LT3970EDDB-3.3-PBF [Linear]
40V, 350mA Step-Down Regulator with 2.5μA Quiescent Current and Integrated Diodes; 40V为350mA降压型稳压器具有2.5μA静态电流和集成二极管
| 型号： | LT3970EDDB-3.3-PBF |
| 厂家： | 
Linear |
| 描述： | 40V, 350mA Step-Down Regulator with 2.5μA Quiescent Current and Integrated Diodes |
| 文件： | 总22页 (文件大小：247K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LT3970/LT3970-3.3/LT3970-5
40V, 350mA Step-Down
Regulator with 2.5µA
Quiescent Current and
Integrated Diodes
FEATURES
DESCRIPTION
Low Ripple Burst Mode® Operation
The LT®3970 is an adjustable frequency monolithic buck
switching regulator that accepts a wide input voltage
range up to 40V, and consumes only 2.5μA of quiescent
current. A high efficiency switch is included on the die
along with the catch diode, boost diode, and the neces-
saryoscillator, controlandlogiccircuitry. LowrippleBurst
Mode operation maintains high efficiency at low output
currents while keeping the output ripple below 5mV in a
typical application. Current mode topology is used for fast
transient response and good loop stability. A catch diode
current limit provides protection against shorted outputs
and overvoltage conditions. An enable pin with accurate
threshold is available, producing a low shutdown current
n
2.5μA I at 12V to 3.3V
Q
IN
OUT
Output Ripple < 5mV
P-P
n
n
n
n
n
Wide Input Voltage Range: 4.2V to 40V Operating
Adjustable Switching Frequency: 200kHz to 2.2MHz
Integrated Boost and Catch Diodes
350mA Output Current
Fixed Output Voltages: 3.3V, 5V
1.8μA I at 12V
Q
IN
n
n
n
n
n
n
n
Accurate 1V Enable Pin Threshold
Low Shutdown Current: I = 0.7μA
Q
Internal Sense Limits Catch Diode Current
Power Good Flag
Output Voltage: 1.21V to 25V
of 0.7μA. A power good flag signals when V
reaches
OUT
Internal Compensation
90% of the programmed output voltage. The LT3970 is
available in small 10-pin MSOP and 3mm × 2mm DFN
packages.
Small 10-Pin MSOP and (3mm × 2mm) DFN Packages
APPLICATIONS
L, LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners.
n
Automotive Battery Regulation
n
Power for Portable Products
n
Industrial Supplies
TYPICAL APPLICATION
5V Step-Down Converter
Efficiency
90
1000
100
10
V
= 12V
V
IN
IN
6V TO 40V
0.22μF
80
70
60
50
40
V
BOOST
LT3970
IN
22μH
22pF
V
OUT
5V
OFF ON
EN
PG
SW
BD
350mA
1M
1
RT
FB
22μF
2.2μF
GND
316k
226k
f = 600kHz
0.1
0.01
3490 TA01a
0.01
0.1
1
10
100
LOAD CURRENT (mA)
3970 TA01b
3970fa
1
LT3970/LT3970-3.3/LT3970-5
(Note 1)
ABSOLUTE MAXIMUM RATINGS
V , EN Voltage .........................................................40V
Operating Junction Temperature Range (Note 2)
LT3970E/LT3970E-X........................... –40°C to 125°C
LT3970I/LT3970I-X ............................ –40°C to 125°C
LT3970H-X......................................... –40°C to 150°C
Storage Temperature Range................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec)
IN
BOOST Pin Voltage ...................................................55V
BOOST Pin Above SW Pin.........................................30V
FB/V , RT Voltage ....................................................6V
OUT
PG, BD Voltage .........................................................30V
MS Only............................................................ 300°C
PIN CONFIGURATION
TOP VIEW
TOP VIEW
1
2
3
4
5
10
9
*FB/V
RT
OUT
*FB/V
1
2
3
4
5
10 RT
EN
PG
OUT
EN
IN
9
8
7
6
PG
11
GND
8
V
BD
IN
V
BD
GND
GND
BOOST
SW
7
GND
GND
BOOST
SW
6
MS PACKAGE
10-LEAD PLASTIC MSOP
DDB PACKAGE
10-LEAD (3mm × 2mm) PLASTIC DFN
θ
= 100°C/W
JA
θ
= 76°C/W
JA
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
*FB for LT3970, V
for LT3970-3.3, LT3970-5.
OUT
ORDER INFORMATION
LEAD FREE FINISH
LT3970EDDB#PBF
LT3970IDDB#PBF
TAPE AND REEL
PART MARKING*
LFCZ
PACKAGE DESCRIPTION
TEMPERATURE RANGE
–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 150°C
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
–40°C to 150°C
LT3970EDDB#TRPBF
LT3970IDDB#TRPBF
LT3970EMS#TRPBF
10-Lead (3mm × 2mm) Plastic DFN
10-Lead (3mm × 2mm) Plastic DFN
10-Lead Plastic MSOP
LFCZ
LT3970EMS#PBF
LTFDB
LTFDB
LFQH
LT3970IMS#PBF
LT3970IMS#TRPBF
10-Lead Plastic MSOP
LT3970EDDB-3.3#PBF
LT3970IDDB-3.3#PBF
LT3970EMS-3.3#PBF
LT3970IMS-3.3#PBF
LT3970HMS-3.3#PBF
LT3970EDDB-5#PBF
LT3970IDDB-5#PBF
LT3970EMS-5#PBF
LT3970IMS-5#PBF
LT3970HMS-5#PBF
LT3970EDDB-3.3#TRPBF
LT3970IDDB-3.3#TRPBF
LT3970EMS-3.3#TRPBF
LT3970IMS-3.3#TRPBF
