LTC3548
1
3548f
, 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.
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%
Very Low Quiescent Current: Only 40A
2.25MHz Constant Frequency Operation
High Switch Current: 0.7A and 1.2A
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
< 1A
Output Voltages from 5V down to 0.6V
Power-On Reset Output
Externally Synchronizable Oscillator
Small Thermally Enhanced MSOP and 3mm 3mm
DFN Packages
Dual Synchronous,
400mA/800mA, 2.25MHz
Step-Down DC/DC Regulator
The LTC
3548 is a dual, constant frequency, synchronous
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. Each output voltage is adjustable
from 0.6V to 5V. Internal synchronous 0.35, 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 Skip 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
current of only 40A. In shutdown, the device draws <1A.
LTC3548 Efficiency Curve
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
AT 400mA
V
OUT1
= 1.8V
AT 800mA
RUN1
POR
SW1
V
FB1
GND
V
FB2
SW2
MODE/SYNC
LTC3548
10F
100k
RESET
33pF
68pF
2.2H
4.7H
887k
604k
301k
280k
4.7F
10F
3548 TA01
LOAD CURRENT (mA)
1
EFFICIENCY (%)
100
95
90
85
80
75
70
65
60
POWER LOSS (mW)
1000
100
10
1
0.1
10
100
1000
3548 TA02
V
IN
= 3.3V, V
OUT
= 1.8V
Burst Mode OPERATION
CHANNEL 1, NO LOAD ON CHANNEL 2
POWER LOSS
EFFICIENCY
LTC3548
2
3548f
TOP VIEW
DD PACKAGE
10-LEAD (3mm 3mm) PLASTIC DFN
DD PIN 11, EXPOSED PAD: PGND
MUST BE CONNECTED TO GND
10
11
9
6
7
8
4
5
3
2
1
V
FB2
RUN2
POR
SW2
MODE/
SYNC
V
FB1
RUN1
V
IN
SW1
GND
V
IN
Voltages ................................................. 0.3V to 6V
V
FB1
, 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
ABSOLUTE AXI U
RATI GS
W
W
W
U
(Note 1)
ELECTRICAL CHARACTERISTICS
The
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25C. 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
FB
Feedback Pin Input Current
30
nA
V
FB
Feedback Voltage (Note 3)
0C T
A
85C
0.588
0.6
0.612
V
40C T
A
85C
0.585
0.6
0.612
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
Active Mode
V
FB1
= V
FB2
= 0.5V
700
950
A
Sleep Mode
V
FB1
= 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
FB
= 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, V
FB
= 0.5V, Duty Cycle <35%
0.95
1.2
1.6
A
Peak Switch Current Limit Channel 2
V
IN
= 3V, V
FB
= 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
FB
= 0V
0.01
1
A
Ambient Operating Temperature
Range (Note 2) ................................... 40C to 85C
Junction Temperature (Note 5) ............................. 125C
Storage Temperature Range ................. 65C to 125C
Lead Temperature (Soldering, 10 sec)
LTC3548EMSE only .......................................... 300C
ORDER PART
NUMBER
DD PART MARKING
T
JMAX
= 125C,
JA
= 45C/W,
JC
= 3C/W
(Soldered to a 4-layer board)
LBNJ
LTC3548EDD
PACKAGE/ORDER I FOR ATIO
U
U
W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ORDER PART
NUMBER
MSE PART MARKING
T
JMAX
= 125C,
JA
= 45C/W,
JC
= 10C/W
(Soldered to a 4-layer board)
LTBNH
LTC3548EMSE
TOP VIEW
1
2
3
4
5
V
FB1
RUN1
V
IN
SW1
GND
10
9
8
7
6
V
FB2
RUN2
POR
SW2
MODE/
SYNC
11
MSE PACKAGE
10-LEAD PLASTIC MSOP
MSE PIN 11, EXPOSED PAD: PGND
MUST BE CONNECTED TO GND
LTC3548
3
3548f
2.5
2.4
2.3
2.2
2.1
2.0
FREQUENCY (MHz)
10
8
6
4
2
0
2
4
6
8
10
FREQUENCY DEVIATION (%)
SUPPLY VOLTAGE (V)
2
3548 G06
3
4
5
6
INPUT VOLTAGE (V)
2
3548 G04
3548 G01
3548 G02
3548 G03
3
4
5
6
TEMPERATURE (C)
50
25
75
3548 G05
25
0
50
100
125
100
95
90
85
80
75
70
65
60
EFFICIENCY (%)
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD
= 180mA
CHANNEL 1; CIRCUIT OF FIGURE 3
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD
= 30mA
CHANNEL 1; CIRCUIT OF FIGURE 3
V
IN
= 3.6V
V
OUT
= 1.8V
I
LOAD
= 80mA TO 800mA
CHANNEL 1; CIRCUIT OF FIGURE 3
V
OUT
= 1.8V, CHANNEL 1
Burst Mode OPERATION
CIRCUIT OF FIGURE 3
800mA
10mA
100mA
1mA
SW
5V/DIV
V
OUT
20mV/DIV
I
L
200mA/DIV
SW
5V/DIV
V
OUT
10mV/DIV
I
L
200mA/DIV
V
OUT
200mV/DIV
I
L
500mA/DIV
I
LOAD
500mA/DIV
2s/DIV
1s/DIV
20s/DIV
V
IN
= 3.6V
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
Load Step
Burst Mode Operation
Pulse Skipping Mode
Efficiency vs Input Voltage
Oscillator Frequency vs Supply
Voltage
Oscillator Frequency vs
Temperature
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired. No pin shall exceed 6V.
