mode Operation
8336 G17
FRONT PAGE CIRCUIT
200μs/DIV
8336 G18
FRONT PAGE CIRCUIT
20
0
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
8336 G16
Rev. A
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5
LT8336
TYPICAL PERFORMANCE CHARACTERISTICS
Minimum On/Off Times vs
Temperature
70
IL
0.5A/DIV
MIN ON TIME
0A
IL
0.5A/DIV
0A
MIN OFF TIME
VSW
10V/DIV
VSW
10V/DIV
MIN ON/OFF TIMES (ns)
60
50
30
20
2μs/DIV
10
0
–50 –25
Switching Waveforms,
Continuous Burst Mode
Operation
Switching Waveforms, Full
Frequency PWM Operation
VOUT = 30V
40
TA ≈ TJ = 25°C, unless otherwise noted.
0
25 50 75 100 125 150
TEMPERATURE (°C)
2μs/DIV
8336 G20
VIN = 3V
ILOAD = 220mA
SYNC/MODE = 0V
BACK PAGE CIRCUIT
VIN = 3V
ILOAD = 110mA
SYNC/MODE = 0V
BACK PAGE CIRCUIT
Switching Waveforms, Light Load
Low IQ Burst Mode Operation
Switching Waveforms,
Discontinuous
Pulse-Skipping Mode
8336 G21
3976 G19
Switching Waveforms,
Discontinuous Burst Mode
Operation
IL
0.5A/DIV
0A
IL
0.5A/DIV
0A
IL
0.1A/DIV
0A
VSW
10V/DIV
VSW
10V/DIV
VSW
10V/DIV
2μs/DIV
VOUT, VIN
1V/DIV
IL
0.5A/DIV
500ns/DIV
8336 G23
8336 G24
VIN = 3V
ILOAD = 50mA
SYNC/MODE = 0V
BACK PAGE CIRCUIT
VIN = 3V
ILOAD = 0mA
SYNC/MODE = 0V
BACK PAGE CIRCUIT
VIN = 3V
ILOAD = 10mA
SYNC/MODE = OPEN
BACK PAGE CIRCUIT
Waveforms, PassThru
Mode Operation
Waveforms, Reverse Current
Protection in PassThru Mode
Switching Waveforms,
Frequency Foldback when VIN is
close to VOUT
VOUT, VIN
1V/DIV
VIN
IL
0.5A/DIV
VSW 100mA
20V/DIV
0.5A
2μs/DIV
ILOAD = 0.5A
VIN = 10.45V
SYNC/MODE = 0V
BACK PAGE CIRCUIT
VIN
IL
0.5A/DIV
–750mA
50μs/DIV
8336 G25
VOUT, VIN
1V/DIV
VOUT
10.6V
VOUT
VSW
20V/DIV
6
10ms/DIV
8336 G22
VOUT
VIN
0.5A
VSW
20V/DIV
8336 G26
SYNC/MODE = 0V
BACK PAGE CIRCUIT
2μs/DIV
8336 G27
ILOAD = 0.5A
VOUT = 10V
SYNC/MODE = 0V
BACK PAGE CIRCUIT
Rev. A
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LT8336
TYPICAL PERFORMANCE CHARACTERISTICS
Conducted EMI Performance
(CISPR25 Class 5 Average)
Conducted EMI Performance
(CISPR25 Class 5 Peak)
80
60
60
50
50
40
30
20
10
40
30
20
10
0
0
–10
–10
–20
0
3
6
9
12
15
18
FREQUENCY (MHz)
21
24
27
–20
30
0
3
6
9
12
15
18
FREQUENCY (MHz)
21
PAGE 18 CIRCUIT, 12V INPUT TO 24V OUTPUT AT 600mA,
SSFM = ON, fSW = 2MHz TO 2.4MHz
PAGE 18 CIRCUIT, 12V INPUT TO 24V OUTPUT AT 600mA,
SSFM = ON, fSW = 2MHz TO 2.4MHz
Radiated EMI Performance
(CISPR25 Class 5 Peak)
Radiated EMI Performance
(CISPR25 Class 5 Average)
60
60
50
50
40
40
AMPLITUDE (dBµV/m)
AMPLITUDE (dBµV/m)
8336 G28
30
20
10
0
–10
–20
CLASS 5 AVERAGE LIMIT
LT8336 AVERAGE EMI
70
AMPLITUDE (dBµV)
AMPLITUDE (dBµV)
80
CLASS 5 PEAK LIMIT
LT8336 PEAK EMI
70
TA ≈ TJ = 25°C, unless otherwise noted.
