LINER LT3970IDDB-5-TRPBF 40v, 350ma step-down regulator with 2.5î¼a quiescent current and integrated diode Datasheet

LT3970/LT3970-3.3/LT3970-5
40V, 350mA Step-Down
Regulator with 2.5µA
Quiescent Current and
Integrated Diodes
FEATURES
DESCRIPTION
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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 necessary oscillator, control and logic circuitry. Low ripple Burst
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
of 0.7μA. A power good flag signals when VOUT reaches
90% of the programmed output voltage. The LT3970 is
available in small 10-pin MSOP and 3mm × 2mm DFN
packages.
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Low Ripple Burst Mode® Operation
2.5μA IQ at 12VIN to 3.3VOUT
Output Ripple < 5mVP-P
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 IQ at 12VIN
Accurate 1V Enable Pin Threshold
Low Shutdown Current: IQ = 0.7μA
Internal Sense Limits Catch Diode Current
Power Good Flag
Output Voltage: 1.21V to 25V
Internal Compensation
Small 10-Pin MSOP and (3mm × 2mm) DFN Packages
APPLICATIONS
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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.
Automotive Battery Regulation
Power for Portable Products
Industrial Supplies
TYPICAL APPLICATION
5V Step-Down Converter
Efficiency
90
1000
VIN = 12V
VIN
6V TO 40V
0.22μF
BOOST
OFF ON
22μH
EN
PG
SW
RT
FB
BD
22pF
2.2μF
226k
f = 600kHz
VOUT
5V
350mA
GND
1M
22μF
80
100
70
10
60
1
50
0.1
316k
POWER LOSS (mW)
LT3970
EFFICIENCY (%)
VIN
3490 TA01a
40
0.01
0.01
0.1
1
10
LOAD CURRENT (mA)
100
3970 TA01b
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1
LT3970/LT3970-3.3/LT3970-5
ABSOLUTE MAXIMUM RATINGS (Note 1)
VIN, EN Voltage .........................................................40V
BOOST Pin Voltage ...................................................55V
BOOST Pin Above SW Pin.........................................30V
FB/VOUT, RT Voltage ....................................................6V
PG, BD Voltage .........................................................30V
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)
MS Only ............................................................ 300°C
PIN CONFIGURATION
TOP VIEW
*FB/VOUT 1
EN 2
VIN 3
TOP VIEW
10 RT
*FB/VOUT
EN
VIN
GND
GND
9 PG
11
GND
8 BD
GND 4
7 BOOST
GND 5
6 SW
10
9
8
7
6
1
2
3
4
5
RT
PG
BD
BOOST
SW
MS PACKAGE
10-LEAD PLASTIC MSOP
DDB PACKAGE
10-LEAD (3mm × 2mm) PLASTIC DFN
θJA = 100°C/W
θJA = 76°C/W
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
*FB for LT3970, VOUT for LT3970-3.3, LT3970-5.
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT3970EDDB#PBF
LT3970EDDB#TRPBF
LFCZ
10-Lead (3mm × 2mm) Plastic DFN
–40°C to 125°C
LT3970IDDB#PBF
LT3970IDDB#TRPBF
LFCZ
10-Lead (3mm × 2mm) Plastic DFN
–40°C to 125°C
LT3970EMS#PBF
LT3970EMS#TRPBF
LTFDB
10-Lead Plastic MSOP
–40°C to 125°C
LT3970IMS#PBF
LT3970IMS#TRPBF
LTFDB
10-Lead Plastic MSOP
–40°C to 125°C
LT3970EDDB-3.3#PBF
LT3970EDDB-3.3#TRPBF
LFQH
10-Lead (3mm × 2mm) Plastic DFN
–40°C to 125°C
LT3970IDDB-3.3#PBF
LT3970IDDB-3.3#TRPBF
LFQH
10-Lead (3mm × 2mm) Plastic DFN
–40°C to 125°C
LT3970EMS-3.3#PBF
LT3970EMS-3.3#TRPBF
LTFQG
10-Lead Plastic MSOP
–40°C to 125°C
LT3970IMS-3.3#PBF
LT3970IMS-3.3#TRPBF
LTFQG
10-Lead Plastic MSOP
–40°C to 125°C
LT3970HMS-3.3#PBF
LT3970HMS-3.3#TRPBF
LTFQG
10-Lead Plastic MSOP
–40°C to 150°C
LT3970EDDB-5#PBF
LT3970EDDB-5#TRPBF
LFQF
10-Lead (3mm × 2mm) Plastic DFN
–40°C to 125°C
LT3970IDDB-5#PBF
LT3970IDDB-5#TRPBF
LFQF
10-Lead (3mm × 2mm) Plastic DFN
–40°C to 125°C
LT3970EMS-5#PBF
LT3970EMS-5#TRPBF
