LINER LTC3525LESC6-3 400ma micropower synchronous step-up dc/dc converter with output disconnect Datasheet

LTC3525L-3
400mA Micropower
Synchronous Step-Up DC/DC
Converter with Output Disconnect
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DESCRIPTIO
FEATURES
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The LTC®3525L-3 is a high efficiency synchronous stepup DC/DC converter with output disconnect that can
start up with an input as low as 0.7V. It offers a compact,
high efficiency alternative to charge pumps in single
cell or dual cell alkaline applications. Only three small
external components are required. The LTC3525L-3
generates a fixed 3V output voltage.
Startup at 0.7V Typical, 0.88V Guaranteed
Up to 95% Efficiency
Output Disconnect and Inrush Current Limit
3V Fixed Output Voltage
Delivers 65mA at 3V from a 1V Input or 160mA
from a 1.8V input
Burst Mode® Operation: IQ = 7µA
VIN: 0.5V to 4.5V
Only Three External Components
VIN > VOUT Operation
<1µA Shutdown Current
Antiringing Control
Short-Circuit and Overtemperature Protection
Tiny 6-Pin SC70 Package
The device includes a 0.5 N-channel MOSFET switch
and a 0.85 P-channel synchronous rectifier. Peak switch
current ranges from 150mA to 400mA, depending on
load, providing enhanced efficiency. Quiescent current
is an ultralow 7µA, maximizing battery life in portable
applications.
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APPLICATIO S
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Other features include <1µA shutdown current, antiringing control and thermal shutdown. The LTC3525L-3
is available in a tiny 6-pin SC70 package.
MP3 Players
Portable Instruments
Glucose Meters
Digital Cameras
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Patents Pending.
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TYPICAL APPLICATIO
LTC3525L-3 Efficiency and Power
Loss vs Load Current
L1*
10µH
100
100
90
VOUT
3V
65mA
0.9V to 1.6V
OFF ON
SHDN
GND
VOUT
GND
1µF
10µF
EFFICIENCY (%)
SW
EFFICIENCY
70
1
60
POWER LOSS
50
0.1
40
3525 TA01
30
20
0.01
*MURATA LQH32CN100K53
POWER LOSS (mW)
VIN
10
80
LTC3525L-3
VIN
VIN = 2.4V
VIN = 1.2V
0.1
1
10
LOAD (mA)
100
0.01
1000
LT3525 • TA02
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LTC3525L-3
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ABSOLUTE
AXI U RATI GS
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PACKAGE/ORDER I FOR ATIO
(Note 1)
VIN, VOUT Voltage ......................................... –0.3V to 6V
SW Voltage .................................................. –0.3V to 6V
SW Voltage < 100ns .................................... –0.3V to 7V
SHDN Voltage .............................................. –0.3V to 6V
Operating Temperature Range
(Notes 2, 5).......................................... –40°C to 85°C
Storage Temperature Range................... –65°C to 125°C
Lead Temperature (Soldering, 10 sec) .................. 300°C
TOP VIEW
SHDN 1
6 SW
GND 2
5 GND
VIN 3
4 VOUT
SC6 PACKAGE
6-LEAD PLASTIC SC70
TJMAX = 125°C
JA = 256°C/W IN FREE AIR, JA = 150°C/W ON BOARD
OVER GROUND PLANE
ORDER PART NUMBER
SC6 PART MARKING
LTC3525LESC6-3
LCPY
Order Options Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking: http://www.linear.com/leadfree/
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
(LTC3525L-3)
The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.
VIN = 1.2V, VSHDN = 1.2V, VOUT = 3V unless otherwise noted.
PARAMETER
CONDITIONS
MIN
TYP
0.7
0.88
V
2.91
3.00
3.09
V
Minimum Input Start-Up Voltage
●
MAX
UNITS
Output Voltage
(Note 6)
Quiescent Current, VOUT
SHDN = VIN (Note 4)
7
15
µA
Quiescent Current, VIN
SHDN = VIN (Note 4)
0.5
3
µA
Quiescent Current, VIN - Shutdown
SHDN = 0V, VOUT = 0V
Not Including Switch Leakage
0.1
1
µA
NMOS Switch Leakage
VIN = VOUT = VSW = 5V, SHDN = 0V
0.1
3
µA
PMOS Switch Leakage
VIN = VSW = 5V, VOUT = 0V, SHDN = 0V
0.1
6
µA
NMOS Switch On Resistance
(Note 3)
0.5
PMOS Switch On Resistance
(Note 3)
0.85
Peak Current Limit
0.4
0.45
SHDN Threshold
0.3
0.5
0.88
V
0.01
1
µA
SHDN Input Current
VSHDN = VIN or VOUT
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 LTC3525LE-3 is guaranteed to meet performance
specifications from 0°C to 85°C. Specifications over the –40°C to 85°C
operating temperature range are assured by design, characterization and
correlation with statistical process controls.
