LTC3631EMS8E#PBF [Linear]
LTC3631 - High Efficiency, High Voltage 100mA Synchronous Step-Down Converter; Package: MSOP; Pins: 8; Temperature Range: -40°C to 85°C;
| 型号： | LTC3631EMS8E#PBF |
| 厂家： | 
Linear |
| 描述： | LTC3631 - High Efficiency, High Voltage 100mA Synchronous Step-Down Converter; Package: MSOP; Pins: 8; Temperature Range: -40°C to 85°C 开关 光电二极管 |
| 文件： | 总22页 (文件大小：524K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LTC3631
High Efficiency, High Voltage
100mA Synchronous
Step-Down Converter
FeaTures
DescripTion
The LTC®3631 is a high voltage, high efficiency step-down
DC/DC converter with internal high side and synchronous
power switches that draws only 12μA typical DC supply
current at no load while maintaining output voltage
regulation.
n
Wide Input Voltage Range: Operation from 4.5V to 45V
n
Overvoltage Lockout Provides Protection Up to 60V
n
Internal High Side and Low Side Power Switches
n
No Compensation Required
100mA Output Current
n
n
Low Dropout Operation: 100% Duty Cycle
The LTC3631 can supply up to 100mA load current and
features a programmable peak current limit that provides
a simple method for optimizing efficiency in lower current
applications. The LTC3631’s combination of Burst Mode®
operation, integrated power switches, low quiescent cur-
rent, and programmable peak current limit provides high
efficiency over a broad range of load currents.
n
Low Quiescent Current: 12µA
n
0.8V 1ꢀ Feedback Voltage Reference
n
Adjustable Peak Current Limit
Internal and External Soft-Start
n
n
Precise RUN Pin Threshold with Adjustable
Hysteresis
n
3.3V, 5V and Adjustable Output Versions
n
Withitswide4.5Vto45Vinputrangeandinternalovervolt-
agemonitorcapableofprotectingthepartfrom60Vsurges,
the LTC3631 is a robust converter suited for regulating a
wide variety of power sources. Additionally, the LTC3631
includes a precise run threshold and a soft-start feature
to guarantee that power system start-up is well-controlled
in any environment.
Only Three External Components Required for Fixed
Output Versions
n
Low Profile (0.75mm) 3mm × 3mm DFN and
Thermally-Enhanced MS8E Packages
applicaTions
n
4mA to 20mA Current Loops
The LTC3631 is available in the thermally enhanced
3mm × 3mm DFN and MS8E packages.
L, LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered trademarks
and ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners.
n
Industrial Control Supplies
n
Distributed Power Systems
n
Portable Instruments
n
Battery-Operated Devices
n
Automotive Power Systems
Efficiency and Power Loss vs Load Current
Typical applicaTion
100
EFFICIENCY
90
80
70
60
50
40
30
20
1000
100
10
5V, 100mA Step-Down Converter
100µH
V
OUT
V
IN
V
SW
LTC3631-5
5V
IN
5V TO 45V
2.2µF
100mA
10µF
RUN
HYST
V
POWER LOSS
OUT
SS
I
SET
GND
1
V
V
= 12V
= 36V
IN
IN
3631 TA01a
0.1
1
10
100
LOAD CURRENT (mA)
3631 TA01b
3631fe
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For more information www.linear.com/LTC3631
LTC3631
(Note 1)
absoluTe MaxiMuM raTings
V Supply Voltage..................................... –0.3V to 60V
Operating Junction Temperature Range
IN
SW Voltage (DC)........................... –0.3V to (V + 0.3V)
(Note 2).................................................. –40°C to 125°C
Storage Temperature Range................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec)
IN
RUN Voltage .............................................. –0.3V to 60V
HYST, I , SS Voltages ............................... –0.3V to 6V
SET
V ............................................................... –0.3V to 6V
MS8E................................................................ 300°C
FB
OUT
V
(Fixed Output Versions)....................... –0.3V to 6V
pin conFiguraTion
TOP VIEW
TOP VIEW
SW 1
SW
1
2
3
4
8
7
6
5
GND
8 GND
V
HYST
IN
9
GND
9
V
SET
2
3
7 HYST
6 V /V
IN
GND
I
I
V
/V
OUT FB
SET
OUT FB
5 RUN
SS 4
SS
RUN
MS8E PACKAGE
8-LEAD PLASTIC MSOP
= 125°C, θ = 40°C/W, θ = 5°-10°C/W
JA JC
EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB
DD PACKAGE
8-LEAD (3mm × 3mm) PLASTIC DFN
T
JMAX
T
= 125°C, θ = 43°C/W, θ = 3°C/W
JA JC
JMAX
EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB
orDer inForMaTion
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC3631EMS8E#PBF
LTC3631EMS8E-3.3#PBF
LTC3631EMS8E-5#PBF
LTC3631IMS8E#PBF
LTC3631IMS8E-3.3#PBF
LTC3631IMS8E-5#PBF
LTC3631EDD#PBF
LTC3631EMS8E#TRPBF
LTFDT
8-Lead Plastic MSOP
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
LTC3631EMS8E-3.3#TRPBF LTFFP
8-Lead Plastic MSOP
LTC3631EMS8E-5#TRPBF
LTC3631IMS8E#TRPBF
LTFFR
LTFDT
8-Lead Plastic MSOP
8-Lead Plastic MSOP
LTC3631IMS8E-3.3#TRPBF LTFFP
8-Lead Plastic MSOP
LTC3631IMS8E-5#TRPBF
LTC3631EDD#TRPBF
LTFFR
LFDV
LFFN
LFFQ
LFDV
LFFN
LFFQ
8-Lead Plastic MSOP
8-Lead (3mm × 3mm) Plastic DFN
8-Lead (3mm × 3mm) Plastic DFN
8-Lead (3mm × 3mm) Plastic DFN
8-Lead (3mm × 3mm) Plastic DFN
8-Lead (3mm × 3mm) Plastic DFN
8-Lead (3mm × 3mm) Plastic DFN
LTC3631EDD-3.3#PBF
LTC3631EDD-5#PBF
LTC3631IDD#PBF
LTC3631EDD-3.3#TRPBF
LTC3631EDD-5#TRPBF
LTC3631IDD#TRPBF
LTC3631IDD-3.3#PBF
LTC3631IDD-5#PBF
LTC3631IDD-3.3#TRPBF
LTC3631IDD-5#TRPBF
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
Consult LTC Marketing for information on non-standard lead based finish parts.
