FEATURES
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LTC3824
High Voltage Step-Down
Controller With 40µA
Quiescent Current
DESCRIPTION
The LTC
®
3824 is a step-down DC/DC controller designed
to drive an external P-channel MOSFET. With a wide input
range of 4V to 60V and a high voltage gate driver, the
LTC3824 is suitable for many industrial and automotive
high power applications. Constant frequency current mode
operation provides excellent performance.
The LTC3824 can be configured for Burst Mode operation.
Burst Mode operation enhances low current efficiency
(only 40μA quiescent current) and extends battery run
time. The switching frequency can be programmed up to
600kHz and is easily synchronizable.
Other features include current limit, soft-start, micropower
shutdown, and Burst Mode disable.
The LTC3824 is available in a 10-lead MSE power package.
L,
LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners. Protected by U.S. Patents
including 5731964.
Wide Input Range: 4V to 60V
Current Mode Constant Frequency PWM
Very Low Dropout Operation: 100% Duty Cycle
Programmable Switching Frequency:
200kHz to 600kHz
Selectable High Efficient Burst Mode
®
Operation:
40μA Quiescent Current
Easy Synchronization
8V, 2A Gate Drive (V
CC
> 10V) for Industrial High
Voltage P-channel MOSFET
Programmable Soft-Start
Programmable Current Limit
Available in a Small 10-Pin Thermally Enhanced
MSE Package
APPLICATIONS
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Industrial and Automotive Power Supplies
Telecom Power Supplies
Distributed Power Systems
TYPICAL APPLICATION
V
IN
5.5V TO 60V
C
IN
33μF
100V
5V/2A Buck Converter
+
C
CAP
0.1μF
CAP
V
CC
Efficiency and Power Loss vs Load Current
100
V
IN
= 12V
V
IN
= 40V
2.5
90
EFFICIENCY (%)
R
S
0.025Ω
EFFICIENCY
2.0
POWER LOSS (W)
80
1.5
SENSE
LTC3824
R
SET
392k
GND
100pF
SYNC/MODE
V
FB
SS
0.1μF
V
C
10k
3.3nF
80.6k
3824 TA01
GATE
70
V
IN
= 40V
POWER LOSS
V
IN
= 12V
50
10
100
LOAD CURRENT (mA)
1000
1.0
22μH
C
OUT
100μF
2
422k
V
OUT
5V
2A
60
0.5
51Ω
0
2000
3824 TA01a
3824fc
1
LTC3824
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW
GND
SYNC/MODE
R
SET
V
C
V
FB
1
2
3
4
5
10
9
8
7
6
CAP
GATE
V
CC
SENSE
SS
11
V
CC
...........................................................................65V
SS, R
SET
, V
FB
..............................................................4V
V
C
...............................................................................3V
SYNC/MODE ...............................................................6V
V
CC
– V
SENSE
..............................................................1V
Maximum Temperatures (Note 2)
LTC3824E............................................. –40°C to 85°C
LTC3824I............................................ –40°C to 125°C
Storage Temperature Range..................... –65° to 150°C
Lead Temperature (Soldering, 10 sec) .................. 300°C
MSE PACKAGE
10-LEAD PLASTIC MSOP
T
JMAX
= 125°C,
θ
JA
= 43°C/W,
θ
JC
= 3°C/W
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC3824EMSE#PBF
LTC3824IMSE#PBF
LEAD BASED FINISH
LTC3824EMSE
LTC3824IMSE
TAPE AND REEL
LTC3824EMSE#TRPBF
LTC3824IMSE#TRPBF
TAPE AND REEL
LTC3824EMSE#TR
LTC3824IMSE#TR
PART MARKING
LTBRZ
LTCGZ
PART MARKING
LTBRZ
LTCGZ
PACKAGE DESCRIPTION
10-Lead Plastic MSOP
10-Lead Plastic MSOP
PACKAGE DESCRIPTION
10-Lead Plastic MSOP
10-Lead Plastic MSOP
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 125°C
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= 12V, R
SET
= 392k, C
CAP
= 0.1μF No load on any outputs, unless
.
otherwise specified.
