LTC3445
2
I C Controllable
Buck Regulator with Two LDOs
in a 4mm × 4mm QFN
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FEATURES
DESCRIPTIO
Buck Regulator
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.
■
High Efficiency: Up to 93%
■
600mA Output Current (VCC1 = 3V, VOUT = 1.3V)
■
Programmable Output Voltage: 0.85V to 1.55V
Thebuckregulatorhasa6-bitprogrammableoutputrange
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.
■
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
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.
■
Dynamically Regulates VCC BATT
I2C
■
Standard (100kHz) or Fast Mode (400kHz)
24-Lead (4mm × 4mm) QFN Package
The LTC3445 contains control circuitry (PowerPath) for
automatic back-up battery selection. VBACKUP is typically
a coin cell.
■
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APPLICATIO S
Typicalsupplycurrentduringoperationisonly360µAand
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.
■
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.
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TYPICAL APPLICATIO
V
CC
Efficiency and Power Loss
V
BACKUP
vs Load Current, V
= 3.6V
CC1
4.7µF
CER
20k
V
V
V
CC1
CC1
CC2
100
90
80
70
60
50
40
30
20
10
0
1000
100
10
V
V
BATTFAULT
nBATT_FAULT
TRACK
V
BACKUP
EFFICIENCY
3V
COIN
CELL
3V
TYP
V
BATT
BACKUP
CC
+
4.7µF
DAC MIN
DAC MAX
CER
2.2µH
0.85V
TO 1.55V
PWR_EN
RUN
SDA
SCL
SW
FB
4.7µF
CER
2
DAC MAX
LTC3445
I C BUS
DAC MIN
1.3V
1.1V
LDO1
V
CC
10µF
CER
705k
503k
604k
604k
POWER LOSS
1.0
V
OR GND
ADD7
ADD6
CC1
CC1
LDO1FB
LDO2
20k
V
OR GND
nV _FAULT
CC
PGOOD
10µF
CER
0.1
1000
0.1
1
10
100
LDO2FB
GND
3445 TA01
LOAD CURRENT (mA)
3445 TA01b
3445fa
1