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LTC3557
Technical data
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LINEAR TECHNOLOGY LTC3557, LTC3557-1 Technical data

LTC3557/LTC3557-1
y
USB Power Manager with
Step-Down Regulators
FEATURES
■
Seamless Transition Between Input Power Sources:
Li-Ion Battery, USB, 5V Wall Adapter or High Voltage Buck Regulator with Bat-Track
■
200mΩ Internal Ideal Diode Plus Optional External
TM
Ideal Diode Controller Provides Low Loss Power Path When Input Current is Limited or Unavailable
■
Triple Adjustable High Effi ciency Step-Down
Switching Regulators (600mA, 400mA, 400mA I
■
Pin Selectable Burst Mode® Operation
■
Full Featured Li-Ion/Polymer Battery Charger
■
1.5A Maximum Charge Current with Thermal Limiting
■
Battery Float Voltage:
OUT
4.2V (LTC3557)
4.1V (LTC3557-1)
■
Low Profi le 4mm × 4mm 28-Pin QFN Package
APPLICATIONS
■
HDD-Based MP3 Players
■
PDA, PMP, PND/GPS
■
USB-Based Handheld Products
DESCRIPTION
The LTC®3557/LTC3557-1 is a highly integrated power management and battery charger IC for single cell Li-Ion/ Polymer battery applications. It includes a PowerPath manager with automatic load prioritization, a battery charger, an ideal diode and numerous internal protection features. Designed specifi cally for USB applications, the LTC3557/LTC3557-1 power manager automatically limits
)
input current to a maximum of either 100mA or 500mA for USB applications or 1A for wall adapter powered applications. Battery charge current is automatically reduced such that the sum of the load current and the charge current does not exceed the programmed input current limit. The LTC3557/LTC3557-1 also includes three adjustable synchronous step-down switching regulators and a high voltage buck regulator output controller with Bat-Track that allows effi cient charging from supplies as high as 38V. The LTC3557/LTC3557-1 is available in a low profi le 4mm × 4mm × 0.75mm 28-pin QFN package.
, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology Corporation. Bat-Track and PowerPath are trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Protected b
U.S. Patents, including 6522118, 6700364. Other patents pending.
TM
TYPICAL APPLICATION
HV SUPPLY
8V TO 38V
(TRANSIENTS
TO 60V)
USB OR
5V ADAPTER
CHARGE
RST
HIGH VOLTAGE
BUCK DC/DC
100mA/500mA
1000mA
CC/CV
CHARGER
LTC3557/LTC3557-1
ALWAYS ON LDO
TRIPLE HIGH EFFICIENCY
STEP-DOWN
SWITCHING REGULATORS
0V
NTC
35571 TA01a
V
OUT
+
SINGLE CELL Li-Ion
3.3V/25mA
0.8V to 3.6V/600mA
0.8V to 3.6V/400mA
0.8V to 3.6V/400mA
Input and Battery Current vs Load Current
600
R
= 2k
PROG
R
CLPROG
500
400
300
200
CURRENT (mA)
100
0
WALL = 0V
–100
0
= 2k
100 200
I
IN
I
BAT
(CHARGING)
(DISCHARGING)
400 600
300 500
I
(mA)
LOAD
I
LOAD
I
BAT
35571 TA01b
35571fc
1
LTC3557/LTC3557-1
ABSOLUTE MAXIMUM RATINGS
(Notes 1-4)
V
, V
, V
BUS
OUT
IN1
, V
IN2
t < 1ms and Duty Cycle < 1% .................. −0.3V to 7V
Steady State ............................................. −0.3V to 6V
BAT, NTC, CHRG, WALL, V
,
C
