LTC3631EMS8E-3.3-TRPBF [Linear]
High Effi ciency, High Voltage 100mA Synchronous Step-Down Converter; 高艾菲效率，高电压百毫安同步降压型转换器
| 型号： | LTC3631EMS8E-3.3-TRPBF |
| 厂家： | 
Linear |
| 描述： | High Effi ciency, High Voltage 100mA Synchronous Step-Down Converter |
| 文件： | 总22页 (文件大小：370K) |
| 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
current, 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
With its wide 4.5V to 45V input range and internal
overvoltage monitor capable of protecting the part from
60V surges, the LTC3631 is a robust converter suited for
regulating a wide variety of power sources. Additionally,
theLTC3631includesapreciserunthresholdandsoft-start
feature to guarantee that the 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
100ꢁH
V
OUT
V
IN
V
SW
LTC3631-5
5V
IN
5V TO 45V
2.2ꢁF
100mA
10ꢁF
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
3631fb
1
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
2
3
4
8
7
6
5
GND
SW
1
2
3
4
8 GND
V
HYST
9
GND
V
SET
SS
7 HYST
6 V /V
IN
9
GND
IN
I
OUT FB
I
V
/V
SET
OUT FB
5 RUN
SS
RUN
MS8E PACKAGE
8-LEAD PLASTIC MSOP
DD PACKAGE
8-LEAD (3mm s 3mm) PLASTIC DFN
T
= 125°C, θ = 40°C/W, θ = 5°-10°C/W
JA JC
JMAX
EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB
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/
3631fb
2
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
ꢁA
ꢁA
ꢁA
Sleep Mode
Shutdown Mode
V
= 0V
RUN
Output Supply (V /V
)
OUT FB
l
l
V
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
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
0.792
3
0.800
5
0.808
7
V
mV
nA
FB
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
ΔV
IN
LINEREG
LTC3631-5, V = 6V to 45V
IN
Operation
V
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
RUN
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
0.07
0
HYSTL
HYST
SS
HYST
I
I
t
I
V
V
= 1.3V
–10
4.5
nA
ꢁA
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
SW
I
SW
= –25mA
= 25mA
3.0
1.5
Ω
Ω
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.
3631fb
3
LTC3631
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency vs Load Current,
OUT = 5V
Efficiency vs Load Current,
VOUT = 3.3V
Efficiency vs Load Current,
VOUT = 2.5V
V
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
IN
= 12V
= 36V
V
V
= 12V
= 36V
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
= 10V
IN
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
3631fb
4
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
20
0
0
0
200
400
600
(kΩ)
800 1000 1200
0
5
10 15 20 25 30 35 40 45 50
15
25
35
5
45
R
INPUT VOLTAGE (V)
ISET
V
IN
VOLTAGE (V)
3631 G10
3631 G11
3631 G12
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
= 10V
V
= 10V
IN
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)
V
VOLTAGE (V)
IN
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
20ꢁs/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
3631fb
5
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
= 0.047ꢁF
5ms/DIV
V
V
= 24V
= 5V
1ms/DIV
V
V
= 10V
= 5V
200ꢁs/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 1ꢁA 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 5ꢁA 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 3ꢁA.
3631fb
6
LTC3631
BLOCK DIAGRAM
V
IN
1ꢁA
2
I
SET
3
C2
–
+
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
+
+
–
5ꢁA
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
d
2.5M 800k
4.2M 800k
3631fb
7
LTC3631
(Refer to Block Diagram)
OPERATION
TheLTC3631isastep-downDC/DCconverterwithinternal
power switches that uses Burst Mode control, combining
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 12ꢁA 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,reducingtheDCsupplycurrentto3ꢁA.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
supplycurrenttoonly12ꢁA.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 current
V voltage through an external resistive divider, the HYST
IN
pin can be used to increase the effective RUN comparator
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 5ꢁA 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
3631fb
8
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 1ꢁA 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
3631fb
9
LTC3631
APPLICATIONS INFORMATION
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
margintoprovideadequateloadcurrentunderallforesee-
able 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.
