step down DC/DC converter. Intended for low power ap-
plications, it operates from 2.5V to 5.5V input voltage
range and has a constant 2.25MHz switching frequency,
allowing the use of tiny, low cost capacitors and inductors
with a profile ≤1mm. Each output voltage is adjustable
from 0.6V to 5V. Internal synchronous 0.35Ω, 0.7A/1.2A
power switches provide high efficiency without the need
for external Schottky diodes.
A user selectable mode input is provided to allow the user
to trade-off noise ripple for low power efficiency. Burst
Mode operation provides high efficiency at light loads,
while pulse-skipping mode provides low noise ripple at
light loads.
To further maximize battery runtime, the P-channel
MOSFETs are turned on continuously in dropout (100%
duty cycle), and both channels draw a total quiescent cur-
rent of only 40μA. In shutdown, the device draws <1μA.
L,
LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners. Protected by U.S. Patents, including 5481178, 6127815, 6304066, 6498466, 6580258
6611131..
High Efficiency: Up to 95%
Very Low Quiescent Current: Only 40μA
Low Output Ripple Burst Mode
®
Operation
2.25MHz Constant-Frequency Operation
High Switch Current: 0.7A and 1.2A
No Schottky Diodes Required
Low R
DS(ON)
Internal Switches: 0.35Ω
Current Mode Operation for Excellent Line
and Load Transient Response
Short-Circuit Protected
Low Dropout Operation: 100% Duty Cycle
Ultralow Shutdown Current: I
Q
< 1μA
Output Voltages from 5V down to 0.6V
Power-On Reset Output
Externally Synchronizable Oscillator
Small Thermally Enhanced MSOP and 3mm
×
3mm
DFN Packages
APPLICATIONS
■
■
■
■
■
■
PDAs/Palmtop PCs
Digital Cameras
Cellular Phones
Portable Media Players
PC Cards
Wireless and DSL Modems
TYPICAL APPLICATION
V
IN
= 2.8V
TO 5.5V
10μF
RUN2
V
IN
RUN1
POR
2.2μH
SW1
33pF
100k
RESET
LTC3548 Efficiency Curve
100
95
90
EFFICIENCY (%)
V
OUT1
= 1.8V
AT 800mA
1000
MODE/SYNC
V
OUT2
= 2.5V
AT 400mA
4.7μH
SW2
68pF
LTC3548
EFFICIENCY
100
POWER LOSS (mW)
85
80
POWER LOSS
75
70
1
V
IN
= 3.3V, V
OUT
= 1.8V
Burst Mode OPERATION
CHANNEL 1, NO LOAD ON CHANNEL 2
1
10
100
LOAD CURRENT (mA)
10
887k
4.7μF
280k
V
FB2
GND
V
FB1
604k
301k
10μF
3548 TA01
65
60
Figure 1. 2.5V/1.8V at 400mA/800mA Step-Down Regulators
0.1
1000
3548 TA02
3548fc
1
LTC3548
ABSOLUTE MAXIMUM RATINGS
(Note 1)
V
IN
Voltages .................................................– 0.3V to 6V
V
FB1
, V
FB2
Voltages ...........................– 0.3V to V
IN
+0.3V
RUN1, RUN2 Voltages ................................ – 0.3V to V
IN
MODE/SYNC Voltage .......................– 0.3V to V
IN
+ 0.3V
SW1, SW2 Voltage ...........................– 0.3V to V
IN
+ 0.3V
POR
Voltage .................................................– 0.3V to 6V
Operating Temperature Range (Note 2)....–40°C to 85°C
Junction Temperature (Note 5) ............................. 125°C
Storage Temperature Range...................– 65°C to 125°C
Lead Temperature (Soldering, 10 sec)