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/
3631fe
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For more information www.linear.com/LTC3631
LTC3631
elecTrical characTerisTics The l denotes the specifications which apply over the full operating
junction temperature range, otherwise specifications are for TA = 25°C (Note 2). VIN = 10V, unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Input Supply (V )
IN
V
IN
Input Voltage Operating Range
4.5
45
V
l
l
UVLO
V
V
Undervoltage Lockout
V
V
Rising
Falling
3.80
3.75
4.15
4.00
150
4.50
4.35
V
V
IN
IN
IN
Hysteresis
mV
OVLO
Overvoltage Lockout
V
IN
V
IN
Rising
Falling
47
45
50
48
2
52
50
V
V
V
IN
Hysteresis
I
Q
DC Supply Current (Note 3)
Active Mode
125
12
3
220
22
6
µA
µA
µA
Sleep Mode
Shutdown Mode
V
= 0V
RUN
Output Supply (V /V
)
OUT FB
l
l
V
OUT
Output Voltage Trip Thresholds
LTC3631-3.3V, V
LTC3631-3.3V, V
Rising
Falling
3.260
3.240
3.310
3.290
3.360
3.340
V
V
OUT
OUT
l
l
LTC3631-5V, V
LTC3631-5V, V
Rising
Falling
4.940
4.910
5.015
4.985
5.090
5.060
V
V
OUT
OUT
l
l
V
V
Feedback Comparator Trip Voltage
Feedback Comparator Hysteresis
Feedback Pin Current
V
Rising
FB
0.792
3
0.800
5
0.808
7
V
mV
nA
FB
HYST
I
Adjustable Output Version, V = 1V
–10
0
10
FB
FB
Feedback Voltage Line Regulation
V
= 4.5V to 45V
0.001
ꢀ/V
∆V
LINEREG
IN
LTC3631-5, V = 6V to 45V
IN
Operation
V
RUN
Run Pin Threshold Voltage
RUN Rising
RUN Falling
Hysteresis
1.17
1.06
1.21
1.10
110
1.25
1.14
V
V
mV
I
Run Pin Leakage Current
RUN = 1.3V
–10
0
10
0.1
10
nA
V
RUN
V
Hysteresis Pin Voltage Low
Hysteresis Pin Leakage Current
Soft-Start Pin Pull-Up Current
Internal Soft-Start Time
RUN < 1V, I
= 1mA
HYST
0.07
0
HYSTL
HYST
SS
I
I
t
I
V
V
= 1.3V
–10
4.5
nA
µA
ms
HYST
< 1.5V
5.5
0.75
6.5
SS
SS Pin Floating
INTSS
PEAK
l
Peak Current Trip Threshold
I
Floating
200
40
225
120
50
280
65
mA
mA
mA
SET
500k Resistor from I to GND
SET
I
Shorted to GND
SET
R
ON
Power Switch On-Resistance
Top Switch
Bottom Switch
I
I
= –25mA
= 25mA
3.0
1.5
Ω
Ω
SW
SW
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.
temperature range. Note that the maximum ambient temperature
consistent with these specifications is determined by specific operating
conditions in conjunction with board layout, the rated package thermal
impedance and other environmental factors. The junction temperature
(T , in °C) is calculated from the ambient temperature (T , in °C) and power
J
A
Note 2: The LTC3631 is tested under pulsed load conditions such that
dissipation (PD, in Watts) according to the formula:
T ≈ T . The LTC3631E is guaranteed to meet specifications from
J
A
0°C to 85°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
LTC3631I is guaranteed over the full –40°C to 125°C operating junction
T = T + (PD • θ )
J A JA
where θ (in °C/W) is the package thermal impedance.
JA
Note 3: Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency. See Applications Information.
3631fe
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For more information www.linear.com/LTC3631
LTC3631
Typical perForMance characTerisTics
Efficiency vs Load Current,
VOUT = 5V
Efficiency vs Load Current,
VOUT = 3.3V
Efficiency vs Load Current,
VOUT = 2.5V
95
90
85
80
75
70
65
60
95
90
85
80
75
70
65
60
90
85
80
75
70
65
60
55
50
V
= 3.3V
V
= 5V
V
= 2.5V
OUT
OUT
OUT
V
= 12V
= 36V
V
V
= 12V
= 36V
IN
IN
IN
FIGURE 10 CIRCUIT
FIGURE 10 CIRCUIT
FIGURE 10 CIRCUIT
V
V
= 12V
= 36V
IN
IN
V
IN
V
= 24V
IN
V
= 24V
IN
V
= 24V
IN
0.1
1
10
100
0.1
1
10
100
0.1
1
10
100
LOAD CURRENT (mA)
LOAD CURRENT (mA)
LOAD CURRENT (mA)
3631 G02
3631 G01
3631 G03
Efficiency vs Input Voltage
Line Regulation
Load Regulation
95
90
85
80
5.05
0.20
0.10
0
I
= 100mA
V
V
= 10
V
= 5V
LOAD
IN
OUT
OUT
FIGURE 10 CIRCUIT
= 5V
FIGURE 10 CIRCUIT
5.04
5.03
5.02
5.01
5.00
4.99
4.98
4.97
4.96
FIGURE 10 CIRCUIT
I
= 100mA
LOAD
I
= 10mA
LOAD
I
= 1mA
LOAD
75
70
65
–0.10
–0.20
30
INPUT VOLTAGE (V)
40
45
10 15
20
25
35
5
10 15 20 25 30 35 40 45
INPUT VOLTAGE (V)
0
10 20 30 40 50
100
60 70 80 90
LOAD CURRENT (mA)
3631 G04
3631 G05
3631 G06
Peak Current Trip Threshold
vs Temperature and ISET
Feedback Comparator Trip
Voltage vs Temperature
Feedback Comparator Hysteresis
vs Temperature
0.801
0.800
0.799
0.798
5.6
5.4
250
225
200
175
150
125
100
75
V
= 10V
V
= 10V
V
IN
= 10V
IN
IN
I
= OPEN
SET
5.2
5.0
R
= 500k
= GND
SET
4.8
4.6
4.4
I
SET
50
25
0
–40
–10
20
50
80
110
–40
–10
20
50
80
110
–40
–10
50
80
110
20
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
LTC1144 • TPC06
3631 G08
3631 G09
3631fe
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For more information www.linear.com/LTC3631
LTC3631
Typical perForMance characTerisTics
Peak Current Trip Threshold
vs RISET
Peak Current Trip Threshold
vs Input Voltage
Quiescent Supply Current
vs Input Voltage
240
220
200
180
160
140
120
100
80
250
225
200
175
150
125
100
75
14
12
V
= 10V
IN
I
OPEN
SET
SLEEP
10
8
R
= 500k
= GND
SET
6
SHUTDOWN
4
I
SET
50
60
2
25
40
0
20
0
0
200
400
600
(kΩ)
800 1000 1200
5
15
25
35
45
0
5
10 15 20 25 30 35 40 45 50
R
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
ISET
3631 G10
3631 G12
3631 G11
Quiescent Supply Current
vs Temperature
Switch On-Resistance
vs Input Voltage
Switch On-Resistance
vs Temperature
5
4
3
14
12
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
V
IN
= 10V
V
= 10V
IN
SLEEP
TOP
10
8
TOP
BOTTOM
6
2
1
0
BOTTOM
4
SHUTDOWN
2
0
0
–10
20
50
110
–10
50
80
110
–40
80
–40
20
0
40
50
10
20
30
TEMPERATURE (°C)
TEMPERATURE (°C)
INPUT VOLTAGE (V)
3631 G13
3631 G15
3631 G14
Switch Leakage Current
vs Temperature
RUN Comparator Threshold
Voltages vs Temperature
Operating Waveforms
0.6
0.5
0.4
0.3
0.2
0.1
0
1.300
1.250
V
IN
= 45V
SWITCH
VOLTAGE
20V/DIV
RISING
1.200
1.150
OUTPUT
VOLTAGE
50mV/DIV
FALLING
1.100
1.050
1.000
INDUCTOR
CURRENT
100mA/DIV
SW = 0V
SW = 45V
3631 G18
V
IN
V
= 36V
20µs/DIV
–40
–10
20
50
80
110
–40
–10
20
50
80
110
= 5V
OUT
LOAD
TEMPERATURE (°C)
TEMPERATURE (°C)
I
= 35mA
3631 G16
3631 G17
3631fe
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For more information www.linear.com/LTC3631
LTC3631
Typical perForMance characTerisTics
Soft-Start Waveform
Load Step Transient Response
Short-Circuit Response
OUTPUT
VOLTAGE
50mV/DIV
OUTPUT
VOLTAGE
2V/DIV
OUTPUT
VOLTAGE
1V/DIV
LOAD
CURRENT
50mA/DIV
INDUCTOR
CURRENT
100mA/DIV
3631 G19
3631 G20
3631 G21
C
= 0.047µF
5ms/DIV
V
V
= 24V
= 5V
1ms/DIV
V
V
= 10V
= 5V
200µs/DIV
SS
IN
OUT
IN
OUT
pin FuncTions
SW (Pin 1): Switch Node Connection to Inductor. This
pin connects to the drains of the internal power MOSFET
switches.
