LTC3554 LINER [Linear Technology], LTC3554 Datasheet - Page 15

• Manufacturer Part Number: LTC3554
• Description: Micropower USB Power Manager with Li-Ion Charger and Two Step-Down Regulators
• Manufacturer: LINER [Linear Technology]

OPERATION
Ideal Diode From BAT to V
The LTC3554 has an internal ideal diode from BAT to V
designed to respond quickly whenever V
BAT. If the load increases beyond the input current limit,
additional current will be pulled from the battery via the ideal
diode. Furthermore, if power to V
then all of the application power will be provided by the
battery via the ideal diode. The ideal diode is fast enough
to keep V
recommended output capacitor. The ideal diode consists
of a precision amplifi er that enables an on-chip P-channel
MOSFET whenever the voltage at V
15mV (V
the internal ideal diode is approximately 240mΩ.
Suspend Mode
When the SUSP pin is pulled high the LTC3554 enters
suspend mode to comply with the USB specifi cation. In
this mode, the power path between V
in a high impedance state to reduce the V
to 15μA. The system load connected to V
through the ideal diode connected to BAT.
V
Current Limit (UVCL)
An internal undervoltage lockout circuit monitors V
and keeps the input current limit circuitry off until V
rises above the rising UVLO threshold (3.8V) and at least
200mV above V
input current limit circuitry if V
within 50mV of V
V
minimize the possibility of oscillation in and out of UVLO
when using resistive input supplies, the input current limit
is reduced as V
OUT
BUS
will be drawn from the battery via the ideal diode. To
Undervoltage Lockout (UVLO) and Undervoltage
FWD
OUT
) below the voltage at BAT. The resistance of
from dropping signifi cantly with just the
BUS
BAT
BAT
. Hysteresis on the UVLO turns off the
. When this happens, system power at
falls below 4.45V typical.
OUT
BUS
BUS
OUT
drops below 3.6V or
BUS
(USB) is removed,
BUS
is approximately
OUT
and V
OUT
input current
drops below
is supplied
OUT
is put
OUT
BUS
BUS
Battery Charger
The LTC3554 includes a constant-current/constant-volt-
age battery charger with automatic recharge, automatic
termination by safety timer, low voltage trickle charging,
bad cell detection and thermistor sensor input for out of
temperature charge pausing. When a battery charge cycle
begins, the battery charger fi rst determines if the battery
is deeply discharged. If the battery voltage is below V
typically 2.9V, an automatic trickle charge feature sets the
battery charge current to 10% of the programmed value. If
the low voltage persists for more than 1/2 hour, the battery
charger automatically terminates. Once the battery voltage
is above 2.9V, the battery charger begins charging in full
power constant current mode. The current delivered to
the battery will try to reach 750V/R
available input power and external load conditions, the
battery charger may or may not be able to charge at the
full programmed current. The external load will always be
prioritized over the battery charge current. The USB cur-
rent limit programming will always be observed and only
additional current will be available to charge the battery.
When system loads are light, battery charge current will
be maximized.
Charge Termination
The battery charger has a built-in safety timer. When the
battery voltage approaches the fl oat voltage, the charge
current begins to decrease as the LTC3554 enters con-
stant-voltage mode. Once the battery charger detects that
it has entered constant-voltage mode, the four hour safety
timer is started. After the safety timer expires, charging
of the battery will terminate and no more current will be
delivered to the battery.
PROG
LTC3554
. Depending on
15
TRKL
3554f
,