step-down DC/DC converter. Intended for medium power
applications, it operates from a 2.5V to 5.5V input voltage
range and has a user configurable operating frequency up
to 4MHz, allowing the use of tiny, low cost capacitors and
inductors 1mm or less in height. The output voltage is
adjustable from 0.8V to 5.5V. Internal synchronous power
switches provide high efficiency. The LTC3561A’s current
mode architecture and external compensation allow the
transient response to be optimized over a wide range of
loads and output capacitors.
To further maximize battery life, the P-channel MOSFET
is turned on continuously in dropout (100% duty cycle).
In shutdown, the device draws <1μA.
, LT, LTC and LTM are registered trademarks of Linear Technology
Corporation. All other trademarks are the property of their respective owners.
Protected by U.S. Patents, including 5481178, 6580258, 6498466, 6611131.
■
■
■
■
■
■
■
Uses Tiny Capacitors and Inductor
High Frequency Operation: Up to 4MHz
Low R
DS(ON)
Internal Switches: 0.15Ω
High Efficiency: Up to 96%
Stable with Ceramic Capacitors
Current Mode Operation for Excellent Line
and Load Transient Response
Short-Circuit Protected
Low Dropout Operation: 100% Duty Cycle
Low Shutdown Current: I
Q
≤ 1μA
Low Quiescent Current: 330μA
Output Voltages from 0.8V to 5V
V
IN
: 2.5V to 5.5V
Small 8-Lead 3mm
×
3mm DFN Package
APPLICATIONS
■
■
■
■
■
Notebook Computers
Digital Cameras
Cellular Phones
Handheld Instruments
Board Mounted Power Supplies
TYPICAL APPLICATION
Step-Down 2.5V/1A Regulator
V
IN
2.5V TO 5.5V
10μF
PV
IN
SV
IN
SW
LTC3561A
I
TH
16.9k
680pF
549k
SHDN/R
T
SGND
PGND
118k
V
FB
22pF
2.2μH
V
OUT
2.5V
1A
22μF
EFFICIENCY (%)
Efficiency and Power Loss vs Output Current
100
90
80
70
60
50
40
30
20
10
0
1
V
OUT
= 2.5V
f
O
= 1MHz
V
IN
= 2.7V
V
IN
= 3.6V
V
IN
= 4.2V
100
1000
10
OUTPUT CURRENT (mA)
0.01
0.1
POWER LOSS (W)
1
249k
0.001
0.0001
10000
3561a TA01a
3561A TA01b
3561af
1
LTC3561A
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW
SHDN/R
T
1
SGND 2
SW 3
PGND 4
9
8 I
TH
7 V
FB
6 SV
IN
5 PV
IN
PV
IN
, SV
IN
Voltages ..................................... –0.3V to 6V
V
FB
, I
TH
, SHDN/R
T
Voltages ..........–0.3V to (V
IN
+ 0.3V)
SW Voltage ..................................–0.3V to (V
IN
+ 0.3V)
Operating Junction Temperature Range
(Notes 2, 5, 8) ........................................ –40°C to 125°C
Storage Temperature Range................... –65°C to 125°C
Lead Temperature (Soldering, 10 sec) .................. 300°C
DD PACKAGE
8-LEAD (3mm 3mm) PLASTIC DFN
T
JMAX
= 125°C,
θ
JA
= 43°C/W,
θ
JC
= 3°C/W
EXPOSED PAD (PIN 9) IS SGND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC3561AEDD#PBF
LTC3561AIDD#PBF
TAPE AND REEL
LTC3561AEDD#TRPBF
LTC3561AIDD#TRPBF
PART MARKING*
LDKB
LDKB
PACKAGE DESCRIPTION
8-Lead (3mm
×
3mm) Plastic DFN
8-Lead (3mm
×
3mm) Plastic DFN
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
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/
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 3.6V, R
T
= 125k unless otherwise specified. (Note 2)
SYMBOL
V
IN
I
FB
V
FB
ΔV
LINEREG
ΔV
LOADREG
g
m(EA)
PARAMETER
Operating Voltage Range
Feedback Pin Input Current
Feedback Voltage
Reference Voltage Line Regulation
Output Voltage Load Regulation
Error Amplifier Transconductance
(Note 3)
(Note 3)
V
IN
= 2.5V to 5.5V
I
TH
= 0.55V to 0.9V
I
TH
Pin Load = ±5μA (Note 3)
●
●
ELECTRICAL CHARACTERISTICS
CONDITIONS
MIN
2.5
0.784
TYP
MAX
5.5
±0.1
UNITS
V
μA
V
%/V
%
μS
0.8
0.04
0.02
300
0.816
0.2
0.2
3561af
2
LTC3561A
ELECTRICAL CHARACTERISTICS
SYMBOL
I
S
V
SHDN/RT
f
OSC
I
LIM
R
DS(ON)
I
SW(LKG)
V
UVLO
t
SOFT-START
PARAMETER
Input DC Supply Current (Note 4)
Active Mode
Shutdown
Shutdown Threshold High Active
Oscillator Resistor
Oscillator Frequency
Peak Switch Current Limit
Top Switch On-Resistance
Bottom Switch On-Resistance
Switch Leakage Current
Undervoltage Lockout Threshold
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 3.6V, R
T
= 125k unless otherwise specified. (Note 2)
CONDITIONS
V
FB
= 0.75V
V
SHDN/RT
= 3.6V
MIN
TYP
330
0.1
V
IN
– 0.6
125k
2.5
2.0
0.15
0.13
0.01
1.8
0.5
2.1
0.8
MAX
450
1
V
IN
– 0.4
1M
2.8
4
2.5
0.18
0.16
1
2.4
1
UNITS
μA
μA
V
Ω
MHz
MHz
A
Ω
Ω
μA
V
ms
R
T
= 125k
(Note 7)
V
FB
= 0.5V
(Note 6)
(Note 6)
V
IN
= 5V, V
SHDN/RT
= 3.6V, V
SW
= 0V or 5V
V
IN
Ramping Down
10% to 90% of Regulation
2.25
1.3
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 LTC3561AEDD is guaranteed to meet specified performance
specifications from 0°C to 85°C junction temperature. Specifications over
the –40°C to 125°C operating junction temperature range are assured by
design, characterization and correlation with statistical process controls.
The LTC3561AIDD is guaranteed over the full –40°C to 125°C operating
junction temperature range.
Note 3:
The LTC3561A is tested in a feedback loop which servos V
FB
to the
midpoint for the error amplifier (V
ITH
= 0.7V).
Note 4:
Dynamic supply current is higher due to the internal gate charge
being delivered at the switching frequency.
Note 5:
T
J
is calculated from the ambient T
A
and power dissipation P
D
according to the following formulas:
T
J
= T
A
+ (P
D
• 43°C/W)
Note 6:
Switch on-resistance is sampled at wafer level measurements and
assured by design, characterization and correlation with statistical process
controls.
Note 7:
4MHz operation is guaranteed by design but not production tested
and is subject to duty cycle limitations (see Applications Information).
Note 8:
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
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