MSE Only .......................................................... 300°C
PIN CONFIGURATION
TOP VIEW
TOP VIEW
V
FB1
RUN1
V
IN
SW1
GND
1
2
3
4
5
11
10 V
FB2
9 RUN2
8
POR
7 SW2
6 MODE/
SYNC
V
FB1
RUN1
V
IN
SW1
GND
1
2
3
4
5
11
10
9
8
7
6
V
FB2
RUN2
POR
SW2
MODE/
SYNC
MSE PACKAGE
10-LEAD PLASTIC MSOP
T
JMAX
= 125°C,
θ
JA
= 45°C/W,
θ
JC
= 10°C/W
EXPOSED PAD (PIN 11) IS PGND, MUST BE CONNECTED TO GND
(SOLDERED TO A 4-LAYER BOARD)
DD PACKAGE
10-LEAD (3mm 3mm) PLASTIC DFN
T
JMAX
= 125°C,
θ
JA
= 45°C/W,
θ
JC
= 3°C/W
EXPOSED PAD (PIN 11) IS PGND, MUST BE CONNECTED TO GND
(SOLDERED TO A 4-LAYER BOARD)
ORDER INFORMATION
LEAD FREE FINISH
LTC3548EDD#PBF
LTC3548IDD#PBF
LTC3548EMSE#PBF
LTC3548IMSE#PBF
TAPE AND REEL
LTC3548EDD#TRPBF
LTC3548IDD#TRPBF
LTC3548EMSE#TRPBF
LTC3548IMSE#TRPBF
PART MARKING*
LBNJ
LBNJ
LTBNH
LTBNH
PACKAGE DESCRIPTION
10-Lead (3mm
×
3mm) Plastic DFN
10-Lead (3mm
×
3mm) Plastic DFN
10-Lead Plastic MSOP
10-Lead Plastic MSOP
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 85°C
–40°C to 85°C
–40°C to 85°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/
ELECTRICAL CHARACTERISTICS
SYMBOL
V
IN
I
FB
V
FB
ΔV
LINEREG
PARAMETER
Operating Voltage Range
Feedback Pin Input Current
Feedback Voltage (Note 3)
Reference Voltage Line Regulation
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 3.6V, unless otherwise specified. (Note 2)
CONDITIONS
l
l
MIN
2.5
0.588
0.585
TYP
MAX
5.5
30
UNITS
V
nA
V
V
%V
3548fc
0°C ≤ T
A
≤ 85°C
–40°C ≤ T
A
≤ 85°C
V
IN
= 2.5V to 5.5V (Note 3)
l
0.6
0.6
0.3
0.612
0.612
0.5
2
LTC3548
ELECTRICAL CHARACTERISTICS
SYMBOL
ΔV
LOADREG
I
S
PARAMETER
Output Voltage Load Regulation
Input DC Supply Current
Active Mode
Sleep Mode
Shutdown
Oscillator Frequency
Synchronization Frequency
Peak Switch Current Limit Channel 1
Peak Switch Current Limit Channel 2
Top Switch On-Resistance
Bottom Switch On-Resistance
Switch Leakage Current
Power-On Reset Threshold
Power-On Reset On-Resistance
Power-On Reset Delay
V
RUN
I
RUN
MODE
RUN Threshold
RUN Leakage Current
Mode Threshold Low
Mode Threshold High
l
l
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 3.6V, unless otherwise specified. (Note 2)
CONDITIONS
(Note 3)
(Note 4)
V
FB1
= V
FB2
= 0.5V
V
FB1
= V
FB2
= 0.63V, MODE/SYNC = 3.6V
RUN = 0V, V
IN
= 5.5V, MODE/SYNC = 0V
V
FB
= 0.6V
V
IN
= 3V, V
FB
= 0.5V, Duty Cycle <35%
V
IN
= 3V, V
FB
= 0.5V, Duty Cycle <35%
(Note 6)
(Note 6)
V
IN
= 5V, V
RUN
= 0V, V
FB
= 0V
V
FB
Ramping Down, MODE/SYNC = 0V
l
MIN
TYP
0.5
700
40
0.1
MAX
UNITS
%
950
60
1
2.7
1.6
0.9
0.45
0.45
1
200
1.5
1
0.5
V
IN
μA
μA
μA
MHz
MHz
A
A
Ω
Ω
μA
%
Ω
Cycles
V
μA
V
V
f
OSC
f
SYNC
I
LIM
R
DS(ON)
I
SW(LKG)
POR
1.8
0.95
0.6
2.25
2.25
1.2
0.7
0.35
0.30
0.01
–8.5
100
262,144
0.3
0
V
IN
– 0.5
1
0.01
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 LTC3548 is guaranteed to meet specified performance 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. The LTC3548I is guaranteed to meet specified
performance over the full –40°C to 85°C temperature range.