LT3970HMS-3.3#TRPBF
LT3970EDDB-5#TRPBF
LT3970IDDB-5#TRPBF
LT3970EMS-5#TRPBF
LT3970IMS-5#TRPBF
LT3970HMS-5#TRPBF
10-Lead (3mm × 2mm) Plastic DFN
10-Lead (3mm × 2mm) Plastic DFN
10-Lead Plastic MSOP
LFQH
LTFQG
LTFQG
LTFQG
LFQF
10-Lead Plastic MSOP
10-Lead Plastic MSOP
10-Lead (3mm × 2mm) Plastic DFN
10-Lead (3mm × 2mm) Plastic DFN
10-Lead Plastic MSOP
LFQF
LTFQD
LTFQD
LTFQD
10-Lead Plastic MSOP
10-Lead Plastic MSOP
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/
3970fa
2
LT3970/LT3970-3.3/LT3970-5
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 12V, VBD = 3.3V unless otherwise noted. (Note 2)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
l
Minimum Input Voltage
Quiescent Current from V
4
4.2
V
V
V
V
V
Low
0.7
1.7
1.2
2.7
3.5
4
μA
μA
μA
μA
IN
EN
EN
EN
EN
High
l
l
High, –40°C to 125°C
High, –40°C to 150°C
LT3970 Feedback Voltage
1.195
1.185
1.21
1.21
1.225
1.235
V
V
l
LT3970-3.3 Output Voltage
LT3970-5 Output Voltage
3.26
3.234
3.217
3.3
3.3
3.3
3.34
3.366
3.366
V
V
V
l
l
–40°C to 125°C
–40°C to 150°C
4.94
4.9
4.875
5
5
5
5.06
5.1
5.1
V
V
V
l
l
–40°C to 125°C
–40°C to 150°C
l
LT3970 FB Pin Bias Current (Note 3)
FB/Output Voltage Line Regulation
Switching Frequency
V
= 1.21V
0.1
20
nA
FB
4.2V < V < 40V
0.0002
0.01
%/V
IN
R = 41.2k, V = 6V
1.76
640
160
2.25
800
200
2.64
960
240
MHz
kHz
kHz
T
T
T
IN
IN
IN
R = 158k, V = 6V
R = 768k, V = 6V
Switch Current Limit
V
V
= 5V, V = 0V
535
350
700
400
175
0.05
650
0.05
875
0.02
1.4
7
865
500
mA
mA
mV
μA
mV
μA
mV
μA
V
IN
FB
Catch Schottky Current Limit
= 5V
IN
Switch V
I
= 200mA
CESAT
SW
Switch Leakage Current
2
2
Catch Schottky Forward Voltage
Catch Schottky Reverse Leakage
Boost Schottky Forward Voltage
Boost Schottky Reverse Leakage
Minimum Boost Voltage (Note 4)
BOOST Pin Current
I
= 100mA, V = V = NC
IN BD
SCH
V
SW
= 12V
I
= 50mA, V = NC, V
= 0V
BOOST
SCH
IN
V
V
= 12V
2
REVERSE
l
= 5V
1.8
10
IN
I
= 200mA, V = 15V
BOOST
mA
nA
V
SW
EN Pin Current
V
EN
= 12V
1
30
l
l
LT3970 EN Voltage Threshold
LT3970-X EN Voltage Threshold
EN Voltage Hysteresis
EN Rising, V ≥ 4.2V
0.94
0.93
1
1.06
1.07
IN
EN Rising, V ≥ 4.2V
1
V
IN
30
mV
mV
mV
%
LT3970 PG Threshold Offset from Feedback Voltage
LT3970 PG Hysteresis
V
V
Rising
Rising
80
120
12
160
13.5
1
FB
LT3970-X PG Threshold Offset from Output Voltage
LT3970-X PG Hysteresis as % of Output Voltage
PG Leakage
6.5
10
FB
1.0
0.01
80
%
V
V
= 3V
μA
μA
ns
PG
PG
l
l
PG Sink Current
= 0.4V
30
Minimum Switch On-Time
90
Minimum Switch Off-Time
V
IN
= 10V
100
160
ns
3970fa
3
LT3970/LT3970-3.3/LT3970-5
ELECTRICAL CHARACTERISTICS
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.
LT3970I is guaranteed over the full –40°C to 125°C operating junction
temperature range. The LT3970H is guaranteed over the full –40°C to
150°C operating junction temperature range. High junction temperatures
degrade operating lifetimes. Operating lifetime is derated at junction
temperatures greater than 125°C.
Note 3: Bias current flows into the FB pin.
Note 4: This is the minimum voltage across the boost capacitor needed to
Note 2: The LT3970E is guaranteed to meet performance specifications
from 0°C to 125°C junction temperature. Specifications over the –40°C
to 125°C operating junction temperature range are assured by design,
characterization, and correlation with statistical process controls. The
guarantee full saturation of the switch.
TYPICAL PERFORMANCE CHARACTERISTICS T = 25°C, unless otherwise noted.
A
Efficiency, VOUT = 3.3V
Efficiency, VOUT = 5V
LT3970 Feedback Voltage
90
90
1.220
FRONT PAGE APPLICATION
80
70
60
50
40
30
20
80
70
V
= 12V
= 36V
1.215
1.210
IN
IN
V
= 12V
= 36V
IN
IN
V
= 24V
V
= 24V
IN
IN
V
V
60
50
1.205
1.200
1.195
FRONT PAGE APPLICATION
V
= 3.3V
40
30
OUT
R1 = 1M
R2 = 576k
0.01
0.1
1
10
100
50
TEMPERATURE (°C)
0.01
0.1
1
10
100
–50 –25
0
25
75 100 125 150
LOAD CURRENT (mA)
LOAD CURRENT (mA)
3970 G02
3970 G01
3970 G03
LT3970-3.3 Output Voltage
LT3970-5 Output Voltage
No-Load Supply Current
3.32
5.04
4.0
3.5
FRONT PAGE APPLICATION
= 3.3V
V
OUT
R1 = 1MΩ
R2 = 576k
LT3970-5
3.31
3.30
5.02
5.00
LT3970-3.3
3.0
2.5
2.0
1.5
3.29
3.28
3.27
4.98
4.96
4.94
25
20
30
50
TEMPERATURE (°C)
50
TEMPERATURE (°C)
5
10
15
35
40
–50 –25
0
25
75 100 125 150
–50 –25
0
25
75 100 125 150
INPUT VOLTAGE (V)
3970 G03a
3970 G03b
3970 G04
3970fa
4
LT3970/LT3970-3.3/LT3970-5
T = 25°C, unless otherwise noted.
