FEATURES
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LTC3548-1
Dual Synchronous, Fixed
Output 2.25MHz Step-Down
DC/DC Regulator
DESCRIPTION
The LTC
®
3548-1 is a dual, fixed output, 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 ≤1mm. The output voltage
for channel 1 is fixed at 1.8V and for channel 2 is fixed
at 1.575V. Internal synchronous 0.35Ω, 1.2A/0.7A power
switches provide high efficiency without the need for ex-
ternal Schottky diodes. Burst Mode
®
operation provides
high efficiency 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.
The LTC3548-1 is available in both thin (0.75mm) and
ultra-thin (0.55mm) 3mm
×
3mm DFN packages.
L,
LT, LTC, LTM 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, 6580258, 6304066, 6127815, 6498466, 6611131.
High Efficiency: Up to 95%
1.8V at 800mA/1.575V at 400mA
Very Low Quiescent Current: Only 40μA
2.25MHz Constant Frequency Operation
High Switch Current: 1.2A and 0.7A
No Schottky Diodes Required
V
IN
: 2.5V to 5.5V
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
Small Thermally Enhanced 3mm
×
3mm
DFN Packages
APPLICATIONS
n
n
n
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PDAs/Palmtop PCs
Digital Cameras
Cellular Phones
Portable Media Players
PC Cards
Wireless and DSL Modems
TYPICAL APPLICATION
LTC3548-1 Efficiency Curve/Power Loss
V
IN
2.7V TO 5.5V
100
C
IN
10μF
CER
4.7μH
SW2
C
FF2
330pF
V
OUT2
V
FB2
GND
SW1
V
OUT1
V
FB1
C
FF1
330pF
95
V
IN
RUN1 RUN2
EFFICIENCY (%)
LTC3548-1
V
OUT2
1.575V
400mA
C
OUT2
10μF
CER
2.2μH
V
OUT1
1.8V
800mA
C
OUT1
10μF
CER
3548-1 F01
1000
90
85
80
75
70
65
60
1
CHANNEL 1
CHANNEL 2
10
100
LOAD CURRENT (mA)
V
OUT1
= 1.8V
100
POWER LOSS (mW)
V
OUT2
= 1.575V
10
1
Figure 1. 1.8V/1.575V at 800mA/400mA Step-Down Regulators
0.1
1000
35481 F01b
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LTC3548-1
ABSOLUTE MAXIMUM RATINGS
(Note 1)
V
IN
Voltages .................................................– 0.3V to 6V
V
FB1
, V
FB2
, V
OUT1
, V
OUT2
,
RUN1, RUN2 Voltages ..................... –0.3V to V
IN
+ 0.3V
SW1, SW2 Voltage ........................... –0.3V to V
IN
+ 0.3V
Ambient Operating Temperature Range
(Note 2)....................................................– 40°C to 85°C
Junction Temperature (Note 5) ............................. 125°C
Storage Temperature Range...................– 65°C to 125°C
PIN CONFIGURATION
TOP VIEW
V
FB1
V
OUT1
V
IN
SW1
GND
1
2
3
4
5
11
10 V
FB2
9 V
OUT2
8 RUN1
7 SW2
6 RUN2
V
FB1
V
OUT1
V
IN
SW1
GND
1
2
3
4
5
11
TOP VIEW
10 V
FB2
9 V
OUT2
8 RUN1
7 SW2
6 RUN2
DD PACKAGE
10-LEAD (3mm
×
3mm) PLASTIC DFN
T
JMAX
= 125°C,
θ
JA
= 40°C/W,
θ
JC
= 3°C/W
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB GND
(SOLDERED TO A 4-LAYER BOARD)
KD PACKAGE
10-LEAD (3mm
×
3mm) PLASTIC UTDFN
T
JMAX
= 125°C,
θ
JA
= 43°C/W,
θ
JC
= 10°C/W
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB GND
(SOLDERED TO A 4-LAYER BOARD)
ORDER INFORMATION
LEAD FREE FINISH