MODE, FB1, FB2, FB3, RST2 ........................ −0.3V to 6V
EN1, EN2, EN3 .............................. −0.3V to V
ILIM0, ILIM1, PROG ....................... −0.3V to V
, I
, I
I
VBUS
VOUT
.....................................................................850mA
I
SW1
, I
I
SW2
SW3
, I
I
RST2
CHRG
I
CLPROG
, I
PROG
.........................................................2A
BAT
............................................................600mA
, I
.................................................75mA
ACPR
..........................................................2mA
OUT
CC
+ 0.3V + 0.3V
Maximum Operating Junction Temperature ..........110°C
Operating Ambient Temperature Range ... −40°C to 85°C
Storage Temperature Range ...................−65°C to 125°C
ORDER INFORMATION
PIN CONFIGURATION
TOP VIEW
CHRG
CLPROG
28 27 26 25 24 23
1
ILIM0
ILIM1
2
WALL
3
LDO3V3
4
SW1
5
V
6
IN1
FB1
7
8 9
10
EN1
MODE
28-LEAD (4mm s 4mm) PLASTIC QFN
EXPOSED PAD (PIN 29) IS GND, MUST BE SOLDERED TO PCB
UF PACKAGE
T
= 110°C, θJA = 37°C/W
JMAX
BUSVOUT
VCACPR
V
29
11 12 13 14
FB3
EN2
EN3
FB2
22
BAT
RST2
GATE
21
PROG
20
NTC
19
V
18
NTC
SW3
17
V
16
IN2
SW2
15
LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE
LTC3557EUF#PBF LTC3557EUF#TRPBF 3557
LTC3557EUF-1#PBF LTC3557EUF-1#TRPBF 35571
Consult LTC Marketing for parts specifi ed with wider operating temperature ranges. Consult LTC Marketing for information on non-standard lead based fi nish parts.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifi cations, go to: http://www.linear.com/tapeandreel/
28-Lead (4mm × 4mm) Plastic QFN −40°C to 85°C 28-Lead (4mm × 4mm) Plastic QFN −40°C to 85°C
POWER MANAGER ELECTRICAL CHARACTERISTICS
The ● denotes the specifi cations which apply over the full operating temperature range, otherwise specifi cations are at TA = 25°C. V
= 5V, V
BUS
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Input Power Supply
V
BUS
I
BUS(LIM)
I
BUSQ
h
CLPROG
V
CLPROG
V
UVLO
= 3.8V, ILIM0 = ILIM1 = 5V, WALL = EN1 = EN2 = EN3 = 0V, R
BAT
Input Supply Voltage 4.35 5.5 V
Total Input Current (Note 5) ILIM0 = 0V, ILIM1 = 0V (1x Mode)
Input Quiescent Current 1x, 5x, 10x Modes
Ratio of Measured V Program Current
CLPROG Servo Voltage in Current Limit 1x Mode
V
Undervoltage Lockout Rising Threshold
BUS
Current to CLPROG
BUS
ILIM0 = 5V, ILIM1 = 5V (5x Mode) ILIM0 = 5V, ILIM1 = 0V (10x Mode)
ILIM0 = 0V, ILIM1 = 5V (Suspend Mode)
1x, 5x, 10x Modes 1000 mA/mA
5x Mode 10x Mode
Falling Threshold
PROG
= 2k, R
CLPROG
●
●
= 2.1k.
80 450 900
3.5
90 475 950
0.35
0.05 0.1
0.2
1.0
2.0
3.8
3.7
100 500
1000
3.9 V
mA mA mA
mA mA
35571fc
V V V
V
2
LTC3557/LTC3557-1
POWER MANAGER ELECTRICAL CHARACTERISTICS
The ● denotes the specifi cations which apply over the full operating temperature range, otherwise specifi cations are at TA = 25°C. V
= 5V, V
BUS
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
V
DUVLO
R
ON_LIM
Battery Charger
V
FLOAT
I
CHG
I
BAT
V
PROG
V
PROG(TRKL)
h
PROG
I
TRKL
V
TRKL
ΔV
RECHRG
t
TERM
t
BADBAT