A
TYPICAL PERFORMANCE CHARACTERISTICS
No-Load Supply Current
Maximum Load Current
Maximum Load Current
15
600
550
500
450
400
350
550
500
450
400
FRONT PAGE APPLICATION
FRONT PAGE APPLICATION
FRONT PAGE APPLICATION
V
= 3.3V
V
V
= 12V
V
= 5V
OUT
IN
OUT
OUT
= 3.3V
12
9
TYPICAL
TYPICAL
R1 = 1M
R2 = 576k
MINIMUM
MINIMUM
6
3
0
350
50
TEMPERATURE (°C)
–50 –25
0
25
75 100 125 150
5
10
15
20
25
30
35
40
5
10
15
20
25
30
35
40
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
3970 G05
3870 G06
3870 G07
Maximum Load Current
Load Regulation
Switch Current Limit
600
500
400
300
200
100
0
0.20
800
700
LIMITED BY CURRENT LIMIT
H GRADE
0.15
0.10
SWITCH PEAK
CURRENT LIMIT
600
500
0.05
0
LIMITED BY MAXIMUM
JUNCTION TEMPERATURE;
θ
JA
= 76°C/W
CATCH DIODE VALLEY CURRENT LIMIT
–0.05
–0.10
–0.15
400
300
200
FRONT PAGE APPLICATION
V
V
= 12V
= 5V
FRONT PAGE APPLICATION
REFERENCED FROM V
IN
OUT
AT 100mA LOAD
OUT
–0.20
50
TEMPERATURE (°C)
0
50
100 150 200 250 300 350
LOAD CURRENT (mA)
3970 G09
–50 –25
0
25
75 100 125 150
0
20
40
60
80
100
DUTY CYCLE (%)
3970 G08
3970 G10
Minimum
Switch On-Time/Switch Off-Time
Switch Current Limit
Switching Frequency
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
800
700
600
500
400
300
200
200
180
160
140
120
100
80
LOAD CURRENT = 175mA
SWITCH PEAK CURRENT LIMIT
MINIMUM OFF-TIME
MINIMUM ON-TIME
CATCH DIODE VALLEY CURRENT LIMIT
60
40
20
0
75 100
–50
–25
0
25 50 75 100 125 150
TEMPERATURE (°C)
–50 –25
0
25 50
125 150
–50
50
100 125
150
–25
0
25
75
TEMPERATURE (oC)
TEMPERATURE (°C)
3970 G12
3970 G11
3970 G13
3970fa
5
LT3970/LT3970-3.3/LT3970-5
T = 25°C, unless otherwise noted.
A
TYPICAL PERFORMANCE CHARACTERISTICS
Switch VCESAT (ISW = 200mA)
vs Temperature
Switch VCESAT
BOOST Pin Current
250
200
150
100
16
400
14
12
300
200
10
8
6
100
0
4
2
100
200
300
500
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
0
400
0
100
200
300
400
500
SWITCH CURRENT (mA)
SWITCH CURRENT (mA)
3970 G14
3970 G16
3970 G15
Minimum Input Voltage,
VOUT = 3.3V
Minimum Input Voltage,
VOUT = 5V
Boost Diode Forward Voltage
5.0
4.5
4.0
3.5
3.0
2.5
6.5
6.0
5.5
5.0
4.5
4.0
1.2
1.0
FRONT PAGE APPLICATION
FRONT PAGE APPLICATION
V
= 3.3V
V
= 5V
OUT
OUT
TO START
0.8
0.6
TO START/RUN
TO RUN
0.4
0.2
0
–50°C
25°C
125°C
150°C
0
50
100
150
200
0
50 100 150 200 250 300 350
LOAD CURRENT (mA)
0
50 100 150 200 250 300 350
LOAD CURRENT (mA)
BOOST DIODE CURRENT (mA)
3970 G19
3970 G17
3970 G18
Catch Diode Leakage
Catch Diode Forward Voltage
Power Good Threshold
20
1.0
0.8
0.6
0.4
0.2
0
92
91
90
89
V
= 12V
R
16
12
8
4
0
–50°C
25°C
125°C
150°C
88
50
TEMPERATURE (°C)
–50 –25
0
25
75 100 125 150
0
100
200
300
400
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
CATCH DIODE CURRENT (mA)
3970 G21
3970 G20
3970 G22
3970fa
6
LT3970/LT3970-3.3/LT3970-5
T = 25°C, unless otherwise noted.
A
TYPICAL PERFORMANCE CHARACTERISTICS
Transient Load Response; Load
Current is Stepped from 10mA
(Burst Mode Operation) to 110mA
Transient Load Response; Load
Current is Stepped from 100mA
to 200mA
EN Threshold
1.050
1.025
1.000
0.975
V
V
OUT
OUT
100mV/DIV
100mV/DIV
I
I
L
L
100mA/DIV
100mA/DIV
3970 G24
3970 G25
100μs/DIV
100μs/DIV
FRONT PAGE APPLICATION
FRONT PAGE APPLICATION
V
V
= 12V
OUT
V
V
= 12V
OUT
IN
IN
= 5V
= 5V
0.950
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
3970 G23
Switching Waveforms,
Burst Mode Operation
Switching Waveforms, Full
Frequency Continuous Operation
V
V
SW
5V/DIV
SW
5V/DIV
I
I
L
L
100mA/DIV
200mA/DIV
V
V
OUT
OUT
5mV/DIV
5mV/DIV
3970 G26
3970 G27
2μs/DIV
1μs/DIV
FRONT PAGE APPLICATION
FRONT PAGE APPLICATION
V
IN
V
= 12V
V
IN
V
= 12V
= 5V
= 10mA
= 5V
= 350mA
OUT
LOAD
OUT
LOAD
I
I
3970fa
7
LT3970/LT3970-3.3/LT3970-5
PIN FUNCTIONS
FB (Pin 1, LT3970 Only): The LT3970 Regulates the FB
Pin to 1.21V. Connect the feedback resistor divider tap to
this pin.
GND(Pins4,5,ExposedPad(Pin11,DFNOnly)):Ground.
Must be soldered to PCB.
SW (Pin 6): The SW pin is the output of an internal power
switch. Connect this pin to the inductor.
V
(Pin1,LT3970-3.3andLT3970-5Only):TheLT3970-
OUT
3.3 and LT3970-5 regulate the V
Pin to 3.3V and 5V
OUT
BOOST (Pin 7): This pin is used to provide a drive volt-
age, higher than the input voltage, to the internal bipolar
NPN power switch.
respectively. This pin connects to the internal feedback
divider that programs the fixed output voltage.
EN (Pin 2): The part is in shutdown when this pin is low
BD (Pin 8): This pin connects to the anode of the boost
diode.ThispinalsosuppliescurrenttotheLT3970’sinternal
regulator when BD is above 3.2V.
and active when this pin is high. The hysteretic threshold
voltage is 1V going up and 0.97V going down. Tie to V
IN
if shutdown feature is not used. The EN threshold is ac-
PG (Pin 9): The PG pin is the open-drain output of an
internal comparator. PG remains low until the FB pin is
within10%ofthefinalregulationvoltage. PGisvalidwhen
curate only when V is above 4.2V. If V is lower than
IN
IN
4.2V, ground EN to place the part in shutdown.
V (Pin 3): The V pin supplies current to the LT3970’s
IN
IN
V is above 4.2V and EN is high.
IN
internal circuitry and to the internal power switch. This
RT (Pin 10): A resistor is tied between RT and ground to
set the switching frequency.
pin must be locally bypassed.