ꢀ
ꢂ
ꢁ
ꢃ ꢀ
ꢃ
VOUT
V
V
IN
OUT ꢅ
L =
• 1–
ꢅ ꢂ
f •I
ꢄ ꢁ
ꢄ
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 is
6
R
= I
• 4.5 • 10
PEAK
ISET
where 50mA < I
< 225mA.
PEAK
The peak current is internally limited to be within the
larger than L , which can be computed as follows:
MIN
range of 50mA to 225mA. Shorting the I pin to ground
SET
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
V
IN(MAX) • tON(MIN)
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 tradeoffs discussed above. For applications
3631fb
20
40 50 60 70 80 90 100
MAXIMUM LOAD CURRENT (mA)
30
3631 F01
Figure 1. RISET Selection
10
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 = 47μH
I
OPEN
600
500
L = 100μH
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 = 220μH
L = 470μH
0
10 15 20 25
INPUT VOLTAGE (V)
40 45
5
30 35
V
IN
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 saturation.
Ferrite core material saturates “hard,” which means that
inductancecollapsesabruptlywhenthepeakdesigncurrent
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 = 47μH
400
V
SET
= 3.3V
OUT
350
300
250
200
150
100
50
I
OPEN
L = 100μH
L = 220μH
L = 470μH
Different core materials and shapes will change the
size/current and price/current relationship of an inductor.
Toroid or shielded pot cores in ferrite or permalloy ma-
terials are small and do not radiate energy but generally
cost more than powdered iron core inductors with similar
characteristics. The choice of which style inductor to use
mainly depends on the price vs size requirements and any
radiated field/EMI requirements. New designs for surface
mount inductors are available from Coiltronics, Coilcraft,
TDK, Toko, Sumida and Vishay.
0
5
25
35 40
10 15 20
30
45
V
INPUT VOLTAGE (V)
IN
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
VOUT
3631 F04
IN
IRMS = IOUT(MAX)
•
•
− 1
V
IN
Figure 4. Recommended Inductor Values for Maximum Efficiency
3631fb
11
LTC3631
APPLICATIONS INFORMATION
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
RMS
OUT
commonly used for design because even significant
deviationsdonotoffermuchrelief.Notethatripplecurrent
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 higher temperature than required. Several capacitors
may also be paralleled to meet size or height requirements
in the design.
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,
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 voltage ripple
during a burst cycle is dominated by the output capacitor
equivalent series resistance (ESR) and can be estimated
by the following equation:
VOUT
160
< ΔVOUT ≤IPEAK •ESR
V
. At best, this ringing can couple to the output and be
IN
mistaken as loop instability. At worst, a sudden inrush
where the lower limit of V /160 is due to the 5mV
OUT
of current through the long wires can potentially cause a
feedback comparator hysteresis.
voltage spike at V large enough to damage the part.
IN
The value of the output capacitor must be large enough
to accept the energy stored in the inductor without a large
changeinoutputvoltage. Settingthisvoltagestepequalto
1ꢀ of the output voltage, the output capacitor must be:
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
Figure 5 shows this circuit and the typical values required
to dampen the ringing.
ꢀ
ꢂ
ꢁ
ꢃ2
I
V
PEAK ꢅ
OUT
COUT > 50 •L •
LTC3631
ꢄ
L
IN
V
IN
Typically, a capacitor that satisfies the ESR requirement is
adequatetofiltertheinductorripple. Toavoidoverheating,
theoutputcapacitormustalsobesizedtohandletheripple
current generated by the inductor. The worst-case ripple
L
C
IN
R =
4 • C
IN
3631 F05
C
IN
IN
current in the output capacitor is given by I
= I
/2.