End-of-Charge Indication Current Ratio (Note 6) 0.085 0.1 0.115 mA/mA
h
C/10
R
ON(CHG)
T
LIM
NTC
V
COLD
V
HOT
V
DIS
I
NTC
= 3.8V, ILIM0 = ILIM1 = 5V, WALL = EN1 = EN2 = EN3 = 0V, R
BAT
V
to V
BUS
Lockout
Differential Undervoltage
OUT
Rising Threshold Falling Threshold
PROG
Input Current Limit Power FET On-Resistance (Between V
V
Regulated Output Voltage LTC3557
BAT
BUS
and V
OUT
)
LTC3557, 0°C ≤ T
≤ 85°C
A
LTC3557-1
Constant Current Mode Charge Current R
Battery Drain Current V
LTC3557-1, 0°C ≤ T
= 1k, Input Current Limit = 2A
PROG
R
= 2k, Input Current Limit = 1A
PROG
R
= 5k, Input Current Limit = 400mA
PROG
> V
BUS
UVLO
V
= 0V, I
BUS
≤ 85°C
A
, Charger Off, I
= 0µA (Ideal Diode Mode)
OUT
OUT
PROG Pin Servo Voltage PROG Pin Servo Voltage in Trickle Charge BAT < V
Ratio of I
to PROG Pin Current 1000 mA/mA
BAT
Trickle Charge Current BAT < V
Trickle Charge Rising Threshold Trickle Charge Falling Threshold
TRKL
TRKL
BAT Rising BAT Falling 2.5
Recharge Battery Threshold Voltage Threshold Voltage Relative to V
Safety Timer Termination Period Timer Starts when BAT = V
Bad Battery Termination Time BAT < V
TRKL
FLOAT
Battery Charger Power FET On-Resistance (Between V
and BAT)
OUT
Junction Temperature in Constant Temperature Mode
Cold Temperature Fault Threshold Voltage Rising NTC Voltage
Hysteresis
Hot Temperature Fault Threshold Voltage Falling NTC Voltage
Hysteresis
NTC Disable Threshold Voltage Falling NTC Voltage
Hysteresis
NTC Leakage Current NTC = V
BUS
= 5V
= 2k, R
CLPROG
= 2.1k.
50
100 mV
−50
0.2
= 0µA
4.179
4.165
4.079
4.065
●
950
●
465
●
180
4.200
4.200
4.100
4.100
1000
500 200
6
55
4.221
4.235
4.121
4.135
1050
535 220
27
100
1.000
0.100
40 50 60 mA
2.85
3.0 V
2.75
FLOAT
−75 −100 −115
– 50mV 3.2 4 4.8 Hour
0.4 0.5 0.6 Hour
200 m
110 °C
●
75 76
1.3
34 35
1.3
1.2 1.7
77 %V
%V
36 %V
%V
2.2 %V
VNTC VNTC
VNTC VNTC
VNTC
50
−50
50 nA
mV
mA mA mA
µA µA
mV
mV
V V V V
V V
V
Ideal Diode
V
FWD
R
DROPOUT
I
MAX
Forward Voltage Detection I
Diode On-Resistance, Dropout I
Diode Current Limit (Note 7) 3.6 A
Always On 3.3V Supply
V
LDO3V3
R
OL(LDO3V3)
R
CL(LDO3V3)
Regulated Output Voltage 0mA < I
Open-Loop Output Resistance BAT = 3.0V, V
Closed-Loop Output Resistance 3.2
= 10mA 5 15 25 mV
OUT
= 1A 200 m
OUT
< 25mA 3.1 3.3 3.5 V
LDO3V3
= 0V 24
BUS
35571fc
3
LTC3557/LTC3557-1
POWER MANAGER ELECTRICAL CHARACTERISTICS
The ● denotes the specifi cations which apply over the full operating temperature range, otherwise specifi cations are at TA = 25°C. V
= 5V, V
BUS
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Wall Adapter
V
ACPR
V
W
ΔV
W
I
QWALL
Logic (I
LIM0
V
IL
V
IH
I
PD
V
CHRG
I
CHRG
= 3.8V, ILIM0 = ILIM1 = 5V, WALL = EN1 = EN2 = EN3 = 0V, R
BAT
ACPR Pin Output High Voltage ACPR Pin Output Low Voltage
I
ACPR
I
ACPR
= 1mA = 1mA
Absolute Wall Input Threshold Voltage WALL Rising
WALL Falling 3.1
Differential Wall Input Threshold Voltage
WALL − BAT Falling WALL − BAT Rising
Wall Operating Quiescent Current
, I
and CHRG)
LIM1
I
+ I
WALL
WALL = V
VOUT
OUT
, I
= 5V
BAT
= 0mA,
PROG
= 2k, R
CLPROG
= 2.1k.