PARAMETER
Supply Voltage (V
CC
)
Supply Current (I
VCC
)
Supply Current (I
VCC
) Burst Mode Operation
Supply Current in Shutdown
VOLTAGE AMPLIFIER gm
Reference Voltage (V
REF
)
Transconductance
FB Input Current
V
C
High
V
C
Low
V
C
Source Current
V
C
Sink Current
V
C
= 0.8V,
ΔI
VC
= ±2μA
V
FB
= V
REF
(Note 3)
I
VC
= 0
I
VC
= 0
V
VC
= 0.5V to 1.3V, V
FB
= V
REF
–100mV (V
SYNC
= 0V)
V
VC
= 0.7V to 1.3V, V
FB
= V
REF
+100mV (V
SYNC
= 0V)
l
l
ELECTRICAL CHARACTERISTICS
CONDITIONS
MIN
l
TYP
0.8
40
7
MAX
60
1.3
65
UNITS
V
mA
μA
μA
4
V
C
≤ 0.4V (Switching Off), V
CC
≤ 60V
V
SYNC
= 0V (Burst Mode Operation Disable)
V
CC
≤ 60V, SYNC/MODE Open, V
C
= 0.6V
V
C
≤ 25mV, V
CC
≤ 60V
0.792
0.788
220
0.8
260
10
1.6
0.35
15
15
0.808
0.812
370
30
0.5
V
V
μmho
nA
V
V
μA
μA
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LTC3824
ELECTRICAL CHARACTERISTICS
PARAMETER
V
C
Threshold for Switching Off
Soft-Start Current I
SS
V
C
Burst Mode Threshold
V
C
Burst Mode Threshold Hysteresis
SENSE Voltage at Burst Mode Operation
Current Limit Threshold (V
CC
–V
SENSE
)
FB Overvoltage Threshold
Sense Input Current
OSCILLATOR
Switching Frequency
Synchronization Pulse Threshold
on SYNC Pin
Synchronization Frequency Range
V
RSET
Minimum On-Time (Measured at GATE Pin)
Switching Frequency Foldback
GATE DRIVER
GATE Bias Voltage (V
CC
–V
CAP
)
GATE Bias Voltage (V
CAP
–GND)
GATE High Voltage (V
CC
–V
GATE
)
GATE Peak Source Current
GATE Low Voltage (V
GATE
–V
CAP
)
GATE Peak Sink Current
9V ≤ V
CC
≤ 60V, I
GATE
= 10mA
V
CC
= 12V, I
GATE
= 15mA
4V ≤ V
CC
≤ 8V, I
GATE
= 10mA
6V ≤ V
CC
≤ 8V, I
GATE
= 15mA, V
CC
= 12V
4V ≤ V
CC
≤ 60V, I
GATE
= –15mA
C
GATE
= 10nF
8V ≤ V
CC
≤ 60V, I
GATE
= 15mA
4V ≤ V
CC
< 8V, I
GATE
= 10mA
C
GATE
= 10nF
l
l
l
The
l
denotes the specifications which apply over the full operating
.
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= 12V, R
SET
= 392k, C
CAP
= 0.1μF No load on any outputs, unless
otherwise specified.
CONDITIONS
V
SYNC/MODE
= 0V (Note 4)
V
SS
= 0.1V to 1.5V
V
CC
≤ 60V, V
C
Rising, SYNC/MODE Open
V
CC
≤ 60V
(V
CC
–V
SENSE
) at 30% Duty Cycle
70% Duty Cycle
V
CC
≤ 60V
V
C
= 1.6V
V
SENSE
= V
CC
R
SET
= 392k
R
SET
= 200k
Rising Edge V
SYNC
R
SET
= 392k
R
SET
= 200k
R
SET
= 392k
3V Buck Converter Circuit, I
LOAD
> 2A
V
FB
= 0.3V
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MIN
TYP
5
0.84
0.04
30
20
MAX
0.4
UNITS
V
μA
V
V
mV
mV
80
100
8
0.1
120
2
230
460
1.3
mV
%
μA
kHz
kHz
V
kHz
kHz
V
ns
170
320
200
400
230
460
1.2
350
35
7.0
6.8
0.2
50
7.9
0.85
0.5
2.5
0.1
0.05
2.5
300
600
75
8.8
1.5
2.8
0.8
0.5
kHz
V
V
V
V
V
A
V
V
A
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 LTC3824E is guaranteed to meet performance specifications
from 0°C to 85°C junction temperature. Specifications over the –40°C
to 85°C temperature range are assured by design characterization and
correlation with statistical process controls. The LTC3824I grade is
guaranteed over the full –40°C to 125°C operating junction temperature
range.
Note 3:
This parameter is tested in a feedback loop that servos V
FB
to the
reference voltage with the V
C
pin forced to 1V.
Note 4:
This specification represents the maximum voltage on V
C
where
switching (GATE pin) is guaranteed to be off.