RMS PEAK
Figure 5. Series RC to Reduce VIN Ringing
Multiple capacitors placed in parallel may be needed to
meet the ESR and RMS current handling requirements.
Output Voltage Programming
Dry 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
For the adjustable version, the output voltage is set by
an external resistive divider according to the following
equation:
ꢀ
ꢃ
R1
R2
VOUT = 0.8V • 1+
ꢂ
ꢅ
ꢁ
ꢄ
3631fb
12
LTC3631
APPLICATIONS INFORMATION
The resistive divider allows the V pin to sense a fraction
The RUN pin can alternatively be configured as a precise
FB
of the output voltage as shown in Figure 6. Output voltage
undervoltage lockout (UVLO) on the V supply with
IN
can range from 0.8V to V .
a resistive divider from V to ground. The RUN pin
IN
IN
comparator 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 be used as shown in Figure 8 to meet specific
V
OUT
R1
V
FB
R2
LTC3631
GND
3631 F06
V voltage requirements.
IN
Figure 6. Setting the Output Voltage
V
IN
R1
To minimize the no-load supply current, resistor values
in the megohm range should be used; however, large
resistor values should be used with caution. The feedback
divider is the only load current when in shutdown. If PCB
leakagecurrenttotheoutputnodeorswitchnodeexceeds
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:
RUN
LTC3631
HYST
R2
R3
3631 F08
Figure 8. Adjustable Undervoltage Lockout
SpecificvaluesfortheseUVLOthresholdscanbecomputed
from the following equations:
ꢁ
ꢃ
ꢂ
ꢄ
ꢁ
ꢃ
ꢂ
ꢄ
ꢆ
ꢅ
VOUT
R1+R2
V
V
ꢀ
ꢃ
OUT ꢆ
IN
R1
R2
ꢀIVIN
=
•
Rising V UVLO Threshold = 1.21V • 1+
ꢂ
ꢅ
IN
ꢅ
ꢁ
ꢄ
ꢀ
ꢃ
R1
R2+R3
Run Pin with Programmable Hysteresis
Falling V UVLO Threshold = 1.10V • 1+
ꢂ
ꢅ
IN
ꢁ
ꢄ
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 ~ 3ꢁA). When the RUN pin is greater than 1.2V,
the controller is enabled. Figure 7 shows examples of
configurations for driving the RUN pin from logic.
The minimum value of these thresholds is limited to the
internalV UVLOthresholdsthatareshownintheElectrical
IN
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
minimizetheimpactofthiscurrentontheoverallefficiency
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:
V
V
IN
SUPPLY
4.7M
LTC3631
RUN
LTC3631
RUN
3631 F07
Figure 7. RUN Pin Interface to Logic
ꢀ
ꢃ
R3
V
•
< 6V
ꢂ
ꢅ
IN(MAX)
R1+R2+R3
ꢁ
ꢄ
3631fb
13
LTC3631
APPLICATIONS INFORMATION
The RUN pin may also be directly tied to the V supply
Unlike the SS pin, the I
pin does not get pulled to
IN
SET
for applications that do not require the programmable
ground during an abnormal event; however, if the I
SET
undervoltage lockout feature. In this configuration,
pin is floating (programmed to 225mA peak current),
switching is enabled when V surpasses the internal
the SS and I pins may be tied together and connected
IN
SET
undervoltage lockout threshold.
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
Soft-Start
this combination is C
• (0.8V/6ꢁA).
SS(ISET)
The internal 0.75ms soft-start is implemented by ramping
boththeeffectivereferencevoltagefrom0Vto0.8Vandthe
Efficiency Considerations
peak current limit set by the I pin (50mA to 225mA).