LTC3548EDD-1#PBF
LTC3548EKD-1#PBF
TAPE AND REEL
LTC3548EDD-1#TRPBF
LTC3548EKD-1#TRPBF
PART MARKING
LBZC
CXVT
PACKAGE DESCRIPTION
10-Lead (3mm
×
3mm) Plastic DFN
10-Lead (3mm
×
3mm) Plastic UTDFN
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
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/
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LTC3548-1
ELECTRICAL CHARACTERISTICS
SYMBOL
V
IN
V
OUT1
V
OUT2
ΔV
LINE REG
ΔV
LOAD REG
I
S
PARAMETER
Operating Voltage Range
Output Voltage
Output Voltage
Reference Voltage Line Regulation
Output Voltage Load Regulation
Input DC Supply Current
Active Mode
Sleep Mode
Shutdown
Oscillator Frequency
Peak Switch Current Limit Channel 1
Peak Switch Current Limit Channel 2
Top Switch On-Resistance
Bottom Switch On-Resistance
Switch Leakage Current
RUN Threshold
RUN Leakage Current
0°C ≤ T
A
≤ 85°C (Note 3)
–40°C ≤ T
A
≤ 85°C (Note 3)
0°C ≤ T
A
≤ 85°C (Note 3)
–40°C ≤ T
A
≤ 85°C (Note 3)
V
IN
= 2.5V to 5.5V (Note 3)
(Note 3)
V
OUT1
= 1.5V, V
OUT2
= 1.3V
V
OUT1
= 1.9V, V
OUT2
= 1.65V
RUN = 0V, V
IN
= 5.5V
V
OUT1
= 1.8V, V
OUT2
= 1.575V
V
IN
= 3V, Duty Cycle <35%
V
IN
= 3V, Duty Cycle <35%
(Note 6)
(Note 6)
V
IN
= 5V, V
RUN
= 0V, V
OUT1
= V
OUT2
= 0
●
●
●
The
l
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
●
●
●
MIN
2.5
1.764
1.755
1.544
1.536
TYP
1.8
1.8
1.575
1.575
0.3
0.5
700
40
0.1
MAX
5.5
1.836
1.836
1.607
1.607
0.5
UNITS
V
V
V
V
V
%/V
%
950
60
1
2.7
1.6
0.9
0.45
0.45
1
1.5
1
μA
μA
μA
MHz
A
A
Ω
Ω
μA
V
μA
f
OSC
I
LIM
R
DS(ON)
I
SW(LKG)
V
RUN
I
RUN
1.8
0.95
0.6
2.25
1.2
0.7
0.35
0.30
0.01
0.3
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 LTC3548-1 is guaranteed to meet specified performance
from 0°C to 85°C. Specifications over the – 40°C and 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
Note 3:
The LTC3548-1 is tested in a proprietary test mode that connects
the output of the error amplifier to 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
•
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
OUT2
200mV/DIV
T
A
= 25°C unless otherwise specified.
Load Step
Load Step
V
OUT1
200mV/DIV
I
L
200mA/DIV
I
LOAD
40mA TO
400mA
200mA/DIV
V
IN
= 3.6V
2μs/DIV
V
OUT1
= 1.8V
I
LOAD
= 60mA
CHANNEL 1; CIRCUIT OF FIGURE 3
3548-1 G01
I
L
200mA/DIV
V
OUT1
20mV/DIV
I
L
500mA/DIV
I
LOAD
80mA TO
800mA
500mA/DIV
20μs/DIV
V
IN
= 3.6V
V
OUT2
= 1.575V
I
LOAD
= 40mA TO 400mA
CHANNEL 2; CIRCUIT OF FIGURE 3
3548-1 G03
V
IN
= 3.6V
20μs/DIV
V
OUT1
= 1.8V
I
LOAD
= 80mA TO 800mA
CHANNEL 1; CIRCUIT OF FIGURE 3
3548-1 G02
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LTC3548-1
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency vs Input Voltage
100
95
90
85
80
75
I
OUT
= 1mA
70
65
60
2
2.5
3
3.5 4 4.5 5
INPUT VOLTAGE (V)
5.5
6
2.0
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
I
OUT
= 800mA
I
OUT
= 10mA
FREQUENCY (MHz)
EFFICIENCY (%)
2.3
FREQUENCY DEVIATION (%)
I
OUT
= 100mA
2.4
2.5
T
A
= 25°C unless otherwise specified.