CLASS 5 PEAK LIMIT
LT8336 PEAK EMI
0
100
200
300
400
500
600
FREQUENCY (MHz)
700
PAGE 18 CIRCUIT, 12V INPUT TO 24V OUTPUT AT 600mA,
SSFM = ON, fSW = 2MHz TO 2.4MHz
800
900
1000
8336 G30
24
27
30
8336 G29
30
20
10
0
–10
–20
CLASS 5 AVERAGE LIMIT
LT8336 AVERAGE EMI
0
100
200
300
400
500
600
FREQUENCY (MHz)
700
PAGE 18 CIRCUIT, 12V INPUT TO 24V OUTPUT AT 600mA,
SSFM = ON, fSW = 2MHz TO 2.4MHz
800
900
1000
8336 G31
Rev. A
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7
LT8336
PIN FUNCTIONS
SYNC/MODE (Pin 1): External Synchronization Input and
Mode Selection Pin. This pin allows five selectable modes
for optimization of performance:
SYNC/MODE PIN INPUT
CAPABLE MODE(S) OF OPERATION
(1) GND or (INTVCC – 0.2V)
Pulse-Skipping/SSFM
(5) External Clock
Pulse-Skipping/Sync
where the selectable modes of operation are:
Burst = low IQ, (low output ripple operation at light loads)
Pulse-Skipping = skipped pulse(s) at light load (aligned clock)
SSFM = spread spectrum frequency modulation for low EMI
Sync = switching frequency synchronized to external clock
The LT8336 automatically selects pulse-skipping mode
with no spread-spectrum frequency modulation during
start-up, and The SYNC/MODE pin input configurations
(1) through (4) are ignored.
The LT8336 automatically select low IQ operation in the
PassThru mode operation, and all the SYNC/MODE pin
input configurations are ignored.
RT (Pin 2): Switching Frequency Adjustment Pin. The
LT8336 switching frequency is programmed by connecting a resistor of the appropriate value from the RT pin to
GND at Pin 3. See the Applications Information section
for more detail. Do not leave the RT pin open.
GND (Pins 3, 5, 8, Exposed Pad Pin 17): Ground. The
exposed pad should be soldered to the PCB ground plane
for good thermal and electrical performance. See the
Applications Information section for sample layout.
FB (Pin 4): Feedback Input Pin. This pin receives the feedback voltage from the external resistor divider between
VOUT and Pin 3 GND. FB pin is one input to the error
amplifier of the output voltage control loop. See the
Applications Information section for sample layout.
VOUT (Pins 6, 7): Output Pins. Connect one 1µF capacitor between VOUT at Pin 6 and GND at Pin 5 only, and a
matching 1µF capacitor between VOUT at Pin 7 and GND
8
at Pin 8 only. These two capacitors complete the Silent
Switcher configuration and must be placed as close to
the IC as possible to achieve lowest EMI. Additional bulk
capacitors of 2.2µF or more should be placed close to
the IC with the positive terminals connected to VOUT, and
negative terminals connected to ground plane. See the
Applications Information section for a sample layout.
SW (Pins 9, 10, 11): The SW pins are the outputs of
the internal power switches. Tie these pins together and
connect them to the inductor and one side of the boost
capacitor CBST.
BST (Pin 12): Top Switch Gate Driver Supply Pin. Place
a 0.1µF capacitor (CBST) between the BST and SW pins
and close to the IC.
VIN (Pin 13): Input Supply Pin. This pin must be connected to the input of the power stage (the inductor’s
input terminal).
EN/UVLO (Pin 14): Enable and Input Undervoltage
Lockout Pin. The IC is shut down when this pin is below
1V (typical). The IC draws a low VIN current of 0.3μA
(typical) when this pin is below 0.15V. The IC is enabled
when this pin is above 1.0V (typical). A resistor divider
from VIN to GND can be used to program a VIN threshold
below which the IC is shut down. See the Applications
Information section for further details. Tie EN/UVLO to
VIN if the shutdown feature is not used.
INTVCC (Pin 15): Internal 3.5V Regulator Bypass Pin.
This pin provides supply for internal drivers and control
circuits. The bypass capacitor for INTVCC should be connected to the ground plane. Do not load the INTVCC pin
with external circuitry. This pin must be bypassed with a
1µF or larger low ESR ceramic capacitor placed close to
the pin.
PG (Pins 16): Power Good Indicator. Open-drain logic
output that is pulled to ground when the output voltage
is greater than ±8% outside the regulated voltage. PG is
also pulled to ground when EN/UVLO is below 1V, INTVCC
has fallen too low, or the IC enters thermal shutdown.
Rev. A
For more information www.analog.com
LT8336
BLOCK DIAGRAM
R4
R3
14
IL
L
VIN
EN/UVLO
13
CBST
CVCC
CIN
15
VIN
INTVCC
12
BST
I_ZERO
3.5V REG
AND UVLO
1V REF
1V
VOUT_OVLO
–
+
VOUT_OVLO
G2
VIN_HIGH
UVLO
VC
INTVCC
16
A4
+
–
A3
+
–
40V
VIN
M2
INTVCC
R1
G1
OSC
A6
C1
M1
SS
+
+
GND
(3, 5, 8, 17)
±8%
R2
SS
FB
BURST
MODE
DETECT
A1
+
–
–
1V
COUT3
FB
FB
4
VOUT
COUT1,2
PG
SHDN
FB
+
–
VOUT
(6, 7)
SYNC/MODE
SHDN
VIN_HIGH
SWITCHING
LOGIC
AND
CHARGE
PUMP
SHDN
R5
A5
I_ZERO
A2
TJ > 170°C
SW (9, 10, 11)
VC
EA
RAMP
GENERATOR
OSC
OSCILLATOR
2
RT
1
SYNC/MODE
8336 BD
RT
Rev. A
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9
LT8336
OPERATION
The LT8336 uses a fixed frequency, current mode control scheme to provide excellent line and load regulation.