SET
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:
Toincreasethedurationofthereferencevoltagesoft-start,
place a capacitor from the SS pin to ground. An internal
5ꢁA pull-up current will charge this capacitor, resulting in
a soft-start ramp time given by:
0.8V
5ꢁA
Efficiency = 100ꢀ – (L1 + L2 + L3 + ...)
t
SS = CSS •
whereL1, L2, etc. aretheindividuallossesasapercentage
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
Thedurationofthe0.75msinternalpeakcurrentsoft-start
efficiency loss at medium to high load currents.
may be increased by placing a capacitor from the I pin
SET
toground.Thepeakcurrentsoft-startwillrampfrom50mA
1. The V operating current comprises two components:
IN
to the final peak current value determined by a resistor
The DC supply current as given in the electrical
characteristics and the internal MOSFET gate charge
currents.Thegatechargecurrentresultsfromswitching
the gate capacitance of the internal power MOSFET
switches. Each time the gate is switched from high to
low to high again, a packet of charge, dQ, moves from
from I
SET
to ground. A 1ꢁA current is sourced out of the
SET
I
pin. With only a capacitor connected between I
SET
and ground, the peak current ramps linearly from 50mA
to 225mA, and the peak current soft-start time can be
expressed as:
V to ground. The resulting dQ/dt is the current out of
IN
0.8V
1ꢁA
t
SS(ISET) = CISET •
V that is typically larger than the DC bias current.
IN
2
2. I R losses are calculated from the resistances of the
A linear ramp of peak current appears as a quadratic
waveform on the output voltage. For the case where the
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
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
of the top and bottom switch R
values and the
DS(ON)
3 • R • C
.
ISET
ISET
duty cycle (DC = V /V ) as follows:
OUT IN
R
= (R
)DC + (R
)(1 – DC)
DS(ON)BOT
3631fb
SW
DS(ON)TOP
14
LTC3631
APPLICATIONS INFORMATION
TheR
forboththetopandbottomMOSFETscanbe
Due to the low peak current of the LTC3631, decoupling
DS(ON)
obtained from the Typical Performance Characteristics
the V supply with a 1ꢁF capacitor is adequate for most
IN
2
curves. Thus, to obtain the I R losses, simply add R
applications.
SW
toR andmultiplytheresultbythesquareoftheaverage
L
C
OUT
will be selected based on the ESR that is required to
output current:
satisfy the output voltage ripple requirement. For a 50mV
output ripple, the value of the output capacitor ESR can
be calculated from:
2
2
I R Loss = I (R + R )
O
SW
L
Other losses, including C and C
ESR dissipative
IN
OUT
losses and inductor core losses, generally account for
ΔV
= 50mV ≤ 225mA • ESR
OUT
less than 2ꢀ of the total power loss.
A capacitor with a 200mΩ ESR satisfies this requirement.
A 10ꢁF ceramic capacitor has significantly less ESR than
200mΩ.
Thermal Considerations
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.
The output voltage can now be programmed by choosing
the values of R1 and R2. Choose R2 = 240k and calculate
R1 as:
ꢀ
ꢂ
ꢁ
ꢃ
VOUT
0.8V
R1=
– 1 •R2 = 750k
ꢅ
ꢄ
Design Example
As a design example, consider using the LTC3631 in an
The undervoltage lockout requirement on V can be
IN
application with the following specifications: V = 24V,
satisfied with a resistive divider from V to the RUN and
IN
IN
V
OUT
=3.3V,I =100mA,f=250kHz.Furthermore,assume
HYST pins. Choose R1 = 2M and calculate R2 and R3 as
follows:
OUT
forthisexamplethatswitchingshouldstartwhenV isgreater
IN
than 12V and should stop when V is less than 8V.