V
/V (Pin 6): Output Voltage Feedback. For the fixed
OUT FB
output versions, connect this pin to the output supply. For
the adjustable version, an external resistive divider should
be used to divide the output voltage down for comparison
to the 0.8V reference.
V (Pin 2): Main Supply Pin. A ceramic bypass capacitor
IN
should be tied between this pin and GND (Pin 8).
HYST (Pin 7): Run Hysteresis Open-Drain Logic Output.
This pin is pulled to ground when RUN (Pin 5) is below
1.2V.ThispincanbeusedtoadjusttheRUNpinhysteresis.
See Applications Information.
I
(Pin 3): Peak Current Set Input. A resistor from this
SET
pin to ground sets the peak current trip threshold. Leave
floating for the maximum peak current (225mA). Short
this pin to ground for the minimum peak current (50mA).
A 1µA current is sourced out of this pin.
GND (Pin 8, Exposed Pad Pin 9): Ground. The exposed
pad must be soldered to the printed circuit board ground
plane for optimal electrical and thermal performance.
SS (Pin 4): Soft-Start Control Input. A capacitor to ground
at this pin sets the ramp time to full current output dur-
ing start-up. A 5µA current is sourced out of this pin. If
left floating, the ramp time defaults to an internal 0.75ms
soft-start.
RUN (Pin 5): Run Control Input. A voltage on this pin
above 1.2V enables normal operation. Forcing this pin
below 0.7V shuts down the LTC3631, reducing quiescent
current to approximately 3µA.
3631fe
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For more information www.linear.com/LTC3631
LTC3631
block DiagraM
V
IN
1µA
2
I
SET
C2
3
–
+
PEAK CURRENT
COMPARATOR
RUN
5
LOGIC
AND
+
–
SW
1
L1
SHOOT-
V
OUT
THROUGH
PREVENTION
C1
1.2V
HYST
7
+
–
REVERSE CURRENT
COMPARATOR
VOLTAGE
REFERENCE
FEEDBACK
COMPARATOR
0.800V
+
+
–
5µA
SS
4
V
/V
OUT FB
GND
8
GND
9
R1
6
3631 BD
R2
IMPLEMENT DIVIDER
EXTERNALLY FOR
ADJUSTABLE VERSION
PART
NUMBER
R1
R2
LTC3631
LTC3631-3.3
LTC3631-5
0
∞
2.5M 800k
4.2M 800k
3631fe
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For more information www.linear.com/LTC3631
LTC3631
(Refer to Block Diagram)
operaTion
TheLTC3631isastep-downDC/DCconverterwithinternal
power switches that uses Burst Mode control, combin-
ing low quiescent current with high switching frequency,
which results in high efficiency across a wide range of
load currents. Burst Mode operation functions by using
short “burst” cycles to ramp the inductor current through
the internal power switches, followed by a sleep cycle
where the power switches are off and the load current is
supplied by the output capacitor. During the sleep cycle,
the LTC3631 draws only 12µA of supply current. At light
loads, the burst cycles are a small percentage of the total
cycle time which minimizes the average supply current,
greatly improving efficiency.
greaterthantheaverageloadcurrent.Forthisarchitecture,
the maximum average output current is equal to half of
the peak current.
The hysteretic nature of this control architecture results
in a switching frequency that is a function of the input
voltage, output voltage and inductor value. This behavior
provides inherent short-circuit protection. If the output
is shorted to ground, the inductor current will decay very
slowly during a single switching cycle. Since the high side
switch turns on only when the inductor current is near
zero,theLTC3631inherentlyswitchesatalowerfrequency
during start-up or short-circuit conditions.
Start-Up and Shutdown
Main Control Loop
IfthevoltageontheRUNpinislessthan0.7V, theLTC3631
enters a shutdown mode in which all internal circuitry is
disabled,reducingtheDCsupplycurrentto3µA.Whenthe
voltageontheRUNpinexceeds1.21V,normaloperationof
the main control loop is enabled. The RUN pin comparator
has 110mV of internal hysteresis, and therefore must fall
below 1.1V to disable the main control loop.
The feedback comparator monitors the voltage on the V
FB
pin and compares it to an internal 800mV reference. If
this voltage is greater than the reference, the comparator
activates a sleep mode in which the power switches and
current comparators are disabled, reducing the V pin
IN
supplycurrenttoonly12µA.Astheloadcurrentdischarges
the output capacitor, the voltage on the V pin decreases.
FB
The HYST pin provides an added degree of flexibility for
the RUN pin operation. This open-drain output is pulled
to ground whenever the RUN comparator is not tripped,
signaling that the LTC3631 is not in normal operation. In
applications where the RUN pin is used to monitor the
When this voltage falls 5mV below the 800mV reference,
the feedback comparator trips and enables burst cycles.
