LTC3547 LINER [Linear Technology], LTC3547 Datasheet

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LTC3547

Manufacturer Part Number
LTC3547
Description
Dual Monolithic 300mA Synchronous Step-Down Regulator
Manufacturer
LINER [Linear Technology]
Datasheet

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APPLICATIO S
FEATURES
1.8V AT
TYPICAL APPLICATIO
300mA
V
OUT2
High Effi ciency Dual Step-Down Outputs: Up to 96%
300mA Output Current per Channel at V
Automatic Low Ripple Burst Mode Operation
(20mV
Only 40µA Quiescent Current During Operation
(Both Channels)
2.25MHz Constant-Frequency Operation
2.5V to 5.5V Input Voltage Range
Low Dropout Operation: 100% Duty Cycle
Internally Compensated for All Ceramic Capacitors
Independent Internal Soft-Start for Each Channel
Current Mode Operation for Excellent Line and Load
Transient Response
0.6V Reference Allows Low Output Voltages
Short-Circuit Protected
Ultralow Shutdown Current: I
Low Profi le (0.75mm) 8-Lead 3mm × 2mm
DFN Package
Cellular Telephones
Digital Still Cameras
Wireless and DSL Modems
PDAs/Palmtop PCs
Portable Media Players
2.5V TO 5.5V
Dual Monolithic Buck Regulator in 8-Lead 3mm × 2mm DFN
P-P
V
4.7µF
IN
)
475k
10pF
U
4.7µF
4.7µH
L2
237k
RUN2
SW2
V
FB2
LTC3547
Q
GND
V
U
IN
< 1µA
RUN1
SW1
V
FB1
4.7µH
IN
L1
150k
= 3V
10pF
475k
DESCRIPTIO
The LTC
synchronous step-down DC/DC converter in a tiny 3mm
× 2mm DFN package. 100% duty cycle provides low drop-
out operation, extending battery life in portable systems.
Low output voltages are supported with the 0.6V feed-
back reference voltage. Each regulator can supply 300mA
continuous output current.
The input voltage range is 2.5V to 5.5V, making it ideal for
Li-Ion and USB powered applications. Supply current dur-
ing operation is only 40µA and drops to < 1µA in shutdown.
Automatic Burst Mode
light loads, further extending battery life.
An internally set 2.25MHz switching frequency allows
the use of tiny surface mount inductors and capacitors.
Internal soft-start reduces inrush current during start-
up. All outputs are internally compensated to work with
ceramic capacitors. The LTC3547 is available in a low
profi le (0.75mm) 3mm × 2mm DFN package. The LTC3547
is also available in a fi xed output voltage confi guration,
eliminating the need for the external feedback networks
(see Table 2).
Burst Mode is a registered trademark of Linear Technology Corporation. All other
trademarks are the property of their respective owners. Protected by U.S. Patents,
including 6580258, 5481178, 6304066, 6127815, 6498466, 6611131.
4.7µF
3547 TA01
V
2.5V AT
300mA
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
OUT1
®
3547 is a dual, 2.25MHz, constant-frequency,
Step-Down Regulator
300mA Synchronous
100
90
80
70
60
50
40
30
20
10
0
U
0.1
®
Effi ciency vs Output Current
Dual Monolithic
operation increases effi ciency at
1
OUTPUT CURRENT (mA)
for V
OUT
10
= 2.5V
LTC3547
100
V
V
V
IN
IN
IN
= 2.7V
= 3.6V
= 4.2V
3547 TA01b
1000
1
0.1
0.01
0.001
0.0001
3547fa
1

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LTC3547 Summary of contents

Page 1

... All outputs are internally compensated to work with ceramic capacitors. The LTC3547 is available in a low profi le (0.75mm) 3mm × 2mm DFN package. The LTC3547 is also available in a fi xed output voltage confi guration, eliminating the need for the external feedback networks (see Table 2) ...

Page 2

... FB1 A LTC3547, –40°C ≤ T ≤ 85°C A LTC3547-1, 0°C ≤ T ≤ 85°C A LTC3547-1, –40°C ≤ T ≤ 85° LTC3547, 0°C ≤ T ≤ 85°C FB2 A LTC3547, –40°C ≤ T ≤ 85°C A LTC3547-1, 0°C ≤ T ≤ 85°C A LTC3547-1, –40°C ≤ T ≤ 85°C ...

Page 3

... Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: The LTC3547E is guaranteed to meet specifi ed performance from 0°C to 85°C. Specifi cations over the –40°C and 85°C operating temperature range are assured by design, characterization and correlation with statistical process controls ...

