ltc3557-ltc3557-1 Linear Technology Corporation, ltc3557-ltc3557-1 Datasheet - Page 9

• Manufacturer Part Number: ltc3557-ltc3557-1
• Description: Usb Power Manager With Li-ion Charger And Three Step-down Regulators
• Manufacturer: Linear Technology Corporation

PIN FUNCTIONS
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
V
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
loads such as a real-time clock or housekeeping micropro-
cessor. 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
SW1 (Pin 5): Power Transmission (Switch) Pin for Step-
Down Switching Regulator 1.
V
tor 1. This pin will generally be connected to V
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.
TYPICAL PERFORMANCE CHARACTERISTICS
OUT
IN1
0.85
0.84
0.83
0.82
0.81
0.80
0.79
0.78
0.77
0.76
0.75
OUT
. The ACPR pin will also be pulled low to indicate that a
(Pin 6): Power Input for Step-Down Switching Regula-
0.1
600mA Step-Down Switching
Regulator Feedback Voltage vs
Output Current
.
1
OUTPUT CURRENT (mA)
PULSE SKIP
OPERATION
Burst Mode
10
100
OUT
35571 G22
3.8V
5V
. It may be used for light
1000
0.85
0.84
0.83
0.82
0.81
0.80
0.79
0.78
0.77
0.76
0.75
OUT
0.1
400mA Step-Down Switching
Regulator Feedback Voltage vs
Output Current
.
BUS
1
OUTPUT CURRENT (mA)
PULSE SKIP
OPERATION
Burst Mode
to
10
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.
100
35571 G23
3.8V
5V
T
A
1000
= 25°C unless otherwise specifi ed
LTC3557/LTC3557-1
50mV/DIV(AC)
200mA/DIV
1V/DIV
V
OUT1
V
I
OUT2
L1
0mA
EN1
0V
Step-Down Switching Regulator
Start-Up Waveform
V
I
MODE = 1
R
OUT2
OUT2
OUT1
= 50mA
= 1.2V
= 8Ω
100μs/DIV
35571fa
35571 G24
9