BLOCK DIAGRAM
V
IN
3
V
IN
C1
INTERNAL 1.21V REF
SHDN
–
+
BD
8
1V
+
–
EN
2
D
BOOST
SLOPE COMP
BOOST
SWITCH LATCH
7
6
R
Q
S
RT
PG
OSCILLATOR
10
9
C3
200kHz TO 2.2MHz
R
T
L1
C2
1.09V
+
–
+
SW
V
V
OUT
C
Burst Mode
DETECT
ERROR
AMP
D
CATCH
–
R2
R1
LT3970-3.3
LT3970-5
ONLY*
LT3970 ONLY
FB
GND
(4, 5)
V
OUT
1
1
R2
R1
3990 BD
*LT3970-3.3: R1 = 12.65M, R2 = 7.35M
LT3970-5: R1 = 15.15M, R2 = 4.85M
3970fa
8
LT3970/LT3970-3.3/LT3970-5
OPERATION
The LT3970 is a constant frequency, current mode step-
down regulator. An oscillator, with frequency set by RT,
sets an RS flip-flop, turning on the internal power switch.
An amplifier and comparator monitor the current flowing
If the EN pin is low, the LT3970 is shut down and draws
0.7μA from the input. When the EN pin exceeds 1V, the
switching regulator will become active.
The switch driver operates from either V or from the
IN
between the V and SW pins, turning the switch off when
IN
BOOST pin. An external capacitor is used to generate a
voltage at the BOOST pin that is higher than the input
supply. This allows the driver to fully saturate the internal
bipolar NPN power switch for efficient operation.
this current reaches a level determined by the voltage at
V (see Block Diagram). An error amplifier measures the
C
output voltage through an external resistor divider tied to
the FB pin and servos the V node. If the error amplifier’s
C
To further optimize efficiency, the LT3970 automatically
switches to Burst Mode operation in light load situations.
Between bursts, all circuitry associated with controlling
the output switch is shut down reducing the input supply
current to 1.7μA.
output increases, more current is delivered to the output;
if it decreases, less current is delivered.
Anothercomparatormonitorsthecurrentflowingthrough
thecatchdiodeandreducestheoperatingfrequencywhen
the current exceeds the 400mA bottom current limit. This
foldback in frequency helps to control the output current
in fault conditions such as a shorted output with high
input voltage. Maximum deliverable current to the output
is therefore limited by both switch current limit and catch
diode current limit.
The LT3970 contains a power good comparator which
trips when the FB pin is at 90% of its regulated value. The
PG output is an open-drain transistor that is off when the
output is in regulation, allowing an external resistor to pull
the PG pin high. Power good is valid when the LT3970 is
enabled and V is above 4.2V.
IN
An internal regulator provides power to the control cir-
cuitry. The bias regulator normally draws power from
the V pin, but if the BD pin is connected to an external
IN
voltage higher than 3.2V, bias power will be drawn from
theexternalsource(typicallytheregulatedoutputvoltage).
This improves efficiency.
3970fa
9
LT3970/LT3970-3.3/LT3970-5
APPLICATIONS INFORMATION
FB Resistor Network
where V is the typical input voltage, V
is the output
IN
OUT
voltage, V is the integrated catch diode drop (~0.7V),
D
The output voltage is programmed with a resistor divider
between the output and the FB pin. Choose the 1% resis-
tors according to:
and V is the internal switch drop (~0.5V at max load).
SW
This equation shows that slower switching frequency is
necessary to accommodate high V /V
ratio.
IN OUT
VOUT
1.21
Lower frequency also allows a lower dropout voltage. The
input voltage range depends on the switching frequency
because the LT3970 switch has finite minimum on and off
times.Theswitchcanturnonforaminimumof~150nsand
turn off for a minimum of ~160ns (note that the minimum
on-time is a strong function of temperature). This means
that the minimum and maximum duty cycles are:
R1=R2
–1
Reference designators refer to the Block Diagram. Note
that choosing larger resistors will decrease the quiescent
current of the application circuit.
Setting the Switching Frequency
DC
DC
= f • t
SW ON(MIN)
MIN
The LT3970 uses a constant frequency PWM architecture
thatcanbeprogrammedtoswitchfrom200kHzto2.2MHz
by using a resistor tied from the RT pin to ground. A table
= 1 – f • t
MAX
SW OFF(MIN)
where f is the switching frequency, the t
is the
ON(MIN)
SW
showing the necessary R value for a desired switching
T
minimum switch on-time (~150ns), and the t
is
OFF(MIN)
frequency is in Table 1.
the minimum switch off-time (~160ns). These equations
show that duty cycle range increases when switching
frequency is decreased.
Table 1. Switching Frequency vs RT Value
SWITCHING FREQUENCY (MHz)
R VALUE (kΩ)
T
0.2
0.3
0.4
0.5
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
768
499
357
280
226
158
124
100
80.6
68.1
57.6
49.9
42.2
A good choice of switching frequency should allow ad-
equate input voltage range (see next section) and keep
the inductor and capacitor values small.
Input Voltage Range
The minimum input voltage is determined by either the
LT3970’s minimum operating voltage of 4.2V or by its
maximum duty cycle (as explained in previous section).
The minimum input voltage due to duty cycle is:
V
OUT + VD
Operating Frequency Trade-Offs
V
=
– VD + VSW
IN(MIN)
1– fSW • tOFF(MIN)
Selectionoftheoperatingfrequencyisatrade-offbetween
efficiency, componentsize, minimumdropoutvoltageand
maximum input voltage. The advantage of high frequency
operationisthatsmallerinductorandcapacitorvaluesmay
be used. The disadvantages are lower efficiency, lower
maximum input voltage, and higher dropout voltage. The
where V
is the minimum input voltage, V
is
OUT
IN(MIN)
the output voltage, V is the catch diode drop (~0.7V),
D
V
is the internal switch drop (~0.5V at max load), f
SW
SW
is the switching frequency (set by RT), and t
is
OFF(MIN)
the minimum switch off-time (160ns). Note that higher
switching frequency will increase the minimum input
voltage. If a lower dropout voltage is desired, a lower
switching frequency should be used.
highest acceptable switching frequency (f
) for a
SW(MAX)
given application can be calculated as follows:
OUT + VD
tON(MIN) V – VSW + VD
V
fSW(MAX)
=
(
)
IN
3970fa
10
LT3970/LT3970-3.3/LT3970-5
APPLICATIONS INFORMATION
The highest allowed V during normal operation
where V is the voltage drop of the catch diode (~0.7V),
D
IN
(V
) is limited by minimum duty cycle and can
be calculated by the following equation:
L is in μH and f is in MHz. The inductor’s RMS current
IN(OP-MAX)
SW
rating must be greater than the maximum load current
and its saturation current should be about 30% higher.
For robust operation in fault conditions (start-up or short
circuit) and high input voltage (>30V), the saturation
current should be above 500mA. To keep the efficiency
high, the series resistance (DCR) should be less than
0.1Ω, and the core material should be intended for high
frequency applications. Table 2 lists several vendors and
suitable types.