Referring to the Block Diagram, the Switching Logic
and Charge Pump block turns on the power switch M1
through driver G1 at the start of each oscillator cycle.
During the M1 switch on-phase, the inductor current IL
flows through M1. A current proportional to the M1 switch
current is added to a stabilizing slope compensation ramp
and the resulting sum is fed into the positive terminal
of the PWM comparator A1. The voltage at the negative
input of A1, labeled “VC”, is set by the error amplifier EA
and is an amplified version of the difference between the
feedback voltage FB and the reference voltage. During
the M1 on-phase, IL increases. When the signal at the
positive input of A1 exceeds VC, A1 sends out a signal to
the Switching Logic and Charge Pump block to turn off
M1. When M1 turns off, the synchronous power switch
M2 turns on until the next clock cycle begins or inductor current IL falls to zero. During the M1 off-phase, IL
decreases. Through this repetitive action, the EA sets the
correct IL peak current level to keep the output in regulation. VIN and VOUT are constantly monitored by the
LT8336. When VIN rises above VOUT (causing A3’s output
high) and at the same time VOUT is higher than its regulation voltage programmed by the FB resistor network,
the LT8336 enters PassThru operation, where M2 is kept
on continuously and M1 is kept off continuously, and the
VOUT is essentially shorted to VIN by the inductor and M2.
See Applications Information section for further details.
one 1µF capacitor between VOUT at pin 6 and GND at pin
5 and a matching 1µF capacitor between VOUT at pin 7
and GND at pin 8 (see Applications Information section
for further details).
The EN/UVLO pin controls whether the LT8336 is enabled
or is in shutdown state. A 1.0V reference and a comparator A2 with 100mV hysteresis (Block Diagram) allow the
user to accurately program the supply voltage at which
the IC turns on and off. See the Applications Information
section for further details.
The LT8336 features a variety of operation modes which
can be selected by SYNC/MODE pin to optimize the converter performance based on the application requirements.
The low ripple Burst Mode operation can be selected to
optimize the efficiency at light loads. The spread spectrum frequency modulation function can be selected to
minimize the EMI emissions.
Pulling SYNC/MODE pin to ground selects Burst Mode
operation. Connecting this SYNC/MODE to ground
through a 50k resistor selects Burst Mode operation with
spread spectrum frequency modulation. Floating SYNC/
MODE pin selects pulse-skipping operation. Connecting
SYNC/MODE pin to INTVCC selects pulse-skipping operation with spread spectrum frequency modulation. If a
clock is applied to the SYNC/MODE pin, the LT8336 synchronizes to an external clock frequency and operates in
pulse-skipping mode. See the Applications Information
section for further details.
LT8336 features Silent Switcher architecture to minimize
EMI emissions while delivering high efficiency. The Silent
Switcher EMI cancellation loops are completed by placing
10
Rev. A
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LT8336
APPLICATIONS INFORMATION
Programming VIN Turn-On and Turn-Off Thresholds
with the EN/UVLO Pin
The falling threshold voltage and rising hysteresis voltage
of the VIN pin can be calculated by Equation 1.
(R3 + R4)
VVIN,FALLING = 1.0V •
R4
(1)
(R3 + R4)
VVIN,RISING = 100mV •
+ VVIN,FALLING
R4
When in Burst Mode operation with light load currents,
the current through the resistor network R3 and R4 can
easily be greater than the supply current consumed by
the LT8336. Therefore, large resistors can be used for R3
and R4 to minimize their effect on efficiency at light loads.
EN/UVLO pin can be tied to VIN if the shutdown feature
is not used, or alternatively, the pin may be tied to a logic
level if shutdown control is required. The IC draws a low
VIN quiescent current of 0.3µA (typical) When EN/UVLO
is below 0.15V.
INTVCC Regulator
An internal low dropout (LDO) regulator produces the 3.5V
supply from VIN that powers the drivers and the internal
bias circuitry. The INTVCC pin must be bypassed to ground
with a minimum of 1μF ceramic capacitor. Good bypassing
is necessary to supply the high transient currents required
by the power MOSFET gate drivers. Applications with high
VIN voltage and high switching frequency increase die temperature because of the higher power dissipation across
the LDO. When VIN is lower than 2.9V, the maximum
programmable switching frequency is lower due to the
voltage drop across the LDO. See the Max Programmable
Switching Frequency vs Input Voltage curve in the Typical
Performance Characteristics section for more information.
Do not connect an external load to the INTVCC pin.
Light Load Current Operation—Burst Mode Operation
or Pulse-Skipping
To enhance the efficiency at light loads, the LT8336 features operate in low ripple Burst Mode operation. When
the LT8336 is enabled for Burst Mode operation, the minimum peak inductor current is set to approximately 700mA
even though the VC node (Block Diagram) indicates a lower
value. In this condition, the LT8336 maintains the output
regulation voltage by reducing the switching frequency
instead of reducing the inductor peak current. In light load
Burst Mode operation the LT8336 delivers single pulses of
current to the output capacitor followed by sleep periods
during which the output power is supplied by the output
capacitor. This low ripple Burst Mode operation minimizes
the input quiescent current and minimizes output voltage
ripple. While in sleep mode the LT8336 VIN pin draws 4µA.