At the beginning of the burst cycle, the internal high side
power switch (P-channel MOSFET) is turned on and the
inductor current begins to ramp up. The inductor current
increases until either the current exceeds the peak cur-
V voltage through an external resistive divider, the HYST
IN
pin can be used to increase the effective RUN comparator
rent comparator threshold or the voltage on the V pin
FB
hysteresis.
exceeds 800mV, at which time the high side power switch
is turned off, and the low side power switch (N-channel
MOSFET)turnson. Theinductorcurrentrampsdownuntil
the reverse current comparator trips, signaling that the
An internal 1ms soft-start function limits the ramp rate of
the output voltage on start-up to prevent excessive input
supply droop. If a longer ramp time and consequently less
supplydroopisdesired,acapacitorcanbeplacedfromthe
SS pin to ground. The 5µA current that is sourced out of
thispinwillcreateasmoothvoltageramponthecapacitor.
If this ramp rate is slower than the internal 1ms soft-start,
current is close to zero. If the voltage on the V pin is
FB
still less than the 800mV reference, the high side power
switch is turned on again and another cycle commences.
The average current during a burst cycle will normally be
3631fe
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For more information www.linear.com/LTC3631
LTC3631
(Refer to Block Diagram)
operaTion
then the output voltage will be limited by the ramp rate
on the SS pin instead. The internal and external soft-start
functions are reset on start-up and after an undervoltage
or overvoltage event on the input supply.
from the I pin to ground. The 1µA current sourced out
SET
of this pin through the resistor generates a voltage that is
translated into an offset in the peak current comparator,
which limits the peak inductor current.
In order to ensure a smooth start-up transition in any
application, the internal soft-start also ramps the peak
inductor current from 50mA during its 1ms ramp time to
the set peak current threshold. The external ramp on the
SS pin does not limit the peak inductor current during
Input Undervoltage and Overvoltage Lockout
The LTC3631 implements a protection feature which dis-
ables switching when the input voltage is not within the
4.5V to 45V operating range. If V falls below 4V typical
IN
(4.35V maximum), an undervoltage detector disables
start-up; however, placing a capacitor from the I
to ground does provide this capability.
pin
SET
switching. Similarly, if V rises above 50V typical (47V
IN
minimum), an overvoltage detector disables switching.
Whenswitchingisdisabled,theLTC3631cansafelysustain
input voltages up to the absolute maximum rating of 60V.
Switching is enabled when the input voltage returns to the
4.5V to 45V operating range.
Peak Inductor Current Programming
The offset of the peak current comparator nominally
provides a peak inductor current of 225mA. This peak
inductor current can be adjusted by placing a resistor
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LTC3631
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ThebasicLTC3631applicationcircuitisshownonthefront
page of this data sheet. External component selection is
determinedbythemaximumloadcurrentrequirementand
beginswiththeselectionofthepeakcurrentprogramming
maximum average output current for this architecture is
limited to half of the peak current. Therefore, be sure to
select a value that sets the peak current with enough mar-
gin to provide adequate load current under all foreseeable
operating conditions.
resistor,R .TheinductorvalueLcanthenbedetermined,
ISET
followed by capacitors C and C
.
IN
OUT
Inductor Selection
Peak Current Resistor Selection
The inductor, input voltage, output voltage and peak cur-
rent determine the switching frequency of the LTC3631.
For a given input voltage, output voltage and peak current,
the inductor value sets the switching frequency when the
output is in regulation. A good first choice for the inductor
value can be determined by the following equation:
Thepeakcurrentcomparatorhasamaximumcurrentlimit
of 225mA nominally, which results in a maximum aver-
age current of 112mA. For applications that demand less
current, the peak current threshold can be reduced to as
little as 50mA. This lower peak current allows the use of
lower value, smaller components (input capacitor, output
capacitor and inductor), resulting in lower input supply
ripple and a smaller overall DC/DC converter.
VOUT
V
V
IN
OUT
L =
• 1–
f •I
PEAK
The threshold can be easily programmed with an ap-
The variation in switching frequency with input voltage
and inductance is shown in the following two figures for
propriately chosen resistor (R ) between the I
pin
ISET
SET
and ground. The value of resistor for a particular peak
current can be computed by using Figure 1 or the follow-
ing equation:
typical values of V . For lower values of I
, multiply
OUT
PEAK
the frequency in Figure 2 and Figure 3 by 225mA/I
.
PEAK
An additional constraint on the inductor value is the
LTC3631’s100nsminimumon-timeofthehighsideswitch.
Therefore, in order to keep the current in the inductor well
controlled, the inductor value must be chosen so that it
6
R
ISET
= I
• 4.5 • 10
PEAK
where 50mA < I
< 225mA.
PEAK
The peak current is internally limited to be within the
is larger than L , which can be computed as follows:
MIN
range of 50mA to 225mA. Shorting the I pin to ground
SET
V
IN(MAX) • tON(MIN)
programs the current limit to 50mA, and leaving it floating
sets the current limit to the maximum value of 225mA.
When selecting this resistor value, be aware that the
LMIN
=
IPEAK(MAX)
where V
is the maximum input supply voltage for
IN(MAX)
the application, t
1100
1000
900
800
700
600
500
400
300
200
100
0
is 100ns, and I
is the
ON(MIN)
PEAK(MAX)
maximum allowed peak inductor current. Although the
above equation provides the minimum inductor value,
higherefficiencyisgenerallyachievedwithalargerinductor
value, which produces a lower switching frequency. For a
given inductor type, however, as inductance is increased
DC resistance (DCR) also increases. Higher DCR trans-
lates into higher copper losses and lower current rating,
both of which place an upper limit on the inductance. The
recommended range of inductor values for small surface
mount inductors as a function of peak current is shown in
Figure 4. The values in this range are a good compromise
between the trade-offs discussed above. For applications
3631fe
20
40 50 60 70 80 90 100
MAXIMUM LOAD CURRENT (mA)
30
3631 F01
Figure 1. RISET Selection
10
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LTC3631
applicaTions inForMaTion
700
where board area is not a limiting factor, inductors with
largercorescanbeused,whichextendstherecommended
range of Figure 4 to larger values.
V
SET
= 5V
OUT
L = 22µH
I
OPEN
600
500
L = 47µH
Inductor Core Selection
400
300
200
100
Once the value for L is known, the type of inductor must
be selected. High efficiency converters generally cannot
affordthecorelossfoundinlowcostpowderedironcores,
forcing the use of the more expensive ferrite cores. Actual
core loss is independent of core size for a fixed inductor
value but is very dependent of the inductance selected.
As the inductance increases, core losses decrease. Un-
fortunately, increased inductance requires more turns of
wire and therefore copper losses will increase.
L = 100µH
L = 220µH
0
10 15 20 25
INPUT VOLTAGE (V)
40 45
5
30 35
3631 F02
Figure 2. Switching Frequency for VOUT = 5V
Ferrite designs have very low core losses and are pre-
ferred at high switching frequencies, so design goals
can concentrate on copper loss and preventing satura-
tion. Ferrite core material saturates “hard,” which means
that inductance collapses abruptly when the peak design
current is exceeded. This results in an abrupt increase in
inductor ripple current and consequently output voltage
ripple. Do not allow the core to saturate!
