LTC3447
I
2
C Controllable Buck
Regulator in 3mm
×
3mm DFN
FEATURES
■
■
■
■
■
■
■
■
■
■
■
■
■
■
■
■
■
■
■
DESCRIPTIO
I
2
C Programmable Output with 21.6mV Resolution
Overtemperature Protected
High Efficiency: Up to 93%
Very Low Quiescent Current: Only 33µA
600mA Output Current at V
IN
= 3V
2.5V to 5.5V Input Voltage Range
1MHz Constant Frequency Operation
No Schottky Diode Required
Low Dropout Operation: 100% Duty Cycle
Stable with Ceramic Capacitors
Shutdown Mode Draws <1µA Supply Current
±2% Output Voltage Accuracy
Standard (100kHz) or Fast Mode (400kHz) I
2
C
6-Bit Voltage DAC (0.69V to 2.05V)
Disable Burst Mode Operation
Enable Power Good Blanking
Optional External Start-Up Resistors
Soft-Start
10 Lead, 3mm × 3mm DFN Package
The LTC
®
3447 is a high efficiency monolithic synchronous
current mode buck regulator. Using an I
2
C interface, the
output voltage can be set between 0.69V and 2.05V using
an internal 6-bit DAC.
The buck regulator has optional external feedback resis-
tors that can be used for setting the initial start up voltage.
The feedback voltage reference for this start-up option
is 0.6V. Once the voltage DAC is updated via the I
2
C, the
buck regulator switches from external to internal feedback
resistors. When there are no external resistors, the default
start-up voltage is 1.38V.
The switching frequency is internally set at 1MHz, al-
lowing the use of small surface mount inductors and
capacitors.
In Burst Mode
®
operation, supply current is only 33µA,
dropping to <1µA in shutdown. The 2.5V to 5.5V input
voltage range makes the LTC3447 ideally suited for single
cell Li-Ion battery-powered applications. 100% duty cycle
capability provides low dropout operation, extending
battery life in portable systems. Automatic Burst Mode
operation increases efficiency at light loads, further ex-
tending battery life.
The internal synchronous switch increases efficiency and
eliminates the need for an external Schottky diode.
APPLICATIO S
■
■
■
Distributed Power Supplies
Notebook Computers
PDAs and Other Handheld Devices
, LTC and LT are registered trademarks of Linear Technology Corporation.
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 5481178, 6580258, 6304066, 6127815,
6498466, 6611131.
TYPICAL APPLICATIO
V
IN
2.5V TO 5.5V
C2
4.7µF
CERAMIC
V
IN
Efficiency and Power Loss vs
Load Current (V
IN
= 3.6V)
100
V
IN
RPU1
20k
90
80
EFFICIENCY (%)
70
60
50
40
30
20
R2
49.9k
I
2
C
V
CCD
PWREN
10k
SDA
SCL
10k
C3
4.7µF
PGOOD
LTC3447
SW
V
CCD
RUN
SDA
SCL
GND
V
OUT
FB
L1
3.3µH
C1
10µF
R1
100k
V
OUT
0.69V
TO 2.05V
AT 600mA*
10
0
1
* 600mA AT V
IN
= 3V
EXPOSED PADDLE
TO GROUND
3447 TA01
U
1000
POWER LOSS (mW)
100
10
PULSE SKIP EFFICIENCY
Burst Mode EFFICIENCY
LOSS
10
100
LOAD CURRENT (mA)
1
1000
3447f
3447 TA01b
U
U
1
LTC3447
ABSOLUTE
(Note 1)
AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW
V
OUT
GND
FB
PGOOD
V
IN
1
2
3
4
5
11
10 SDA
9 V
CCD
8 SCL
7 RUN
6 SW
V
IN
, V
CCD
Voltages ....................................... –0.3V to 6V
RUN, V
OUT
, FB Voltages .............................. – 0.3V to V
IN
SW Voltage ................................... –0.3V to (V
IN
+ 0.3V)
SCL, SDA Voltages ................................... – 0.3V to V
CCD
P-Channel Switch Source Current (DC) ...............800mA
N-Channel Switch Sink Current (DC) ...................800mA
Peak SW Sink and Source Current ...........................1.3A
Operating Temperature Range (Note 2) ...–40°C to 85°C
Junction Temperature (Note 3) ............................. 125°C
Storage Temperature Range...................–65°C to 125°C
ORDER PART
NUMBER
LTC3447EDD
DD PART
MARKING
LBKB
DD PACKAGE
10-LEAD (3mm x 3mm)PLASTIC DFN
EXPOSED PAD IS GND (PIN 11)
MUST BE SOLDERED TO PCB
T
JMAX
= 125°C,
θ
JA
= 43°C/W,
θ
JC
= 2.96°C/W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
SYMBOL
RUN
PGOOD
R
VOUT
V
OUT(MIN)
V
OUT(MAX)
V
OUT
ΔV
OUT
I
PK
V
LOADREG
V
IN
I
S
PARAMETER
Run Threshold
Reports Undervoltage
Feedback Resistance
Regulated Output Voltage
Regulated Output Voltage
Output Voltage Step Size (6-bits)
Output Voltage Line Regulation
Peak Inductor Current
Output Voltage Load Regulation
Input Voltage Range
Input DC Bias Current
Burst Mode Operation
Active Mode
Shutdown
Nominal Oscillator Frequency
R
DS(ON)
of P-Channel FET
R
DS(ON)
of N-Channel FET
SW Leakage
Optional Start-Up Feedback Voltage
Feedback Input Current
I
2
C Clock Logic Threshold
I
2
C Clock Logic Hysteresis
I
2
C Data Logic Threshold
I
2
C Data Logic Hysteresis
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.