As the output load decreases, the frequency of single
current pulses decreases and the percentage of time the
LT8336 is in sleep mode increases, resulting in much
higher light load efficiency than for typical converters.
By maximizing the time between pulses, the converter
VIN pin quiescent current approaches 4μA for a typical
application when there is no output load. To optimize the
quiescent current performance at light loads, the current
in the feedback resistor divider should be minimized as it
appears to the output as load current.
In order to achieve higher light load efficiency, more energy
should be delivered to the output during the single small
pulses in Burst Mode operation such that the LT8336 can
stay in sleep mode longer between each pulse. This can be
achieved by using a larger value inductor. For example, while
a smaller inductor value would typically be used for a high
switching frequency application, if high light load efficiency
is desired, a larger inductor value should be chosen. See the
Burst Mode Efficiency vs Inductor Value curve in the Typical
Performance Characteristics section for more information.
While in Burst Mode operation the bottom switch
peak current is approximately 700mA as shown in the
Switching Waveforms in Burst Mode operation curve
in the Typical Performance Characteristics section. This
behavior results in larger output voltage ripple compared
to that in pulse-skipping mode operation which has lower
bottom switch peak current. However, the output voltage
ripple can be reduced proportionally by increasing the
output capacitance. When adjusting output capacitance,
a careful evaluation of system stability should be made
to ensure adequate design margin. As the load ramps
upward from zero, the switching frequency keeps increasing until reaching the switching frequency programmed
by the resistor at the RT pin. The output load at which the
Rev. A
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11
LT8336
APPLICATIONS INFORMATION
LT8336 reaches the programmed frequency varies based
on input voltage, output voltage, and inductor choice.
Switching Frequency and Synchronization
The choice of switching frequency is a trade-off between
efficiency and component size. Low frequency operation
improves efficiency by reducing the power switches’
switching losses and gate drive current. However, lower
frequency operation requires a physically larger inductor.
The LT8336 uses a constant-frequency architecture that
can be programmed over a 300kHz to 3MHz range with
a single external resistor from the RT pin to ground, as
shown in Block Diagram. A table for selecting the value
of RT for a given switching frequency is shown in Table 1.
Figure 1 shows the RT Value vs Switching Frequency curve.
Table 1. SW Frequency (fSW) vs RT Value
fSW (MHz)
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.6
RT (kΩ)
357
267
210
174
147
127
113
102
90.9
84.5
76.8
71.5
64.9
61.9
fSW (MHz)
1.7
1.8
1.9
2.0*
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
3.0
RT (kΩ)
57.6
53.6
51.1
47.5
45.2
43.2
40.2
39.2
37.4
35.7
34.0
32.4
30.9
30.1
*Programming 2MHz will ensure fSW stays above 1.85MHz (out of AM band).
12
RT(Ω)
Pulse-skipping mode operation offers two major differences from Burst Mode operation. First, the internal
clock stays awake at all times and all switching cycles are
aligned to the clock. In this mode the internal circuitry is
awake at all times, increasing quiescent current to hundred μA compared to the 4μA of VIN pin quiescent current in Burst Mode operation. Second, as the load ramps
upward from zero, the switching frequency programmed
by the resistor at the RT pin is reached at a lower output
load than in Burst Mode operation, therefore, pulse-skipping mode operation exhibits lower output ripple as well
as lower audio noise and RF interference.
1M
100k
10k
0
500 1000 1500 2000 2500
SWITCHING FREQUENCY (kHz)
3000
8336 F01
Figure 1. RT Value vs Switching Frequency
The operating frequency of the LT8336 can be synchronized to an external clock source with 100ns minimum
pulse width. By providing a digital clock signal to the
SYNC/MODE pin, the LT8336 operates at the SYNC pulse
frequency and automatically enters pulse-skipping mode
operation at light load. If this feature is used, an RT resistor should be chosen to program a switching frequency
as close as possible to the SYNC pulse frequency.
Spread Spectrum Frequency Modulation
The LT8336 features spread spectrum frequency modulation to further reduce EMI emissions. The user can
select spread spectrum frequency modulation with Burst
Mode operation by connecting the SYNC/MODE pin to
ground through a 50k resistor, or spread spectrum frequency modulation with pulse-skipping operation by connecting the SYNC/MODE pin to INTVCC. When spectrum
frequency modulation is selected, a stepped triangular
frequency modulation is used to vary the internal oscillator frequency between the value programmed by the
RT resistor to approximately 20% higher than that value.
The modulation frequency is approximately 0.45% of the
switching frequency. For example, when the LT8336 is
programmed to 2MHz, and spread spectrum frequency
modulation is selected, the oscillator frequency varies
from 2MHz to 2.4MHz at a 9kHz rate (see Oscillator
Frequency with Spread Spectrum Modulation curve in
the Typical Performance Characteristics section). When
operating at light load, the spread spectrum frequency
modulation is more effective in pulse-skipping mode than
Rev. A
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LT8336
APPLICATIONS INFORMATION
in Burst Mode operation, due to the fact that pulse-skipping operation maintains the programmed switching frequency down to a much lower load current as compared
to Burst Mode operation.
