LT3470
Micropower Buck Regulator
with Integrated Boost and
Catch Diodes
FEATURES
■
■
■
■
■
■
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DESCRIPTIO
■
■
Low Quiescent Current: 26
µ
A at 12V
IN
to 3.3V
OUT
Integrated Boost and Catch Diodes
Input Range: 4V to 40V
Low Output Ripple: <10mV
< 1µA in Shutdown Mode
Output Voltage: 1.25V to 16V
200mA Output Current
Hysteretic Mode Control
– Low Ripple Burst Mode
®
Operation at Light Loads
– Continuous Operation at Higher Loads
Solution Size as Small as 50mm
2
Low Profile (1mm) ThinSOT Package
The LT
®
3470 is a micropower step-down DC/DC converter
that integrates a 300mA power switch, catch diode and
boost diode into a low profile (1mm) ThinSOT
TM
package.
The LT3470 combines Burst Mode and continuous opera-
tion to allow the use of tiny inductor and capacitors while
providing a low ripple output to loads of up to 200mA.
With its wide input range of 4V to 40V, the LT3470 can
regulate a wide variety of power sources, from 2-cell
Li-Ion batteries to unregulated wall transformers and lead-
acid batteries. Quiescent current in regulation is just 26µA
in a typical application while a zero current shutdown
mode disconnects the load from the input source, simpli-
fying power management in battery-powered systems.
Fast current limiting and hysteretic control protects the
LT3470 and external components against shorted out-
puts, even at 40V input.
, LTC and LT are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Burst Mode is a registered trademark of Linear Technology Corporation.
ThinSOT is a trademark of Linear Technology Corporation.
APPLICATIO S
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Automotive Battery Regulation
Power for Portable Products
Distributed Supply Regulation
Industrial Supplies
Wall Transformer Regulation
TYPICAL APPLICATIO
V
IN
7V TO 40V
V
IN
OFF ON
SHDN
BOOST
Efficiency and Power Loss vs Load Current
90
V
IN
= 12V
1000
0.22µF
LT3470
SW
BIAS
22pF
2.2µF
FB
GND
200k
1%
604k
1%
22µF
33µH
V
OUT
5V
200mA
80
70
100
EFFICIENCY (%)
60
50
40
30
20
10
0.1
0.1
1
10
LOAD CURRENT (mA)
100
3470 TA02
U
POWER LOSS (mW)
10
1
3470f
U
U
1
LT3470
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
SHDN 1
NC 2
V
IN
3
GND 4
8 FB
7 BIAS
6 BOOST
5 SW
V
IN
, SHDN Voltage .................................................. 40V
BOOST Pin Voltage ................................................. 47V
BOOST Pin Above SW Pin ...................................... 25V
FB Voltage ................................................................ 5V
BIAS Voltage ............................................................ 25V
SW Voltage ................................................................V
IN
Maximum Junction Temperature ......................... 125°C
Operating Temperature Range (Note 2) .. – 40°C to 85°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER PART
NUMBER
LT3470ETS8
LT3470ITS8
TS8 PART MARKING
LTBDM
LTBPW
TS8 PACKAGE
8-LEAD PLASTIC TSOT-23
T
JMAX
= 125°C,
θ
JA
= 140°C/ W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The
●
denotes specifications which apply over the full operating temperature range, otherwise specifications are T
A
= 25°C.
V
IN
= 10V, V
SHDN
= 10V, V
BOOST
= 15V, V
BIAS
= 3V unless otherwise specified.
PARAMETER
Minimum Input Voltage
Quiescent Current from V
IN
V
SHDN
= 0.2V
V
BIAS
= 3V, Not Switching
V
BIAS
= 0V, Not Switching
V
SHDN
= 0.2V
V
BIAS
= 3V, Not Switching
V
BIAS
= 0V, Not Switching
V
FB
Falling
V
FB
= 1V
●
CONDITIONS
●
●
MIN
TYP
0.1
10
35
0.1
25
0.1
MAX
4
0.5
18
50
0.5
60
1.5
1.265
80
150
0.01
1.5
300
435
UNITS
V
µA
µA
µA
µA
µA
µA
V
nA
nA
%/V
ns
µA
mV
mA
mA
Quiescent Current from Bias
●
●
FB Comparator Trip Voltage
FB Pin Bias Current (Note 3)
FB Voltage Line Regulation
Minimum Switch Off-Time (Note 5)
Switch Leakage Current
Switch V
CESAT
Switch Top Current Limit
Switch Bottom Current Limit
1.228
1.250
35
35
0.0006
500
0.7
4V < V
IN
< 40V
I
SW
= 100mA
V
FB
= 0V
V
FB
= 0V
250
215
325
225
2
U
3470f
W
U
U
W W
W
LT3470
ELECTRICAL CHARACTERISTICS
The
●
denotes specifications which apply over the full operating temperature range, otherwise specifications are T
A
= 25°C.
V
IN
= 10V, V
SHDN
= 10V, V
BOOST
= 15V, V
BIAS
= 3V unless otherwise specified.
PARAMETER
Catch Schottky Drop
Catch Schottky Reverse Leakage
Boost Schottky Drop
Boost Schottky Reverse Leakage
Minimum Boost Voltage (Note 4)
BOOST Pin Current
SHDN Pin Current
SHDN Input Voltage High
SHDN Input Voltage Low
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The LT3470E is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls. The LT3470I specifications are
guaranteed over the –40°C to 125°C temperature range.
