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PDF LTC3445 Data sheet ( Hoja de datos )
| Número de pieza | LTC3445 | |
| Descripción | I2C Controllable Buck Regulator | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LTC3445 (archivo pdf) en la parte inferior de esta página. Total 24 Páginas | ||
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LTC3445www.DataSheet4U.com
I2C Controllable
Buck Regulator with Two LDOs
in a 4mm × 4mm QFN
FEATURES
Buck Regulator
■ High Efficiency: Up to 93%
■ 600mA Output Current (VCC1 = 3V, VOUT = 1.3V)
■ Programmable Output Voltage: 0.85V to 1.55V
■ 2.5V to 5.5V Input Voltage Range
■ 1.5MHz Constant Frequency or Spread Spectrum
Option
■ Soft-Start
LDOs
■ Two LDO Regulators: 0.3V Dropout at 50mA
PowerPath Controller
■ Dynamically Regulates VCC BATT
I2C
■ Standard (100kHz) or Fast Mode (400kHz)
■ 24-Lead (4mm × 4mm) QFN Package
U
APPLICATIO S
■ Intel’s Microprocessor Supply (PXA27X)
■ Portable Instruments
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation.
PowerPath is a trademark of Linear Technology Corporation.
I2C is a trademark of Philips Electronics N.V.
Protected by U.S. Patents, including 5481178, 6580258, 6304066, 6127815, 6498466,
6611131, Spread Spectrum patent pending.
DESCRIPTIO
The LTC®3445 contains a high efficiency monolithic syn-
chronous current mode buck regulator, two LDO regula-
tors, a PowerPathTM controller and an I2CTM interface.
The buck regulator has a 6-bit programmable output range
of 0.85V to 1.55V. Also, the buck regulator uses either a
constant (1.5MHz) or a spread spectrum switching fre-
quency. Using the spread spectrum option allows for a
lower noise regulated output as well as low noise at the
input. In addition, the regulated output voltage slew rate is
programmable via the I2C interface.
The LTC3445 contains two LDO voltage regulators. The
regulator output voltages are externally resistor program-
mable. Each LDO is capable of delivering up to 50mA.
The LTC3445 contains control circuitry (PowerPath) for
automatic back-up battery selection. VBACKUP is typically
a coin cell.
Typical supply current during operation is only 360µA and
drops to 27µA in shutdown. The 2.5V to 5.5V input
voltage range makes the LTC3445 ideal for single Li-Ion
battery-powered applications. Automatic Burst Mode®
operation increases efficiency at light loads, further ex-
tending battery life.
TYPICAL APPLICATIO
VCC
4.7µF
CER
3V
COIN
+
VBACKUP
CELL
PWR_EN
I2C BUS
VCC
20k
nVCC_FAULT
VCC1 OR GND
VCC1 OR GND
VCC1 VCC2 VCC1
VTRACK
VBACKUP
BATTFAULT
VCC BATT
RUN SW
SDA
LTC3445
FB
SCL LDO1
ADD7
ADD6
PGOOD
LDO1FB
LDO2
GND LDO2FB
VBACKUP
2.2µH
705k
20k
4.7µF
CER
4.7µF
CER
nBATT_FAULT
3VTYP
0.85V
TO 1.55V
1.3V
604k 10µF
CER
503k
604k
1.1V
10µF
CER
3445 TA01
Efficiency and Power Loss
vs Load Current, VCC1 = 3.6V
100
90
80
70
60
50
40
30
20
10
0
0.1
EFFICIENCY
DAC MAX
DAC MIN
1000
100
DAC MAX
DAC MIN
POWER LOSS
10
1.0
1 10 100
LOAD CURRENT (mA)
0.1
1000
3445 TA01b
3445fa
1
1 page  
TYPICAL PERFOR A CE CHARACTERISTICS
LTC3445www.DataSheet4U.com
Buck Efficiency and Power Loss
vs Load Current, VCC1 = 2.5V
100
1000
90
EFFICIENCY
80
70 DAC MIN DAC MAX
60
100
50
DAC MAX
40
10
30 POWER LOSS
1.0
20
DAC MIN
10
0 0.1
0.1 1 10 100 1000
LOAD CURRENT (mA)
3445 G04
Buck Efficiency and Power Loss
vs Load Current, VCC1 = 4.2V
