LTC3445
I
2
C Controllable
Buck Regulator with Two LDOs
in a 4mm
×
4mm QFN
FEATURES
Buck Regulator
■
High Efficiency: Up to 93%
■
600mA Output Current (V
CC1
= 3V, V
OUT
= 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 V
CC
BATT
I
2
C
■
Standard (100kHz) or Fast Mode (400kHz)
■
24-Lead (4mm
×
4mm) QFN Package
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 I
2
C
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 I
2
C 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.
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.
I
2
C is a trademark of Philips Electronics N.V.
Protected by U.S. Patents, including 5481178, 6580258, 6304066, 6127815, 6498466,
6611131, Spread Spectrum patent pending.
TYPICAL APPLICATIO
V
CC
4.7µF
CER
V
BACKUP
V
CC1
V
TRACK
V
BACKUP
V
BACKUP
V
CC2
V
CC1
V
CC
BATT
2.2µH
PWR_EN
I
2
C BUS
V
CC
20k
nV
CC
_FAULT
V
CC1
OR GND
V
CC1
OR GND
ADD7
ADD6
PGOOD
GND
LDO1FB
LDO2
503k
LDO2FB
3445 TA01
20k
nBATT_FAULT
4.7µF
CER
4.7µF
CER
705k
604k
10µF
CER
1.1V
604k
10µF
CER
3V
TYP
BATTFAULT
3V
COIN
CELL
+
RUN
SDA
SCL
LTC3445
SW
FB
LDO1
EFFICIENCY (%)
0.85V
TO 1.55V
1.3V
U
Efficiency and Power Loss
vs Load Current, V
CC1
= 3.6V
100
90
80
70
60
50
40
30
20
10
0
0.1
1
10
100
LOAD CURRENT (mA)
0.1
1000
3445 TA01b
U
U
1000
EFFICIENCY
DAC MAX
DAC MIN
100
POWER LOSS (mW)
DAC MAX
10
DAC MIN
1.0
POWER LOSS
3445fa
1
LTC3445
ABSOLUTE
(Note 1)
AXI U
RATI GS
PACKAGE/ORDER I FOR ATIO
BATTFAULT
V
CC1
, V
CC2
, SDA, SCL Voltages .................. – 0.3V to 6V
RUN, V
TRACK
, V
BACKUP
, PGOOD, ADD7,
ADD6, FB, V
CC
BATT,
BATTFAULT Voltages .............................. – 0.3V to V
CC1
SW Voltage ................................ – 0.3V to (V
CC1
+ 0.3V)
LDO1FB, LDO2FB Voltages ..................... – 0.3V to V
CC2
LDO1, LDO2 Voltages ................ – 0.3V to (V
CC2
+ 0.3V)
LDO1, LDO2 Source Current ............................... 50mA
V
CC
BATT Source Current ...................................... 8mA
P-Channel Switch Source Current (DC) ............. 800mA
N-Channel Switch Sink Current (DC) ................. 800mA
Peak SW Sink and Source Current ........................ 1.3A
LDO1, LDO2, V
CC
BATT Output Short-Circuit
Duration .......................................................... Indefinite
Operating Temperature Range (Note 2) ...–40°C to 85°C
Junction Temperature (Note 3) ............................ 125°C
Storage Temperature Range ................. –65°C to 125°C
TOP VIEW
LDO2FB
LDO1FB
LDO2
LDO1
V
CC2
24 23 22 21 20 19
V
TRACK
1
V
BACKUP
2
V
CC1
3
PGOOD 4
ADD7 5
SDA 6
7
NC
18 V
CC
BATT
17 FB
16 NC
25
15 RUN
14 SW
13 NC
8
SCL
9 10 11 12
ADD6
GND
V
CC1
NC
UF PACKAGE
24-LEAD (4mm
×
4mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 37°C/W,
θ
JC
= 2.6°C/W
EXPOSED PAD (PIN 25) IS GND, MUST BE SOLDERED TO PCB
ORDER PART NUMBER
LTC3445EUF
UF PART MARKING
3445
Order Options
Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking:
http://www.linear.com/leadfree/
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
SYMBOL
V
CC1,
V
CC2
RUN
PGOOD
I
S
PARAMETER
Input Voltage Range
Run Threshold
Reports Undervoltage of any Regulator
DC Bias Current (Shutdown)
DC Bias Current (Buck, LDO1, LDO2 Disabled)
Buck Regulator
R
FB
V
OUT(MIN)
V
OUT(MAX)
V
OUT(STEP)
Feedback Resistance
Regulated Output Voltage
Regulated Output Voltage
Output Voltage Step Size (0 to 48)
Output Voltage Slew Rate = 00
Output Voltage Slew Rate = 01
Output Voltage Slew Rate = 10
Output Voltage Slew Rate = 11
I
PK
V
LOADREG
Peak Inductor Current
Output Voltage Load Regulation
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC1
= V
CC2
= 3.6V, unless otherwise noted.
