ltc3566 Linear Technology Corporation, ltc3566 Datasheet - Page 14

• Manufacturer Part Number: ltc3566
• Description: High Ef?ciency Usb Power Manager Plus 1a Buck-boost Converter
• Manufacturer: Linear Technology Corporation

LTC3566
OPERATION
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
micro-controller 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
dropout at loads less than 25mA as V
If the LDO output is not used, it should be disabled by
connecting it to V
V
An internal undervoltage lockout circuit monitors V
keeps the PowerPath switching regulator off until V
rises above 4.30V and is about 200mV above the battery
voltage. Hysteresis on the UVLO turns off the regulator if
V
this happens, system power at V
the battery via the ideal diode.
Battery Charger
The LTC3566 includes a constant-current/constant-volt-
age battery charger with automatic recharge, automatic
14
OR WALL
ADAPTER
TO USB
BUS
BUS
drops below 4.00V or to within 50mV of BAT. When
Undervoltage Lockout (UVLO)
11
2
I
V
SWITCH
CLPROG
BUS
1.188V
OUT
/N
.
AVERAGE INPUT
CURRENT LIMIT
CONTROLLER
–
+
OUT
GATE DRIVE
PWM AND
, and therefore will enter
OUT
will be drawn from
OUT
AVERAGE OUTPUT
VOLTAGE LIMIT
CONTROLLER
falls near 3.3V.
Figure 3. PowerPath Block Diagram
–
+
+
BUS
3.6V
CONSTANT CURRENT
CONSTANT VOLTAGE
and
BUS
BATTERY CHARGER
0.3V
+ –
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
fi rst determines if the battery is deeply discharged. If the
battery voltage is below V
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
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.
PROG
. Depending on available input power and external
IDEAL
DIODE
OV
15mV
–
+
+
–
GATE
V
OUT
BAT
SW
TRKL
12
10
8
9
3566 F03
, typically 2.85V, an automatic
+
SINGLE CELL
Li-Ion
OPTIONAL
EXTERNAL
IDEAL DIODE
PMOS
SYSTEM LOAD
3.5V TO
(BAT + 0.3V)
3566p