LTFQD
10-Lead Plastic MSOP
–40°C to 125°C
LT3970IMS-5#PBF
LT3970IMS-5#TRPBF
LTFQD
10-Lead Plastic MSOP
–40°C to 125°C
LT3970HMS-5#PBF
LT3970HMS-5#TRPBF
LTFQD
10-Lead Plastic MSOP
–40°C to 150°C
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
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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
l
Minimum Input Voltage
Quiescent Current from VIN
MIN
VEN Low
VEN High
VEN High, –40°C to 125°C
VEN High, –40°C to 150°C
LT3970 Feedback Voltage
l
l
TYP
MAX
4
4.2
V
0.7
1.7
1.2
2.7
3.5
4
μA
μA
μA
μA
l
1.195
1.185
1.21
1.21
1.225
1.235
V
V
–40°C to 125°C
–40°C to 150°C
l
l
3.26
3.234
3.217
3.3
3.3
3.3
3.34
3.366
3.366
V
V
V
–40°C to 125°C
–40°C to 150°C
l
l
4.94
4.9
4.875
5
5
5
5.06
5.1
5.1
V
V
V
l
LT3970-3.3 Output Voltage
LT3970-5 Output Voltage
LT3970 FB Pin Bias Current (Note 3)
VFB = 1.21V
FB/Output Voltage Line Regulation
4.2V < VIN < 40V
Switching Frequency
RT = 41.2k, VIN = 6V
RT = 158k, VIN = 6V
RT = 768k, VIN = 6V
Switch Current Limit
Catch Schottky Current Limit
Switch VCESAT
ISW = 200mA
0.1
20
nA
0.0002
0.01
%/V
1.76
640
160
2.25
800
200
2.64
960
240
MHz
kHz
kHz
VIN = 5V, VFB = 0V
535
700
865
mA
VIN = 5V
350
400
500
mA
175
Switch Leakage Current
0.05
ISCH = 100mA, VIN = VBD = NC
650
Catch Schottky Reverse Leakage
VSW = 12V
0.05
Boost Schottky Forward Voltage
ISCH = 50mA, VIN = NC, VBOOST = 0V
875
Boost Schottky Reverse Leakage
VREVERSE = 12V
Catch Schottky Forward Voltage
UNITS
Minimum Boost Voltage (Note 4)
VIN = 5V
BOOST Pin Current
ISW = 200mA, VBOOST = 15V
l
mV
2
μA
mV
2
μA
mV
0.02
2
μA
1.4
1.8
V
7
10
mA
EN Pin Current
VEN = 12V
1
30
nA
LT3970 EN Voltage Threshold
EN Rising, VIN ≥ 4.2V
l
0.94
1
1.06
V
LT3970-X EN Voltage Threshold
EN Rising, VIN ≥ 4.2V
l
0.93
1
1.07
V
80
120
160
mV
EN Voltage Hysteresis
LT3970 PG Threshold Offset from Feedback Voltage
30
VFB Rising
LT3970 PG Hysteresis
LT3970-X PG Threshold Offset from Output Voltage
12
VFB Rising
6.5
LT3970-X PG Hysteresis as % of Output Voltage
10
mV
13.5
1.0
PG Leakage
VPG = 3V
PG Sink Current
VPG = 0.4V
l
0.01
VIN = 10V
l
Minimum Switch On-Time
Minimum Switch Off-Time
mV
30
%
%
1
μA
80
μA
90
ns
100
160
ns
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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.
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
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
guarantee full saturation of the switch.
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise noted.
Efficiency, VOUT = 3.3V
Efficiency, VOUT = 5V
LT3970 Feedback Voltage
90
90
1.220
FRONT PAGE APPLICATION
60
VIN = 24V
EFFICIENCY (%)
EFFICIENCY (%)
70
80
VIN = 12V
VIN = 24V
VIN = 36V
50
40
FRONT PAGE APPLICATION
VOUT = 3.3V
R1 = 1M
R2 = 576k
30
20
0.01
0.1
1
10
LOAD CURRENT (mA)
70
VIN = 36V
60
50
30
0.01
100
1.210
1.205
1.200
40
0.1
1
10
LOAD CURRENT (mA)
100
1.195
–50 –25
LT3970-3.3 Output Voltage
LT3970-5 Output Voltage
No-Load Supply Current
3.31
5.02
3.5
3.28
3.27
–50 –25
SUPPLY CURRENT (µA)
4.0
OUTPUT VOLTAGE (V)
5.04
3.29
5.00
4.98
25 50
75 100 125 150
TEMPERATURE (°C)
3970 G03a
4.94
–50 –25
FRONT PAGE APPLICATION
VOUT = 3.3V
R1 = 1MΩ
R2 = 576k
LT3970-5
LT3970-3.3
3.0
2.5
2.0
4.96
0
25 50
75 100 125 150
TEMPERATURE (°C)
3970 G03
3.32
3.30
0
3970 G02
3970 G01
OUTPUT VOLTAGE (V)
1.215
VIN = 12V
FEEDBACK VOLTAGE (V)
80
0
25 50
75 100 125 150
TEMPERATURE (°C)
3970 G03b
1.5
5
10
25
30
15
20
INPUT VOLTAGE (V)
35
40
3970 G04
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LT3970/LT3970-3.3/LT3970-5
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise noted.