CONDITIONS
●
●
MIN
2.5
0.3
3
TYP
1
27
105
340
MAX
5.5
1.5
50
150
UNITS
V
V
mA
µA
µA
kΩ
PGOOD = 0.4V
RUN = 0
RUN = V
CC1
●
I
OUT
= 100mA, Burst Mode Operation
Disabled
I
OUT
= 100mA, Burst Mode Operation
Disabled
I
OUT
= 100mA
I
OUT
= 100mA, V
OUT
= 0.85V to 1.55V
I
OUT
= 100mA, V
OUT
= 0.85V to 1.55V
I
OUT
= 100mA, V
OUT
= 0.85V to 1.55V
I
OUT
= 100mA, V
OUT
= 0.85V to 1.55V
V
CC1
= 3V, V
FB
= 0.5V or V
OUT
= 90%,
Duty Cycle < 35%
●
●
●
0.824
1.504
13.1
0.850
1.55
14.7
11.3
7.5
3.8
0.9
0.875
1.597
16.1
mV/µs
mV/µs
mV/µs
mV/µs
1.25
A
%
3445fa
0.75
1
0.5
2
U
V
V
mV
W
U
U
W W
W
LTC3445
ELECTRICAL CHARACTERISTICS
SYMBOL
I
S
PARAMETER
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC1
= V
CC2
= 3.6V, unless otherwise noted.
CONDITIONS
MIN
TYP
220
6
●
MAX
UNITS
µA
µA
Additional Input DC Bias Current For Buck (Note 4)
Active Mode
V
OUT
= 90%, I
LOAD
= 0A
Sleep Mode
V
OUT
= 103%, I
LOAD
= 0A
Nominal Oscillator Frequency
R
DS(ON)
of P-Channel FET
R
DS(ON)
of N-Channel FET
SW Leakage
Additional DC Bias for LDO1
Regulated Output Voltage
Line Regulation
Load Regulation
Dropout Voltage
2.5V < V
IN
< 5.5V, 1mA < I
LOAD
< 50mA
∆V
CC2
= 2.5V to 5.5V, I
LOAD
= 1mA, V
OUT
= 1.2V
V
CC2
= 2.5V,
∆I
LOAD
= 1mA to 50mA, V
OUT
= 1.2V
I
LOAD
= 50mA
I
LOAD
= 0mA
●
f
OSC
R
PFET
R
NFET
I
LSW
LDO1
I
S
V
OUT
V
OUT
= 100%
V
OUT
= 0V
I
SW
= 100mA
I
SW
= –100mA
V
RUN
= 0V, V
SW
= 0V or 5V, V
CC1
= 5V
1.2
1.5
300
0.45
0.325
1
23
1.8
MHz
kHz
Ω
Ω
µA
30
V
CC2
–
0.3
µA
V
mV
mV
V
V
µA
V
mV
mV
V
V
V
V
V
µA
V
mA
V
V
V
0.582
1
0.3
0.582
0.6
23
5
15
0.618
30
V
CC2
–
0.3
V
FB
LDO2
I
S
V
OUT
LDO Feedback Voltage
Additional DC Bias for LDO2
Regulated Output Voltage
Line Regulation
Load Regulation
Dropout Voltage
2.5V < V
IN
< 5.5V, 1mA < I
LOAD
< 50mA
∆V
CC2
= 2.5V to 5.5V, I
LOAD
= 1mA, V
OUT
= 1.2V
V
CC2
= 2.5V,
∆I
LOAD
= 1mA to 50mA, V
OUT
= 1.2V
I
LOAD
= 50mA
I
LOAD
= 0mA
●
0.582
1
0.3
0.582
3
0.6
5
15
0.618
V
CC1
–
0.2
V
FB
V
TRACK
V
TRACK
–
V
CC
BATT
V
BACKUP
I
BACKUP
V
CC
BATT
I
VCCBATT
LDO Feedback Voltage
Tracked Input Voltage
Tracked Output Voltage at V
CC
BATT
Backup Battery Voltage
Backup Battery Bias Current
V
CC
