35482f.pm65
LTC3548-2
1
35482f
APPLICATIO S
U
FEATURES
TYPICAL APPLICATIO
U
DESCRIPTIO
U
PDAs/Palmtop PCs
Digital Cameras
Cellular Phones
Portable Media Players
PC Cards
Wireless and DSL Modems
High Efficiency: Up to 95%
1.8V/800mA Fixed Output and 400mA Adjustable
Output Voltage
Only 40
A Quiescent Current (Both Channels)
2.25MHz Constant Frequency Operation
High Switch Current Limits: 1.2A and 0.7A
No Schottky Diodes Required
Low R
DS(ON)
Internal Switches: 0.35
Current Mode Operation for Excellent Line
and Load Transient Response
Short-Circuit Protected
Low Dropout Operation: 100% Duty Cycle
Ultralow Shutdown Current: I
Q
< 1
A
Power-On Reset Output
Externally Synchronizable Oscillator
Small Thermally Enhanced 3mm
3mm DFN Package
Dual Synchronous,
Fixed/Adjustable Output, 2.25MHz
Step-Down DC/DC Regulator
The LTC
3548-2 is a dual, constant frequency, synchro-
nous step down DC/DC converter. Intended for low power
applications, 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
1.2mm. For channel 1, the output voltage
is fixed at 1.8V/800mA; for channel 2, the output voltage
is adjustable from 0.6V to V
IN
. Internal synchronous
0.35
, 1.2A/0.7A 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 Skip Mode provides low noise ripple at light
loads.
To further maximize battery run time, the P-channel
MOSFETs are turned on continuously in dropout (100%
duty cycle), and both channels draw a total quiescent
current of only 40
A. In shutdown, the device draws <1A.
Efficiency and Power Loss
vs Load Current
Figure 1. 2.5V/1.8V at 400mA/800mA Step-Down Regulators
RUN2
V
IN
V
IN
2.8V TO 5.5V
V
OUT2
2.5V
400mA
V
OUT1
1.8V
800mA
RUN1
POR
SW1
V
OUT1
GND
V
FB2
SW2
MODE/SYNC
LTC3548-2
10
F
100k
RESET
68pF
2.2
H
4.7
H
887k
280k
10
F
35482 F01
4.7
F
, 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. Protected by U.S. Patents including 5481178,
6580258, 6304066, 6127815, 6498466, 6611131.
LOAD CURRENT (mA)
1
80
EFFICIENCY (%)
POWER LOSS (mW)
90
100
10
100
1000
35482 F01b
70
75
85
95
65
60
1
100
1000
10
0.1
EFFICIENCY
POWER LOSS
V
IN
= 3.6V
V
OUT
= 1.8V
Burst Mode OPERATION
CHANNEL 1
NO LOAD ON CHANNEL 2
LTC3548-2
2
35482f
V
IN
Voltages ................................................. 0.3V to 6V
V
OUT1
, V
FB2
, RUN1, RUN2
Voltages .......................................... 0.3V to V
IN
+ 0.3V
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
Ambient Operating Temperature Range
(Note 2) .................................................. 40
C to 85C
Junction Temperature (Note 5) ............................. 125
C
Storage Temperature Range ................. 65
C to 125C
ABSOLUTE AXI U
RATI GS
W
W
W
U
(Note 1)
ORDER PART NUMBER
DD PART MARKING
T
JMAX
= 125
C,
JA
= 40
C/W,
JC
= 3
C/W (4-LAYER BOARD)
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB GND
LCDK
LTC3548EDD-2
PACKAGE/ORDER I FOR ATIO
U
U
W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
TOP VIEW
DD PACKAGE
10-LEAD (3mm
3mm) PLASTIC DFN
10
11
9
6
7
8
4
5
3
2
1
V
FB2
RUN2
POR
SW2
MODE/
SYNC
V
OUT1
RUN1
V
IN
SW1
GND
ELECTRICAL CHARACTERISTICS