FRONT PAGE APPLICATION
VIN = 12V
VOUT = 3.3V
R1 = 1M
R2 = 576k
LOAD CURRENT (mA)
SUPPLY CURRENT (μA)
12
Maximum Load Current
550
9
6
Maximum Load Current
600
FRONT PAGE APPLICATION
VOUT = 3.3V
MINIMUM
450
400
3
0
350
25 50
75 100 125 150
TEMPERATURE (°C)
5
10
30
15
20
25
INPUT VOLTAGE (V)
3970 G05
Maximum Load Current
MINIMUM
450
350
40
5
Load Regulation
H GRADE
LIMITED BY MAXIMUM
JUNCTION TEMPERATURE;
θJA = 76°C/W
200
FRONT PAGE APPLICATION
VIN = 12V
VOUT = 5V
0
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
0.05
0
–0.05
–0.10
–0.15 FRONT PAGE APPLICATION
REFERENCED FROM VOUT AT 100mA LOAD
–0.20
50
100 150 200 250 300 350
0
500
CATCH DIODE VALLEY CURRENT LIMIT
400
300
200
0
200
SWITCH ON-TIME/SWITCH OFF-TIME (ns)
700
2.0
FREQUENCY (MHz)
1.8
400
1.6
1.4
1.2
1.0
0.8
0.6
300
0.4
0.2
25 50 75 100 125 150
TEMPERATURE (oC)
3970 G11
40
60
DUTY CYCLE (%)
0
–50 –25
0
100
80
Minimum
Switch On-Time/Switch Off-Time
2.2
CATCH DIODE VALLEY CURRENT LIMIT
20
3970 G10
2.4
SWITCH PEAK CURRENT LIMIT
0
600
Switching Frequency
500
SWITCH PEAK
CURRENT LIMIT
3970 G09
800
200
–50 –25
700
LOAD CURRENT (mA)
Switch Current Limit
40
Switch Current Limit
0.10
3970 G08
600
35
800
0.15
LOAD REGULATION (%)
400
30
15
20
25
INPUT VOLTAGE (V)
10
3870 G07
SWITCH CURRENT LIMIT (mA)
LIMITED BY CURRENT LIMIT
LOAD CURRENT (mA)
35
0.20
500
SWITCH CURRENT LIMIT (mA)
500
3870 G06
600
100
TYPICAL
400
0
–50 –25
300
FRONT PAGE APPLICATION
VOUT = 5V
550
TYPICAL
500
LOAD CURRENT (mA)
No-Load Supply Current
15
25 50 75 100 125 150
TEMPERATURE (°C)
3970 G12
LOAD CURRENT = 175mA
180
160
140
120
MINIMUM OFF-TIME
100
80
60
MINIMUM ON-TIME
40
20
0
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
3970 G13
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LT3970/LT3970-3.3/LT3970-5
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise noted.
Switch VCESAT (ISW = 200mA)
vs Temperature
Switch VCESAT
250
BOOST Pin Current
16
400
200
150
BOOST PIN CURRENT (mA)
SWITCH VCESAT (mV)
SWITCH VCESAT (mV)
14
300
200
100
12
10
8
6
4
100
–50 –25
0
0
25 50 75 100 125 150
TEMPERATURE (°C)
2
0
100
300
400
200
SWITCH CURRENT (mA)
3970 G14
6.5
FRONT PAGE APPLICATION
VOUT = 3.3V
3.0
FRONT PAGE APPLICATION
VOUT = 5V
0
5.5
TO RUN
5.0
50
100 150 200 250
LOAD CURRENT (mA)
0
50
100 150 200 250
LOAD CURRENT (mA)
0.8
16
0.4
–50°C
25°C
125°C
150°C
400
3970 G20
–50°C
25°C
125°C
150°C
0
350
50
100
150
BOOST DIODE CURRENT (mA)
200
3970 G19
Power Good Threshold
92
VR = 12V
91
THRESHOLD (%)
0.6
CATCH DIODE LEAKAGE (μA)
20
100
300
200
CATCH DIODE CURRENT (mA)
300
Catch Diode Leakage
Catch Diode Forward Voltage
0
0.4
3970 G18
1.0
0.2
0.6
0
4.0
350
300
0.8
0.2
3970 G17
CATCH DIODE VF (V)
1.0
TO START
4.5
2.5
0
Boost Diode Forward Voltage
BOOST DIODE VF (V)
3.5
500
1.2
6.0
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
4.5
TO START/RUN
200
300
400
SWITCH CURRENT (mA)
3970 G16
Minimum Input Voltage,
VOUT = 5V
4.0
100
3970 G15
Minimum Input Voltage,
VOUT = 3.3V
5.0
0
500
12
8
90
89
4
0
–50 –25
0
25 50
75 100 125 150
TEMPERATURE (°C)
3970 G21
88
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
3970 G22
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LT3970/LT3970-3.3/LT3970-5
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise noted.