BATT Output
Max V
CC
BATT Output Current
PowerPath Controller
3V < V
TRACK
< V
CC1
– 0.2V
–0.2
2
0
0.2
5.5
V
CC1
= V
TRACK
= 0V, V
BACKUP
= 2.5V
V
TRACK
= 0V, V
CC1
= 4V, I
VCCBAT
= 8mA
V
CC1
= 2.5V
Where BATTFAULT Goes High
Where BATTFAULT Goes Low
V
CC1
= 0V to 4.2V, 4.2 to 0V
(Note 5)
(Note 5)
(Note 5)
2.65
2.4
2.85
4
3
8
2.8
2.5
0.3
6.5
3.1
2.9
2.6
BATTFAULT V
CC1
High Level (Good)
V
CC1
Low Level (Bad)
Hysteresis
I
2
C Interface
f
I2C(MAX)
t
BUF
t
HD(RSTA)
Maximum I
2
C Operating Frequency
Bus Free Time Between Stop and Start
Condition
Hold Time After (Repeated)
Start Condition
400
1.3
600
kHz
µs
ns
3445fa
3
LTC3445
ELECTRICAL CHARACTERISTICS
SYMBOL
t
SU(RSTA)
t
SU(STOP)
t
HD(DIN)
t
SU(DAT)
V
THR
V
HYS
I
LVTRACK
I
LVBACKUP
I
LADD7
I
LADD6
I
LSCL
I
LSDA
I
LLDO1
I
LLDO2
I
LLDO1FB
I
LLDO2FB
I
LBATTFAULT
I
FB1,2
PARAMETER
Repeated Start Condition Setup Time
Stop Condition Setup Time
Data Hold Time, Input
Data Setup Time
SCL and SDA Logic Input Threshold
SCL and SDA Logic Input Hysteresis
V
TRACK
Leakage
V
BACKUP
Leakage
ADD7 Leakage
ADD6 Leakage
SCL Leakage
SCL Leakage
LDO1 Leakage
LDO2 Leakage
LDO1FB Leakage
LDO2FB Leakage
BATTFAULT Leakage
LDO Feedback Input Current
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC1
= V
CC2
= 3.6V, unless otherwise noted.
CONDITIONS
(Note 5)
(Note 5)
(Note 5)
(Note 5)
1.8
(Note 5)
V
CC
= 3.6V
V
CC
= 3.6V
V
CC
= 3.6V
V
CC
= 3.6V
V
CC
= 3.6V
V
CC
= 3.6V
V
CC
= 3.6V, RUN = 0
V
CC
= 3.6V, RUN = 0
V
CC
= 3.6V, RUN = 0
V
CC
= 3.6V, RUN = 0
V
CC
= 3.6V
V
FB1
= 0.6V
●
●
●
●
●
●
●
●
●
●
●
MIN
TYP
MAX
600
600
0
100
UNITS
ns
ns
ns
ns
V
mV
50
1.44
2.2
1
1
1
1
1
1
1
1
1
1
1
µA
µA
µA
µA
µA
µA
µA
µA
µA
µA
µA
µA
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The LTC3445EUF is guaranteed to meet performance specifica-
tions from 0°C to 70°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
Note 3:
T
J
is calculated from the ambient temperature, T
A
, and power
dissipation, P
D
, according to the following formula:
T
J
= T
A
+ P
D
• 37°C/W
Note 4:
Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency.
Note 5:
Determined by design, not production tested.
