LTC3557 Datasheet, PDF (9/28 Pages) Linear Technology – USB Power Manager with Li-Ion Charger and Three Step-Down Regulators

LTC3557/LTC3557-1
TYPICAL PERFORMANCE CHARACTERISTICS T_A = 25°C unless otherwise specified
600mA Step-Down Switching
Regulator Feedback Voltage
vs Output Current
0.85
0.84
0.83
0.82
Burst Mode
OPERATION
0.81
0.80
PULSE SKIP
0.79
0.78
0.77
0.76
0.75
0.1
1
10
100
OUTPUT CURRENT (mA)
3.8V
5V
1000
35571 G22
400mA Step-Down Switching
Regulator Feedback Voltage
vs Output Current
Step-Down Switching Regulator
Start-Up Waveform
0.85
0.84
0.83
0.82
Burst Mode
OPERATION
0.81
V_OUT2
50mV/DIV(AC)
V_OUT1
1V/DIV
0.80
0.79
PULSE SKIP
0.78
0V
I_L1
200mA/DIV
0mA
0.77
0.76
0.75
0.1
1
10
100
OUTPUT CURRENT (mA)
3.8V
5V
1000
EN1
V_OUT2 = 1.2V
I_OUT2 = 50mA
MODE = 1
R_OUT1 = 8Ω
100μs/DIV
35571 G24
35571 G23
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_BUS to
V_OUT. The ACPR pin will also be pulled low to indicate that a
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_OUT. It may be used
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.
V_IN1 (Pin 6): Power Input for Step-Down Switching
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 fixed 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 fixed 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 fixed 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 final
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.
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