Transient Load Response; Load
Current is Stepped from 10mA
(Burst Mode Operation) to 110mA
EN Threshold
Transient Load Response; Load
Current is Stepped from 100mA
to 200mA
THRESHOLD VOLTAGE (V)
1.050
1.025
VOUT
100mV/DIV
VOUT
100mV/DIV
1.000
IL
100mA/DIV
IL
100mA/DIV
100μs/DIV
FRONT PAGE APPLICATION
VIN = 12V
VOUT = 5V
0.975
0.950
–50 –25
0
3970 G24
100μs/DIV
FRONT PAGE APPLICATION
VIN = 12V
VOUT = 5V
3970 G25
25 50 75 100 125 150
TEMPERATURE (°C)
3970 G23
Switching Waveforms,
Burst Mode Operation
Switching Waveforms, Full
Frequency Continuous Operation
VSW
5V/DIV
VSW
5V/DIV
IL
100mA/DIV
IL
200mA/DIV
VOUT
5mV/DIV
VOUT
5mV/DIV
2μs/DIV
FRONT PAGE APPLICATION
VIN = 12V
VOUT = 5V
ILOAD = 10mA
3970 G26
1μs/DIV
FRONT PAGE APPLICATION
VIN = 12V
VOUT = 5V
ILOAD = 350mA
3970 G27
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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 (Pins 4, 5, Exposed Pad (Pin 11, DFN Only)): 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.
VOUT (Pin 1, LT3970-3.3 and LT3970-5 Only): The LT39703.3 and LT3970-5 regulate the VOUT Pin to 3.3V and 5V
respectively. This pin connects to the internal feedback
divider that programs the fixed output voltage.
BOOST (Pin 7): This pin is used to provide a drive voltage, higher than the input voltage, to the internal bipolar
NPN power switch.
EN (Pin 2): The part is in shutdown when this pin is low
and active when this pin is high. The hysteretic threshold
voltage is 1V going up and 0.97V going down. Tie to VIN
if shutdown feature is not used. The EN threshold is accurate only when VIN is above 4.2V. If VIN is lower than
4.2V, ground EN to place the part in shutdown.
BD (Pin 8): This pin connects to the anode of the boost
diode. This pin also supplies current to the LT3970’s internal
regulator when BD is above 3.2V.
PG (Pin 9): The PG pin is the open-drain output of an
internal comparator. PG remains low until the FB pin is
within 10% of the final regulation voltage. PG is valid when
VIN is above 4.2V and EN is high.
VIN (Pin 3): The VIN pin supplies current to the LT3970’s
internal circuitry and to the internal power switch. This
pin must be locally bypassed.
RT (Pin 10): A resistor is tied between RT and ground to
set the switching frequency.
BLOCK DIAGRAM
3
VIN
C1
VIN
INTERNAL 1.21V REF
1V
2
EN
–
+
8
+
SHDN
–
BD
DBOOST
SLOPE COMP
BOOST
SWITCH LATCH
7
R
10
RT
9
RT
OSCILLATOR
200kHz TO 2.2MHz
PG
+
+
1.09V
ERROR
AMP
–
VC
LT3970 ONLY
FB
GND
(4, 5)
R2
1
R1
C3
SW
Burst Mode
DETECT
–
R2
Q
S
DCATCH
L1
VOUT
6
C2
R1
LT3970-3.3
LT3970-5
ONLY*
VOUT
1
3990 BD
*LT3970-3.3: R1 = 12.65M, R2 = 7.35M
LT3970-5: R1 = 15.15M, R2 = 4.85M
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LT3970/LT3970-3.3/LT3970-5
OPERATION
The LT3970 is a constant frequency, current mode stepdown 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
between the VIN and SW pins, turning the switch off when
this current reaches a level determined by the voltage at
VC (see Block Diagram). An error amplifier measures the
output voltage through an external resistor divider tied to
the FB pin and servos the VC node. If the error amplifier’s
output increases, more current is delivered to the output;
if it decreases, less current is delivered.
Another comparator monitors the current flowing through
the catch diode and reduces the operating frequency when
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.
An internal regulator provides power to the control circuitry. The bias regulator normally draws power from
the VIN pin, but if the BD pin is connected to an external
voltage higher than 3.2V, bias power will be drawn from
the external source (typically the regulated output voltage).
This improves efficiency.
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 VIN or from the
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.
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.
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 VIN is above 4.2V.
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LT3970/LT3970-3.3/LT3970-5
APPLICATIONS INFORMATION
FB Resistor Network
The output voltage is programmed with a resistor divider
between the output and the FB pin. Choose the 1% resistors according to:
R1=R2
VOUT
–1
1.21
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
The LT3970 uses a constant frequency PWM architecture
that can be programmed to switch from 200kHz to 2.2MHz
by using a resistor tied from the RT pin to ground. A table
showing the necessary RT value for a desired switching
frequency is in Table 1.