Note 3: Specification is guaranteed by design and not 100% tested in
production.
A
Note 4: Current Measurements are performed when the LTC3525L-3 is not
switching.
Note 5: This IC includes overtemperature protection that is intended
to protect the device during momentary overload conditions. Junction
temperature will exceed 125°C when overtemperature protection is active.
Continuous operation above the specified maximum operating junction
temperature may impair device reliability.
Note 6: Consult LTC Marketing for other output voltage options.
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LTC3525L-3
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TYPICAL PERFOR A CE CHARACTERISTICS TA = 25°C unless otherwise noted.
Maximum Startup Load vs VIN
(Resistive Load)
No-Load Input Current vs VIN
30
30
250
25
25
200
20
LOAD (mA)
300
20
LTC3525L-3
IIN (µA)
150
15
15
100
10
10
50
5
5
0
0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00
VIN (V)
0
1.0
1.5
VIN (V)
2.0
2.5
1.0
1.5
2.0
VIN (V)
3525 G02
3525 G01
Efficiency and Power Loss
vs Load
2.5
3.0
3525 G03
Load Regulation
100
2.5
100
VIN = 1.2V
2.0
90
1.5
10
80
1
60
POWER LOSS
50
POWER LOSS (mW)
EFFICIENCY
70
0.1
40
CHANGE IN VOUT (%)
0
0.5
EFFICIENCY (%)
IOUT (mA)
Maximum Output Current vs VIN
(for VOUT to Drop 2.5%)
1.0
0.5
COUT = 22µF
0
COUT = 10µF
–0.5
–1.0
–1.5
30
20
0.01
VIN = 2.4V
VIN = 1.2V
0.1
1
10
LOAD (mA)
100
0.01
1000
3525 G24
–2.0
–2.5
0
10
20
30 40 50
LOAD (mA)
60
70
80
3525 G06
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LTC3525L-3
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TYPICAL PERFOR A CE CHARACTERISTICS TA = 25°C unless otherwise noted.
VOUT Variation vs Temperature
(Normalized to 25°C)
0.4
35
0.3
30
0.2
25
20
COUT = 10µF
15
Startup Delay Coming Out of
Shutdown
120
100
SWITCHING DELAY (µs)
40
CHANGE IN VOUT (%)
BURST FREQUENCY (kHz)
Light Load Burst Frequency
vs Load
0.1
0
–0.1
–0.2
10
COUT = 22µF
0
0.1
1
LOAD (mA)
10
60
40
20
–0.3
5
80
–0.4
–40–30–20–10 0 10 20 30 40 50 60 70 80
TEMPERATURE (°C)
0
1.0
1.5
2.0
2.5 3.0
VIN (V)
3525 G13
3525 G12
Input Current and VOUT at Startup
3.5
4.0
4.5
3525 G14
Output Voltage Ripple
VIN = 1.2V
IOUT =
5mA
IOUT =
40mA
VOUT
1V/DIV
50mV/DIV
IOUT =
80mA
INPUT
CURRENT
100mA/DIV
500µs/DIV
3525 G15
VIN = 1.2V
COUT = 10µF
50µs/DIV
3525 G16
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LTC3525L-3
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TYPICAL PERFOR A CE CHARACTERISTICS TA = 25°C unless otherwise noted.