IN
ꢀ
ꢂ
ꢂ
ꢁ
ꢃ
ꢅ
ꢅ
ꢄ
1.21V
IN(RISING) – 1.21V
R2 =
R3 =
•R1= 224k
First, calculate the inductor value that gives the required
switching frequency:
V
ꢀ
ꢃ ꢀ
• 1–
ꢃ
ꢀ
ꢂ
ꢂ
ꢁ
ꢃ
ꢅ
ꢅ
ꢄ
3.3V
250kHz • 225mA
3.3V
24V
1.1V
IN(FALLING) – 1.1V
L =
ꢆ 47μH
ꢂ
ꢅ ꢂ
ꢅ
•R1– R2 = 90.8k
ꢁ
ꢄ ꢁ
ꢄ
V
Next, verify that this value meets the L
For this input voltage and peak current, the minimum
inductor value is:
requirement.
MIN
Choose standard values for R2 = 226k and R3 = 91k.
The I pin should be left open in this example to select
SET
maximum peak current (225mA). Figure 9 shows a
complete schematic for this design example.
24V •100ns
LMIN
=
≅ 10ꢁH
225mA
47μH
V
OUT
V
IN
V
SW
LTC3631
3.3V
IN
24V
100mA
10μF
Therefore, theminimuminductorrequirementissatisfied,
and the 47μH inductor value may be used.
2M
1μF
RUN
I
SET
SS
226k
91k
750k
240k
Next,C andC
areselected.Forthisdesign,C should
IN
V
HYST
IN
OUT
FB
GND
be sized for a current rating of at least:
3631 F09
3.3V
24V
24V
3.3V
IRMS = 100mA •
•
– 1≅ 35mARMS
Figure 9. 24V to 3.3V, 100mA Regulator at 250kHz
3631fb
15
LTC3631
APPLICATIONS INFORMATION
PC Board Layout Checklist
Example Layout
L1
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:
V
IN
V
OUT
V
SW
IN
LTC3631
R1
R2
RUN
HYST
SS
C
C
OUT
IN
V
FB
1. Largeswitchedcurrentsflowinthepowerswitchesand
input capacitor. The loop formed by these components
should be as small as possible. A ground plane is
recommended to minimize ground impedance.
I
SET
GND
C
R
SS
SET
3631 F09a
2. Connect the (+) terminal of the input capacitor, C , as
IN
close as possible to the V pin. This capacitor provides
IN
L1
the AC current into the internal power MOSFETs.
V
IN
V
OUT
C
C
OUT
IN
3. Keep the switching node, SW, away from all sensitive
smallsignalnodes.Therapidtransitionsontheswitching
node can couple to high impedance nodes, in particular
V , and create increased output ripple.
FB
R1
4. Floodallunusedareaonalllayerswithcopper. Flooding
with copper will reduce the temperature rise of power
components. You can connect the copper areas to any
R2
DC net (V , V , GND or any other DC rail in your
IN OUT
R
C
SS
SET
GND
system).
VIAS TO GROUND PLANE
VIAS TO INPUT SUPPLY (V
)
IN
OUTLINE OF LOCAL GROUND PLANE
3631fb
16
LTC3631
TYPICAL APPLICATIONS
L1
100μH
V
IN
V
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
100
L1
I
OPEN
SET
100μH
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
OUT
1μF
1M
C
OUT
I
V
FB
SET
10μF
V
= –12V
OUT
HYST
GND
SS
R2
71.5k
V
OUT
–12V
C
C
: TDK C3225X7R1H105KT
IN
OUT
3631 TA04a
: MURATA GRM32DR71C106KA01
L1: TYCO/COEV DQ6545-101M
25 30
VOLTAGE (V)
5
10 15 20
35 40 45
V
IN
3631 TA04b
3631fb
17
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
3631fb
18
LTC3631
PACKAGE DESCRIPTION
DD Package
8-Lead Plastic DFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1698)
0.675 p0.05
3.5 p0.05
2.15 p0.05 (2 SIDES)
1.65 p0.05
PACKAGE
OUTLINE
0.25 p 0.05
0.50
BSC
2.38 p0.05
(2 SIDES)
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
R = 0.115
0.38 p 0.10
TYP
5
8
3.00 p0.10
(4 SIDES)
1.65 p 0.10
(2 SIDES)
PIN 1
TOP MARK
(NOTE 6)
(DD) DFN 1203
4
1
0.25 p 0.05
0.75 p0.05
0.200 REF
0.50 BSC
2.38 p0.10
(2 SIDES)
0.00 – 0.05
BOTTOM VIEW—EXPOSED PAD
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
3631fb
19
LTC3631
PACKAGE DESCRIPTION
MS8E Package
8-Lead Plastic MSOP, Exposed Die Pad
(Reference LTC DWG # 05-08-1662 Rev E)
BOTTOM VIEW OF
EXPOSED PAD OPTION
2.06 p 0.102
(.081 p .004)
1.83 p 0.102
(.072 p .004)
1
0.29
REF
0.889 p 0.127
(.035 p .005)
2.794 p 0.102
(.110 p .004)
0.05 REF
DETAIL “B”
5.23
(.206)
MIN
3.20 – 3.45
2.083 p 0.102
(.082 p .004)
CORNER TAIL IS PART OF
THE LEADFRAME FEATURE.