V
− 0.3
OUT
025
V
440 µA
OUT
0 0.3
4.3
4.45 V
3.2
75 150
Input Low Voltage ILIM0, ILIM1 0.4 V
Input High Voltage ILIM0, ILIM1 1.2 V
Static Pull-Down Current ILIM0, ILIM1; V CHRG Pin Output Low Voltage I
= 10mA 0.15 0.4 V
CHRG
= 1V 2 µA
PIN
CHRG Pin Input Current BAT = 4.5V, CHRG = 5V 0 1 µA
mV mV
V V
V
SWITCHING REGULATOR ELECTRICAL CHARACTERISTICS
The ● denotes the specifi cations which apply over the full operating temperature range, otherwise specifi cations are at TA = 25°C. V
= V
= V
OUT
IN1
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Step-Down Switching Regulators 1, 2 and 3
, V
V
IN1
IN2
V
UVL0 V
OUT
f
OSC
V
IL
V
IH
I
PD
Step-Down Switching Regulator 1
I
VIN1
I
LIM1
V
FB1
I
FB1
D1 Maximum Duty Cycle FB1 = 0V, EN1 = 3.8V 100 %
R
P1
R
N1
R
SW1(PD)
= 3.8V, MODE = EN1 = EN2 = EN3 = 0V.
IN2
Input Supply Voltage (Note 9)
V
OUT OUT
Falling Rising
and V
V
IN1
Impedance. Switching Regulators are Disabled Below V
Connected to V
IN2
UVLO
OUT
Through Low
OUT
●
2.7 5.5 V
2.5 2.7
2.8 2.9
Oscillator Frequency 1.91 2.25 2.59 MHz
Input Low Voltage MODE, EN1, EN2, EN3 0.4 V
Input High Voltage MODE, EN1, EN2, EN3 1.2 V
Static Pull-Down Current MODE, EN1, EN2, EN3 (V
Pulse-Skip Mode Input Current (Note 10) I
Burst Mode Input Current (Note 10) I
Shutdown Input Current I
= 0, EN1 = 3.8V, MODE = 0V 220 µA
OUT
= 0, EN1 = MODE = 3.8V 35 50 µA
OUT
= 0, EN1 = 0V, FB1 = 0V 0.01 1 µA
OUT
= 1V) 1 µA
PIN
Peak PMOS Current Limit EN1 = 3.8V, MODE = 0V or 3.8V (Note 7) 900 1200 1500 mA
Feedback Voltage EN1 = 3.8V, MODE = 0V
EN1 = MODE = 3.8V
FB1 Input Current (Note 10) EN1 = 3.8V
R
of PMOS EN1 = 3.8V 0.3
DS(ON)
R
of NMOS EN1 = 3.8V 0.4
DS(ON)
●
0.78
●
0.78
−0.05
0.8
0.8
0.82
0.824
0.05 µA
SW1 Pull-Down in Shutdown EN1 = 0V 10 k
V V
V V
4
35571fc
LTC3557/LTC3557-1
SWITCHING REGULATOR ELECTRICAL CHARACTERISTICS
The ● denotes the specifi cations which apply over the full operating temperature range, otherwise specifi cations are at TA = 25°C. V
= V
= V
OUT
IN1
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Step-Down Switching Regulator 2
I
VIN2
I
LIM2
V
FB2
I
FB2
D2 Maximum Duty Cycle FB2 = 0V, EN2 = 3.8V 100 %
R
P2
R
N2
R
SW2(PD)
V
RST2
I
RST2
V
TH(RST2)
t
RST2
Step-Down Switching Regulator 3
I
VIN2
I
LIM3
V
FB3
I
FB3
D3 Maximum Duty Cycle FB3 = 0V, EN3 = 3.8V 100 %
R
P3
R
N3
R
SW3(PD)
= 3.8V, MODE = EN1 = EN2 = EN3 = 0V.