Output Voltage Ripple
Output Voltage Ripple
IOUT =
5mA
IOUT =
5mA
IOUT =
40mA
50mV/DIV
IOUT =
100mA
50mV/DIV
IOUT =
190mA
IOUT =
80mA
VIN = 1.2V
COUT = 22µF
50µs/DIV
3525 G17
VIN = 2.4V
COUT = 22µF
50mA Load Step Response
OUTPUT
RIPPLE
50mV/DIV
LOAD
CURRENT
20mA/DIV
LOAD
CURRENT
50mA/DIV
500µs/DIV
3525 G18
100mA Load Step Response
OUTPUT
RIPPLE
50mV/DIV
VIN = 1.2V
COUT = 22µF
50µs/DIV
3525 G21
VIN = 2.4V
COUT = 22µF
500µs/DIV
3525 G22
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LTC3525L-3
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PI FU CTIO S
SHDN (Pin 1): Logic Controlled Shutdown Input. Connect
to a voltage >0.88V to enable the LTC3525L-3. Connect to
a voltage <0.3V to disable the LTC3525L-3.
VOUT (Pin 4): Output Voltage Sense and the Output of the
Synchronous Rectifier. Connect the output filter capacitor
from VOUT to GND, close to the IC. A minimum value of
10µF ceramic is recommended. Use 22µF for reduced
output ripple. The output disconnect feature disconnects
VOUT from VIN when SHDN is <0.3V.
GND (Pins 2, 5): Ground.
VIN (Pin 3): Input Voltage. The LTC3525L-3 is powered
from VIN until VOUT exceeds VIN. Once VOUT is greater
than (VIN + 0.2V typical), it is powered from VOUT. Place
a ceramic bypass capacitor from VIN to GND. A minimum
value of 1µF is recommended.
SW (Pin 6): Switch Pin. Connect an inductor from this
pin to VIN. An internal antiringing resistor is connected
across SW and VIN after the inductor current has dropped
to zero to minimize EMI.
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BLOCK DIAGRA
VIN
VIN
SW
6
3
VOUT
VSEL
VBEST
WELL
SWITCH
VOUT
VB
4
SHDN
1
SHUTDOWN
SHUTDOWN GATE DRIVERS
AND
ANTI-CROSS
CONDUCTION
+
–
OFFSET
ADJUST
VREF
IPK
UVLO
–
VREF
UVLO
VOUT
+
+
IPK
COMPARATOR
STARTUP
–
ADJUST
LOGIC
IVAL
–
+
SHUTDOWN
IVALLEY
COMPARATOR
TSD
–
WAKE
+
THERMAL
SHUTDOWN
OFFSET
INTEGRATOR
FB
VREF
SLEEP
COMPARATOR
ADJUST
5
2
GND
3525 BD
GND
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LTC3525L-3
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OPERATIO
The LTC3525L-3 is a high performance Burst Mode
operation only, synchronous boost converter requiring only
three small external components. Its simplicity and small
size make it a high efficiency alternative to charge pump
designs. It is designed to start up from a single alkaline
or nickel cell, with input voltages as low as 0.7V typical
or 0.88V maximum, or from two or three cells (or a Li-ion
battery), with voltages as high as 4.5V. Once started, VIN
can be as low as 0.5V (depending on load current) and
maintain regulation. The output voltage is preset internally
to 3V. Peak switch current is 400mA minimum, providing
regulation with load currents up to 160mA, depending on
input voltage.
Shutdown
Synchronous rectification provides high efficiency operation while eliminating the need for an external Schottky
diode. True output disconnect eliminates inrush current
at start-up, and allows VOUT to be disconnected from VIN,
for zero shutdown current.
A start-up oscillator allows the LTC3525L-3 to start with input voltages as low as 0.7V. It remains in start-up mode until
two conditions are met. VOUT must exceed VIN by at least
0.2V typical and either VIN or VOUT must be greater than
1.8V typical.
The output disconnect feature also allows the LTC3525L-3
to maintain regulation with an input voltage equal to or
greater than VOUT. Note, however, that the synchronous
rectifier is not enabled in this mode resulting in lower
efficiency and reduced output current capability.
During startup, the synchronous rectifier is not enabled,
and the internal P-channel synchronous rectifier acts as
a follower, causing the peak voltage on SW to reach (VIN
+ 1V) typical. This limits inrush current by maintaining
control of the inductor current when VOUT is less than VIN.
To reduce power dissipation in the P-channel synchronous
rectifier when the output is shorted, a foldback feature is
incorporated that reduces the peak inductor current when
VIN is more than 1.7V greater than VOUT.