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)
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
IN
Operating Voltage Range
2.5
5.5
V
I
FB2
Feedback Pin Input Current
30
nA
V
FB2
Feedback Voltage of Channel 2 (Note 3)
0
C T
A
85C
0.588
0.6
0.612
V
40
C T
A
85C
0.585
0.6
0.612
V
V
OUT1
Output Voltage of Channel 1 (Note 3)
0
C T
A
85C
1.764
1.8
1.836
V
40
C T
A
85C
1.755
1.8
1.836
V
V
LINE REG
Reference Voltage Line Regulation
V
IN
= 2.5V to 5.5V (Note 3)
0.3
0.5
%/V
V
LOAD REG
Output Voltage Load Regulation
(Note 3)
0.5
%
I
S
Input DC Supply Current (Note 4)
Active Mode
V
OUT1
= 1.5V, V
FB2
= 0.5V
700
950
A
Sleep Mode
V
OUT1
= 1.9V, V
FB2
= 0.63V, MODE/SYNC = 3.6V
40
60
A
Shutdown
RUN = 0V, V
IN
= 5.5V, MODE/SYNC = 0V
0.1
1
A
f
OSC
Oscillator Frequency
V
OUT1
= 1.8V, V
FB2
= 0.6V
1.8
2.25
2.7
MHz
f
SYNC
Synchronization Frequency
2.25
MHz
I
LIM
Peak Switch Current Limit Channel 1
V
IN
= 3V, Duty Cycle <35%
0.95
1.2
1.6
A
Peak Switch Current Limit Channel 2
V
IN
= 3V, V
FB2
= 0.5V, Duty Cycle <35%
0.6
0.7
0.9
A
R
DS(ON)
Top Switch On-Resistance
(Note 6)
0.35
0.45
Bottom Switch On-Resistance
(Note 6)
0.30
0.45
I
SW(LKG)
Switch Leakage Current
V
IN
= 5V, V
RUN
= 0V, V
FB2
= 0V, V
OUT1
= 0V
0.01
1
A
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/
LTC3548-2
3
35482f
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
Load Step
Burst Mode Operation
Pulse Skipping Mode
Efficiency vs Input Voltage
Oscillator Frequency
vs Input Voltage
Oscillator Frequency
vs Temperature
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 LTC3548-2 is guaranteed to meet specified performance from
0
C to 85C. Specifications over the 40C and 85C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
Note 3: The LTC3548-2 is tested in a proprietary test mode that connects
the output of the error amplifier with an outside servo loop.
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
JA
).
Note 6: The DFN switch on-resistance is guaranteed by correlation to
wafer level measurements.
ELECTRICAL CHARACTERISTICS
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)
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
POR
Power-On Reset Threshold
V
OUT1
, V
FB2
Ramping Down, MODE/SYNC = 0V
8.5
%
Power-On Reset On-Resistance
100
200
Power-On Reset Delay
262,144
Cycles
V
RUN
RUN Threshold
0.3
1
1.5
V
I
RUN
RUN Leakage Current
0.01
1
A
T
A
= 25
C unless otherwise specified.
35482 G01
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD
= 60mA
CHANNEL 1; CIRCUIT OF FIGURE 3
SW
5V/DIV
V
OUT
20mV/DIV
I
L
200mA/DIV
2
s/DIV
35482 G02
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD
= 30mA
CHANNEL 1; CIRCUIT OF FIGURE 3
SW
5V/DIV
V
OUT
10mV/DIV
I
L
200mA/DIV
1
s/DIV
35482 G03
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD
= 80mA TO 800mA
CHANNEL 1; CIRCUIT OF FIGURE 3
V
OUT
200mV/DIV
I
L
500mA/DIV
I
LOAD
500mA/DIV
20
s/DIV
INPUT VOLTAGE (V)
2
35482 G04
3
4
5
6
100
95
90
85
80
75
70
65
60
EFFICIENCY (%)
V
OUT
= 1.8V, CHANNEL 1
Burst Mode OPERATION
CIRCUIT OF FIGURE 3
800mA
10mA
100mA
1mA
2.5
2.4
2.3
2.2
2.1
2.0