IN2
Pulse-Skip Mode Input Current (Note 10) I
Burst Mode Input Current (Note 10) I
Shutdown Input Current I
= 0, EN2 = 3.8V, MODE = 0V 220 µA
OUT
= 0, EN2 = MODE = 3.8V 35 50 µA
OUT
= 0, EN2 = 0V, FB2 = 0V 0.01 1 µA
OUT
Peak PMOS Current Limit EN2 = 3.8V, MODE = 0V or 3.8V (Note 7) 600 800 1000 mA
Feedback Voltage EN2 = 3.8V, MODE = 0V
EN2 = MODE = 3.8V
FB2 Input Current (Note 10) EN2 = 3.8V
R
of PMOS EN2 = 3.8V 0.6
DS(ON)
R
of NMOS EN2 = 3.8V 0.6
DS(0N)
SW2 Pull-Down in Shutdown EN2 = 0V 10 Power-On RST2 Pin Output Low Voltage I Power-On RST2 Pin Input Current (Note 10) V
= 1mA, FB2 = 0V, EN2 = 3.8V 0.1 0.35 V
RST2
= 5.5V, EN2 = 3.8V 1 µA
RST2
Power-On RST2 Pin Threshold (Note 8)
●
0.78
●
0.78
−0.05
0.8
0.8
0.82
0.824
0.05 µA
kΩ
−8
Power-On RST2 Pin Delay From RST2 Threshold to RST2 Hi-Z 230 ms
Pulse-Skip Mode Input Current (Note 10) I
Burst Mode Input Current (Note 10) I
Shutdown Input current I
= 0, EN3 = 3.8V, MODE = 0V 220 µA
OUT
= 0, EN3 = MODE = 3.8V 35 50 µA
OUT
= 0, EN3 = 0V, FB3 = 0V 0.01 1 µA
OUT
Peak PMOS Current Limt EN3 = 3.8V, MODE = 0V or 3.8V (Note 7) 600 800 1000 mA
Feedback Voltage EN3 = 3.8V, MODE = 0V
EN3 = MODE = 3.8V
FB3 Input Current (Note 10) EN3 = 3.8V
R
of PMOS EN3 = 3.8V 0.6
DS(ON)
R
of NMOS EN3 = 3.8V 0.6
DS(ON)
●
0.78
●
0.78
−0.05
0.8
0.8
0.82
0.824
0.05 µA
SW3 Pull-Down in Shutdown EN3 = 0V 10 k
V V
Ω Ω
%
V V
Note 1. Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime.
Note 2. The LTC3557/LTC3557-1 is guaranteed to meet performance specifi cations from 0°C to 85°C. Specifi cations over the −40°C to 85°C operating temperature range are assured by design, characterization and correlation with statistical process controls.
Note 3. This IC includes overtemperature protection that is intended to protect the device during momentary overload conditions. Junction temperatures will exceed 110°C when overtemperature protection is active. Continuous operation above the specifi ed maximum operating junction temperature may result in device degradation or failure.
Note 4. V
is the greater of V
CC
BUS
, V
OUT
or BAT.
Note 5. Total input current is the sum of quiescent current, I measured current given by V
Note 6. h
is expressed as a fraction of measured full charge current
C/10
CLPROG/RCLPROG
• (h
CLPROG
+ 1)
BUSQ
, and
with indicated PROG resistor. Note 7. The current limit features of this part are intended to protect the
IC from short term or intermittent fault conditions. Continuous operation above the maximum specifi ed pin current rating may result in device degradation or failure.
Note 8. RST2 threshold is expressed as a percentage difference from the FB2 regulation voltage. The threshold is measured for FB2 rising.
Note 9. V
not in UVLO.
OUT
Note 10. FB high, not switching.