I
SW
= 100mA
V
SHDN
= 2.5V
2.5
0.2
CONDITIONS
I
SH
= 100mA
V
SW
= 10V
I
SH
= 30mA
V
SW
= 10V, V
BIAS
= 0V
●
MIN
TYP
630
0.2
650
0.2
1.7
7
1
MAX
775
2
775
2
2.2
12
5
UNITS
mV
µA
mV
µA
V
mA
µA
V
V
Note 3:
Bias current flows out of the FB pin.
Note 4:
This is the minimum voltage across the boost capacitor needed to
guarantee full saturation of the switch.
Note 5:
This parameter is assured by design and correlation with statistical
process controls.
TYPICAL PERFOR A CE CHARACTERISTICS
Efficiency, V
OUT
= 3.3V
90
80
L = TOKO D52LC 47µH
T
A
= 25°C
V
IN
= 12V
V
IN
= 7V
90
80
EFFICIENCY (%)
70
V
IN
= 24V
60
50
L = TOKO D52LC 47µH
T
A
= 25°C
V
IN
= 12V
EFFICIENCY (%)
70
V
IN
= 24V
60
50
40
30
0.1
V
IN
= 36V
V
FB
(V)
10
1
LOAD CURRENT (mA)
U W
100
3470 G01
Efficiency, V
OUT
= 5V
1.260
V
FB
vs Temperature
1.255
V
IN
= 36V
1.250
1.245
40
30
0.1
10
1
LOAD CURRENT (mA)
100
3470 G02
1.240
–50
–25
75
0
25
50
TEMPERATURE (°C)
100
125
3470 G03
3470f
3
LT3470
TYPICAL PERFOR A CE CHARACTERISTICS
Top and Bottom Switch Current
Limits (V
FB
= 0V) vs Temperature
400
350
40
50
CURRENT LIMIT (mA)
300
V
IN
CURRENT (µA)
BIAS CURRENT (µA)
250
200
150
100
50
0
– 50 – 25
0
50
75
25
TEMPERATURE (°C)
100
125
SHDN Bias Current
vs Temperature
9
8
V
SHDN
= 36V
7
40
50
SHDN CURRENT (µA)
FB CURRENT (nA)
6
5
4
3
2
1
0
–50
–25
V
SHDN
= 2.5V
FB CURRENT (µA)
0
25
50
75
TEMPERATURE (°C)
Switch V
CESAT
(I
SW
= 100mA)
vs Temperature
300
250
SWITCH V
CESAT
(mV)
SCHOTTKY V
F
(V)
200
150
100
50
0
–50 –25
0.5
0.4
0.3
0.2
0.1
SCHOTTKY V
F
(V)
50
25
75
0
TEMPERATURE (°C)
4
U W
3470 G04
V
IN
Quiescent Current
vs Temperature
30
25
BIAS < 3V
30
BIAS Quiescent Current
(Bias > 3V) vs Temperature
20
15
10
5
0
–50 –25
20
BIAS > 3V
10
0
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
125
50
25
75
0
TEMPERATURE (°C)
100
125
3470 G05
3470 G06
FB Bias Current (V
FB
= 1V)
vs Temperature
120
100
80
60
40
20
FB Bias Current (V
FB
= 0V)
vs Temperature
30
20
10
100
125
0
–50 –25
50
25
0
75
TEMPERATURE (°C)
100
125
0
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
3470 G07
3470 G08
3470 G09
Boost Diode V
F
(I
F
= 50mA)
vs Temperature
0.8
0.7
0.6
0.7
0.6
0.5
0.4
0.3
0.2
0.1
Catch Diode V
F
(I
F
= 100mA)
vs Temperature
100
125
0
– 50 – 25
0
50
75
25
TEMPERATURE (°C)
100
125
0
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
3470 G10
3470 G11
3470 G12
3470f
LT3470
TYPICAL PERFOR A CE CHARACTERISTICS
Diode Leakage (V
R
= 36V)
vs Temperature
25
BOOST
CATCH
SCHOTTKY DIODE LEAKAGE (µA)
BOOST PIN CURRENT (mA)
20
15
SWITCH V
CESAT
(mV)
10
5
0
–50
–25
50
25
0
75
TEMPERATURE (°C)
Catch Diode Forward Voltage
1.0
900
800
0.8
700
SCHOTTKY V
F
(V)
SCHOTTKY V
F
(V)
0.6
0.4
0.2
0
0
200
100
300
CATCH DIODE CURRENT (mA)
Minimum Input Voltage, V
OUT
= 3.3V
6.0
5.5
7
INPUT VOLTAGE (V)
T
A
= 25°C
5.0
4.5
4.0
3.5
3.0
0
50
100
150
LOAD CURRENT (mA)
200
3470 G18
INPUT VOLTAGE (V)
U W
100
3470 G13
Switch V
CESAT
700
600
500
400
300
200
100
0
125
BOOST Pin Current
14
12
10
8
6
4
2
0
0
100
300
SWITCH CURRENT (mA)
200
400
3470 G14
0
100
300
SWITCH CURRENT (mA)
200
400
3470 G15
Boost Diode Forward Voltage
600
500
400
300
200
100
0
400
3470 G16
0
100
50
150
BOOST DIODE CURRENT (mA)
200
3470 G17
Minimum Input Voltage, V
OUT
= 5V
8
T
A
= 25°C
V
IN
TO START
V
IN
TO START
6
V
IN
TO RUN
5
V
IN
TO RUN
4
0
100
150
50
LOAD CURRENT (mA)
200
3470 G19
3470f
5
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