FREQUENCY (MHz)
TEMPERATURE (
C)
50
25
75
35482 G05
25
0
50
100
125
V
IN
= 3.6V
10
8
6
4
2
0
2
4
6
8
10
FREQUENCY DEVIATION (%)
V
IN
(V)
2
35482 G06
3
4
5
6
LTC3548-2
4
35482f
Efficiency vs Load Current
Load Regulation
Line Regulation
Efficiency vs Load Current
Efficiency vs Load Current
Efficiency vs Load Current
Reference Voltage
vs Temperature
R
DS(ON)
vs Input Voltage
R
DS(ON)
vs Junction Temperature
0.615
0.610
0.605
0.600
0.595
0.590
0.585
REFERENCE VOLTAGE (V)
TEMPERATURE (
C)
50
25
75
35482 G07
25
0
50
100
125
V
IN
= 3.6V
V
IN
(V)
1
500
450
400
350
300
250
200
4
6
35482 G08
2
3
5
7
R
DS(ON)
(m
)
MAIN
SWITCH
SYNCHRONOUS
SWITCH
JUNCTION TEMPERATURE (
C)
50
550
500
450
400
350
300
250
200
150
100
25
75
3548 G09
25
0
50
100
150
125
R
DS(ON)
(m
)
MAIN SWITCH
SYNCHRONOUS SWITCH
V
IN
= 3.6V
V
IN
= 4.2V
V
IN
= 2.7V
LOAD CURRENT (mA)
1
EFFICIENCY (%)
100
95
90
85
80
75
70
65
60
10
100
1000
35482 G10
V
IN
= 3.6V, V
OUT
= 1.8V
NO LOAD ON OTHER CHANNEL
CHANNEL 1; CIRCUIT OF FIGURE 3
Burst Mode OPERATION
PULSE SKIP MODE
LOAD CURRENT (mA)
1
V
OUT
ERROR (%)
2.0
1.5
1.0
0.5
0
0.5
1.0
1.5
2.0
10
100
1000
35482 G11
Burst Mode OPERATION
PULSE SKIP MODE
V
IN
= 3.6V, V
OUT
= 1.8V
NO LOAD ON OTHER CHANNEL
CHANNEL 1; CIRCUIT OF FIGURE 3
V
IN
(V)
2
V
OUT
ERROR (%)
0.5
0.4
0.3
0.2
0.1
0
0.1
0.2
0.3
0.4
0.5
4
6
35482 G12
3
5
V
OUT
= 1.8V
I
OUT
= 200mA
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
T
A
= 25
C unless otherwise specified.
LOAD CURRENT (mA)
1
EFFICIENCY (%)
100
95
90
85
80
75
70
65
60
10
100
1000
35482 G13
V
OUT2
= 1.5V
Burst Mode OPERATION
NO LOAD ON OTHER CHANNEL
CIRCUIT OF FIGURE 3
V
IN
= 2.7V
V
IN
= 4.2V
V
IN
= 3.6V
LOAD CURRENT (mA)
1
EFFICIENCY (%)
100
95
90
85
80
75
70
65
60
10
100
1000
35482 G14
V
OUT2
= 2.5V
Burst Mode OPERATION
NO LOAD ON OTHER CHANNEL
CIRCUIT OF FIGURE 3
V
IN
= 2.7V
V
IN
= 4.2V
V
IN
= 3.6V
LOAD CURRENT (mA)
1
EFFICIENCY (%)
100
95
90
85
80
75
70
65
60
10
100
1000
35482 G15
V
OUT2
= 3.3 V
Burst Mode OPERATION
NO LOAD ON OTHER CHANNEL
CIRCUIT OF FIGURE 3
V
IN
= 5V
LTC3548-2
5
35482f
V
OUT1
(Pin 1): Output Voltage Feedback for Channel 1. An
internal resistive divider divides the output voltage down
for comparison to the internal reference voltage.
RUN1 (Pin 2): Regulator 1 Enable. Forcing this pin to V
IN
enables regulator 1, while forcing it to GND causes regu-
lator 1 to shut down. This pin must be driven; do not float.
V
IN
(Pin 3): Input 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. Connect to the () terminal of C
OUT
,
and () terminal of C
IN
.
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, respec-
tively. Do not float this pin. The oscillation frequency can
U
U
U
PI FU CTIO S
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 regu-
lator 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. Nominal voltage for this pin is 0.6V.
Exposed Pad (GND) (Pin 11): Ground. Connect to the
() terminal of C
OUT
, and () terminal of C
IN
. Must be
connected to PCB ground for electrical contact and rated
thermal performance.
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