35571fc
5
LTC3557/LTC3557-1
TYPICAL PERFORMANCE CHARACTERISTICS
= 25°C unless otherwise specifi ed
T
A
Input Supply Current vs Temperature
0.8 V
= 5V
BUS
1x MODE
0.7
0.6
0.5
(mA)
0.4
VBUS
I
0.3
0.2
0.1
0
–25 0 50
–50
TEMPERATURE (°C)
Input Current Limit vs Temperature
1200
V
= 5V
BUS
1100
1000
900
800
700
(mA)
600
500
VBUS
I
400
300
200
100
0
–50
R
CLPROG
–25
= 2.1k
0
TEMPERATURE (°C)
Input Supply Current vs Temperature (Suspend Mode)
0.10 V
= 5V
BUS
0.08
0.06
(mA)
VBUS
0.04
I
0.02
0
25
75 100 125
35571 G01
–50 –25
0
TEMPERATURE (°C)
50
25
75
100
125
35571 G02
Battery Drain Current vs Temperature
0.20
0.18
2 BUCKS ENABLED
0.16
0.14
0.12
(mA)
0.10
BAT
I
0.08
0.06
0.04
V
BAT
MODE = 3.8V
0
–50
= 3.8V
–25
0
TEMPERATURE (°C)
0.02
3 BUCKS ENABLED
1 BUCK ENABLED
N0 BUCKS ENABLED
50
25
100
125
35571 G03
75
Charge Current vs Temperature
Input RON vs Temperature
300
I
= 400mA
OUT
10x MODE
5x MODE
1x MODE
50
25
75
100
125
35571 G04
280
260
240
220
180
(m)
ON
R
160
140
120
100
V
= 4.5V
BUS
V
= 5V
BUS
V
= 5.5V
BUS
0
–50
0
–25
TEMPERATURE (°C)
50
25
75
100
125
35571 G05
(Thermal Regulation)
600
500
400
(mA)
300
BAT
I
200
V
= 5V
BUS
100
10x MODE
= 2k
R
PROG
0
–50
–25 0
TEMPERATURE (°C)
50 100 125
25 75
35571 G06
Battery Current and Voltage vs Time (LTC3557)
600
500
400
(mA)
300
BAT
I
200
1450mAhr CELL
= 5V
V
100
BUS
= 2k
R
PROG
= 2k
R
CLPROG
0
0
234
1
6
C/10
TIME (HOUR)
CHRG
V
BAT
SAFETY
TIMER
TERMINATION
I
BAT
56
35571 G07
Battery Regulation (Float)
V
Load Regulation
6
5
V
BAT
4
AND V
3
CHRG
(V)
2
1
0
4.22
4.20
4.18
4.16
(V)
4.14
FLOAT
V
4.12
4.10
4.08
4.06
FLOAT
LTC3557
LTC3557-1
200 400 800
0
I
BAT
(mA)
600
V
= 5V
BUS
10x MODE
35571 G08
1000
Voltage vs Temperature
4.22 I
= 2mA
BAT
4.20
4.18
4.16
(V)
4.14
FLOAT
V
4.12
4.10
4.08
4.06
–50
–25
0
TEMPERATURE (°C)
25
LTC3557
LTC3557-1
50
75
100
125
35571 G09
35571fc
TYPICAL PERFORMANCE CHARACTERISTICS
Forward Voltage vs Ideal Diode
I
600
500
400
(mA)
300
BAT
I
200
100
vs V
BAT
0
2.0
BAT
2.8 3.2 3.6
2.4
V
BUS
10x MODE R
PROG
R
CLPROG
V
(V)
BAT
= 5V
= 2k
= 2k
4.0 4.4
35571 G10
Current (No External FET)
0.25 V
= 0V
BUS
= 25°C
T
A
(V)
FWD
V
0.20
0.15
0.10
0.05
0
0
V
BAT
0.4 0.6 0.8
0.2
= 3.6V
I
BAT
V
(A)
BAT
= 3.2V
V
BAT
LTC3557/LTC3557-1
T
= 25°C unless otherwise specifi ed
A
Forward Voltage vs Ideal Diode Current (with Si2333DS External FET)
40
V
= 3.8V
BAT
= 0V
V
BUS
35
= 25°C
T
A
30
= 4.2V
1.0 1.2
35571 G11
(mV)
FWD
V
25
20
15
10
5
0
0.2 0.4 0.8
0
0.6
I
(A)
BAT
1.0
35571 G12
Input Connect Waveform
V
BUS
5V/DIV
V
OUT
5V/DIV
I
BUS
0.5A/DIV
I
BAT
0.5A/DIV
V
BAT
I
OUT
R
CLPROG
R
PROG
= 3.75V
= 100mA
= 2k
1ms/DIV
= 2k
Switching from Suspend Mode to 5x Mode
ILIM0
5V/DIV
V
OUT
5V/DIV
I
BUS
0.5A/DIV
I
BAT
0.5A/DIV
35571 G25
Input Disconnect Waveform
V
BUS
5V/DIV
V
OUT
5V/DIV