CONDITIONS
PGOOD = 0.4V
●
●
●
MIN
0.3
3
0.669
1.989
20.3
TYP
1
460
0.69
2.05
21.6
0.2
0.2
MAX
1.5
0.711
2.112
22.9
1.2
1
1.25
5.5
UNITS
V
mA
kΩ
V
V
mV
%/V
%/V
A
%
V
µA
µA
µA
MHz
kHz
Ω
Ω
µA
V
nA
V
mV
V
mV
V
IN
= 2.5V to 5.5V (Note 6)
Duty Cycle < 35%, Wafer Level
●
0.75
●
1
0.5
2.5
34
280
0.1
1
160
0.32
0.22
±0.1
0.6
2.5
V
CCD/2
300
V
CCD/2
300
f
OSC
R
PFET
R
NFET
I
LSW
FB
I
FB
SCL
THR
SCL
HYST
SDA
THR
SDA
HYST
(Note 4)
I
LOAD
= 0A
V
OUT
= 90%, I
LOAD
= 0A
V
RUN
= 0V, V
IN
= 5.5V
V
OUT
= 100%
V
OUT
= 0V
I
SW
= 100mA, Wafer Level
I
SW
= –100mA, Wafer Level
V
RUN
= 0V, V
SW
= 0V or 5V, V
IN
= 5V
Regulated Feedback Voltage
(Note 5)
(Note 5)
(Note 5)
(Note 5)
●
0.7
60
400
1
1.3
±1
10
2
U
3447f
W
U
U
W W
W
LTC3447
ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER
I
2
C Interface Timing
f
I2C, MAX
Maximum I
2
C Operating Frequency
t
BUF
Bus Free Time Between Stop and Start Condition
t
HD,RSTA
Hold Time After (Repeated) Start Condition
t
SU,RSTA
Repeated Start Condition Setup Time
t
SU,STOP
Stop Condition Setup Time
t
HD,DIN
Data Hold Time, Input
t
HD,DOUT
Data Hold Time, Output
t
SU,DAT
Data Setup Time
t
SP
Pulse Width of Spikes
Suppressed by Input Filter
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.
CONDITION
(Note 5)
(Note 5)
(Note 5)
(Note 5)
(Note 5)
(Note 5)
(Note 5)
(Note 5)
(Note 5)
MIN
TYP
MAX
400
1.3
0.6
0.6
20
0
280
50
UNITS
kHz
µs
µs
µs
µs
ns
ns
ns
ns
410
670
150
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The LTC3447E is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C operating
temperature are assured by design, characterization and correlation with
statistical process controls.
Note 3:
T
J
is calculated from the ambient temperature, T
A
, and the power
dissipation, P
D
, according to the following formula:
T
J
= T
A
+ P
D
• 43°C/W
This IC includes overtemperature protection that is intended to protect
the device during momentary overload conditions. Junction temperature
will exceed 125°C when overtemperature protection is active. Continuous
operation above the specified maximum operating junction temperature
may impair device reliability.
Note 4:
Dynamic supply current is higher due to gate charge being
delivered at the switching frequency.
Note 5:
Determined by design, not production tested.
Note 6:
The LTC3447 is tested in a proprietary test mode that connects
V
OUT
to FB.