V
OUT + VD
V
=
– VD + VSW
IN(OP-MAX)
fSW • tON(MIN)
where t
is the minimum switch on-time (~150ns).
ON(MIN)
However, the circuit will tolerate inputs up to the absolute
maximumratingsoftheV andBOOSTpins,regardlessof
IN
chosenswitchingfrequency.Duringsuchtransientswhere
V ishigherthanV
,theswitchingfrequencywill
IN(OP-MAX)
IN
This simple design guide will not always result in the
optimum inductor selection for a given application. As a
general rule, lower output voltages and higher switching
frequency will require smaller inductor values. If the ap-
plication requires less than 350mA load current, then a
lesser inductor value may be acceptable. This allows use
of a physically smaller inductor, or one with a lower DCR
resulting in higher efficiency. There are several graphs in
theTypicalPerformanceCharacteristicssectionofthisdata
sheet that show the maximum load current as a function
of input voltage for several popular output voltages. Low
inductance may result in discontinuous mode operation,
which is acceptable but reduces maximum load current.
For details of maximum output current and discontinu-
ous mode operation, see Linear Technology Application
be reduced below the programmed frequency to prevent
damage to the part. The output voltage ripple and inductor
current ripple may also be higher than in typical operation,
however the output will still be in regulation.
Inductor Selection
For a given input and output voltage, the inductor value
and switching frequency will determine the ripple current.
The ripple current increases with higher V or V
and
IN
OUT
decreases with higher inductance and faster switching
frequency. A good starting point for selecting the induc-
tor value is:
V
OUT + VD
fSW
L = 3
Note 44.Finally,fordutycyclesgreaterthan50%(V /V
OUT IN
> 0.5), there is a minimum inductance required to avoid
subharmonic oscillations. See Application Note 19.
Table 2. Inductor Vendors
VENDOR
URL
Coilcraft
www.coilcraft.com
www.sumida.com
www.tokoam.com
www.we-online.com
www.cooperet.com
www.murata.com
Input Capacitor
Sumida
Bypass the input of the LT3970 circuit with a ceramic
capacitor of X7R or X5R type. Y5V types have poor
performance over temperature and applied voltage, and
should not be used. A 1μF to 4.7μF ceramic capacitor
is adequate to bypass the LT3970 and will easily handle
Toko
Würth Elektronik
Coiltronics
Murata
3970fa
11
LT3970/LT3970-3.3/LT3970-5
APPLICATIONS INFORMATION
the ripple current. Note that larger input capacitance is
required when a lower switching frequency is used (due
to longer on-times). If the input power source has high
impedance, or there is significant inductance due to
long wires or cables, additional bulk capacitance may be
necessary. This can be provided with a low performance
electrolytic capacitor.
LT3970toproducetheDCoutput. Inthisroleitdetermines
the output ripple, so low impedance (at the switching
frequency) is important. The output ripple decreases with
increasing output capacitance, down to approximately
1mV. See Figure 1. Note that a larger phase lead capacitor
should be used with a large output capacitor.
18
FRONT PAGE APPLICATION
C
= 47pF FOR C
≥ 47μF
16
14
12
10
8
LEAD
OUT
Step-down regulators draw current from the input sup-
ply in pulses with very fast rise and fall times. The input
capacitor is required to reduce the resulting voltage ripple
attheLT3970andtoforcethisveryhighfrequencyswitch-
ing current into a tight local loop, minimizing EMI. A 1μF
capacitor is capable of this task, but only if it is placed
closetotheLT3970(seethePCBLayoutsection).Asecond
precautionregardingtheceramicinputcapacitorconcerns
themaximuminputvoltageratingoftheLT3970.Aceramic
input capacitor combined with trace or cable inductance
forms a high quality (under damped) tank circuit. If the
LT3970 circuit is plugged into a live supply, the input volt-
agecanringtotwiceitsnominalvalue, possiblyexceeding
theLT3970’svoltagerating.Thissituationiseasilyavoided
(see the Hot Plugging Safely section).
6
4
V
= 24V
60
IN
2
V
= 12V
IN
0
0
80
100
20
40
C
(μF)
OUT
3970 F01
Figure 1. Worst-Case Output Ripple Across Full Load Range
When choosing a capacitor, look carefully through the
data sheet to find out what the actual capacitance is under
operating conditions (applied voltage and temperature).
A physically larger capacitor or one with a higher voltage
rating may be required. Table 3 lists several capacitor
vendors.
Output Capacitor and Output Ripple
The output capacitor has two essential functions. It stores
energy in order to satisfy transient loads and stabilize the
LT3970’s control loop. Ceramic capacitors have very low
equivalent series resistance (ESR) and provide the best
ripple performance. A good starting value is:
Table 3. Recommended Ceramic Capacitor Vendors
MANUFACTURER
AVX
WEBSITE
www.avxcorp.com
www.murata.com
www.t-yuden.com
www.vishay.com
www.tdk.com
50
VOUT • fSW
Murata
COUT
=
Taiyo Yuden
Vishay Siliconix
TDK
where f is in MHz and C
is the recommended output
OUT
SW
capacitance in ꢀF. Use X5R or X7R types. This choice will
provide low output ripple and good transient response.
Transientperformancecanbeimprovedwithahighervalue
capacitorifcombinedwithaphaseleadcapacitor(typically
22pF) between the output and the feedback pin. A lower
value of output capacitor can be used to save space and
cost but transient performance will suffer.
Ceramic Capacitors
Ceramic capacitors are small, robust and have very low
ESR. However, ceramic capacitors can cause problems
whenusedwiththeLT3970duetotheirpiezoelectricnature.
When in Burst Mode operation, the LT3970’s switching
frequency depends on the load current, and at very light
loads the LT3970 can excite the ceramic capacitor at audio
frequencies, generating audible noise. Since the LT3970
The second function is that the output capacitor, along
with the inductor, filters the square wave generated by the
3970fa
12
LT3970/LT3970-3.3/LT3970-5
APPLICATIONS INFORMATION
700
operates at a lower current limit during Burst Mode
operation, the noise is typically very quiet to a casual ear.
If this is unacceptable, use a high performance tantalum
or electrolytic capacitor at the output.
FRONT PAGE APPLICATION
600
500
400
300
200
100
A final precaution regarding ceramic capacitors concerns
the maximum input voltage rating of the LT3970. As pre-
viously mentioned, a ceramic input capacitor combined
with trace or cable inductance forms a high quality (under
damped)tankcircuit. IftheLT3970circuitispluggedintoa
live supply, the input voltage can ring to twice its nominal
value,possiblyexceedingtheLT3970’srating.Thissituation
is easily avoided (see the Hot Plugging Safely section).