500
450
L = 22µH
400
V
SET
= 3.3V
OUT
350
300
250
200
150
100
50
I
OPEN
L = 47µH
L = 100µH
L = 220µH
Different core materials and shapes will change the size/
currentandprice/currentrelationshipofaninductor.Toroid
or shielded pot cores in ferrite or permalloy materials are
small and do not radiate energy but generally cost more
than powdered iron core inductors with similar charac-
teristics. The choice of which style inductor to use mainly
dependsonthepricevssizerequirementsandanyradiated
field/EMI requirements. New designs for surface mount
inductors are available from Coiltronics, Coilcraft, TDK,
Toko, Sumida and Vishay.
0
5
35 40
10 15 20
25
INPUT VOLTAGE (V)
30
45
3631 F03
Figure 3. Switching Frequency for VOUT = 3.3V
10000
1000
100
10
C and C
Selection
IN
OUT
The input capacitor, C , is needed to filter the trapezoidal
IN
current at the source of the top high side MOSFET. To
prevent large ripple voltage, a low ESR input capacitor
sized for the maximum RMS current should be used.
Approximate RMS current is given by:
10
100
1000
PEAK INDUCTOR CURRENT (mA)
VOUT
V
IN
V
IN
VOUT
3631 F04
IRMS = IOUT(MAX)
•
•
− 1
Figure 4. Recommended Inductor Values for Maximum Efficiency
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Tantalum, special polymer, aluminum electrolytic, and
ceramic capacitors are all available in surface mount
packages. Special polymer capacitors offer very low ESR
but have lower capacitance density than other types.
Tantalum capacitors have the highest capacitance density
but it is important only to use types that have been surge
tested for use in switching power supplies. Aluminum
electrolytic capacitors have significantly higher ESR but
can be used in cost-sensitive applications provided that
consideration is given to ripple current ratings and long-
termreliability.CeramiccapacitorshaveexcellentlowESR
characteristics but can have high voltage coefficient and
audible piezoelectric effects. The high quality factor (Q)
of ceramic capacitors in series with trace inductance can
also lead to significant ringing.
This formula has a maximum at V = 2V , where
IN
OUT
I
= I /2. This simple worst-case condition is com-
RMS
OUT
monlyusedfordesignbecauseevensignificantdeviations
do not offer much relief. Note that ripple current ratings
from capacitor manufacturers are often based only on
2000 hours of life which makes it advisable to further
derate the capacitor, or choose a capacitor rated at a
highertemperaturethanrequired.Severalcapacitorsmay
also be paralleled to meet size or height requirements in
the design.
The output capacitor, C , filters the inductor’s ripple
OUT
current and stores energy to satisfy the load current when
the LTC3631 is in sleep. The output ripple has a lower limit
of V /160 due to the 5mV typical hysteresis of the feed-
OUT
back comparator. The time delay of the comparator adds
an additional ripple voltage that is a function of the load
current. During this delay time, the LTC3631 continues to
switch and supply current to the output. The output ripple
can be approximated by:
Using Ceramic Input and Output Capacitors
Higher value, lower cost ceramic capacitors are now be-
coming available in smaller case sizes. Their high ripple
current, high voltage rating and low ESR make them ideal
for switching regulator applications. However, care must
be taken when these capacitors are used at the input and
output. When a ceramic capacitor is used at the input and
thepowerissuppliedbyawalladapterthroughlongwires,
a load step at the output can induce ringing at the input,
–6
LOAD
VOUT
160
IPEAK
2
4 •10
COUT
ΔVOUT
≈
–I
+
Theoutputrippleisamaximumatnoloadandapproaches
lower limit of V /160 at full load. Choose the output
OUT
capacitor C
to limit the output voltage ripple at mini-
mum load current.
V . At best, this ringing can couple to the output and be
OUT
IN
mistaken as loop instability. At worst, a sudden inrush
of current through the long wires can potentially cause a
The value of the output capacitor must be large enough
to accept the energy stored in the inductor without a large
change in output voltage. Setting this voltage step equal
to 1ꢀ of the output voltage, the output capacitor must be:
voltage spike at V large enough to damage the LTC3631.
IN
For applications with inductive source impedance, such
as a long wire, a series RC network may be required in
parallel with C to dampen the ringing of the input supply.
IN
2
I
V
Figure 5 shows this circuit and the typical values required
PEAK
OUT
COUT > 50 •L •
to dampen the ringing.
Typically, a capacitor that satisfies the voltage ripple re-
quirementisadequatetofiltertheinductorripple. Toavoid
overheating, the output capacitor must also be sized to
handle the ripple current generated by the inductor. The
worst-case ripple current in the output capacitor is given
LTC3631
L
IN
V
IN
L
C
IN
R =
4 • C
IN
3631 F05
C
IN
IN
by I
= I
/2. Multiple capacitors placed in parallel
RMS
PEAK
maybeneededtomeettheESRandRMScurrenthandling
requirements.
Figure 5. Series RC to Reduce VIN Ringing
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Output Voltage Programming
controller is enabled. Figure 7 shows examples of con-
figurations for driving the RUN pin from logic.
For the adjustable version, the output voltage is set by
an external resistive divider according to the following
equation:
V
V
IN
SUPPLY
4.7M
LTC3631
RUN
LTC3631
RUN
R1
R2
VOUT = 0.8V • 1+
3631 F07
The resistive divider allows the V pin to sense a fraction
FB
of the output voltage as shown in Figure 6. Output voltage
Figure 7. RUN Pin Interface to Logic
can range from 0.8V to V .
IN
The RUN pin can alternatively be configured as a precise
V
OUT
undervoltage lockout (UVLO) on the V supply with a
IN
resistive divider from V to ground. The RUN pin com-
R1
IN
V
FB
parator nominally provides 10ꢀ hysteresis when used in
this method; however, additional hysteresis may be added
with the use of the HYST pin. The HYST pin is an open-
drain output that is pulled to ground whenever the RUN
comparator is not tripped. A simple resistive divider can
R2
LTC3631
GND
3631 F06
Figure 6. Setting the Output Voltage
be used as shown in Figure 8 to meet specific V voltage
requirements.
