LTC3566 Datasheet, PDF (14/28 Pages) Linear Technology – High Effi ciency USB Power Manager Plus 1A Buck-Boost Converter

LTC3566
OPERATION
TO USB
OR WALL
ADAPTER
V_BUS
21
I_SWITCH/N
PWM AND
GATE DRIVE
SW
22
V_OUT
20
CONSTANT CURRENT
CONSTANT VOLTAGE
BATTERY CHARGER
IDEAL
DIODE
+
OV
–
15mV ^+–
GATE
18
SYSTEM LOAD
3.5V TO
(BAT + 0.3V)
OPTIONAL
EXTERNAL
IDEAL DIODE
PMOS
CLPROG –
2
+
1.188V
AVERAGE INPUT
CURRENT LIMIT
CONTROLLER
0.3V
+–
3.6V
AVERAGE OUTPUT
VOLTAGE LIMIT
CONTROLLER
Figure 3. PowerPath Block Diagram
BAT
19
3566 F03
+ _{SINGLE CELL}
Li-Ion
3.3V Always-On Supply
The LTC3566 includes a low quiescent current low dropout
regulator that is always powered. This LDO can be used to
provide power to a system pushbutton controller, standby
microcontroller or real time clock. Designed to deliver up
to 25mA, the always-on LDO requires at least a 1μF low
impedance ceramic bypass capacitor for compensation.
The LDO is powered from V_OUT, and therefore will enter
dropout at loads less than 25mA as V_OUT falls near 3.3V.
If the LDO3V3 output is not used, it should be disabled
by connecting it to V_OUT.
V_BUS Undervoltage Lockout (UVLO)
An internal undervoltage lockout circuit monitors V_BUS and
keeps the PowerPath switching regulator off until V_BUS
rises above 4.30V and is about 200mV above the battery
voltage. Hysteresis on the UVLO turns off the regulator if
V_BUS drops below 4.00V or to within 50mV of BAT. When
this happens, system power at V_OUT will be drawn from
the battery via the ideal diode.
Battery Charger
The LTC3566 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.
Battery Preconditioning
When a battery charge cycle begins, the battery charger
first determines if the battery is deeply discharged. If the
battery voltage is below V_TRKL, typically 2.85V, 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 and indicates via the CHRG pin that the battery
was unresponsive.
Once the battery voltage is above 2.85V, the battery charger
begins charging in full power constant-current mode. The
current delivered to the battery will try to reach 1022V/
R_PROG. Depending on available input power and external
load conditions, the battery charger may or may not be
able to charge at the full programmed rate. The external
load will always be prioritized over the battery charge
current. The USB current limit programming will always
be observed and only additional power will be available to
charge the battery. When system loads are light, battery
charge current will be maximized.
3566fa
14