Note 3:
The LTC3548 is tested in a proprietary test mode that connects V
FB
to the output of the error amplifier.
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 formula: T
J
= T
A
+ (P
D
•
θ
JA
).
Note 6:
The DFN switch on-resistance is guaranteed by correlation to
wafer level measurements.
TYPICAL PERFORMANCE CHARACTERISTICS
Burst Mode Operation
SW
5V/DIV
V
OUT
20mV/DIV
SW
5V/DIV
V
OUT
10mV/DIV
T
A
= 25°C unless otherwise specified.
Load Step
V
OUT
200mV/DIV
I
L
500mA/DIV
I
LOAD
500mA/DIV
Pulse-Skipping Mode
I
L
200mA/DIV
I
L
200mA/DIV
V
IN
= 3.6V
2μs/DIV
V
OUT
= 1.8V
I
LOAD
= 180mA
CHANNEL 1; CIRCUIT OF FIGURE 3
3548 G01
V
IN
= 3.6V
1μs/DIV
V
OUT
= 1.8V
I
LOAD
= 30mA
CHANNEL 1; CIRCUIT OF FIGURE 3
3548 G02
V
IN
= 3.6V
20μs/DIV
V
OUT
= 1.8V
I
LOAD
= 80mA TO 800mA
CHANNEL 1; CIRCUIT OF FIGURE 3
3548 G03
3548fc
3
LTC3548
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency vs Input Voltage
100
95
90
EFFICIENCY (%)
10mA
85
80
75
70
65
60
2
V
OUT
= 1.8V, CHANNEL 1
Burst Mode OPERATION
CIRCUIT OF FIGURE 3
3
4
INPUT VOLTAGE (V)
3548 G04
T
A
= 25°C unless otherwise specified.
Oscillator Frequency
vs Supply Voltage
10
8
FREQUENCY DEVIATION (%)
6
4
2
0
–2
–4
–6
–8
Oscillator Frequency
vs Temperature
2.5
V
IN
= 3.6V
100mA
FREQUENCY (MHz)
2.4
1mA
800mA
2.3
2.2
2.1
5
6
2.0
–50 –25
–10
50
25
75
0
TEMPERATURE (°C)
100
125
2
3
4
SUPPLY VOLTAGE (V)
5
6
3548 G06
3548 G05
Reference Voltage vs Temperature
0.615
0.610
REFERENCE VOLTAGE (V)
0.605
0.600
0.595
0.590
0.585
–50 –25
V
IN
= 3.6V
500
R
DS(ON)
vs Input Voltage
550
T
A
= 25°C
450
450
R
DS(ON)
(mΩ)
R
DS(ON)
(mΩ)
400
350
300
250
200
SYNCHRONOUS
SWITCH
MAIN
SWITCH
400
350
300
250
200
150
1
2
3
4
V
IN
(V)
5
6
7
3548 G08
R
DS(ON)
vs Junction Temperature
V
IN
= 2.7V
V
IN
= 4.2V
V
IN
= 3.6V
500
50
25
75
0
TEMPERATURE (°C)
100
125
100
–50 –25
MAIN SWITCH
SYNCHRONOUS SWITCH
25 50 75 100 125 150
0
JUNCTION TEMPERATURE (°C)
3548 G09
3548 G07
Efficiency vs Load Current
100
95
90
EFFICIENCY (%)
85
80
75
70
65
60
1
V
IN
= 3.6V, V
OUT
= 1.8V
NO LOAD ON OTHER CHANNEL
CHANNEL 1; CIRCUIT OF FIGURE 3
10
100
LOAD CURRENT (mA)
1000
3548 G11
Load Regulation
2.0
1.5
0.5
0.4
Burst Mode OPERATION
V
OUT
ERROR (%)
0.3
0.2
0.1
0
–0.1
–0.2
–0.3
–0.4
–0.5
Line Regulation
V
OUT
= 1.8V
I
OUT
= 200mA
T
A
= 25°C
Burst Mode OPERATION
V
OUT
ERROR (%)
1.0
0.5
0
–0.5
–1.0
–1.5
–2.0
PULSE-SKIPPING MODE
PULSE-SKIPPING MODE
V
IN
= 3.6V, V
OUT
= 1.8V
NO LOAD ON OTHER CHANNEL
CHANNEL 1; CIRCUIT OF FIGURE 3
1
