LTC3445_15 Datasheet, PDF (1/24 Pages) Linear Technology – I2C Controllable Buck Regulator with Two LDOs

LTC3445
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 PowerPath^TM controller and an I²C^TM 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. V_BACKUP 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
V_CC
4.7µF
CER
3V
COIN
+
V_BACKUP
CELL
PWR_EN
I²C BUS
V_CC
20k
nV_CC_FAULT
V_CC1 OR GND
V_CC1 OR GND
V_CC1 V_CC2 V_CC1
V_TRACK
V_BACKUP
BATTFAULT
V_CC BATT
RUN
SW
SDA
FB
LTC3445
SCL
LDO1
ADD7
ADD6
PGOOD
LDO1FB
LDO2
GND ^LDO2FB
V_BACKUP
2.2µH
705k
20k
4.7µF
CER
4.7µF
CER
nBATT_FAULT
3V_TYP
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, V_CC1 = 3.6V
100
90
80
70
60
50
40
30
20
10
0
0.1
EFFICIENCY
DAC MAX
DAC MIN
1000
100
DAC MAX
10
DAC MIN
POWER LOSS
1.0
1
10
100
LOAD CURRENT (mA)
0.1
1000
3445 TA01b
3445fa
1