IN
To minimize the no-load supply current, resistor values in
themegohmrangeshouldbeused;however,largeresistor
values should be used with caution. The feedback divider
is the only load current when in shutdown. If PCB leak-
age current to the output node or switch node exceeds
the load current, the output voltage will be pulled up. In
normal operation, this is generally a minor concern since
the load current is much greater than the leakage. The
increase in supply current due to the feedback resistors
can be calculated from:
V
IN
R1
RUN
LTC3631
HYST
R2
R3
3631 F08
Figure 8. Adjustable Undervoltage Lockout
VOUT
R1+R2
V
V
OUT
IN
ΔIVIN
=
•
SpecificvaluesfortheseUVLOthresholdscanbecomputed
from the following equations:
R1
R2
Run Pin with Programmable Hysteresis
Rising V UVLO Threshold = 1.21V • 1+
IN
The LTC3631 has a low power shutdown mode controlled
by the RUN pin. Pulling the RUN pin below 0.7V puts the
LTC3631 into a low quiescent current shutdown mode
(IQ ~ 3µA). When the RUN pin is greater than 1.2V, the
R1
R2+R3
Falling V UVLO Threshold = 1.10V • 1+
IN
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from I
SET
to ground. A 1µA current is sourced out of the
The minimum value of these thresholds is limited to
SET
I
pin. With only a capacitor connected between I
the internal V UVLO thresholds that are shown in the
SET
IN
and ground, the peak current ramps linearly from 50mA
to 225mA, and the peak current soft-start time can be
expressed as:
Electrical Characteristics table. The current that flows
through this divider will directly add to the shutdown,
sleep and active current of the LTC3631, and care should
be taken to minimize the impact of this current on the
overall efficiency of the application circuit. Resistor values
in the megohm range may be required to keep the impact
on quiescent shutdown and sleep currents low. Be aware
that the HYST pin cannot be allowed to exceed its absolute
maximum rating of 6V. To keep the voltage on the HYST
pin from exceeding 6V, the following relation should be
satisfied:
0.8V
1µA
tSS(ISET) = CISET
•
A linear ramp of peak current appears as a quadratic
waveform on the output voltage. For the case where the
peak current is reduced by placing a resistor from I
SET
to ground, the peak current offset ramps as a decaying
exponential with a time constant of R • C . For this
ISET
ISET
case, the peak current soft-start time is approximately
R3
V
•
< 6V
3 • R • C
.
ISET
ISET
IN(MAX)
R1+R2+R3
Unlike the SS pin, the I
pin does not get pulled to
SET
ground during an abnormal event; however, if the I
The RUN pin may also be directly tied to the V supply
SET
IN
pin is floating (programmed to 225mA peak current),
for applications that do not require the programmable un-
dervoltagelockoutfeature.Inthisconfiguration,switching
the SS and I pins may be tied together and connected
SET
to a capacitor to ground. For this special case, both the
peak current and the reference voltage will soft-start on
power-up and after fault conditions. The ramp time for
is enabled when V surpasses the internal undervoltage
IN
lockout threshold.
Soft-Start
this combination is C
• (0.8V/6µA).
SS(ISET)
The internal 0.75ms soft-start is implemented by ramping
both the effective reference voltage from 0V to 0.8V and
Efficiency Considerations
Theefficiencyofaswitchingregulatorisequaltotheoutput
power divided by the input power times 100ꢀ. It is often
useful to analyze individual losses to determine what is
limiting the efficiency and which change would produce
the most improvement. Efficiency can be expressed as:
thepeakcurrentlimitsetbytheI pin(50mAto225mA).
SET
Toincreasethedurationofthereferencevoltagesoft-start,
place a capacitor from the SS pin to ground. An internal
5µA pull-up current will charge this capacitor, resulting in
a soft-start ramp time given by:
Efficiency = 100ꢀ – (L1 + L2 + L3 + ...)
0.8V
5µA
tSS = CSS
•
where L1, L2, etc. are the individual losses as a percent-
age of input power.
When the LTC3631 detects a fault condition (input supply
undervoltage or overvoltage) or when the RUN pin falls
below 1.1V, the SS pin is quickly pulled to ground and the
internal soft-start timer is reset. This ensures an orderly
restart when using an external soft-start capacitor.
Although all dissipative elements in the circuit produce
losses, two main sources usually account for most of
2
the losses: V operating current and I R losses. The V
IN
IN
operating current dominates the efficiency loss at very
2
low load currents whereas the I R loss dominates the
efficiency loss at medium to high load currents.
Thedurationof the0.75ms internalpeak currentsoft-start
may be increased by placing a capacitor from the I pin
SET
1. The V operating current comprises two components:
IN
toground.Thepeakcurrentsoft-startwillrampfrom50mA
The DC supply current as given in the electrical charac-
to the final peak current value determined by a resistor
teristics and the internal MOSFET gate charge currents.
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LTC3631
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The gate charge current results from switching the gate
capacitance of the internal power MOSFET switches.
Each time the gate is switched from high to low to
First, calculate the inductor value that gives the required
switching frequency:
3.3V
250kHz • 225mA
3.3V
24V
Ê
ˆ Ê
ˆ
high again, a packet of charge, dQ, moves from V to
L =
• 1–
@ 47µH
IN
Á
Ë
˜ Á
¯ Ë
˜
¯
ground. The resulting dQ/dt is the current out of V
IN
that is typically larger than the DC bias current.
Next, verify that this value meets the L
requirement.
MIN
2
2. I R losses are calculated from the resistances of the
For this input voltage and peak current, the minimum
inductor value is:
internal switches, R , and external inductor R . When
SW
L
switching, the average output current flowing through
the inductor is “chopped” between the high side PMOS
switch and the low side NMOS switch. Thus, the series
resistance looking back into the switch pin is a function
24V • 100ns
LMIN
=
≅ 10µH
225mA
Therefore, theminimuminductorrequirementissatisfied,
and the 47μH inductor value may be used.
of the top and bottom switch R
values and the
DS(ON)
duty cycle (DC = V /V ) as follows:
OUT IN
Next,C andC areselected.Forthisdesign,C should
IN
OUT
IN
R
SW
= (R )DC + (R )(1 – DC)
DS(ON)TOP DS(ON)BOT
be sized for a current rating of at least:
The R
for both the top and bottom MOSFETs can
DS(ON)
3.3V
24V
24V
3.3V
be obtained from the Typical Performance Characteris-
IRMS = 100mA •
•
– 1 ≅ 35mARMS
2
tics curves. Thus, to obtain the I R losses, simply add
R
to R and multiply the result by the square of the
SW
L
Due to the low peak current of the LTC3631, decoupling
the V supply with a 1µF capacitor is adequate for most
average output current:
IN
2
2
I R Loss = I (R + R )
applications.
O
SW
L
Other losses, including C and C
ESR dissipative
OUT
C
will be selected based on the output voltage ripple
IN
OUT
requirement. For a 2ꢀ (67mV) output voltage ripple at no
losses and inductor core losses, generally account for
load, C
can be calculated from:
less than 2ꢀ of the total power loss.
OUT
225mA • 4 •10–6
COUT
=
Thermal Considerations
3.3V
160
2 67mV –
The LTC3631 does not dissipate much heat due to its high
efficiency and low peak current level. Even in worst-case
conditions (high ambient temperature, maximum peak
current and high duty cycle), the junction temperature
will exceed ambient temperature by only a few degrees.
