LTC3557-1 Linear Technology, LTC3557-1 Datasheet - Page 10

• Manufacturer Part Number: LTC3557-1
• Description: USB Power Manager
• Manufacturer: Linear Technology

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LTC3557/LTC3557-1
PIN FUNCTIONS
V
lators 2 and 3. This pin will generally be connected to V
SW3 (Pin 17): Power Transmission (Switch) Pin for Step-
Down Switching Regulator 3.
V
this pin to the NTC pin will bias the NTC thermistor.
NTC (Pin 19): The NTC pin connects to a battery’s thermistor
to determine 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 drops back into range. A low drift bias resistor is re-
quired from V
NTC to ground. If the NTC function is not desired, the NTC
pin should be grounded.
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 input power is available in constant current
mode, this pin servos to 1V. The voltage on this pin always
represents the actual charge current.
GATE (Pin 21): Ideal Diode Gate Connection. This pin con-
trols the gate of an optional external P-channel MOSFET
transistor used to supplement the internal ideal diode. The
source of the P-channel MOSFET should be connected to
V
tant to maintain high impedance on this pin and minimize
all leakage paths.
BAT (Pin 22): Single Cell Li-Ion Battery Pin. Depending on
available power and load, a Li-Ion battery on BAT will either
deliver system power to V
charged from the battery charger.
V
and Input Voltage of the Battery Charger. The majority of
the portable product should be powered from V
LTC3557/LTC3557-1 will partition the available power
between 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
10
IN2
NTC
OUT
OUT
I
CHG
(Pin 16): Power Input for Step-Down Switching Regu-
(Pin 18): Output Bias Voltage for NTC. A resistor from
and the drain should be connected to BAT. It is impor-
(Pin 23): Output Voltage of the PowerPath Controller
( ) =
A
OUT
ensures that V
NTC
1000
R
PROG
to NTC and a thermistor is required from
V
OUT
OUT
through the ideal diode or be
OUT
is powered even if the load
and the internal battery
OUT
. The
OUT
.
exceeds the allotted input current from V
power source is removed. V
a low impedance multilayer ceramic capacitor. The total
capacitance on V
over operating voltage and temperature.
V
nected to the USB port of a computer or a DC output wall
adapter. V
multilayer ceramic capacitor.
⎯ A ⎯ C ⎯ P ⎯ R (Pin 25): Wall Adapter Present Output (Active Low).
A low on this pin indicates that the wall adapter input com-
parator has had its input pulled above its input threshold
(typically 4.3V). This pin can be used to drive the gate of an
external P-channel MOSFET to provide power to V
a power source other than a USB port.
V
pin can be used to drive the V
high voltage buck switching regulator. An external P-chan-
nel MOSFET is required to provide power to V
gate tied to the ⎯ A ⎯ C ⎯ P ⎯ R pin. The V
the LT
CLPROG (Pin 27): Input Current Program and Input Current
Monitor Pin. A resistor from CLPROG to ground determines
the upper limit of the current drawn from the V
the input current limit). A precise fraction of the input cur-
rent, h
erPath delivers current until the CLPROG pin reaches 2.0V
(10x Mode), 1.0V (5x Mode) or 0.2V (1x Mode). Therefore,
the current drawn from V
given by h
resistor R
⎯ C ⎯ H ⎯ R ⎯ G (Pin 28): 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 (i.e., fl oat charge current less than 1/10th pro-
grammed charge current), unresponsive battery (i.e., its
voltage remains below 2.8V after 1/2 hour of charging) and
battery temperature out of range. ⎯ C ⎯ H ⎯ R ⎯ G requires a pull-up
resistor and/or LED to provide indication.
Exposed Pad (Pin 29): Ground. The exposed package pad
is ground and must be soldered to the PC board for proper
functionality and for maximum heat transfer.
BUS
C
(Pin 26): High Voltage Buck Regulator Control Pin. This
(Pin 24): USB Input Voltage. V
®
CLPROG
3480, LT3481 and LT3505.
CLPROG
BUS
CLPROG
, is sent to the CLPROG pin. The input Pow-
should be bypassed with a low impedance
OUT
should be set to no less than 2.1k.
and R
should maintain a minimum of TBDμF
CLPROG
BUS
OUT
C
C
will be limited to an amount
pin of an approved external
pin is designed to work with
. In USB applications the
should be bypassed with
BUS
will usually be con-
BUS
or if the V
BUS
OUT
OUT
pin (i.e.,
with its
from
35571f
BUS