VIN to VOUT PassThru Mode Operation
In the boost pre-regulator applications for automotive
stop-start and cold crank, VIN is normally above the regulated VOUT voltage. In this condition, LT8336 enters
PassThru operation. LT8336 is designed to have an
accurate, well controlled PassThru operation with low
quiescent current consumption. If VIN transiently falls
below the VOUT regulation setpoint, the boost converter
commences switching to maintain the output voltage in
regulation.
As shown in Block Diagram, VIN is compared with VOUT
using the comparator A3 with 0.6V hysteresis. When VIN
rises above VOUT (causing A3’s output high), and at the
same time VOUT is higher than its regulation voltage programmed by the FB resistor network, the LT8336 boost
converter enters PassThru operation, where the synchronous power switch M2 is kept on continuously and the
power switch M1 is kept off continuously. The voltage
across the boost capacitor (CBST), VBST_SW, is constantly
monitored. When VBST_SW drops below 3.2V, an internal charge pump is turned on to charge VBST_SW up to
3.6V, and then turned off. In PassThru mode the VOUT is
essentially shorted to VIN by the inductor and M2, and VIN
pin quiescent current is limited to 15µA (typ) regardless
of the SYNC/MODE pin’s configuration. VOUT pin draws
30µA (typ). A typical waveforms drawing is shown in the
Typical Performance Characteristics section.
Several conditions cause the LT8336 to exit from the
PassThru mode operation. First, when VOUT drops below
its regulation voltage programmed by the FB resistor network, LT8336 exits from PassThru mode operation and
normal boost switching operation resumes to maintain
the regulated VOUT voltage. Second, when VOUT is still
higher than its regulation voltage but VIN drops below
VOUT by the comparator A3’s hysteresis of 0.6V (typ) or
more to cause A3’s output low, M2 is turned off to prevent
the reverse current from VOUT to VIN from ramping up.
LT8336 is back to the PassThru mode when A3’s output
is high again. Third, when VOUT is still higher than its
regulation voltage but M2’s reverse current (flowing from
its drain to source) rises above 750mA (typ), M2 is turned
off to prevent the reverse current from VOUT to VIN from
ramping up. LT8336 re-enters the PassThru mode when
A3’s output is high again. Waveforms for typical reverse
current protection are shown in the Typical Performance
Characteristics section.
To ensure the PassThru mode operation works properly,
the LT8336’s VIN pin must be connect to the input of the
power stage (the input terminal of inductor as shown in
Block Diagram).
FB Resistor Network and the Quiescent Current at
No-Load
The output voltage is programmed with a resistor divider
between the output and the FB pin. Choose the resistor
values according to Equation 2.
⎛V
⎞
R1 = R2 • ⎜ OUT – 1⎟
⎝ 1V
⎠
(2)
Reference designators refer to Block Diagram. The 1%
resistors are recommended to maintain output voltage
accuracy.
If low input quiescent current and good light-load efficiency are desired, use large resistor values for the FB
resistor divider. The current flowing in the divider acts as
a load current, and will increase the no-load input current
to the converter.
When VIN < VOUT, the converter Burst Mode quiescent
current at no-load can be estimated using Equation 3.
⎛ V
⎞ ⎛V
⎞
IQ ≈ 4µA + ⎜ OUT + 1µA ⎟ • ⎜ OUT ⎟ • 1.25
⎝ R1 + R2
⎠ ⎝ VIN ⎠
(3)
where 4μA is the VIN pin quiescent current of the LT8336,
and the second term is the current drawn by the feedback
divider and VOUT pin (1μA) reflected to the input of the
boost operating.
For a 12V input, 24V output boost converter with R1 = 1M
and R2 = 43.2k, it can be calculated that the converter
draws approximately 64μA from the 12V supply at
Rev. A
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13
LT8336
APPLICATIONS INFORMATION
no-load. Note that this equation implies that the no-load
current is a function of VIN.
When VIN is higher than the regulated VOUT voltage,
LT8336 enters PassThru operation and VOUT is essentially shorted to VIN by the inductor and M2. The converter quiescent current at no-load can be estimated using
Equation 4.
IQ ≈ 45µA +
VIN
R1 + R2
(4)
where 45μA is the sum of the VIN pin and VOUT pin quiescent current of the LT8336, and the second term is the
current drawn by the feedback divider.
For a 25V VIN with R1 = 1M and R2 = 43.2k, it can be
calculated that the converter draws approximately 70μA
from the 25V supply at no-load.
When using large FB resistors, a 4.7pF to 22pF phase-lead
capacitor should be connected from VOUT to FB, and a
careful evaluation of system stability should be made to
ensure adequate design margin.
waveforms in these VIN approaching VOUT conditions are
shown in the Typical Performance Characteristics section.
Start-Up
To limit the peak switch current and VOUT overshoot
during start-up, the LT8336 contains internal circuitry to
provide soft-start operation (refer to the error amplifier EA
in Block Diagram). During start-up, the internal soft-start
circuity slowly ramps the internal SS signal from zero to
1V. When the SS voltage falls between the FB initial voltage and 1V, the LT8336 regulates the FB pin voltage to the
SS voltage instead of 1V. In this way the output capacitor
is charged gradually towards its final value while limiting
the start-up peak switch currents.