The operating quiescent current is only 7µA typical, allowing the converter to maintain high efficiency at extremely
light loads.
The LTC3525L-3 is shut down by pulling SHDN below
0.3V, and made active by raising it above 0.88V. Note that
SHDN can be driven as high as 6V, however, if it is more
than 0.9V above the higher of VIN or VOUT, the SHDN input
current will increase from zero to 1.5µA.
After the SHDN pin rises, there is a short delay before
switching starts. The delay is 20µs to 120µs, depending
on input voltage (see Typical Performance Characteristics
curve).
Start-Up
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LTC3525L-3
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OPERATIO
INDUCTOR
CURRENT
100mA/DIV
LOAD
CURRENT
50mA/DIV
10µs/DIV
3525 F01
Figure 1. Inductor Current Changing as a Function of Load
Normal Operation
Power Adjust Feature
Once VOUT has increased more than 0.2V typical above
VIN, and either voltage is above 1.8V, normal operation
begins, with synchronous rectification enabled. In this
mode, the internal N-channel MOSFET connected between
SW and GND stays on until the inductor current reaches a
maximum peak value, after which it is turned off and the
P-channel synchronous rectifier is turned on. It stays on,
delivering current to the output, until the inductor current
has dropped below a minimum value at which point it
turns off and the cycle repeats. When the output voltage
reaches its regulated value both switches are turned off
and the LTC3525L-3 goes to sleep, during which time the
output capacitor supplies current to the load. Once the
output voltage drops below the regulation value the IC
leaves sleep mode and switching is resumed.
The LTC3525L-3 incorporates a feature that maximizes
efficiency at light load while providing increased power
capability at heavy load by adjusting the peak and valley
of the inductor current as a function of load. Lowering the
peak inductor current to 150mA at light load optimizes
efficiency by reducing conduction losses in the internal
MOSFET switches. As the load increases, the peak inductor
current is automatically increased to a maximum of 400mA.
At intermediate loads, the peak inductor current may vary
from 150mA to 400mA. Figure 1 shows an example of
how the inductor current changes as the load increases.
Please note that output capacitor values greater than 47µF
will result in higher peak currents than necessary at light
load. This will lower the light load efficiency.
The LTC3525L-3 has been designed for low output voltage
ripple. The output voltage ripple is typically only 20mV
peak-to-peak at light load and 60mV peak-to-peak at
full load using the minimum recommended 10µF output
capacitor. An anti-ring circuit damps any oscillation at the
switch node when the inductor current falls to zero.
The valley of the inductor current is automatically adjusted
as well, to maintain a relatively constant inductor ripple
current. This keeps the switching frequency relatively
constant.
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LTC3525L-3
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OPERATIO
The maximum average load current that can be supported
is given by:
IO(MAX) =
0.3 • VIN • η
Amps
VO
Where is the efficiency (see Typical Performance Characteristics).
The “burst” frequency (how often the LTC3525L-3 delivers a burst of current pulses to the load) is determined
by the internal hysteresis (output voltage ripple), the load
current and the amount of output capacitance. All Burst
Mode operation or hysteretic converters will enter the
audible frequency range when the load is light enough.
However, due to the low peak inductor current at light load,
circuits using the LTC3525L-3 do not typically generate
any audible noise.
Component Selection
Inductor values between 4.7µH and 15µH are recommended. In most applications 10µH will yield the best
compromise between size and efficiency. The inductor
should be a low-loss ferrite design and must be rated for
peak currents of at least 400mA without saturating. Induc-
tors with lower DC resistance will improve efficiency. Note
that the inductor value does not have a significant effect
on ripple current, so while lower values will increase the
operating frequency, they do not reduce output voltage
ripple.
Some recommended inductor examples are Murata
LQH32C, Coilcraft LPO4812, LPO3310, DO3314, DS1608
and MSS4020, Sumida CDRH2D14 and Taiyo Yuden
NR3015T.
A ceramic input bypass capacitor should be located as
close as possible to the VIN and GND pins of the IC. A
minimum value of 1µF is recommended. If the battery is
more than a few inches away, a bulk tantalum decoupling
cap of at least 10µF is recommended on VIN.