A 9.7µF capacitor gives this typical output voltage ripple
at no load. Choose a 10µF capacitor as a standard value.
The output voltage can now be programmed by choosing
the values of R1 and R2. Choose R2 = 240k and calculate
R1 as:
Design Example
As a design example, consider using the LTC3631 in an
application with the following specifications: V = 24V,
VOUT
0.8V
IN
R1=
– 1 •R2 = 750k
V
= 3.3V, I
= 100mA, f = 250kHz. Furthermore, as-
OUT
OUT
sume for this example that switching should start when V
IN
is greater than 12V and should stop when V is less than 8V.
IN
3631fe
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LTC3631
applicaTions inForMaTion
2. Connect the (+) terminal of the input capacitor, C , as
The undervoltage lockout requirement on V can be
IN
IN
close as possible to the V pin. This capacitor provides
satisfied with a resistive divider from V to the RUN
IN
IN
and HYST pins. Choose R1 = 2M and calculate R2 and
R3 as follows:
the AC current into the internal power MOSFETs.
3. Keep the switching node, SW, away from all sensitive
smallsignalnodes.Therapidtransitionsontheswitching
node can couple to high impedance nodes, in particular
1.21V
IN(RISING) – 1.21V
R2 =
R3 =
•R1= 224k
V
V , and create increased output ripple.
FB
4. Flood allunused area on alllayers with copper. Flooding
with copper will reduce the temperature rise of power
components. You can connect the copper areas to any
1.1V
IN(FALLING) – 1.1V
•R1– R2 = 94.8k
V
DC net (V , V , GND or any other DC rail in your
IN OUT
system).
Choose standard values for R2 = 226k and R3 = 95.3k.
The I pin should be left open in this example to select
SET
Example Layout
maximum peak current (225mA). Figure 9 shows a com-
plete schematic for this design example.
L1
V
IN
V
OUT
V
SW
IN
LTC3631
47µH
R1
R2
V
OUT
RUN
HYST
SS
V
IN
V
SW
LTC3631
3.3V
IN
C
24V
C
IN
V
OUT
FB
100mA
10µF
2M
I
1µF
SET
RUN
I
SET
GND
C
R
SS
SET
226k
SS
750k
240k
3631 F09a
V
FB
HYST
GND
95.3k
3631 F09
L1
Figure 9. 24V to 3.3V, 100mA Regulator at 250kHz
V
IN
V
C
IN
C
OUT
OUT
PC Board Layout Checklist
When laying out the printed circuit board, the following
checklist should be used to ensure proper operation of
the LTC3631. Check the following in your layout:
R1
1. Large switched currents flow in the power switches
and input capacitor. The loop formed by these compo-
nents should be as small as possible. A ground plane
is recommended to minimize ground impedance.
R2
R
C
SS
SET
GND
VIAS TO GROUND PLANE
VIAS TO INPUT SUPPLY (V
)
IN
OUTLINE OF LOCAL GROUND PLANE
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LTC3631
Typical applicaTions
L1
100µH
V
V
IN
OUT
V
SW
LTC3631
IN
5V TO 45V
5V
C
R1
1.47M
C
IN
OUT
4.7µF
100µF
RUN
V
FB
R2
280k
HYST
I
SS
SET
C
GND
SS
47nF
3631 F10a
C
C
: TDK C5750X7R2A475MT
IN
: AVX 1812D107MAT
OUT
L1: TDK SLF7045T-101MR50-PF
Figure 10. High Efficiency 5V Regulator
3.3V, 100mA Regulator with Peak Current Soft-Start, Small Size
Soft-Start Waveforms
L1
22µH
V
OUT
V
IN
V
SW
LTC3631
RUN
3.3V
IN
4.5V TO 24V
OUTPUT
VOLTAGE
1V/DIV
C
R1
100mA
C
IN
OUT
1µF
294k
10µF
V
FB
R2
93.1k
I
SET
SS
HYST
GND
3642 TA03a
C
SS
22nF
INDUCTOR
CURRENT
50mA/DIV
C
C
: TDK C3216X7R1E105KT
IN
: AVX 08056D106KAT2A
OUT
L1: MURATA LQH43CN220K03
3631 TA03b
500µs/DIV
Positive-to-Negative Converter
Maximum Load Current vs Input Voltage
L1
100µH
100
I
OPEN
SET
V
= –3V
V
OUT
V
IN
90
80
70
60
50
40
30
20
V
SW
LTC3631
RUN
IN
4.5V TO 33V
C
IN
R1
= –5V
1µF
OUT
1M
C
OUT
I
V
FB
SET
10µF
V
OUT
= –12V
HYST
GND
SS
R2
71.5k
V
OUT
–12V
C
C
: TDK C3225X7R1H105KT
: MURATA GRM32DR71C106KA01
IN
OUT
3631 TA04a
L1: TYCO/COEV DQ6545-101M
25 30
10 15 20
INPUT VOLTAGE (V)
5
35 40 45
3631 TA04b
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LTC3631
Typical applicaTions
Small Size, Limited Peak Current, 20mA Regulator
L1
470µH
V
OUT
V
IN
V
SW
LTC3631
5V
IN
7V TO 45V
C
R3
R1
20mA
C
IN
OUT
1µF 470k
470k
10µF
RUN
V
FB
R4
100k
R2
88.7k
HYST
SS
3631 TA05a
R5
33k
I
GND
SET
C
C
: TDK C3225X7R1H105KT
IN
: AVX 08056D106KAT2A
OUT
L1: MURATA LQH43CN471K03
High Efficiency 15V, 20mA Regulator
Efficiency vs Load Current
100
95
90
85
80
75
70
65
L1
1000µH
V
OUT
V
V
= 24V
= 36V
V
IN
IN
IN
15V
V
SW
LTC3631
IN
15V TO 45V
20mA
C
R1
C
IN
OUT
1µF
3M
4.7µF
RUN
V
FB
R2
169k
I
SET
V
= 45V
IN
SS
HYST
GND
3631 TA07a
C
C
: AVX 18125C105KAT2A
IN
OUT
: TDK C3216X7R1E475KT
L1: TDK SLF7045T-102MR14
60
0.1
1
10
100
LOAD CURRENT (mA)
3631 TA07b
3631fe
18
For more information www.linear.com/LTC3631
LTC3631
package DescripTion
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
DD Package
8-Lead Plastic DFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1698 Rev C)
0.70 ±0.05
3.5 ±0.05
2.10 ±0.05 (2 SIDES)
1.65 ±0.05
PACKAGE
OUTLINE
0.25 ± 0.05
0.50
BSC
2.38 ±0.05
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
R = 0.125
0.40 ± 0.10
TYP
5
8
3.00 ±0.10
(4 SIDES)
1.65 ± 0.10
(2 SIDES)
PIN 1
TOP MARK
(NOTE 6)
(DD8) DFN 0509 REV C
4
1
0.25 ± 0.05
0.75 ±0.05
0.200 REF
0.50 BSC
2.38 ±0.10
BOTTOM VIEW—EXPOSED PAD
0.00 – 0.05
NOTE:
1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-1)
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION
ON TOP AND BOTTOM OF PACKAGE
3631fe
19
For more information www.linear.com/LTC3631
LTC3631
package DescripTion
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
MS8E Package
8-Lead Plastic MSOP, Exposed Die Pad
(Reference LTC DWG # 05-08-1662 Rev K)
BOTTOM VIEW OF
EXPOSED PAD OPTION
1.88
(.074)
1
0.29
REF
1.88 ±0.102
(.074 ±.004)
1.68
(.066)
0.889 ±0.127
(.035 ±.005)
0.05 REF
DETAIL “B”
5.10
(.201)
MIN
3.20 – 3.45
(.126 – .136)
1.68 ±0.102
(.066 ±.004)
CORNER TAIL IS PART OF
THE LEADFRAME FEATURE.