Referring to Figure 2, the start-up time TSTART_UP is
the time period from EN/UVLO transitioning high to PG
transitioning high, indicating VOUT has reached approximately 90% of its regulation voltage programmed by FB
resistor network. When VIN > 3.6V, TSTART_UP is approximately given by Equation 5.
TSTART _UP = 0.25ms +
2100
fSW
(5)
Overvoltage Lockout
The VOUT pin voltage is constantly monitored by the
LT8336. An overvoltage condition occurs when VOUT pin
voltage exceeds approximately 40V. Switching is stopped
at such condition. Normal switching is resumed when the
VOUT pin voltage drops back to 40V or lower.
When VIN < 3.6V, TSTART_UP is approximately given by
Equation 6.
Switching Frequency Foldback when VIN Approaches VOUT
In some applications, VIN may rise to a voltage very close
to VOUT. In this condition the switching regulator must
operate at a very low duty cycles to keep VOUT in regulation. However, the minimum on-time limitation may
prevent the switcher from attaining a sufficiently low duty
cycle at the programmed switching frequency. As a result
a typical boost converter may experience a large output
ripple under these conditions. The LT8336 addresses this
issue by adopting a switching frequency foldback function
to smoothly decrease the switching frequency when its
minimum on-time starts to limit the switcher from attaining a sufficiently low duty cycle. The typical switching
14
TSTART _UP = 0.25ms +
3.5V
2100
•
VIN − 0.1V fSW
(6)
24V
VOUT
10V/DIV
IL
1A/DIV
EN/UVLO
2V/DIV
tSTART_UP
tMODE_DELAY
1ms/DIV
8336 F02
VIN = 12V
FRONT PAGE CIRCUIT
Figure 2. Typical Start-Up Waveforms
The LT8336 selects pulse-skipping mode with no spread
spectrum frequency modulation during start-up, and the
SYNC/MODE pin configuration is ignored. The LT8336
Rev. A
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LT8336
APPLICATIONS INFORMATION
reads SYNC/MODE pin configuration after the start-up
delay given by Equation 7.
TMODE _DELAY = 0.22ms +
4096
fSW
(7)
If the LT8336 boost converter is plugged into a live supply, the VOUT could ring to twice the voltage of VIN, due to
the resonant circuit composed by L, COUT1-3, and the body
diode of M2 (refer to Block Diagram). If such over-shoot
exceeds the VOUT rating, it must be limited to protect
the load and the converter. For these situations, a small
Schottky diode or silicon diode can be connected between
VIN and VOUT to deactivate the resonant circuit and limit
the VOUT over-shoot as shown in Figure 3. With the diode
connected, the LT8336 boost is also more robust against
output fault conditions such as output short circuit or
overload, due to the fact that the diode diverts a great
amount of output current from the LT8336. The diode
can be rated for about one half to one fifth of the full load
current since it only conducts current during start-up or
output fault conditions.
VOUT
COUT3
L
SW
CIN
VOUT
COUT1,2
LT8336
VIN
GND
8336 F03
Figure 3. A Simplified LT8336 Power Stage with a
Diode Added Between VIN and VOUT
Inductor Selection
When operating in continuous conduction mode (CCM),
the duty cycle can be calculated based on the output voltage (VOUT) and the input voltage (VIN). The maximum duty
cycle (DMAX) occurs when the converter has the minimum
input voltage given by Equation 8.
DMAX =
Given an operating input voltage range, and having chosen the operating frequency and ripple current in the
inductor, the inductor value of the boost converter can
be determined using Equation 9.
L=
D
VIN
The inductor ripple current ∆ISW has a direct effect on the
choice of the inductor value, the converter’s maximum
output current capability, and the light load efficiency in
Burst Mode operation. Choosing smaller values of ∆ISW
increases output current capability and light load efficiency in Burst Mode operation, but require large inductance values and reduce the current loop gain. Accepting
larger values of ∆ISW provides fast transient response and
allows the use of low inductance values, but results in
higher input current ripple, greater core losses, lower light
load efficiency in Burst Mode operation, and lower output
current capability. Large values of ΔISW at high duty cycle
operation may result in sub-harmonic oscillation. ∆ISW =
0.3A to 0.6A generally provides a good starting value for
many applications, and careful evaluation of system stability should be made to ensure adequate design margin.
VOUT – VIN(MIN)
VOUT
(8)
Discontinuous conduction mode (DCM) provides higher
conversion ratios at a given frequency at the cost of
reduced efficiencies and higher switching currents.
VIN(MIN)
∆ISW • fSW
•DMAX
(9)
The LT8336 limits the peak switch current in order to protect the switches and the system from overload faults. The
bottom switch current limit is controlled to 3A (typical)
regardless of the duty cycle. The peak inductor current is
equal to the LT8336 bottom switch current limit. The user
should choose an inductor with sufficient saturation and
RMS current ratings to handle the inductor’s peak current.