I
BUS
0.5A/DIV
I
BAT
0.5A/DIV
V
= 3.75V
BAT
= 100mA
I
OUT
= 2k
R
CLPROG
= 2k
R
PROG
WALL Connect Waveform
WALL
5V/DIV
V
OUT
5V/DIV
I
WALL
0.5A/DIV
I
BAT
0.5A/DIV
1ms/DIV
35571 G26
ILIM0/ILIM1
5V/DIV
I
BUS
0.5A/DIV
I
BAT
0.5A/DIV
WALL
5V/DIV
V
OUT
5V/DIV
I
WALL
0.5A/DIV
I
0.5A/DIV
Switching from 1x to 5x Mode
V
BAT
I
OUT
R
CLPROG
R
PROG
= 3.75V = 50mA
= 2k
1ms/DIV
= 2k
WALL Disconnect Waveform
BAT
35571 G27
V
= 3.75V
BAT
= 100mA
I
OUT
R
CLPROG
= 2k
R
PROG
ILIM1 = 5V
= 2k
100µs/DIV
35571 G28
V I R
BAT
OUT
PROG
= 3.75V
= 100mA
= 2k
1ms/DIV
35571 G29
V I R
BAT
OUT
PROG
= 3.75V
= 100mA
= 2k
1ms/DIV
35571 G30
35571fc
7
LTC3557/LTC3557-1
0
0
0
5
TYPICAL PERFORMANCE CHARACTERISTICS
Oscillator Frequency vs Temperature
2.5
2.4
2.3
2.2
2.1
2.0
(MHz)
OSC
1.9
f
1.8
1.7
1.6
1.5 –50
–25
VIN = 2.9V
50
25
0
TEMPERATURE (°C)
Step-Down Switching Regulator 3
1.8V Output Effi ciency vs I
100
90
Burst Mode
80
OPERATION
70
60
50
40
EFFICIENCY (%)
30
20
10
0
0.01
0.1 1 10 100 100 I
OUT3
PULSE SKIP
(mA)
VIN = 3.8V
VIN = 5V
VIN = 2.7V
75
OUT3
V
OUT3
V
IN3
V
IN3
100
35571 G13
= 1.8V
= 3.8V = 5V
35571 G16
125
Step-Down Switching Regulator 1
3.3V Output Effi ciency vs I
100
Burst Mode
90
OPERATION
80
70
60
50
40
EFFICIENCY (%)
30
20
10
0
0.01
0.1 1 10 100 100 I
OUT1
PULSE SKIP
(mA)
Step-Down Switching Regulator Pulse Skip Supply Current vs V
400
V
= 1.2V
OUTX
= 0mA
I
OUTX
350
300
250
(µA)
IN
I
200
150
100
2.5
3.0 3.5 4.0 4.5 V
(V)
INX
V
OUT1
V V
TA = 25°C unless otherwise specifi ed
Step-Down Switching Regulator 2
OUT1
= 3.3V = 3.8V
IN1
= 5V
IN1
35571 G14
1.2V Output Effi ciency vs I
100
90
Burst Mode
80
OPERATION
70
60
50
40
EFFICIENCY (%)
30
20
10
0
0.01
0.1 1 10 100 100
Step-Down Switching Regulator Short-Circuit Current
INX
110°C
75°C
25°C
–45°C
5.0
vs Temperature
1200
1100
1000
900
800
700
600
SHORT-CIRCUIT CURRENT (mA)
500
400
–25 0 50
–50
TEMPERATURE (°C)
PULSE SKIP
I
(mA)
OUT2
600mA BUCK
400mA BUCK
25
OUT2
V
= 1.2V
OUT2
V
= 3.8V
IN2
= 5V
V
IN2
35571 G15
75 100 125
35571 G18
50mV/DIV
50mV/DIV
I
OUT2
8
Step-Down Switching Regulator Output Transient (MODE = 1)
V
OUT2
(AC)
V
OUT3
(AC)
300mA
5mA
V I
OUT3
OUT2 OUT3
= 1.2V = 1.8V
= 16mA
50µs/DIVV
35571 G1
50mV/DIV
50mV/DIV
I
OUT2
Step-Down Switching Regulator Output Transient (MODE = 0)
V
OUT2
(AC)
V
OUT3
(AC)
300mA
5mA
V I
OUT3
OUT2 OUT3
= 1.2V = 1.8V
= 100mA
50µs/DIVV
0.9
0.8
0.7
0.6
0.5
0.4
0.3
SWITCH IMPEDANCE ()
35571 G2
0.2
0.1
Step-Down Switching Regulator Switch Impedance vs Temperature
V
= 3.2V
INX
400mA
400mA
NMOS
0
–50
–25
PMOS
600mA NMOS
0
25 12
TEMPERATURE (°C)
50
600mA PMOS
75 100
35571 G21
35571fc
LTC3557/LTC3557-1
4
TYPICAL PERFORMANCE CHARACTERISTICS
600mA Step-Down Switching Regulator Feedback Voltage vs Output Current
0.85
0.84
0.83
0.82
0.81
0.80
0.79
