LTC3555 Linear Technology, LTC3555 Datasheet - Page 12

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

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LTC3555
PIN FUNCTIONS
SW1 (Pin 17): Power Transmission Pin for Switching
Regulator 1.
V
This pin will generally be connected to V
capacitor is recommended on this pin.
FB1 (Pin 19): Feedback Input for Switching Regulator 1.
When regulator 1’s control loop is complete, this pin servos
to a fi xed voltage of 0.8V.
PROG (Pin 20): Charge Current Program and Charge
Current Monitor Pin. Connecting a resistor from PROG
to ground programs the charge current. If suffi cient in-
put power is available in constant-current mode, this pin
servos to 1V. The voltage on this pin always represents
the actual charge current.
⎯ C ⎯ H ⎯ R ⎯ G (Pin 21): Open-Drain Charge Status Output. The
⎯ C ⎯ H ⎯ R ⎯ G pin indicates the status of the battery charger. Four
possible states are represented by ⎯ C ⎯ H ⎯ R ⎯ G : charging, not
charging, unresponsive battery and battery temperature
out of range. ⎯ C ⎯ H ⎯ R ⎯ G is modulated at 35kHz and switches
between a low and a high duty cycle for easy recogni-
tion by either humans or microprocessors. See Table 1.
⎯ C ⎯ H ⎯ R ⎯ G requires a pull-up resistor and/or LED to provide
indication.
GATE (Pin 22): Analog Output. This pin controls the gate
of an optional external P-channel MOSFET transistor used
to supplement the ideal diode between V
external ideal diode operates in parallel with the internal
ideal diode. The source of the P-channel MOSFET should
be connected to V
to BAT. If the external ideal diode FET is not used, GATE
should be left fl oating.
12
IN1
(Pin 18): Power Input for Switching Regulator 1.
OUT
and the drain should be connected
OUT
OUT
. A 1μF MLCC
and BAT. The
BAT (Pin 23): Single Cell Li-Ion Battery Pin. Depending on
available V
deliver power to V
from V
V
Controller and Input Voltage of the Battery Charger. The
majority of the portable product should be powered from
V
tween the external load on V
charger. Priority is given to the external load and any extra
power is used to charge the battery. An ideal diode from
BAT to V
exceeds the allotted power from V
source is removed. V
impedance ceramic capacitor.
V
power to V
from a DC source such as a USB port or wall adapter.
SW (Pin 26): Power Transmission Pin for the USB Power
Path. The SW pin delivers power from V
step-down switching regulator. A 3.3μH inductor should
be connected from SW to V
I
control the current limit of the PowerPath switching
regulator. See Table 3. Both of the I
are logically OR-ed with their corresponding bits in the
I
Exposed Pad (Pin 29): Ground. The Exposed Pad should
be connected to a continuous ground plane on the second
layer of the printed circuit board by several vias directly
under the LTC3555.
LIM0
2
OUT
OUT
BUS
C serial port. See Table 2.
. The LTC3555 will partition the available power be-
, I
(Pin 24): Output voltage of the Switching PowerPath
(Pin 25): Primary Input Power Pin. This pin delivers
OUT
LIM1
OUT
OUT
BUS
via the battery charger.
(Pins 27, 28): Logic Inputs. I
ensures that V
via the SW pin by drawing controlled current
power, a Li-Ion battery on BAT will either
OUT
through the ideal diode or be charged
OUT
should be bypassed with a low
OUT
OUT
OUT
is powered even if the load
.
and the internal battery
BUS
LIM0
or if the V
BUS
and I
LIM0
to V
OUT
BUS
and I
LIM1
power
via the
LIM1
pins
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