FOR REFERENCE ONLY
DETAIL “B”
8
NO MEASUREMENT PURPOSE
3.00 ±0.102
(.118 ±.004)
(NOTE 3)
0.65
(.0256)
BSC
0.52
(.0205)
REF
0.42 ±0.038
(.0165 ±.0015)
8
7 6 5
TYP
RECOMMENDED SOLDER PAD LAYOUT
3.00 ±0.102
(.118 ±.004)
(NOTE 4)
4.90 ±0.152
(.193 ±.006)
DETAIL “A”
0.254
(.010)
0° – 6° TYP
GAUGE PLANE
1
2
3
4
0.53 ±0.152
(.021 ±.006)
1.10
(.043)
MAX
0.86
(.034)
REF
DETAIL “A”
0.18
(.007)
SEATING
PLANE
0.22 – 0.38
(.009 – .015)
TYP
0.1016 ±0.0508
(.004 ±.002)
0.65
(.0256)
BSC
MSOP (MS8E) 0213 REV K
NOTE:
1. DIMENSIONS IN MILLIMETER/(INCH)
2. DRAWING NOT TO SCALE
3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.
MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
6. EXPOSED PAD DIMENSION DOES INCLUDE MOLD FLASH. MOLD FLASH ON E-PAD
SHALL NOT EXCEED 0.254mm (.010") PER SIDE.
3631fe
20
For more information www.linear.com/LTC3631
LTC3631
revision hisTory (Revision history begins at Rev B)
REV
DATE
DESCRIPTION
PAGE NUMBER
B
05/10 Updated Absolute Maximum Ratings and Order Information Sections
Updated Note 2
2
3
Updated Graphs G09, G18 and G19
Updated GND pin text in Pin Functions
Text added to “Output Voltage Programming” section
“Example Layout” Art added
4, 5, 6
6
12
16
22
22
12
15
16
16
11
Updated Typical Application
Updated Related Parts
C
D
E
10/10 Updated C and C
Selection section
IN
OUT
Updated Efficiency Considerations section
08/11 Updated equation in Design Example section
Updated Figure 9
05/13 Clarified inductor values in Figures 2 and 3
3631fe
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
21
LTC3631
Typical applicaTion
5V, 100mA Regulator for Automotive Applications
L1
100µH
V
*
OUT
5V
100mA
V
BATT
V
SW
LTC3631
RUN
IN
4.5V TO 45V
AND SURVIVES
TRANSIENTS
UP TO 60V
C
IN
2.2µF
R1
C
OUT
470k
10µF
V
FB
R2
88.7k
I
SET
SS
HYST
GND
3631 TA06a
C
: TDK C3225X7R2A225M
: KEMET C1210C106K4RAC
*V
V
FOR V
< 5V
IN
OUT = BATT
BATT
C
OUT
L1: COILTRONICS DRA73-101-R
relaTeD parTs
PART NUMBER DESCRIPTION
COMMENTS
LTC3632
LTC3642
LTC1474
50V, 20mA Synchronous Micropower Step-Down DC/DC Converter V : 4.5V to 50V (60V
), V
= 0.8V, I = 12µA,
IN
MAX
OUT(MIN) Q
I
= 3µA, 3mm × 3mm DFN, MS8E
SD
45V, 50mA Synchronous Micropower Step-Down DC/DC Converter V : 4.5V to 45V (60V
), V
= 0.8V, I = 12µA,
IN
MAX
OUT(MIN) Q
I
= 3µA, 3mm × 3mm DFN8, MS8E
SD
18V, 250mA (I ), High Efficiency Step-Down DC/DC Converter
V : 3V to 18V, V
= 1.2V, I = 10µA, I = 6µA, MS8E
OUT
IN
OUT(MIN) Q SD
LT1934/LT1934-1 36V, 250mA (I ), Micropower Step-Down DC/DC Converter with
V : 3.2V to 34V, V
= 1.25V, I = 12µA, I < 1µA,
OUT(MIN) Q SD
OUT
IN
™ Package
Burst Mode Operation
ThinSOT
LT1939
25V, 2A, 2.5MHz High Efficiency DC/DC Converter and LDO
Controller
V : 3.6V to 25V, V
= 0.8V, I = 2.5mA, I < 10µA,
OUT(MIN) Q SD
IN
3mm × 3mm DFN10
LT1976/LT1977
LT3437
60V, 1.2A (I ), 200kHz/500kHz, High Efficiency Step-Down DC/DC V : 3.3V to 60V, V
= 1.2V, I = 100µA, I < 1µA,
Q SD
OUT
IN
OUT(MIN)
Converter with Burst Mode Operation
TSSOP16E
60V, 400mA (I ), Micropower Step-Down DC/DC Converter with
V : 3.3V to 60V, V
= 1.25V, I = 100µA, I < 1µA,
Q SD
OUT
IN
OUT(MIN)
Burst Mode Operation
3mm × 3mm DFN10, TSSOP16E
V : 4V to 40V, V = 1.2V, I = 26µA, I < 1µA,
LT3470
40V, 250mA (I ), High Efficiency Step-Down DC/DC Converter
OUT
IN
OUT(MIN)
Q
SD
with Burst Mode Operation
2mm × 3mm DFN8, ThinSOT
V : 3.6V to 38V, V = 0.78V, I = 70µA, I < 1µA,
LT3685
36V with Transient Protection to 60V, 2A (I ), 2.4MHz, High
OUT
IN
OUT(MIN)
Q
SD
Efficiency Step-Down DC/DC Converter
3mm × 3mm DFN10, MSOP10E
3631fe
LT 0513 REV E • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
22
(408)432-1900 FAX: (408) 434-0507 www.linear.com/LTC3631
●
●
LINEAR TECHNOLOGY CORPORATION 2009
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