FEEDBACK (V)
0.78
0.77
0.76
0.75
0.1 10 100 1000
Burst Mode OPERATION
PULSE SKIP
1 OUTPUT CURRENT (mA)
3.8V 5V
35571 G22
400mA Step-Down Switching Regulator Feedback Voltage vs Output Current
0.85
0.84
0.83
0.82
0.81
0.80
0.79
FEEDBACK (V)
0.78
0.77
0.76
0.75
0.1 10 100 1000
Burst Mode
OPERATION
PULSE SKIP
1 OUTPUT CURRENT (mA)
PIN FUNCTIONS
TA = 25°C unless otherwise specifi ed
Step-Down Switching Regulator Start-Up Waveform
V
OUT2
50mV/DIV(AC)
V
OUT1
1V/DIV
0V
I
L1
200mA/DIV
0mA
EN1
3.8V 5V
35571 G23
= 1.2V
OUT2
= 50mA
I
OUT2
MODE = 1
= 8
R
OUT1
100µs/DIVV
35571 G2
ILIM0, ILIM1 (Pins 1, 2): Input Current Control Pins. ILIM0 and ILIM1 control the input current limit. See Table 1. Both pins are pulled low by a weak current sink.
WALL (Pin 3): Wall Adapter Present Input. Pulling this pin above 4.3V will disconnect the power path from V
. The ACPR pin will also be pulled low to indicate that a
V
OUT
BUS
to
wall adapter has been detected.
LDO3V3 (Pin 4): Always On 3.3V LDO Output. The LDO3V3 pin provides a regulated, always-on 3.3V supply voltage. This pin gets its power from V
. It may be used
OUT
for light loads such as a real-time clock or housekeeping microprocessor. A 1µF capacitor is required from LDO3V3 to ground if it will be called upon to deliver current. If the LDO3V3 output is not used it should be disabled by connecting it to V
OUT
.
SW1 (Pin 5): Power Transmission (Switch) Pin for Step-Down Switching Regulator 1.
(Pin 6): Power Input for Step-Down Switching
V
IN1
Regulator 1. This pin will generally be connected to V
OUT
.
FB1 (Pin 7): Feedback Input for Step-Down Switching Regulator 1. This pin servos to a fi xed voltage of 0.8V when the control loop is complete.
MODE (Pin 8): Low Power Mode Enable. When this pin is pulled high, the three step-down switching regulators are set to low power Burst Mode operation.
EN1 (Pin 9): Logic Input Enables Step-Down Switching Regulator 1.
EN2 (Pin 10): Logic Input Enables Step-Down Switching Regulator 2.
EN3 (Pin 11): Logic Input Enables Step-Down Switching Regulator 3.
FB3 (Pin 12): Feedback Input for Step-Down Switching Regulator 3. This pin servos to a fi xed voltage of 0.8V when the control loop is complete.
FB2 (Pin 13): Feedback Input for Step-Down Switching Regulator 2. This pin servos to a fi xed voltage of 0.8V when the control loop is complete.
RST2 (Pin 14): This is an open-drain output which indicates that step-down switching regulator 2 has settled to its fi nal value. It can be used as a power on reset for the primary microprocessor or to enable the other buck regulators for supply sequencing.
SW2 (Pin 15): Power Transmission (Switch) Pin for Step-Down Switching Regulator 2.
35571fc
9
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