Note 2: The LTC3548 is guaranteed to meet specified performance from
0C to 70C. Specifications over the 40C and 85C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
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
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
= 25C. V
IN
= 3.6V, unless otherwise specified. (Note 2)
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
POR
Power-On Reset Threshold
V
FB
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
= 25C unless otherwise specified.
LTC3548
4
3548f
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
3548 G15
3
5
V
OUT
= 1.8V
I
OUT
= 200mA
T
A
= 25C
V
IN
(V)
1
500
450
400
350
300
250
200
4
6
3548 G08
2
3
5
7
R
DS(ON)
(m
)
MAIN
SWITCH
SYNCHRONOUS
SWITCH
0.615
0.610
0.605
0.600
0.595
0.590
0.585
REFERENCE VOLTAGE (V)
JUNCTION TEMPERATURE (C)
50
550
500
450
400
350
300
250
200
150
100
25
75
3548 G09
25
0
50
100
150
125
TEMPERATURE (C)
50
25
75
3548 G07
25
0
50
100
125
R
DS(ON)
(m
)
MAIN SWITCH
SYNCHRONOUS SWITCH
V
IN
= 3.6V
V
IN
= 3.6V
V
IN
= 4.2V
V
IN
= 2.7V
T
A
= 25C
LOAD CURRENT (mA)
1
EFFICIENCY (%)
100
90
80
70
60
50
40
10
100
1000
3548 G10
3.6V
2.7V
4.2V
V
OUT
= 2.5V, CHANNEL 1
Burst Mode OPERATION
NO LOAD ON OTHER CHANNEL
CIRCUIT OF FIGURE 3
LOAD CURRENT (mA)
1
EFFICIENCY (%)
100
95
90
85
80
75
70
65
60
10
100
1000
3548 G13
2.7V
4.2V
V
OUT
= 1.2V, CHANNEL 1
Burst Mode OPERATION
NO LOAD ON OTHER CHANNEL
CIRCUIT OF FIGURE 3
LOAD CURRENT (mA)
1
EFFICIENCY (%)
100
95
90
85
80
75
70
65
60
10
100
1000
3548 G14
2.7V
4.2V
LOAD CURRENT (mA)
1
EFFICIENCY (%)
100
95
90
85
80
75
70
65
60
10
100
1000
3548 G11
V
IN
= 3.6V, V
OUT
= 1.8V
NO LOAD ON OTHER CHANNEL
CHANNEL 1; CIRCUIT OF FIGURE 3
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
3548 G12
Burst Mode OPERATION
Burst Mode OPERATION
PULSE SKIP MODE
PULSE SKIP MODE
V
OUT
= 1.5V, CHANNEL 1
Burst Mode OPERATION
NO LOAD ON OTHER CHANNEL
CIRCUIT OF FIGURE 3
3.6V
3.6V
V
IN
= 3.6V, V
OUT
= 1.8V
NO LOAD ON OTHER CHANNEL
CHANNEL 1; CIRCUIT OF FIGURE 3
Efficiency vs Load Current
Load Regulation
Line Regulation
Efficiency vs Load Current
Efficiency vs Load Current
Efficiency vs Load Current
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
Reference Voltage vs
Temperature
R
DS(ON)
vs Input Voltage
R
DS(ON)
vs Junction Temperature
LTC3548
5
3548f
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 regu-
lator 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): Main 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): Power Ground. Connect to
the () terminal of C
OUT
, and () terminal of C
IN
. Must be
connected to electrical ground on PCB.
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