The output capacitor should also be a ceramic, located close
to the VOUT and GND pins. A minimum value of 10µF is
recommended. Increasing the value of the output capacitor
to 22µF will result in lower output ripple. Higher capacitor
values will only offer a small reduction in output ripple,
while reducing light load efficiency by causing the peak
inductor current to increase above its minimum value of
150mA. The input and output capacitors should be X5R
or X7R types, not Y5V.
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LTC3525L-3
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PACKAGE DESCRIPTIO
Table 1. Inductor Vendor Information
SUPPLIER
PHONE
FAX
WEBSITE
Murata
USA: (814) 237-1431
USA: (814) 238-0490
www.murata.com
Coilcraft
(847) 639-6400
(847) 639-1469
www.coilcraft.com
Sumida
USA: (847) 956-0666
USA: (847) 956-0702
www.sumida.com
Taiyo Yuden
(408) 573-4150
(408) 573-4159
www.t-yuden.com
Table 2. Capacitor Vendor Information
SUPPLIER
PHONE
FAX
WEBSITE
Murata
USA: (814) 237-1431
USA: (814) 238-0490
www.murata.com
Taiyo Yuden
(408) 573-4150
(408) 573-4159
www.t-yuden.com
TDK
(847) 803-6100
(847) 803-6296
www.component.tdk.com
AVX
(803) 448-9411
(803) 448-1943
www.avxcorp.com
SHDN
SHDN
SW
LTC3525L-3
VIN
GND
GND
VIN
VOUT
VOUT
3525 F02
Figure 2. Recommended Component Placement
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LTC3525L-3
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PACKAGE DESCRIPTIO
SC6 Package
6-Lead Plastic SC70
(Reference LTC DWG # 05-08-1638 Rev B)
0.47
MAX
0.65
REF
1.80 – 2.20
(NOTE 4)
1.00 REF
INDEX AREA
(NOTE 6)
1.80 – 2.40 1.15 – 1.35
(NOTE 4)
2.8 BSC 1.8 REF
PIN 1
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR
0.10 – 0.40
0.65 BSC
0.15 – 0.30
6 PLCS (NOTE 3)
0.80 – 1.00
0.00 – 0.10
REF
1.00 MAX
GAUGE PLANE
0.15 BSC
0.26 – 0.46
0.10 – 0.18
(NOTE 3)
SC6 SC70 1205 REV B
NOTE:
1. DIMENSIONS ARE IN MILLIMETERS
2. DRAWING NOT TO SCALE
3. DIMENSIONS ARE INCLUSIVE OF PLATING
4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
5. MOLD FLASH SHALL NOT EXCEED 0.254mm
6. DETAILS OF THE PIN 1 IDENTIFIER ARE OPTIONAL,
BUT MUST BE LOCATED WITHIN THE INDEX AREA
7. EIAJ PACKAGE REFERENCE IS EIAJ SC-70
8. JEDEC PACKAGE REFERENCE IS MO-203 VARIATION AB
3525lf
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.
11
LTC3525L-3
TYPICAL APPLICATIONS
Single Cell to 3V Converter Using 1mm High Monolithic Inductor
2-Alkaline or NiMH to 3V
10µH*
6.8µH*
0.9V to 1.6V
3
1
2
LTC3525L-3
VIN
SW
SHDN
VOUT
GND
GND
1.8V to 3.2V
6
3
VOUT
3V
65mA
4
5
10µF
4V
1µF
1
2
LTC3525L-3
VIN
SW
SHDN
VOUT
GND
GND
6
VOUT
3V
160mA
4
5
1µF
10µF
3525 TA05
3525 TA03
*MURATA LQH32CN1002K53
*FDK MIP3226D6R8M
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with Output Disconnect
95% Efficiency, VIN: 0.85V to 4.5V, VOUT(MAX) = 5V,
IQ = 7µA, ISD <1µA, SC70 Package
LTC3526/LTC3526B
500mA (ISW), 1MHz, High Efficiency Step-Up DC/DC Converter
94% Efficiency, VIN: 0.5V to 5V, VOUT(MAX) = 5.25V,
IQ = 9µA/300µA, ISD <1µA, 2mm × 2mm DFN Package
ThinSOT is a trademark of Linear Technology Corporation.
3525lf
12 LinearTechnology Corporation
LT/LWI 1206 • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
LINEAR TECHNOLOGY CORPORATION 2006
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