FOR REFERENCE ONLY
(.126 – .136)
DETAIL “B”
8
NO MEASUREMENT PURPOSE
3.00 p 0.102
0.52
(.0205)
REF
(.118 p .004)
(NOTE 3)
0.65
(.0256)
BSC
0.42 p 0.038
(.0165 p .0015)
TYP
8
7 6 5
RECOMMENDED SOLDER PAD LAYOUT
3.00 p 0.102
(.118 p .004)
(NOTE 4)
4.90 p 0.152
(.193 p .006)
DETAIL “A”
0o – 6o TYP
0.254
(.010)
GAUGE PLANE
1
2
3
4
0.53 p 0.152
(.021 p .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 p 0.0508
(.004 p .002)
0.65
(.0256)
BSC
MSOP (MS8E) 0908 REV E
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
3631fb
20
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
Updated Typical Application
22
Updated Related Parts
22
3631fb
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
IN
*V
V
FOR V
< 5V
OUT = BATT
BATT
C
: KEMET C1210C106K4RAC
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 = 12ꢁA,
OUT(MIN) Q
IN
MAX
I
= 3ꢁA, 3mm × 3mm DFN, MS8E
SD
45V, 50mA Synchronous Micropower Step-Down DC/DC Converter V : 4.5V to 45V (60V
), V
MAX
= 0.8V, I = 12ꢁA,
OUT(MIN) Q
IN
SD
I
= 3ꢁA, 3mm × 3mm DFN8, MS8E
18V, 250mA (I ), High Efficiency Step-Down DC/DC Converter
V : 3V to 18V, V
= 1.2V, I = 10ꢁA, I = 6ꢁA, 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 = 12ꢁA, I < 1ꢁA,
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 < 10ꢁA,
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 = 100ꢁA, I < 1ꢁA,
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 = 100ꢁA, I < 1ꢁA,
Q SD
OUT
IN
OUT(MIN)
Burst Mode Operation
3mm × 3mm DFN10, TSSOP16E
LT3470
40V, 250mA (I ), High Efficiency Step-Down DC/DC Converter
V : 4V to 40V, V = 1.2V, I = 26ꢁA, I < 1ꢁA,
OUT
IN
OUT(MIN)
Q
SD
with Burst Mode Operation
2mm × 3mm DFN8, ThinSOT
LT3685
36V with Transient Protection to 60V, 2A (I ), 2.4MHz, High
V : 3.6V to 38V, V = 0.78V, I = 70ꢁA, I < 1ꢁA,
OUT
IN
OUT(MIN)
Q
SD
Efficiency Step-Down DC/DC Converter
3mm × 3mm DFN10, MSOP10E
3631fb
LT 0510 REV B • PRINTED IN USA
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
22
●
●
© LINEAR TECHNOLOGY CORPORATION 2009
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
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