0
200
LOAD CURRENT (mA)
300 350
0
50
100 150
250
3070 F03
Figure 3. Switching Frequency in Burst Mode Operation
Low Ripple Burst Mode Operation
At higher output loads (above ~45mA for the front page
application) the LT3970 will be running at the frequency
To enhance efficiency at light loads, the LT3970 operates
inlowrippleBurstModeoperationwhichkeepstheoutput
capacitor charged to the proper voltage while minimizing
the input quiescent current. During Burst Mode opera-
tion, the LT3970 delivers single cycle bursts of current to
the output capacitor followed by sleep periods where the
output power is delivered to the load by the output capaci-
tor. Because the LT3970 delivers power to the output with
single, low current pulses, the output ripple is kept below
5mV for a typical application. See Figure 2.
programmed by the R resistor, and will be operating in
T
standard PWM mode. The transition between PWM and
low ripple Burst Mode is seamless, and will not disturb
the output voltage.
BOOST and BD Pin Considerations
CapacitorC3andtheinternalboostSchottkydiode(seethe
Block Diagram) are used to generate a boost voltage that
is higher than the input voltage. In most cases a 0.22μF
capacitor will work well. Figure 4 shows two ways to ar-
range the boost circuit. The BOOST pin must be more than
1.9V above the SW pin for best efficiency. For outputs of
2.2V and above, the standard circuit (Figure 4a) is best.
For outputs between 2.2V and 2.5V, use a 0.47μF boost
capacitor. For output voltages below 2.2V, the boost diode
can be tied to the input (Figure 4b), or to another external
supply greater than 2.2V. However, the circuit in Figure 4a
is more efficient because the BOOST pin current and BD
pin quiescent current come from a lower voltage source.
Also, be sure that the maximum voltage ratings of the
BOOST and BD pins are not exceeded.
Astheloadcurrentdecreasestowardsanoloadcondition,
the percentage of time that the LT3970 operates in sleep
mode increases and the average input current is greatly
reducedresultinginhighefficiencyevenatverylowloads.
Note that during Burst Mode operation, the switching
frequency will be lower than the programmed switching
frequency. See Figure 3.
V
SW
5V/DIV
I
L
100mA/DIV
V
OUT
5mV/DIV
The minimum operating voltage of an LT3970 application
is limited by the minimum input voltage (4.2V) and by the
maximum duty cycle as outlined in a previous section. For
outputvoltagesgreaterthan3.4V, theminimuminputvolt-
age is also limited by the boost circuit for proper start-up.
If the input voltage is ramped slowly, the boost capacitor
3970 F02
2μs/DIV
FRONT PAGE APPLICATION
V
V
= 12V
IN
= 5V
OUT
LOAD
I
= 10mA
Figure 2. Burst Mode Operation
3970fa
13
LT3970/LT3970-3.3/LT3970-5
APPLICATIONS INFORMATION
V
OUT
5.0
4.5
4.0
3.5
3.0
2.5
FRONT PAGE APPLICATION
= 3.3V
V
BD
OUT
V
V
BOOST
LT3970
IN
IN
C3
SW
GND
TO START/RUN
(4a) For V
≥ 2.2V
OUT
BD
0
50 100 150 200 250 300 350
V
V
BOOST
LT3970
IN
IN
LOAD CURRENT (mA)
C3
6.5
6.0
5.5
5.0
4.5
4.0
V
FRONT PAGE APPLICATION
OUT
SW
OUT
V
= 5V
GND
TO START
3970 F04
(4b) For V
< 2.2V; V < 27V
IN
OUT
TO RUN
Figure 4. Two Circuits for Generating the Boost Voltage
may not be fully charged. Because the boost capacitor is
charged with the energy stored in the inductor, the circuit
will rely on some minimum load current to get the boost
circuit running properly. This minimum load will depend
on input and output voltages, and on the arrangement of
the boost circuit. The minimum load generally goes to
zero once the circuit has started. Figure 5 shows a plot
of minimum load to start and to run as a function of input
voltage. In many cases the discharged output capacitor
will present a load to the switcher, which will allow it to
0
50 100 150 200 250 300 350
3970 F05
LOAD CURRENT (mA)
Figure 5. The Minimum Input Voltage Depends on
Output Voltage, Load Current and Boost Circuit
Adding a resistor divider from V to EN programs the
IN
LT3970 to regulate the output only when V is above a
IN
start. The plots show the worst-case situation where V
desired voltage (see Figure 6). This threshold voltage,
IN
is ramping very slowly. For lower start-up voltage, the
V
, can be adjusted by setting the values R3 and R4
IN(EN)
boost diode can be tied to V ; however, this restricts the
such that they satisfy the following equation:
IN
input range to one-half of the absolute maximum rating
R3+R4
of the BOOST pin.
V
=
•1V
IN(EN)
R4
Enable Pin
where output regulation should not start until V is above
IN(EN)
IN
The LT3970 is in shutdown when the EN pin is low and
active when the pin is high. The rising threshold of the EN
comparatoris1V,witha30mVhysteresis.Thisthresholdis
accurate when V is above 4.2V. If V is lower than 4.2V,
tie EN pin to GND to place the part in shutdown.
V
. Note that due to the comparator’s hysteresis,
regulation will not stop until the input falls slightly below
V
IN(EN)
.
IN
IN
3970fa
14
LT3970/LT3970-3.3/LT3970-5
APPLICATIONS INFORMATION
160
V
= 6V
IN(EN)
LT3970
V
V
IN
IN
R3 = 5M
R4 = 1M
120
80
R3
R4
1V
+
–
SHDN
EN
40
3970 F06
0
4
Figure 6. Enable
3
2
1
0
Be aware that while V is below 4.2V, the input current
IN
may rise up to several hundred μA and the part may begin
to switch while the internal circuitry starts up. Figure 7
shows the startup behavior of a typical application with
0
1
2
3
4
5
6
7
8
INPUT VOLTAGE (V)
different programmed V
.
IN(EN)
160
120
80
V
= 12V
IN(EN)
R3 = 11M
R4 = 1M
Shorted and Reversed Input Protection
Iftheinductorischosensothatitwon’tsaturateexcessively,
a LT3970 buck regulator will tolerate a shorted output.
There is another situation to consider in systems where
the output will be held high when the input to the LT3970
is absent. This may occur in battery charging applications
or in battery backup systems where a battery or some
other supply is diode ORed with the LT3970’s output. If
40
0
4
3
2
1
0
the V pin is allowed to float and the EN pin is held high
(either by a logic signal or because it is tied to V ), then
IN
IN
theLT3970’sinternalcircuitrywillpullitsquiescentcurrent
through its SW pin. This is fine if the system can tolerate
a few μA in this state. If the EN pin is grounded, the SW
0
2
4
6
8
10
12
14
INPUT VOLTAGE (V)
3970 F07
pin current will drop to 0.7μA. However, if the V pin is
Figure 7. VIN Start-Up of Front Page Application with VOUT = 3.3V,
No-Load Current, and VIN(EN) programmed as in Figure 6.