TI I G DIAGRA
SDA
t
LOW
SCL
t
HD, STA
t
r
START
COMMAND
t
HIGH
W
t
SU, DAT
t
HD, DAT
t
SU, STA
t
HD, STA
t
SU, STO
t
BUF
t
f
REPEATED
START
COMMAND
STOP
COMMAND
START
COMMAND
3447 F01
UW
Figure 1. Timing Diagram
3447f
3
LTC3447
TYPICAL PERFOR A CE CHARACTERISTICS
DAC Nonlinearity
0.5
0.4
0.3
0.2
ERROR (LSB)
0.1
0
–0.1
–0.2
–0.3
–0.4
–0.5
0
10
20
30
DAC
40
50
60
3447 G04
EFFICIENCY (%)
60
50
40
30
20
10
0
1
V
OUTMIN
EFFICIENCY (%)
DNL
EffIciency and Power Loss vs
Load Current (V
IN
= 2.5V)
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
1
10
100
LOAD CURRENT (mA)
1
1000
3447 G03
V
OUTMAX
V
OUTMIN
100
2.05 DAC = MAX
V
OUTMAX
(V)
V
IN
= 3.6V
V
IN
= 2.5V
2.00 DAC = MIN
V
IN
= 3.6V
V
IN
= 2.5V
1.95
0.65
0.70
0.75
BIAS CURRENT (µA)
V
OUTMIN
(V)
LOSS
MAX
LOSS
MIN
10
Frequency vs Supply Voltage
1.12
1.10
1.08
FREQUENCY (MHz)
FREQUENCY (MHz)
1.06
1.04
1.02
1.00
0.98
0.96
0.94
0.92
2.5
3.5
4.5
SUPPLY VOLTAGE (V)
5.5
3447 G07
1.12
1.06
1.00
0.94
0.88
0.82
0.76
0.70
– 40 –20
0
20 40 60 80 100 120
TEMPERATURE (°C)
3447 G08
BIAS CURRENT (mA)
4
U W
INL
Efficiency and Power Loss vs
Load Current (V
IN
= 5.5V)
100
90
80
POWER LOSS (mW)
70
100
V
OUTMAX
1000
100
90
80
70
60
50
40
30
20
10
10
100
LOAD CURRENT (mA)
1
1000
3447 GO1
EffIciency and Power Loss vs
Load Current (V
IN
= 3.6V)
1000
V
OUTMAX
V
OUTMIN
POWER LOSS (mW)
100
LOSS
MAX
LOSS
MIN
10
LOSS
MAX
LOSS
MIN
10
0
1
10
100
LOAD CURRENT (mA)
1
1000
3447 G02
Output Voltage vs Load Current
1000
2.10
0.80
350
300
250
200
150
100
50
1.90
0.60
1000
3447 G05
Bias Current vs Supply Voltage
PULSE SKIP
POWER LOSS (mW)
0
200
600
800
400
LOAD CURRENT (mA)
BURST
0
2.5
4.5
3.5
SUPPLY VOLTAGE (V)
5.5
3447 G06
Frequency vs Temperature
1.30
1.24
1.18
360
Bias Current and Shutdown
Current vs Temperature
BIAS CURRENT
V
IN
= 5.5V
V
IN
= 3.6V
310
V
IN
= 2.5V
2.0
1.5
260
SHUTDOWN CURRENT
V
IN
= 5.5V
210
V
IN
= 3.6V
V
IN
= 2.5V
160
–40 –20
0
20
40
60
80 100 120
0
1.0
0.5
3.0
2.5
SHUTDOWN CURRENT (µA)
TEMPERATURE (°C)
3447 G09
3447f
LTC3447
TYPICAL PERFOR A CE CHARACTERISTICS
R
DS(ON)
vs Supply Voltage
0.60
0.55
0.50
R
DS(ON)
(Ω)
R
DS(ON)
(Ω)
0.45
0.40
0.35
0.30
0.25
0.20
2.5
3.5
4.5
5.5
NFET
PFET
0.60
0.55
0.50
V
OUTMAX
(V)
0.45
0.40
0.35
0.30
0.25
0.20
– 40 –20
0
20 40 60 80 100 120
TEMPERATURE (°C)
3447 G11
SUPPLY VOLTAGE (V)
3447 G10
Feedback Reference vs Supply
Voltage
610
618
612
605
606
V
FB
(V)
600
FB (V)
600
595
588
590
582
– 40 –20
2.5
3.5
4.5
SUPPLY VOLTAGE (V)
Soft-Start with No Load
500mV/DIV
500mV/DIV
V
OUT
500mV/DIV
5V/DIV
PGOOD
100mA/DIV
200mA/DIV
INDUCTOR CURRENT
200µs/DIV
3447 G16
U W
3447 G13
R
DS(ON)
vs Temperature
V
IN
= 3.6V
2.060
2.055
2.050
PFET
2.045
2.040
2.035
2.030
2.025
Output Voltage vs Supply Voltage
0.720
DAC = MAX
0.715
0.710
0.705
0.700
DAC = MIN
0.695
0.690
0.685
0.680
5.5
3447 G12
V
OUTMIN
(V)
NFET
2.020
2.5
3.5
4.5
SUPPLY VOLTAGE (V)
Feedback Voltage vs
Temperature
Load Step (200mA to 400mA)
V
OUT
50mV/DIV
LOAD CURRENT
594
200mA/DIV
5.5
0
20
40
60
80 100 120
40µs/DIV
3447 G15
TEMPERATURE (°C)
3447 G15
V
OUT(MIN)
to V
OUT(MAX)
Transition
PULSE SKIP MODE
V
OUT
500mV/DIV
V
OUT(MAX)
to V
OUT(MIN)
Transition
BURST MODE OPERATION
V
OUT
INDUCTOR CURRENT
200mA/DIV
INDUCTOR CURRENT
5V/DIV
PGOOD
100µs/DIV
3447 G17
5V/DIV
PGOOD
100µs/DIV
3447 G18
3447f
5
京公网安备 11010802033920号
EEWORLD