Table 1. Switching Frequency vs RT Value
SWITCHING FREQUENCY (MHz)
RT VALUE (kΩ)
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
Operating Frequency Trade-Offs
Selection of the operating frequency is a trade-off between
efficiency, component size, minimum dropout voltage and
maximum input voltage. The advantage of high frequency
operation is that smaller inductor and capacitor values may
be used. The disadvantages are lower efficiency, lower
maximum input voltage, and higher dropout voltage. The
highest acceptable switching frequency (fSW(MAX)) for a
given application can be calculated as follows:
fSW(MAX ) =
VOUT + VD
tON(MIN) ( VIN – VSW + VD )
where VIN is the typical input voltage, VOUT is the output
voltage, VD is the integrated catch diode drop (~0.7V),
and VSW is the internal switch drop (~0.5V at max load).
This equation shows that slower switching frequency is
necessary to accommodate high VIN/VOUT ratio.
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. The switch can turn on for a minimum of ~150ns and
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:
DCMIN = fSW • tON(MIN)
DCMAX = 1 – fSW • tOFF(MIN)
where fSW is the switching frequency, the tON(MIN) is the
minimum switch on-time (~150ns), and the tOFF(MIN) is
the minimum switch off-time (~160ns). These equations
show that duty cycle range increases when switching
frequency is decreased.
A good choice of switching frequency should allow adequate 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:
VIN(MIN) =
VOUT + VD
–V +V
1– fSW • tOFF(MIN) D SW
where VIN(MIN) is the minimum input voltage, VOUT is
the output voltage, VD is the catch diode drop (~0.7V),
VSW is the internal switch drop (~0.5V at max load), fSW
is the switching frequency (set by RT), and tOFF(MIN) is
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.
3970fa
10
LT3970/LT3970-3.3/LT3970-5
APPLICATIONS INFORMATION
The highest allowed V IN during normal operation
(VIN(OP-MAX)) is limited by minimum duty cycle and can
be calculated by the following equation:
VIN(OP-MAX ) =
VOUT + VD
–V +V
fSW • tON(MIN) D SW
where tON(MIN) is the minimum switch on-time (~150ns).
However, the circuit will tolerate inputs up to the absolute
maximum ratings of the VIN and BOOST pins, regardless of
chosen switching frequency. During such transients where
VIN is higher than VIN(OP-MAX), the switching frequency will
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 VIN or VOUT and
decreases with higher inductance and faster switching
frequency. A good starting point for selecting the inductor value is:
L=3
VOUT + VD
fSW
Table 2. Inductor Vendors
where VD is the voltage drop of the catch diode (~0.7V),
L is in μH and fSW is in MHz. The inductor’s RMS current
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.
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 application 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
the Typical Performance Characteristics section of this data
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 discontinuous mode operation, see Linear Technology Application
Note 44. Finally, for duty cycles greater than 50% (VOUT/VIN
> 0.5), there is a minimum inductance required to avoid
subharmonic oscillations. See Application Note 19.
VENDOR
URL
Coilcraft
www.coilcraft.com
Input Capacitor
Sumida
www.sumida.com
Toko
www.tokoam.com
Würth Elektronik
www.we-online.com
Coiltronics
www.cooperet.com
Murata
www.murata.com
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
3970fa
11
LT3970/LT3970-3.3/LT3970-5
APPLICATIONS INFORMATION
Step-down regulators draw current from the input supply in pulses with very fast rise and fall times. The input
capacitor is required to reduce the resulting voltage ripple
at the LT3970 and to force this very high frequency switching current into a tight local loop, minimizing EMI. A 1μF
capacitor is capable of this task, but only if it is placed
close to the LT3970 (see the PCB Layout section). A second
precaution regarding the ceramic input capacitor concerns
the maximum input voltage rating of the LT3970. A ceramic
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 voltage can ring to twice its nominal value, possibly exceeding
the LT3970’s voltage rating. This situation is easily avoided
(see the Hot Plugging Safely section).
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:
50
COUT =
VOUT • fSW
where fSW is in MHz and COUT is the recommended output
capacitance in μF. Use X5R or X7R types. This choice will
provide low output ripple and good transient response.
Transient performance can be improved with a higher value
capacitor if combined with a phase lead capacitor (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.
The second function is that the output capacitor, along
with the inductor, filters the square wave generated by the
LT3970 to produce the DC output. In this role it determines
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
WORST-CASE OUTPUT RIPPLE (mV)
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.
FRONT PAGE APPLICATION
CLEAD = 47pF FOR COUT ≥ 47μF
16
14
12
10
8
6
4
VIN = 24V
2
VIN = 12V
0
0
20
60
40
COUT (μF)
80
100
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.
Table 3. Recommended Ceramic Capacitor Vendors
MANUFACTURER
WEBSITE
AVX
www.avxcorp.com
Murata
www.murata.com
Taiyo Yuden
www.t-yuden.com
Vishay Siliconix
www.vishay.com
TDK
www.tdk.com
Ceramic Capacitors
Ceramic capacitors are small, robust and have very low
ESR. However, ceramic capacitors can cause problems
when used with the LT3970 due to their piezoelectric nature.
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
3970fa
12
LT3970/LT3970-3.3/LT3970-5
APPLICATIONS INFORMATION
A final precaution regarding ceramic capacitors concerns
the maximum input voltage rating of the LT3970. As previously mentioned, a ceramic 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 voltage can ring to twice its nominal
value, possibly exceeding the LT3970’s rating. This situation
is easily avoided (see the Hot Plugging Safely section).
