monolithic synchronous buck regulators using a constant
frequency, current mode architecture. The regulators op-
erate independently with separate run pins. The 2.25V to
5.5V input voltage range makes the LTC3545/LTC3545-1
well suited for single Li-Ion battery-powered applications.
Low ripple pulse skip mode or high efficiency Burst Mode
operation is externally selectable. PWM pulse skip mode
operation provides very low output ripple voltage while
Burst Mode operation increases efficiency at low output
loads.
Switching frequency is internally set to 2.25MHz, or the
switching frequency can be synchronized to an external
1MHz to 3MHz clock. Power good indicators easily allow
power on sequencing between the three regulators.
The internal synchronous switches increase efficiency and
eliminate external Schottky diodes. Low output voltages are
supported with the 0.6V feedback reference voltage.
The LTC3545-1 replaces the SYNC/MODE function with a
third PGOOD pin and forces Burst Mode operation.
■
■
■
■
■
■
Three 800mA Outputs
High Efficiency: Up to 95%
2.25V to 5.5V Input Voltage Range
Low Ripple (<20mV
P-P
) Burst Mode
®
Operation
I
Q
: 58μA
2.25MHz Constant Frequency Operation or
Synchronizable to External 1MHz to 3MHz Clock
Power Good Indicators Ease Supply Sequencing
0.6V Reference Allows Low Output Voltages
Current Mode Operation/Excellent Transient Response
Low Profile 16-Lead 3mm
×
3mm QFN Package
APPLICATIONS
■
■
■
■
■
Smart Phones
Wireless and DSL Modems
Digital Still Cameras
Portable Instruments
Point of Load Regulation
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 6580258, 5481178, 6127815, 6498466, 6611131.
TYPICAL APPLICATION
High Efficiency Triple Step-Down Converter with Power Sequencing
V
IN
2.25V TO 5.5V
C4 10μF
GNDA
R8
500k
R7
500k
RUN1
PGOOD1
RUN2
PGOOD2
RUN3
L1
1.5μH
C6
20pF
LTC3545
L3
1.5μH
SW3
C8
20pF
V
FB2
R4
226k
R3
226k
C2
10μF
V
IN
PV
IN
C5
10μF
PGND
L2
1.5μH
C7
20pF
Efficiency and Loss vs Load Current
100
90
80
EFFICIENCY (%)
V
OUT2
1.2V
70
60
50
40
30
20
10
V
OUT3
1.5V
C3
10μF
R5
301k
3545 TA01
1
0.1
LOSS (W)
SW2
0.01
0.001
V
IN
= 2.5V
V
IN
= 3.6V
V
IN
= 4.2V
0.01
0.1
0.001
LOAD CURRENT (A)
1
3545 TA01b
SYNC/MODE
SW1
V
OUT1
1.8V
C1
10μF
0
0.0001
0.0001
V
FB1
R1
511k
R2
255k
GNDA
PGND
V
FB3
R6
200k
T
A
= 25°C
V
OUT
= 2V
Burst Mode OPERATION
f
OSC
= 2.25MHz
SINGLE CHANNEL
35451fb
1
LTC3545/LTC3545-1
ABSOLUTE MAXIMUM RATINGS
(Note 1)
Input Supply Voltage .................................... –0.3V to 6V
RUNx, PGOODx............................. –0.3V to (V
IN
+ 0.3V)
V
FBx
, SYNC/MODE ........................ –0.3V to (V
IN
+ 0.3V)
SWx .............................................. –0.3V to (V
IN
+ 0.3V)
P-Switch Source Current (DC) (Note 8) ...................1.1A
N-Channel Sink Current (DC) (Note 8) .....................1.1A
Peak SW Sink and Source Current (Note 8) .............1.3A
Operating Junction Temperature Range
(Note 2) ............................................. –40°C to 125°C
Storage Temperature Range................... –65°C to 125°C
PIN CONFIGURATION
LTC3545
TOP VIEW
GNDA
RUN1
V
FB1
V
IN
LTC3545-1
TOP VIEW
GNDA
RUN1
V
FB1
12 V
FB2
17
11 V
FB3
10 RUN3
9
5
SW2
6
PGND
7
PV
IN
8
SW3
PGOOD3
V
IN
16 15 14 13
SW1 1
PGOOD1 2
RUN2 3
PGOOD2 4
5
SW2
6
PGND
7
PV
IN
8
SW3
17
12 V
FB2
11 V
FB3
10 RUN3
9
SYNC/MODE
SW1 1
PGOOD1 2
RUN2 3
PGOOD2 4
16 15 14 13
UD PACKAGE
16-LEAD (3mm 3mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 55°C/W
EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB
UD PACKAGE
16-LEAD (3mm 3mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 55°C/W
EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC3545EUD#PBF
LTC3545IUD#PBF
LTC3545EUD-1#PBF
LTC3545IUD-1#PBF
TAPE AND REEL
LTC3545EUD#TRPBF
LTC3545IUD#TRPBF
LTC3545EUD-1#TRPBF
LTC3545IUD-1#TRPBF
PART MARKING*
LCSR
LCSR
LDDP
LDDP
PACKAGE DESCRIPTION
16-Lead (3mm
×
3mm) Plastic QFN
16-Lead (3mm
×
3mm) Plastic QFN
16-Lead (3mm
×
3mm) Plastic QFN
16-Lead (3mm
×
3mm) Plastic QFN
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
–40°C to 125°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
V
FBx
PARAMETER
Input Voltage Range
Regulated Feedback Voltage (Note 5)
General Characteristics
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= PV
IN
= 3.6V unless otherwise noted. (Note 2)
CONDITIONS
●
MIN
2.25
0.592
0.588
0.588
TYP
MAX
5.5
UNITS
V
V
V
V
%/V
35451fb
T
A
= 25°C
0°C ≤ T
A
≤ 85°C
LTC3545IUD; –40°C < T
A
< 125°C
V
IN
= 2.25V to 5.5V
●
●
●
0.6
0.6
0.6
0.08
0.608
0.612
0.612
0.15
ΔV
FBx
Reference Voltage Line Regulation (Note 5)
2
LTC3545/LTC3545-1
ELECTRICAL CHARACTERISTICS
SYMBOL
V
LOADREG
I
FBx
I
S
PARAMETER
Output Voltage Load Regulation (Notes 5, 6)
Feedback Pin Leakage (Note 5)
Input DC Bias Current (All Regulators Enabled)
Pulse Skip (Active Mode)
Burst Mode Operation (All Regulators Sleeping)
Shutdown (RUN
X
= 0V)
Oscillator Frequency
Synchronization Frequency
RUNx Input High Voltage
RUNx Input Low Voltage
RUN Leakage Current
SWx Leakage
SYNC Leakage
Power Good Threshold–Deviation From V
FB
Steady State (0.6V)
Power Good Pull-Down On-Resistance
V
RUNx
= 0V, V
SWx
= 0V or 5.5V, V
IN
= 5.5V
V
RUN
= 0V, V
SYNC
= 0V or 5.5V,
V
IN
= 5.5V
V
FBx
Ramping Up
V
FBx
Ramping Down
I
PGD
= 50mA
●
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
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