Page 4

... LTC3547 W U TYPICAL PERFOR A CE CHARACTERISTICS Oscillator Frequency vs Temperature 2.6 2 4.2V IN 2.4 2 3. 2.7V IN 2.1 2.0 1.9 1.8 – 50 – 100 TEMPERATURE (°C) 3547 G04 Reference Voltage vs Temperature 612 608 604 600 596 592 588 – – TEMPERATURE (°C) 3547 G07 Effi ciency vs Load Current ...

Page 5

... V OUT 1V/DIV I L 200mA/DIV 200µs/DIV 1.8V OUT I = 300mA LOAD OUT COUPLED 100mV/DIV I L 200mA/DIV I LOAD 200mA/DIV 3547 G18 LTC3547 V = 1.8V OUT I = 100mA LOAD 3 3.5 4 4.5 5 5.5 V (V) IN 3547 G14 Load Step OUT COUPLED 100mV/DIV I L 200mA/DIV I LOAD 200mA/DIV 3547 G16 10µ ...

Page 6

... LTC3547 CTIO S V (Pin 1): Regulator 1 Output Feedback. Receives FB1 the feedback voltage from the external resistor divider across the regulator 1 output. Nominal voltage for this pin is 0.6V. RUN1 (Pin 2): Regulator 1 Enable. Forcing this pin to V enables regulator 1, while forcing it to GND causes IN regulator 1 to shut down ...

Page 7

... P-channel switch increases with decreasing input supply voltage (see Typical Performance Characteristics). Therefore, the user should calculate the worst-case power dissipation when the LTC3547 is used at 100% duty cycle with low input voltage (see Thermal Considerations in the ) is reached. The Applications Information Section). ...

Page 8

... The choice of which style inductor to use often depends more on the price vs size requirements, and any radiated fi eld/EMI requirements, decreases than on what the LTC3547 requires to operate. Table 1 L shows some typical surface mount inductors that work IN well in LTC3547 applications. ...

Page 9

... ESR make them ideal for switching regulator applications. Because the LTC3547 control loop does not depend on the output capacitor’s ESR for stable operation, ceramic capacitors can be used freely to achieve very low output ripple and small circuit size ...

Page 10

... The resistor divider is chosen such that the V input current is 3µA. For these versions the FB V pin should be connected directly the fi xed output voltages available for the LTC35476-1. Table 2. Fixed Output Voltage Versions PART NUMBER V OUT1 LTC3547 Adjustable LTC3547-1 1 ...

Page 11

... Effi ciency = 100% – ( ...) where L1, L2, etc., are the individual losses as a percent- age of input power. Although all dissipative elements in the circuit produce losses, four sources usually account for the losses in LTC3547 circuits quiescent current, 2) switching IN 2 losses losses, 4) other system losses ...

Page 12

... J RISE AMBIENT As a worst-case example, consider the case when the LTC3547 is in dropout on both channels at an input volt- age of 2.7V with a load current of 300mA and an ambi- ent temperature of 70°C. From the Typical Performance Characteristics graph of Switch Resistance, the R of the main switch is 0.9Ω. Therefore, power dissipated ...

Page 13

... U U APPLICATIO S I FOR ATIO V IN 2.5V TO 5.5V V OUT2 C OUT2 BOLD LINES INDICATE HIGH CURRENT PATHS Figure 2. LTC3547 Layout Diagram (See Board Layout Checklist) VIA TO GND VIA RUN2 V RUN1 IN LTC3547 L2 SW2 SW1 FB2 FB1 R4 GND FB1 ...

Page 14

... LTC3547 U U APPLICATIO S I FOR ATIO Design Example As a design example, consider using the LTC3547 in a portable application with a Li-Ion battery. The battery provides a V ranging from 2.8V to 4.2V. The load on IN each channel requires a maximum of 300mA in active mode and 2mA in standby mode. The output voltages are ...

Page 15

... I LOAD 200mA/DIV Figure 4c. Transient Response U DDB Package 8-Lead Plastic DFN (3mm × 2mm) (Reference LTC DWG # 05-08-1702 Rev B) 3.00 ±0.10 (2 SIDES) PIN 1 BAR TOP MARK (SEE NOTE 6) 0.200 REF LTC3547 3547 F04c 10µs/DIV 2.5V OUT I = 20mA TO 300mA LOAD R = 0.115 0.40 ± 0.10 TYP ...

Page 16

... L1, L2: MURATA LQH32CN4R7M33 1.8V/1.2V Dual 300mA Buck Converter IN C1 4.7µ RUN2 V RUN1 IN 4.7µH 4.7µH SW2 SW1 LTC3547 FB1 FB2 C GND OUT2 4.7µF C1 TAIYO YUDEN JMK316BJ475ML OUT1 OUT2 L1, L2: MURATA LQH32CN4R7M33 COMMENTS 95% Effi ciency <1µA, ThinSOT SD 96% Effi ...

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