FRONT PAGE APPLICATION
600
500
400
300
200
100
0
0
50
100 150 200 250
LOAD CURRENT (mA)
300
350
3070 F03
Figure 3. Switching Frequency in Burst Mode Operation
Low Ripple Burst Mode Operation
To enhance efficiency at light loads, the LT3970 operates
in low ripple Burst Mode operation which keeps the output
capacitor charged to the proper voltage while minimizing
the input quiescent current. During Burst Mode operation, 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 capacitor. 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.
As the load current decreases towards a no load condition,
the percentage of time that the LT3970 operates in sleep
mode increases and the average input current is greatly
reduced resulting in high efficiency even at very low loads.
Note that during Burst Mode operation, the switching
frequency will be lower than the programmed switching
frequency. See Figure 3.
VSW
5V/DIV
IL
100mA/DIV
VOUT
5mV/DIV
2μs/DIV
FRONT PAGE APPLICATION
VIN = 12V
VOUT = 5V
ILOAD = 10mA
700
SWITCHING FREQUENCY (kHz)
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.
3970 F02
Figure 2. Burst Mode Operation
At higher output loads (above ~45mA for the front page
application) the LT3970 will be running at the frequency
programmed by the RT resistor, and will be operating in
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
Capacitor C3 and the internal boost Schottky diode (see the
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 arrange 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.
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
output voltages greater than 3.4V, the minimum input voltage is also limited by the boost circuit for proper start-up.
If the input voltage is ramped slowly, the boost capacitor
3970fa
13
LT3970/LT3970-3.3/LT3970-5
APPLICATIONS INFORMATION
VOUT
5.0
FRONT PAGE APPLICATION
VOUT = 3.3V
BD
VIN
BOOST
4.5
C3
LT3970
INPUT VOLTAGE (V)
VIN
SW
GND
(4a) For VOUT ≥ 2.2V
VIN
TO START/RUN
3.5
3.0
2.5
BD
VIN
4.0
0
50
BOOST
C3
LT3970
SW
6.5
VOUT
100 150 200 250
LOAD CURRENT (mA)
300
350
300
350
FRONT PAGE APPLICATION
VOUT = 5V
GND
3970 F04
(4b) For VOUT < 2.2V; VIN < 27V
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
start. The plots show the worst-case situation where VIN
is ramping very slowly. For lower start-up voltage, the
boost diode can be tied to VIN; however, this restricts the
input range to one-half of the absolute maximum rating
of the BOOST pin.
Enable Pin
The LT3970 is in shutdown when the EN pin is low and
active when the pin is high. The rising threshold of the EN
comparator is 1V, with a 30mV hysteresis. This threshold is
accurate when VIN is above 4.2V. If VIN is lower than 4.2V,
tie EN pin to GND to place the part in shutdown.
INPUT VOLTAGE (V)
6.0
TO START
5.5
TO RUN
5.0
4.5
4.0
0
50
100 150 200 250
LOAD CURRENT (mA)
3970 F05
Figure 5. The Minimum Input Voltage Depends on
Output Voltage, Load Current and Boost Circuit
Adding a resistor divider from VIN to EN programs the
LT3970 to regulate the output only when VIN is above a
desired voltage (see Figure 6). This threshold voltage,
VIN(EN), can be adjusted by setting the values R3 and R4
such that they satisfy the following equation:
VIN(EN) =
R3 + R4
• 1V
R4
where output regulation should not start until VIN is above
VIN(EN). Note that due to the comparator’s hysteresis,
regulation will not stop until the input falls slightly below
VIN(EN).
3970fa
14
LT3970/LT3970-3.3/LT3970-5
APPLICATIONS INFORMATION
160
LT3970
VIN
R3
1V
EN
+
–
INPUT CURRENT (μA)
VIN
SHDN
R4
VIN(EN) = 6V
R3 = 5M
R4 = 1M
120
80
40
0
3970 F06
4
OUTPUT VOLTAGE (V)
Figure 6. Enable
Be aware that while VIN is below 4.2V, the input current
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
different programmed VIN(EN).
2
1
0
0
1
2
3
4
5
6
7
8
INPUT VOLTAGE (V)
INPUT CURRENT (μA)
160
Shorted and Reversed Input Protection
VIN(EN) = 12V
R3 = 11M
R4 = 1M
120
80
40
0
4
OUTPUT VOLTAGE (V)
If the inductor is chosen so that it won’t saturate excessively,
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
the VIN pin is allowed to float and the EN pin is held high
(either by a logic signal or because it is tied to VIN), then
the LT3970’s internal circuitry will pull its quiescent current
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
pin current will drop to 0.7μA. However, if the VIN pin is
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 VIN pin. Figure 8
shows a circuit that will run only when the input voltage
is present and that protects against a shorted or reversed
input.