Input Capacitor Selection
The input ripple current in a boost converter is relatively
low (compared with the output ripple current), because
this current is continuous. The voltage rating of the input
capacitor, CIN, should comfortably exceed the maximum
input voltage. Although ceramic capacitors can be relatively tolerant of overvoltage conditions, aluminum electrolytic capacitors are not. Be sure to characterize the
input voltage for any possible overvoltage transients that
could apply excess stress to the input capacitors.
Rev. A
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15
LT8336
APPLICATIONS INFORMATION
The value of CIN is a function of the source impedance,
and in general, the higher the source impedance, the
higher the required input capacitance.
The RMS CIN ripple current can be estimated by Equation 10.
IRMS(CIN) = 0.3 • ∆IL
(10)
Output Capacitor Selection
The output capacitor has two essential functions. First, it
filters the LT8336’s discontinuous top switch current 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 LT8336’s
control loop. The X5R or X7R type ceramic capacitors
have very low equivalent series resistance (ESR), which
provides low output ripple and good transient response.
Transient performance can be improved with higher output capacitance and the addition of a feedforward capacitor placed between VOUT and FB. When a feedforward
capacitor is used or output capacitance is adjusted, a
careful evaluation of system stability should be made to
ensure adequate design margin. Increasing the output
capacitance will also decrease the output voltage ripple.
Lower value of output capacitance can be used to save
space and cost, but transient performance will suffer and
loop instability may result.
with an electrolytic capacitor. When choosing a capacitor,
special attention should be given to capacitor's 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. For good starting values, refer
to the Typical Applications section.
Board Layout
The LT8336 is specifically designed to minimize EMI
emissions and also to maximize efficiency when switching at high frequencies. Figure 4 shows a recommended
R2
R1
R5
COUT1
16
1
CVCC
VOUT
COUT3
COUT2
CBST
Besides the bulk output capacitors, two small output
ceramic capacitors, 1µF each, should be placed as close
as possible to the IC to complete the Silent Switcher cancellation loops.
See the Board Layout section for more detail. XR7 or
X5R capacitors are recommended for best performance
across temperature and output voltage variations. Note
that larger output capacitance is required when a lower
switching frequency is used. If there is significant inductance to the load due to long wires or cables, additional
bulk capacitance may be necessary. This can be provided
RT
C1
R3
R4
L
CIN1
VIN
GND
GND
8336 F04
GROUND VIA
PG SIGNAL VIA
Figure 4. A Recommended PCB Layout for the LT8336
Rev. A
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LT8336
APPLICATIONS INFORMATION
PCB layout. For more detail and PCB design files refer to
the demo board guide for the LT8336.
For optimal performance the LT8336 requires the use of
multiple VOUT bypass capacitors. It is recommended to
connect one 1µF capacitor between VOUT at Pin 6 and
GND at Pin 5 only, and a matching 1µF capacitor between
VOUT at Pin 7 and GND at Pin 8 only to complete the Silent
Switcher EMI cancellation loops. These two capacitors
must be placed as close as possible to the IC, and the
loops formed by these two capacitors should be symmetrical and as small as possible to achieve an optimized
EMI cancellation performance. Capacitors with small case
size, such as 0402 or 0603, are optimal due to the low
parasitic inductance. Additional bulk capacitors of 2.2µF
or more should be placed close to the IC with the positive terminals connected to VOUT, and negative terminals
connected to ground plane. The bypass capacitors for VIN
and INTVCC pins should also be connected to the ground
plane.
The output capacitors, along with the inductor and input
capacitors, should be placed on the same side of the
circuit board, and their connections should be made on
that layer. Place a local, unbroken power ground plane
under the application circuit on the layer closest to the
surface layer. The SW and BST nodes should be as small
as possible.
Keep the FB and RT nodes small so that the ground traces
will shield them from the noise generated by the SW and
BST nodes. It is recommended to use the GND at Pin 3
for the ground connection of the resistors connecting FB
pin or RT Pin (refer to Figure 4).
extend the ground plane as much as possible, and add
many thermal vias to additional power ground planes
within the circuit board.
Thermal Considerations
Care should be taken in the layout of the PCB to ensure
good heat sinking of the LT8336. The power ground
plane should consist of large copper layers with thermal
vias; these layers spread heat dissipated by the LT8336.
Placing additional vias can reduce thermal resistance further. The maximum load current should be derated as
the junction temperature approaches its maximum temperature rating. Power dissipation within the LT8336 can
be estimated by calculating the total power loss from an
efficiency measurement and subtracting the inductor loss.
The junction temperature can be calculated by multiplying the total LT8336 power dissipation by the thermal
resistance from junction to ambient and adding the ambient temperature. The LT8336 includes internal overtemperature protection that is intended to protect the device
during momentary overload conditions. The overtemperature protection shuts down the LT8336 when the junction
temperature exceeds 170°C (typ). The internal soft-start
is triggered when the junction temperature drops below
165°C (typ). The maximum rated junction temperature
is exceeded when this protection is active. Continuous
operation above the specified absolute maximum operating junction temperature (see Absolute Maximum Ratings
section) may impair device reliability or permanently damage the device.