3824fc
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LTC3824
TYPICAL PERFORMANCE CHARACTERISTICS
(V
CC
-V
CAP
) vs I
GATE
at V
DRIVE
Low
8.5
8.4
2
8.3
V
CC
-V
CAP
(V)
8.2
8.1
8.0
7.9
7.8
7.7
7.6
0
10
20
30
I
GATE
(mA)
40
50
3824 G01
T
A
= 25°C unless otherwise noted.
Switching Frequency Change
vs V
CC
at R
SET
= 392kΩ
3
I
CC
vs V
CC
3
2
I
CC
(mA)
V
FB
= 0.75V
1
V
FB
= 0.85V
ΔFREQUENCY
(kHz)
50
60
3824 G02
1
0
–1
–2
0
0
10
20
30
V
CC
(V)
40
–3
0
10
20
30
V
CC
(V)
40
50
60
3824 G03
V
REF
Change vs V
CC
0.4
700
600
0.2
FREQUENCY (kHz)
ΔV
REF
(mV)
500
Switching Frequency vs R
SET
2
ΔV
REF
vs Temperature
1
ΔV
REF
(mV)
400
3824 G05
3824 G06
0
400
300
0
–0.2
200
–0.4
0
10
20
30
V
CC
(V)
40
50
60
3824 G04
–1
100
100
200
R
SET
(kΩ)
300
–2
–40
–20
75
0
25
50
DIE TEMPERATURE (°C)
100
125
Burst Mode Disabled at
I
LOAD
= 200mA, V
OUT
= 5V
I
LOAD
= 200mA
Burst Mode Operation V
OUT
= 3V
V
IN
=12V, V
OUT
= 3V, I
LOAD
= 200mA
V
OUT
10mV/DIV
V
OUT
50mV/DIV
INDUCTOR
CURRENT
1A/DIV
INDUCTOR
CURRENT
1A/DIV
4μs/DIV
3824 G10
20μs/DIV
3824 G08
3824fc
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LTC3824
TYPICAL PERFORMANCE CHARACTERISTICS
T
A
= 25°C unless otherwise noted.
Burst Mode Operation V
OUT
= 5V
V
IN
=12V, V
OUT
= 5V, I
LOAD
= 200mA
OUTPUT VOLTAGE
AC COUPLED
100mV/DIV
Load Current Step Response
V
OUT
50mV/DIV
INDUCTOR
CURRENT
1A/DIV
INDUCTOR
CURRENT
2A/DIV
50μs/DIV
3824 G09
100μs/DIV
3824 G10
PIN FUNCTIONS
GND (Pin 1):
Chip Ground Pin.
SYNC/MODE (Pin 2):
Synchronization Input and Burst
Mode Operation Enable/Disable. If this pin is left open
or pulled higher than 2V, Burst Mode operation will be
enabled at light load and the typical threshold of entering
Burst Mode operation is one third of current limit. If this
pin is grounded or the synchronization pulse is present
with a frequency greater than 20kHz then Burst Mode
operation is disabled and the LTC3824 goes into pulse
skipping at light loads. To synchronize the LTC3824, the
duty cycle of the synchronizing pulse can range from 10%
to 70% and the synchronizing frequency has to be higher
than the programmed frequency.
R
SET
(Pin 3):
A resistor from R
SET
to ground sets the
LTC3824 switching frequency.
V
C
(Pin 4):
The Output of the voltage error amplifier gm
and the control signal of the current mode PWM control
loop. Switching starts at 0.7V, and higher V
C
corresponds
to higher inductor current. When V
C
is pulled below 25mV,
the LTC3824 goes into micropower shutdown.
V
FB
(Pin 5):
Error Amplifier Inverting Input. A resistor
divider to this pin sets the output voltage. When V
FB
is
less than 0.5V, the switching frequency will fold back to
50kHz to reduce the minimum on-cycle.
SS (Pin 6):
Soft-Start Pin. A capacitor on this pin sets
the output ramp-up rate. The typical time for SS to
reach the programmed level is (C • 0.8V)/7μA.
SENSE (Pin 7):
Current Sense Input Pin. A sense re-
sistor, R
S
, from V
IN
to SENSE sets the current limit to
100mV/R
S
.
V
CC
(Pin 8):
Chip Power Supply. Power supply bypass-
ing is required.
GATE (Pin 9):
Gate Drive for The External P-channel
MOSFET. Typical peak drive current is 2.5A and the drive
voltage is clamped to 8V when V
CC
is higher than 9V.
CAP (Pin 10):
A Low ESR Capacitor of at Least 0.1μF is
required from this pin to V
CC
to bypass the internal regula-
tor for biasing the gate driver circuitry.
Exposed Pad (Pin 11):
GND. Must be soldered to PCB with
expanded metal trace for rated thermal performance.
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