3
3
2
1
0
0
2
4
6
8
10
12
14
INPUT VOLTAGE (V)
3970 F07
Figure 7. VIN Start-Up of Front Page Application with VOUT = 3.3V,
No-Load Current, and VIN(EN) programmed as in Figure 6.
D4
MBRS140
VIN
BD
VIN
BOOST
LT3970
EN
SW
GND
FB
VOUT
+
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
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
currents flow in the LT3970’s VIN and SW pins, the internal
catch diode and the input capacitor. The loop formed by
these components should be as small as possible. These
components, along with the inductor and output capacitor,
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.
GND
GND
1
10
EN
2
9
VIN
3
8
4
7
5
6
PG
VOUT
GND
VIAS TO LOCAL GROUND PLANE
VIAS TO VOUT
3970 F09
Figure 9. A Good PCB Layout Ensures Proper, Low EMI Operation
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 capacitors can cause problems if the LT3970 is plugged into
a live supply. The low loss ceramic capacitor, combined
with stray inductance in series with the power source,
forms an under damped tank circuit, and the voltage at
the VIN pin of the LT3970 can ring to twice the nominal
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
this overshoot. See Linear Technology Application Note 88
for a complete discussion.
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.
Power dissipation within the LT3970 can be estimated by
calculating the total power loss from an efficiency measurement and subtracting inductor loss. The die temperature
is calculated by multiplying the LT3970 power dissipation
by the thermal resistance from junction to ambient.
Finally, be aware that at high ambient temperatures the
internal Schottky diode will have significant leakage current
(see Typical Performance Characteristics) increasing the
quiescent current of the LT3970 converter.
Other Linear Technology Publications
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.
3970fa
16
LT3970/LT3970-3.3/LT3970-5
TYPICAL APPLICATIONS
3.3V Step-Down Converter
VIN
4.2V TO 40V
5V Step-Down Converter
VIN
6V TO 40V
C3
0.22μF
VIN
BOOST
OFF ON
EN
PG
VIN
L1
22μH
LT3970
SW
BD
R1
1M
RT
226k
R2
576k
OFF ON
EN
PG
C1
2.2μF
EN
PG
OFF ON
0.22μF
VIN
22μH
OFF ON
OFF ON
EN
PG
SW
RT
FB
226k
f = 600kHz
C3
0.22μF
VIN
R1
1M
R2
931k
3490 TA04
C2
47μF
BOOST
LT3970
VOUT
2.5V
350mA
BD
GND
22μF
3490 TA03b
VIN
4.2V TO 27V
L1
15μH
47pF
C1
2.2μF
VOUT
1.8V Step-Down Converter
C3
0.47μF
BOOST
VOUT
5V
350mA
BD
f = 600kHz
2.5V Step-Down Converter
LT3970
22μH
SW
GND
226k
3490 TA03a
VIN
4.2V TO 40V
EN
PG
RT
2.2μF
22μF
BOOST
LT3970-5
VOUT
3.3V
350mA
VOUT
f = 600kHz
VIN
3490 TA03
VIN
6V TO 40V
BD
GND
226k
R2
316k
5V Step-Down Converter
SW
RT
2.2μF
C2
22μF
FB
GND
BOOST
LT3970-3.3
R1
1M
f = 600kHz
0.22μF
VIN
BD
RT
3.3V Step-Down Converter
VIN
4.2V TO 40V
VOUT
5V
350mA
SW
226k
3490 TA02
f = 600kHz
L1
22μH
22pF
C2
22μF
FB
GND
BOOST
LT3970
VOUT
3.3V
350mA
22pF
C1
2.2μF
C3
0.22μF
OFF ON
C1
2.2μF
EN
BD
PG
SW
RT
FB
226k
f = 600kHz
L1
10μH
47pF
GND
VOUT
1.8V
350mA
R1
487k
C2
47μF
R2
1M
3490 TA05
3970fa
17
LT3970/LT3970-3.3/LT3970-5
TYPICAL APPLICATIONS
12V Step-Down Converter
VIN
14V TO 40V
5V, 2MHz Step-Down Converter
VIN
8.5V TO 16V
TRANSIENTS
TO 40V
C3
0.1μF
VIN
BOOST
L1
33μH
LT3970
OFF ON
EN
PG
SW
RT
FB
R1
1M
22pF
C1
2.2μF
GND
226k
VIN
VOUT
12V
350mA
BD
BOOST
LT3970
OFF ON
EN
PG
L1
10μH
C1
1μF
BD
RT
49.9k
VOUT
5V
350mA
SW
22pF
C2
22μF
R2
113k
C3
0.1μF
R1
1M
FB
GND
R2
316k
C2
10μF
3490 TA06
f = 600kHz
f = 2MHz
3490 TA07
5V Step-Down Converter with Reduced Input Current During Start-Up
VIN
6V TO 40V
kΩ
+
0.22μF