TYPICAL PERFOR A CE CHARACTERISTICS
Supply Current vs Supply Voltage
500
1.6
1.5
400
SUPPLY CURRENT (µA)
1.4
V
OUT
(V)
V
OUT(N)
– V
OUT(N–1)
(V)
ALL ON
BUCK
ONE LDO
TWO LDOs
RUN = HIGH
RUN = LOW
2.8
4.4 4.8
3.2 3.6 4
SUPPLY VOLTAGE (V)
5.2 5.6
3445 G01
300
200
100
0
2.4
4
U W
V
OUT
vs DAC
0mA
600mA
V
OUT
Step Size vs DAC
0.016
0.014
100mA
0.012
0.010
0.008
0.006
0.004
0.002
0
–0.002
1.3
1.2
1.1
1.0
0.9
0.8
0
10
20
30 40 50
DAC VALUE
60
70
80
0
10
20
30 40 50
DAC VALUE
60
70
80
3445 G02
3445 G03
3445fa
LTC3445
TYPICAL PERFOR A CE CHARACTERISTICS
Buck Efficiency and Power Loss
vs Load Current, V
CC1
= 2.5V
100
90
80
70
DAC MIN
DAC MAX
100
EFFICIENCY
1000
100
90
80
70
EFFICIENCY (%)
60
50
40
30
20
10
0
0.1
1
10
100
LOAD CURRENT (mA)
0.1
1000
3445 G04
60
50
40
30
20
10
0
0.1
1
DAC MAX
DAC MIN
10
100
LOAD CURRENT (mA)
0.1
1000
3445 G05
DAC MAX
POWER LOSS
10
BUCK OUTPUT (V)
EFFICIENCY (%)
DAC MIN
Buck Output Voltage
vs Load Current
1.580
1.560
DAC = MAX
V
CC2
LEAKAGE CURRENT (µA)
1.2
1.0
0.8
0.6
0.4
0.2
1.540
1.520
1.500
1.480
1.460
–100
V
CC2
LEAKAGE CURRENT (µA)
BUCK OUTPUT (V)
100
500
700
300
LOAD CURRENT (mA)
R
DS(ON)
vs Input Voltage
600
550
500
R
DS(ON)
(mΩ)
R
DS(ON)
(mΩ)
450
400
350
300
250
2.2 2.6
3
3.4 3.8 4.2 4.6
INPUT VOLTAGE (V)
5
5.4 5.8
3445 G10
500
R
DS(ON)
(mΩ)
MAIN SWITCH
SYNCHRONOUS SWITCH
U W
900
Buck Efficiency and Power Loss
vs Load Current, V
CC1
= 4.2V
1000
EFFICIENCY
DAC MAX
DAC MIN
100
POWER LOSS (mW)
Buck Output Voltage
vs Load Current
0.900
DAC = MIN
0.850
POWER LOSS (mW)
10
0.800
1.0
POWER LOSS
1.0
0.750
0.700
–100
100
500
700
300
LOAD CURRENT (mA)
900
3445 G06
I
VCC2
vs Temperature (RUN = V
CC1
)
V
CC2
= 2.5V
V
CC2
= 3.6V
V
CC2
= 4.2V
V
CC2
= 5.5V
1.2
1.0
0.8
0.6
0.4
0.2
I
VCC2
vs Temperature (RUN = 0V)
V
CC2
= 2.5V
V
CC2
= 3.6V
V
CC2
= 4.2V
V
CC2
= 5.5V
0
–50
–10
30
70
110
TEMPERATURE (°C)
150
3445 G08
0
–50
–10
30
70
110
TEMPERATURE (°C)
150
3445 G09
3445 G07
Synchronous Switch R
DS(ON)
vs Temperature
700
V
CC1
= 2.5V
V
CC1
= 3.6V
V
CC1
= 4.2V
V
CC1
= 5.5V
800
Main Switch R
DS(ON)
vs Temperature
V
CC1
= 2.5V
V
CC1
= 3.6V
V
CC1
= 4.2V
V
CC1
= 5.5V
600
700
600
400
500
300
400
200
–40 –20 0
20 40 60 80 100 120 140
TEMPERATURE (°C)
3445 G11
300
–40 –20 0
20 40 60 80 100 120 140
TEMPERATURE (°C)
3445 G12
3445fa
5
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