100
90 EFFICIENCY
1000
80 DAC MAX DAC MIN
70
100
60
50 10
40
30
20
DAC MAX
POWER LOSS 1.0
10
0
0.1
DAC MIN
1 10 100
LOAD CURRENT (mA)
0.1
1000
3445 G05
Buck Output Voltage
vs Load Current
1.580
DAC = MAX
1.560
1.540
IVCC2 vs Temperature (RUN = VCC1)
1.2
VCC2 = 2.5V
VCC2 = 3.6V
1.0 VCC2 = 4.2V
VCC2 = 5.5V
0.8
Buck Output Voltage
vs Load Current
0.900
DAC = MIN
0.850
0.800
0.750
0.700
–100
100 300 500 700
LOAD CURRENT (mA)
900
3445 G06
IVCC2 vs Temperature (RUN = 0V)
1.2
VCC2 = 2.5V
VCC2 = 3.6V
1.0 VCC2 = 4.2V
VCC2 = 5.5V
0.8
1.520 0.6 0.6
1.500 0.4 0.4
1.480 0.2 0.2
1.460
–100
100 300 500 700
LOAD CURRENT (mA)
900
3445 G07
RDS(ON) vs Input Voltage
600
550
500
MAIN SWITCH
450
400
SYNCHRONOUS SWITCH
350
300
250
2.2 2.6 3 3.4 3.8 4.2 4.6 5 5.4 5.8
INPUT VOLTAGE (V)
3445 G10
0
–50
–10 30 70 110
TEMPERATURE (°C)
150
3445 G08
Synchronous Switch RDS(ON)
vs Temperature
700
VCC1 = 2.5V
VCC1 = 3.6V
600
VCC1 = 4.2V
VCC1 = 5.5V
500
400
300
200
–40 –20 0
20 40 60 80 100 120 140
TEMPERATURE (°C)
3445 G11
0
–50
–10 30
70 110
TEMPERATURE (°C)
150
3445 G09
Main Switch RDS(ON)
vs Temperature
800
VCC1 = 2.5V
VCC1 = 3.6V
700
VCC1 = 4.2V
VCC1 = 5.5V
600
500
400
300
–40 –20 0
20 40 60 80 100 120 140
TEMPERATURE (°C)
3445 G12
3445fa
5
5 Page 
WU W
TI I G DIAGRA
SDA
tLOW
tSU(DAT)
SCL
tHD(STA)
START
CONDITION
tHIGH
tr tf
tHD(DAT)
tSU(STA)
tHD(STA)
REPEATED START
CONDITION
LTC3445www.DataSheet4U.com
tBUF
tSUSTO
3445 TD
STOP
START
CONDITION CONDITION
I2C Fast Mode Timing Specifications (for Reference)
SYMBOL
fI2C(MAX)
tBUF
tHD(RSTA)
tSU(RSTA)
tSU(STOP)
tHD(DAT)
tSU(DAT)
tLOW
tHIGH
tSP
tf
PARAMETER
Maximum I2C Operating Frequency
Bus Free Time Between Stop and Start Condition
Hold Time After (Repeated) Start Condition
Repeated Start Condition Setup Time
Stop Condition Setup Time
Data Hold Time
Data Setup Time
Clock Low Period
Clock High Period
Pulse Width of Spikes Suppressed by Input Filter
Clock, Data Fall Time (Note 1)
tr Clock, Data Rise Time (Note 1)
Note 1: CB = Capacitance of one bus line.
MIN
0
1.3
0.6
0.6
0.6
0
100
1.3
0.6
0
20 + 0.1
• CB
20 + 0.1
• CB
TYP
MAX
400
0.9
50
300
300
UNITS
kHz
µs
µs
µs
µs
ns
ns
µs
µs
ns
ns
ns
U
OPERATIO (refer to Figure 1)
BUCK REGULATOR
Main Control Loop
The LTC3445 uses a constant or spread spectrum fre-
quency, current mode step-down architecture (Figure 2).
Both the main (P-channel MOSFET) and synchronous
(N-channel MOSFET) switches are internal. During normal
operation, the internal top power MOSFET is turned on
each cycle when the oscillator sets the RS latch, and
turned off when the current comparator, ICOMP, resets the
RS latch. The peak inductor current at which ICOMP resets
the RS latch is controlled by the output of error amplifier
EA. When the load current increases, it causes a slight
decrease in the feedback voltage, FB, relative to an internal
reference voltage, which in turn, causes the EA’s output
voltage to increase until the average inductor current
matches the new load current. While the top MOSFET is
off, the bottom MOSFET is turned on until either the
inductor current starts to reverse, as indicated by the
current reversal comparator IRCMP, or the beginning of the
next clock cycle.
3445fa
11
11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet LTC3445.PDF ] | |
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