VIN
5M
–
BOOST
LT3970
22μH
SW
1M
EN
PG
2.2μF
RT
FB
BD
22pF
226k
1M
22μF
GND
316k
3490 TA08a
f = 600kHz
Input Current During Start-Up
VOUT
5V
350mA
Start-Up from High Impedance Input Source
4.5
EN PROGRAMMED TO 6V
4.0
INPUT CURRENT (mA)
3.5
3.0
2.5
2.0
INPUT CURRENT
DROPOUT
CONDITIONS
VIN
5V/DIV
FRONT PAGE
APPLICATION
VOUT
2V/DIV
FRONT PAGE
APPLICATION
WITH EN
PROGRAMMED
TO 6V
1.5
1.0
0.5
5ms/DIV
FRONT PAGE APPLICATION
VOUT = 5V
1k INPUT SOURCE RESISTANCE
2.5mA LOAD
0
3970 TA08c
–0.5
0
2
6
8
4
INPUT VOLTAGE (V)
10
12
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)
0.64 ±0.05
(2 SIDES)
3.00 ±0.10
(2 SIDES)
R = 0.05
TYP
R = 0.115
TYP
6
0.40 ± 0.10
10
0.70 ±0.05
2.55 ±0.05
1.15 ±0.05
PACKAGE
OUTLINE
0.25 ± 0.05
0.50 BSC
2.39 ±0.05
(2 SIDES)
PIN 1 BAR
TOP MARK
(SEE NOTE 6)
0.200 REF
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
2.00 ±0.10
(2 SIDES)
0.75 ±0.05
0.64 ± 0.05
(2 SIDES)
5
0.25 ± 0.05
0 – 0.05
PIN 1
R = 0.20 OR
0.25 s 45°
CHAMFER
1
(DDB10) DFN 0905 REV Ø
0.50 BSC
2.39 ±0.05
(2 SIDES)
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
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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)
0.50
0.305 p 0.038
(.0197)
(.0120 p .0015)
BSC
TYP
RECOMMENDED SOLDER PAD LAYOUT
0.254
(.010)
10 9 8 7 6
3.00 p 0.102
(.118 p .004)
(NOTE 4)
4.90 p 0.152
(.193 p .006)
DETAIL “A”
0.497 p 0.076
(.0196 p .003)
REF
0o – 6o TYP
GAUGE PLANE
1 2 3 4 5
0.53 p 0.152
(.021 p .006)
DETAIL “A”
0.86
(.034)
REF
1.10
(.043)
MAX
0.18
(.007)
SEATING
PLANE
0.17 – 0.27
(.007 – .011)
TYP
0.50
(.0197)
BSC
0.1016 p 0.0508
(.004 p .002)
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
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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 representation 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
LT3971
38V, 1.2A (IOUT), IQ = 2.8μA High Efficiency Step-Down DC/DC
Converter
VIN: 4.3V to 38V, VOUT(MIN) = 1.2V, IQ = 2.8μA, ISD < 1μA,
MSOP-10E, 3mm × 3mm DFN-10
LT3991
55V, 1.2A (IOUT), IQ = 2.8μA High Efficiency Step-Down DC/DC
Converter
VIN: 4.3V to 55V, VOUT(MIN) = 1.2V, IQ = 2.8μA, ISD < 1μA,
MSOP-10E, 3mm × 3mm DFN-10
LT3689
36V, 60V Transient Protection, 800mA, 2.2MHz High Efficiency
Micropower Step-Down DC/DC Converter with POR Reset and
Watchdog Timer
VIN: 3.6V to 36V, Transient to 60V, VOUT(MIN) = 0.8V, IQ = 75μA,
ISD < 1μA, 3mm × 3mm QFN-16
LT3682
36V, 60VMAX, 1A, 2.2MHz High Efficiency Micropower Step-Down
DC/DC Converter
VIN: 3.6V to 36V, VOUT(MIN) = 0.8V, IQ = 75μA, ISD < 1μA,
3mm × 3mm DFN-12
LT3480
36V with Transient Protection to 60V, 2A (IOUT), 2.4MHz, High
Efficiency Step-Down DC/DC Converter with Burst Mode® Operation
VIN: 3.6V to 38V, VOUT(MIN) = 0.78V, IQ = 70μA, ISD < 1μA,
3mm × 3mm DFN-10, MSOP-10E
LT3685
36V with Transient Protection to 60V, 2A (IOUT), 2.4MHz, High
Efficiency Step-Down DC/DC Converter
VIN: 3.6V to 38V, VOUT(MIN) = 0.78V, IQ = 70μA, ISD < 1μA,
3mm × 3mm DFN-10, MSOP-10E
LT3481
34V with Transient Protection to 36V, 2A (IOUT), 2.8MHz, High
Efficiency Step-Down DC/DC Converter with Burst Mode Operation
VIN: 3.6V to 34V, VOUT(MIN) = 1.26V, IQ = 50μA, ISD < 1μA,
3mm × 3mm DFN-10, MSOP-10E
LT1976/LT1977
60V, 1.2A (IOUT), 200/500kHz, High Efficiency Step-Down DC/DC
Converter with Burst Mode Operation
VIN: 3.3V to 60V, VOUT(MIN) = 1.20V, IQ = 100μA, ISD < 1μA,
TSSOP-16E
3970fa
22 Linear Technology Corporation
LT 0510 REV A • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
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