The exposed pad on the bottom of the package should
be soldered to the ground plane to reduce the package
thermal resistance. To keep the thermal resistance low,
Rev. A
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17
LT8336
TYPICAL APPLICATIONS
Low IQ, Low EMI, 24V Output Boost Converter with SSFM*
VIN
8V TO 16V
INPUT EMI FILTER
L2
0.47µH
10µF
25V
X7R
L1
6.8µH
+ 47µF
35V
10µF
25V
X7R
0.1µF
1M
UVLOFALLING = 7.2V
SW
VIN
BST
EN/UVLO
OUTPUT EMI FILTER
FB1
VOUT
162k
PG
4.7pF
RT
INTVCC
1µF
1M
FB
SYNC/MODE
49.9k
0.1µF
50V
X7R
LT8336
GND
43.2k
1µF
50V
X7R
×2
10µF
50V
X7R
×2
VOUT
24V
0.6A AT 8V VIN
1.2A AT 16V VIN
0.1µF
50V
X7R
47.5k
2MHz
8336 TA02a
L1: COILCRAFT XEL4030-682ME
L2: WURTH ELEKTRONIK 74479299147
FB1: WURTH ELEKTRONIK 742792040
*THIS CIRCUIT IS THE FRONT PAGE CIRCUIT WITH INPUT/OUTPUT FILTERS ADDED AND Burst Mode OPERATION WITH SSFM SELECTED.
THE EMI PERFORMANCE IS SHOWN IN THE TYPICAL PERFORMANCE CHARACTERISTICS SECTION.
18
Rev. A
For more information www.analog.com
LT8336
TYPICAL APPLICATIONS
8V to 16V Input, 36V Output Boost Converter
VIN
8V TO 16V
L1
15µH
10µF
25V
X7R
0.1µF
SW
VIN
1M
UVLOFALLING = 7.2V
BST
EN/UVLO
VOUT
36V
0.4A AT 8V VIN
1.6A AT 16V VIN
VOUT
162k
LT8336
PG
4.7pF
RT
INTVCC
1µF
1M
FB
SYNC/MODE
GND
28.7k
1µF
50V
X7R
×2
10µF
50V
X7R
×2
102k
1MHz
8336 TA03a
L: COILCRAFT XEL5050-153ME
Efficiency and Power Loss
vs Output Current
10k
100
90
1k
70
100
60
50
10
40
30
20
10
0
0.1
VIN = 16V
VIN = 8V
Burst Mode OPERATION
1
10
100
OUTPUT CURRENT (mA)
POWER LOSS (mW)
EFFICIENCY (%)
80
1
0.1
1k
8336 TA03b
Rev. A
For more information www.analog.com
19
LT8336
TYPICAL APPLICATIONS
2.7V to 28V Input, 28V Output Boost Converter
VIN
2.7V TO 28V
L
8.2µH
10µF
50V
X7R
0.1µF
SW
VIN
1M
UVLOFALLING = 2.7V
BST
EN/UVLO
VOUT*
28V
0.6A
VOUT
590k
PG
LT8336
1M
4.7pF
RT
INTVCC
1µF
1µF
50V
X7R
×2
FB
SYNC/MODE
37.4k
GND
102k
1MHz
L: COILCRAFT XEL5050-822ME
*WHEN VIN < 8V, MAXIMUM LOAD CURRENT AVAILABLE IS REDUCED.
8336 TA04a
Efficiency and Power Loss
vs Output Current
Efficiency vs Input Voltage
10k
100
100
90
95
1k
100
60
50
10
40
20
10
0
0.1
VIN = 12V
EFFICIENCY
POWER LOSS
Burst Mode OPERATION
1
10
100
OUTPUT CURRENT (mA)
90
EFFICIENCY (%)
70
POWER LOSS (mW)
EFFICIENCY (%)
80
30
85
80
75
70
1
ILOAD = 0.2A
Burst Mode OPERATION
65
1k
0.1
60
8336 F04b
20
10µF
50V
X7R
×2
0
5
10
15
20
INPUT VOLTAGE (V)
25
30
8336 TA04c
Rev. A
For more information www.analog.com
LT8336
TYPICAL APPLICATIONS
Automotive Pre-Boost Converter for Stop-Start and Cold Crank with 20V Regulated Output and High Efficiency PassThru Mode
VIN
6V TO 40V
L
22µH
10µF
50V
X7R
0.1µF
SW
VIN
1M
BST
EN/UVLO
UVLOFALLING = 6V
VOUT*
20V
0.6A
VOUT
200k
PG
LT8336
1M
4.7pF
RT
INTVCC
1µF
1µF
50V
X7R
×2
FB
SYNC/MODE
43.2k
GND
267k
400kHz
L: COILCRAFT XEL5050-223ME
*WHEN VIN > 24V, VOUT FOLLOWS VIN
WHEN VIN 10V, VOUT FOLLOWS VIN
WHEN VIN < 8V, MAXIMUM LOAD CURRENT AVAILABLE IS REDUCED
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LT8330
1A (ISW), 60V, 2MHz High Efficiency Boost/SEPIC/
Inverting DC/DC Converter
VIN = 3V to 40V, VOUT(MAX) = 60V, IQ = 6µA (Burst Mode Operation),
ISD =
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