LTC3555 Linear Technology, LTC3555 Datasheet - Page 11

• Manufacturer Part Number: LTC3555
• Description: High Efficiency USB Power Manager + Triple Step-Down DC/DC
• Manufacturer: Linear Technology

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PIN FUNCTIONS
LDO3V3 (Pin 1): 3.3V LDO Output Pin. This pin provides
a regulated always-on 3.3V supply voltage. LDO3V3
gets its power from V
such as a watch dog microprocessor or real time clock.
A 1μF capacitor is required from LDO3V3 to ground. If
the LDO3V3 output is not used it should be disabled by
connecting it to V
CLPROG (Pin 2): USB Current Limit Program and Moni-
tor Pin. A resistor from CLPROG to ground determines
the upper limit of the current drawn from the V
A fraction of the V
when the synchronous switch of the PowerPath switching
regulator is on. The switching regulator delivers power until
the CLPROG pin reaches 1.188V. Several V
settings are available via user input which will typically
correspond to the 500mA and 100mA USB specifi cations.
A multi-layer ceramic averaging capacitor or R-C network
is required at CLPROG for fi ltering.
NTC (Pin 3): Input to the Thermistor Monitoring Circuits.
The NTC pin connects to a battery’s thermistor to deter-
mine if the battery is too hot or too cold to charge. If the
battery’s temperature is out of range, charging is paused
until it re-enters the valid range. A low drift bias resistor
is required from V
from NTC to ground. If the NTC function is not desired,
the NTC pin should be grounded.
FB2 (Pin 4): Feedback Input for Switching Regulator 2.
When regulator 2’s control loop is complete, this pin servos
to 1 of 16 possible set-points based on the commanded
value from the I
V
pin will generally be connected to V
capacitor is recommended on this pin.
SW2 (Pin 6): Power Transmission Pin for Switching
Regulator 2.
EN2 (Pin 7): Logic Input. This logic input pin indepen-
dently enables switching regulator 2. This pin is logically
OR-ed with its corresponding bit in the I
See Table 2.
IN2
(Pin 5): Power Input for Switching Regulator 2. This
2
C serial port. See Table 4.
OUT
BUS
BUS
.
to NTC and a thermistor is required
OUT
current is sent to the CLPROG pin
. It may be used for light loads
OUT
BUS
. A 1μF MLCC
2
C serial port.
current limit
BUS
pin.
DV
serial port is not needed it can be disabled by grounding
DV
cally passed to the individual logic input pins.
SCL (Pin 9): Clock Input Pin for the I
I
is grounded, the SCL pin is equivalent to the B5 bit in the
I
the operating modes of switching regulators 1, 2 and 3
when DV
SDA (Pin 10): Data Input Pin for the I
I
is grounded, the SDA pin is equivalent to the B6 bit in the
I
the operating modes of switching regulators 1, 2 and 3
when DV
V
This pin will generally be connected to V
capacitor is recommended on this pin.
SW3 (Pin 12): Power Transmission Pin for Switching
Regulator 3.
EN3 (Pin 13): Logic Input. This logic input pin indepen-
dently enables switching regulator 3. This pin is logically
OR-ed with its corresponding bit in the I
See Table 2.
FB3 (Pin 14): Feedback Input for Switching Regulator 3.
When regulator 3’s control loop is complete, this pin servos
to 1 of 16 possible set-points based on the commanded
value from the I
⎯ R ⎯ S ⎯ T ⎯ 3 (Pin 15): Logic Output. This in an open-drain output
which indicates that switching regulator 3 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 switching
regulators for supply sequencing.
EN1 (Pin 16): Logic Input. This logic input pin indepen-
dently enables switching regulator 1. This pin is logically
OR-ed with its corresponding bit in the I
See Table 2.
2
2
2
2
IN3
C logic levels are scaled with respect to DV
C serial port. SCL in conjunction with SDA determine
C logic levels are scaled with respect to DV
C serial port. SDA in conjunction with SCL determine
CC
CC
. When DV
(Pin 11): Power Input for Switching Regulator 3.
(Pin 8): Logic Supply for the I
CC
CC
is grounded. See Tables 2 and 5.
is grounded. See Tables 2 and 5.
2
CC
C serial port. See Table 4.
is grounded, chip control is automati-
2
C Serial Port. If the
2
2
C Serial Port. The
C Serial Port. The
LTC3555
OUT
2
2
. A 1μF MLCC
C serial port.
C serial port.
CC
CC
. If DV
. If DV
11
3555f
CC
CC