IN
grounded while the output is held high, regardless of EN,
parasitic diodes inside the LT3970 can pull current from
the output through the SW pin and the V pin. Figure 8
IN
D4
MBRS140
BD
BOOST
LT3970
shows a circuit that will run only when the input voltage
is present and that protects against a shorted or reversed
input.
V
V
IN
IN
EN
SW
V
OUT
GND
FB
+
BACKUP
3970 F08
Figure 8. Diode D4 Prevents a Shorted Input from Discharging a
Backup Battery Tied to the Output. It Also Protects the Circuit from
a Reversed Input. The LT3970 Runs Only when the Input is Present
3970fa
15
LT3970/LT3970-3.3/LT3970-5
APPLICATIONS INFORMATION
PCB Layout
with stray inductance in series with the power source,
forms an under damped tank circuit, and the voltage at
For proper operation and minimum EMI, care must be
taken during printed circuit board layout. Figure 9 shows
the recommended component placement with trace,
ground plane and via locations. Note that large, switched
the V pin of the LT3970 can ring to twice the nominal
IN
input voltage, possibly exceeding the LT3970’s rating and
damaging the part. If the input supply is poorly controlled
or the user will be plugging the LT3970 into an energized
supply, the input network should be designed to prevent
thisovershoot.SeeLinearTechnologyApplicationNote 88
for a complete discussion.
currents flow in the LT3970’s V and SW pins, the internal
IN
catch diode and the input capacitor. The loop formed by
these components should be as small as possible. These
components,alongwiththeinductorandoutputcapacitor,
should be placed on the same side of the circuit board,
and their connections should be made on that layer. Place
a local, unbroken ground plane below these components.
The SW and BOOST nodes should be as small as possible.
Finally, keep the FB nodes small so that the ground traces
will shield them from the SW and BOOST nodes. The
Exposed Pad on the bottom of the DFN package must be
soldered to ground so that the pad acts as a heat sink. To
keep thermal resistance low, extend the ground plane as
much as possible, and add thermal vias under and near
the LT3970 to additional ground planes within the circuit
board and on the bottom side.
High Temperature Considerations
For higher ambient temperatures, care should be taken
in the layout of the PCB to ensure good heat sinking
of the LT3970. The Exposed Pad on the bottom of the
DFN package must be soldered to a ground plane. This
ground should be tied to large copper layers below with
thermal vias; these layers will spread the heat dissipated
by the LT3970. Placing additional vias can reduce thermal
resistance further. In the MSOP package, the copper lead
frame is fused to GND (Pin 5) so place thermal vias near
this pin. The maximum load current should be derated
as the ambient temperature approaches the maximum
junction rating.
GND
GND
Power dissipation within the LT3970 can be estimated by
calculatingthetotalpowerlossfromanefficiencymeasure-
ment and subtracting inductor loss. The die temperature
is calculated by multiplying the LT3970 power dissipation
by the thermal resistance from junction to ambient.
1
2
3
4
5
10
9
EN
PG
V
IN
8
7
6
Finally, be aware that at high ambient temperatures the
internalSchottkydiodewillhavesignificantleakagecurrent
(see Typical Performance Characteristics) increasing the
quiescent current of the LT3970 converter.
V
GND
OUT
3970 F09
VIAS TO LOCAL GROUND PLANE
VIAS TO V
OUT
Other Linear Technology Publications
Figure 9. A Good PCB Layout Ensures Proper, Low EMI Operation
Application Notes 19, 35 and 44 contain more detailed
descriptions and design information for buck regulators
and other switching regulators. The LT1376 data sheet
has a more extensive discussion of output ripple, loop
compensation and stability testing. Design Note 100
shows how to generate a bipolar output supply using a
buck regulator.
Hot Plugging Safely
The small size, robustness and low impedance of ceramic
capacitors make them an attractive option for the input
bypass capacitor of LT3970 circuits. However, these ca-
pacitors can cause problems if the LT3970 is plugged into
a live supply. The low loss ceramic capacitor, combined
3970fa
16
LT3970/LT3970-3.3/LT3970-5
TYPICAL APPLICATIONS
3.3V Step-Down Converter
5V Step-Down Converter
V
V
IN
6V TO 40V
IN
4.2V TO 40V
C3
0.22μF
C3
0.22μF
V
BOOST
LT3970
V
BOOST
LT3970
IN
IN
L1
L1
22μH
22μH
V
V
OUT
OUT
3.3V
5V
OFF ON
EN
PG
SW
BD
OFF ON
EN
PG
SW
BD
350mA
350mA
R1
R1
22pF
22pF
1M
1M
C1
2.2μF
C1
2.2μF
C2
22μF
C2
22μF
RT
FB
RT
FB
GND
GND
R2
576k
R2
316k
226k
226k
3490 TA02
3490 TA03
f = 600kHz
f = 600kHz
3.3V Step-Down Converter
5V Step-Down Converter
V
V
IN
6V TO 40V
IN
4.2V TO 40V
0.22μF
22μH
0.22μF
22μH
V
BOOST
V
BOOST
LT3970-5
IN
IN
LT3970-3.3
V
V
OUT
OUT
3.3V
5V
OFF ON
EN
SW
BD
OFF ON
EN
PG
SW
BD
350mA
350mA
PG
RT
V
OUT
RT
V
OUT
2.2μF