Oscillator Frequency
vs Input Voltage
10
8
6
4
2
0
–2
–4
–6
–8
–10
2
3
4
INPUT VOLTAGE (V)
3548-1 G05
3548-1 G06
Oscillator Frequency
vs Temperature
V
IN
= 3.6V
2.2
2.1
5
6
3548-1 G04
Output Voltage Error
vs Temperature
1
0.8
OUTPUT VOLTAGE ERROR (%)
0.6
0.4
R
DS(ON)
(mΩ)
0.2
0
–0.2
–0.4
–0.6
–0.8
–1
–50
200
–25
50
25
0
75
TEMPERATURE (°C)
100
125
V
IN
= 3.6V
500
450
R
DS(ON)
vs Input Voltage
550
500
450
R
DS(ON)
(mΩ)
400
350
300
250
SYNCHRONOUS
SWITCH
MAIN
SWITCH
400
350
300
250
200
150
1
2
5
4
INPUT VOLTAGE (V)
3
6
7
3548-1 G08
R
DS(ON)
vs Junction Temperature
V
IN
= 2.7V
V
IN
= 4.2V
V
IN
= 3.6V
100
–50 –25
MAIN SWITCH
SYNCHRONOUS SWITCH
25 50 75 100 125 150
0
JUNCTION TEMPERATURE (°C)
3548-1 G09
3548-1 G07
Efficiency vs Load Current
100
95
90
V
OUT
ERROR (%)
EFFICIENCY (%)
85
80
75
70
65
60
1
10
100
LOAD CURRENT (mA)
1000
3548-1 G11
Load Regulation
2.0
1.5
1.0
0.5
0.4
0.3
V
OUT
ERROR (%)
V
OUT1
= 1.8V
0.5
0
–0.5
–1.0
–1.5
–2.0
1
10
100
LOAD CURRENT (mA)
1000
3548-1 G12
Line Regulation
V
OUT1
= 1.8V
V
OUT2
= 1.575V
0.2
0.1
0
V
OUT1
= 1.8V
V
OUT2
= 1.575V
V
OUT2
= 1.575V
–0.1
–0.2
–0.3
–0.4
–0.5
2.5
3
4
4.5
3.5
LOAD CURRENT (mA)
5
5.5
3548-1 G15
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LTC3548-1
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency vs Load Current
100
95
90
EFFICIENCY (%)
85
80
75
70
65
60
1
V
OUT1
= 1.8V
NO LOAD ON OTHER CHANNEL
CIRCUIT OF FIGURE 3
10
100
LOAD CURRENT (mA)
1000
3548-1 G16
T
A
= 25°C unless otherwise specified.
Efficiency vs Load Current
100
95
V
IN
= 3.6V
V
IN
= 2.7V
EFFICIENCY (%)
V
IN
= 3.6V
90
85
80
75
70
65
60
1
V
IN
= 2.7V
V
IN
= 4.2V
V
IN
= 4.2V
V
OUT2
= 1.575V
NO LOAD ON OTHER CHANNEL
CIRCUIT OF FIGURE 3
10
100
LOAD CURRENT (mA)
1000
3548-1 G17
PIN FUNCTIONS
V
FB1
(Pin 1):
Output Feedback for Channel 1. Receives the
feedback voltage from internal resistive divider across the
output. Normal voltage for this pin is 0.6V.
V
OUT1
(Pin 2):
Output Voltage Feedback Pin for Channel 1.
An internal resistive divider divides the output voltage down
for comparison to the internal reference voltage.
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
(see Figure 4).
RUN2 (Pin 6):
Regulator 2 Enable. Forcing this pin to V
IN
en-
ables regulator 2, while forcing it to GND causes regulator 2
to shut down. This pin must be driven; do not float.
SW2 (Pin 7):
Regulator 2 Switch Node Connection to the
Inductor. This pin swings from V
IN
to GND.
RUN1 (Pin 8):
Regulator 1 Enable. Forcing this pin to V
IN
en-
ables regulator 1, while forcing it to GND causes regulator 1
to shut down. This pin must be driven; do not float.
V
OUT2
(Pin 9):
Output Voltage Feedback Pin for Channel 2.
An internal resistive divider divides the output voltage down
for comparison to the internal reference voltage.
V
FB2
(Pin 10):
Output Feedback for Channel 2. Receives
the feedback voltage from internal resistive divider across
the output. Normal 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 con-
nected to electrical ground on PCB (see Figure 4).
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