10
100
LOAD CURRENT (mA)
1000
3548 G12
2
3
4
V
IN
(V)
5
6
3548 G15
3548fc
4
LTC3548
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency vs Load Current
100
2.7V
90
4.2V
EFFICIENCY (%)
EFFICIENCY (%)
80
70
60
V
OUT
= 2.5V, CHANNEL 1
50 Burst Mode OPERATION
NO LOAD ON OTHER CHANNEL
CIRCUIT OF FIGURE 3
40
1
10
100
LOAD CURRENT (mA)
3.6V
100
95
90
85
4.2V
80
75
70
V
OUT
= 1.5V, CHANNEL 1
Burst Mode OPERATION
65
NO LOAD ON OTHER CHANNEL
CIRCUIT OF FIGURE 3
60
1
10
100
LOAD CURRENT (mA)
3.6V
2.7V
EFFICIENCY (%)
T
A
= 25°C unless otherwise specified.
Efficiency vs Load Current
100
95
90
85
80
75
70
Efficiency vs Load Current
3.6V
2.7V
4.2V
1000
3548 G10
1000
3548 G14
V
OUT
= 1.2V, CHANNEL 1
Burst Mode OPERATION
65
NO LOAD ON OTHER CHANNEL
CIRCUIT OF FIGURE 3
60
1
10
100
LOAD CURRENT (mA)
1000
3548 G13
PIN FUNCTIONS
V
FB1
(Pin 1):
Output Feedback. Receives the feedback
voltage from the external resistive divider across the
output. Nominal voltage for this pin is 0.6V.
RUN1 (Pin 2):
Regulator 1 Enable. Forcing this pin to V
IN
enables regulator 1, while forcing it to GND causes regulator
1 to shut down. This pin must be driven; do not float.
V
IN
(Pin 3):
Main Power Supply. Must be closely decoupled
to GND.
SW1 (Pin 4):
Regulator 1 Switch Node Connection to the
Inductor. This pin swings from V
IN
to GND.
GND (Pin 5):
Ground. This pin is not connected internally.
Connect to PCB ground for optimum shielding.
MODE/SYNC (Pin 6):
Combination Mode Selection and
Oscillator Synchronization. This pin controls the operation
of the device. When tied to V
IN
or GND, Burst Mode
operation or pulse-skipping mode is selected, respectively.
Do not float this pin. The oscillation frequency can be
synchronized to an external oscillator applied to this pin
and pulse-skipping mode is automatically selected.
SW2 (Pin 7):
Regulator 2 Switch Node Connection to the
Inductor. This pin swings from V
IN
to GND.
POR
(Pin 8):
Power-On Reset . This common-drain logic
output is pulled to GND when the output voltage falls
below –8.5% of regulation and goes high after 117ms
when both channels are within regulation.
RUN2 (Pin 9):
Regulator 2 Enable. Forcing this pin to V
IN
enables regulator 2, while forcing it to GND causes regulator
2 to shut down. This pin must be driven; do not float.
V
FB2
(Pin 10):
Output Feedback. Receives the feedback
voltage from the external resistive divider across the output.
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