2.2μF
22μF
22μF
GND
GND
226k
f = 600kHz
226k
3490 TA03a
3490 TA03b
f = 600kHz
2.5V Step-Down Converter
1.8V Step-Down Converter
V
V
IN
IN
4.2V TO 40V
4.2V TO 27V
C3
0.47μF
C3
0.22μF
V
BOOST
LT3970
V
BOOST
LT3970
IN
IN
L1
L1
10μH
15μH
V
V
OUT
OUT
2.5V
OFF ON
EN
PG
SW
BD
1.8V
OFF ON
EN
BD
PG
SW
350mA
350mA
R1
R1
47pF
47pF
1M
487k
C1
2.2μF
C2
47μF
C1
2.2μF
C2
47μF
RT
FB
RT
FB
GND
GND
R2
931k
R2
1M
226k
226k
3490 TA04
3490 TA05
f = 600kHz
f = 600kHz
3970fa
17
LT3970/LT3970-3.3/LT3970-5
TYPICAL APPLICATIONS
12V Step-Down Converter
5V, 2MHz Step-Down Converter
V
V
IN
IN
8.5V TO 16V
TRANSIENTS
TO 40V
14V TO 40V
C3
C3
0.1μF
0.1μF
V
BOOST
LT3970
IN
L1
33μH
V
BOOST
LT3970
IN
L1
10μH
V
OUT
V
12V
OFF ON
EN
PG
SW
BD
OUT
5V
OFF ON
EN
PG
SW
BD
350mA
350mA
R1
22pF
R1
1M
22pF
C1
2.2μF
C2
22μF
RT
FB
1M
C1
1μF
C2
10μF
RT
FB
GND
R2
113k
226k
GND
R2
316k
49.9k
f = 2MHz
3490 TA06
f = 600kHz
3490 TA07
5V Step-Down Converter with Reduced Input Current During Start-Up
V
IN
kΩ
6V TO 40V
+
–
0.22μF
22μH
V
BOOST
LT3970
IN
5M
V
OUT
5V
EN
PG
SW
BD
350mA
1M
22pF
1M
RT
FB
22μF
2.2μF
GND
316k
226k
3490 TA08a
f = 600kHz
Input Current During Start-Up
Start-Up from High Impedance Input Source
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
EN PROGRAMMED TO 6V
INPUT CURRENT
DROPOUT
V
IN
5V/DIV
CONDITIONS
FRONT PAGE
APPLICATION
V
OUT
2V/DIV
FRONT PAGE
APPLICATION
WITH EN
PROGRAMMED
TO 6V
3970 TA08c
5ms/DIV
FRONT PAGE APPLICATION
V
OUT
= 5V
1k INPUT SOURCE RESISTANCE
2.5mA LOAD
–0.5
0
2
6
8
10
12
4
INPUT VOLTAGE (V)
3970 TA08b
3970fa
18
LT3970/LT3970-3.3/LT3970-5
PACKAGE DESCRIPTION
DDB Package
10-Lead Plastic DFN (3mm × 2mm)
(Reference LTC DWG # 05-08-1722 Rev Ø)
R = 0.115
0.64 0.05
(2 SIDES)
0.40 0.10
3.00 0.10
(2 SIDES)
TYP
6
R = 0.05
TYP
10
0.70 0.05
2.55 0.05
1.15 0.05
2.00 0.10
PIN 1 BAR
TOP MARK
PIN 1
(2 SIDES)
R = 0.20 OR
(SEE NOTE 6)
0.25 s 45°
PACKAGE
OUTLINE
0.64 0.05
(2 SIDES)
0.25 0.05
CHAMFER
5
1
(DDB10) DFN 0905 REV Ø
0.25 0.05
0.50 BSC
0.75 0.05
0.200 REF
0.50 BSC
2.39 0.05
(2 SIDES)
2.39 0.05
(2 SIDES)
0 – 0.05
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING CONFORMS TO VERSION (WECD-1) IN JEDEC PACKAGE OUTLINE M0-229
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 THE TOP AND BOTTOM OF PACKAGE
3970fa
19
LT3970/LT3970-3.3/LT3970-5
PACKAGE DESCRIPTION
MS Package
10-Lead Plastic MSOP
(Reference LTC DWG # 05-08-1661 Rev E)
0.889 p 0.127
(.035 p .005)
5.23
(.206)
MIN
3.20 – 3.45
(.126 – .136)
3.00 p 0.102
(.118 p .004)
(NOTE 3)
0.497 p 0.076
(.0196 p .003)
REF
0.50
0.305 p 0.038
(.0120 p .0015)
TYP
(.0197)
10 9
8
7 6
BSC
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 5
0.53 p 0.152
(.021 p .006)
0.86
(.034)
REF
1.10
(.043)
MAX
DETAIL “A”
0.18
(.007)
SEATING
PLANE
0.17 – 0.27
(.007 – .011)
TYP
0.1016 p 0.0508
(.004 p .002)
0.50
(.0197)
BSC
MSOP (MS) 0307 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
3970fa
20
LT3970/LT3970-3.3/LT3970-5
REVISION HISTORY
REV
DATE
DESCRIPTION
PAGE NUMBER
A
5/10
Added LT3970-3.3 and LT3970-5
1 - 22
3970fa
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
LT3970/LT3970-3.3/LT3970-5
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
V : 4.3V to 38V, V
LT3971
38V, 1.2A (I ), I = 2.8μA High Efficiency Step-Down DC/DC
= 1.2V, I = 2.8μA, I < 1μA,
Q SD
OUT
Q
IN
OUT(MIN)
Converter
MSOP-10E, 3mm × 3mm DFN-10
LT3991
LT3689
55V, 1.2A (I ), I = 2.8μA High Efficiency Step-Down DC/DC
V : 4.3V to 55V, V = 1.2V, I = 2.8μA, I < 1μA,
OUT
Q
IN
OUT(MIN)
Q
SD
Converter
MSOP-10E, 3mm × 3mm DFN-10
36V, 60V Transient Protection, 800mA, 2.2MHz High Efficiency
Micropower Step-Down DC/DC Converter with POR Reset and
Watchdog Timer
V : 3.6V to 36V, Transient to 60V, V
= 0.8V, I = 75μA,
Q
IN
OUT(MIN)
I
< 1μA, 3mm × 3mm QFN-16
SD
LT3682
36V, 60V
, 1A, 2.2MHz High Efficiency Micropower Step-Down
V : 3.6V to 36V, V
= 0.8V, I = 75μA, I < 1μA,
OUT(MIN) Q SD
MAX
IN
DC/DC Converter
3mm × 3mm DFN-12
LT3480
36V with Transient Protection to 60V, 2A (I ), 2.4MHz, High
V : 3.6V to 38V, V
= 0.78V, I = 70μA, I < 1μA,
Q SD
OUT
IN
OUT(MIN)
Efficiency Step-Down DC/DC Converter with Burst Mode® Operation 3mm × 3mm DFN-10, MSOP-10E
LT3685
36V with Transient Protection to 60V, 2A (I ), 2.4MHz, High
V : 3.6V to 38V, V
= 0.78V, I = 70μA, I < 1μA,
OUT
IN
OUT(MIN) Q SD
Efficiency Step-Down DC/DC Converter
3mm × 3mm DFN-10, MSOP-10E
LT3481
34V with Transient Protection to 36V, 2A (I ), 2.8MHz, High
V : 3.6V to 34V, V = 1.26V, I = 50μA, I < 1μA,
OUT
IN
OUT(MIN)
Q
SD
Efficiency Step-Down DC/DC Converter with Burst Mode Operation
3mm × 3mm DFN-10, MSOP-10E
LT1976/LT1977
60V, 1.2A (I ), 200/500kHz, High Efficiency Step-Down DC/DC
V : 3.3V to 60V, V
= 1.20V, I = 100μA, I < 1μA,
OUT(MIN) Q SD
OUT
IN
Converter with Burst Mode Operation
TSSOP-16E
3970fa
LT 0510 REV A • 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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