Datasheet

LTC3556
11
3556f
PIN FUNCTIONS
LDO3V3 (Pin 1): 3.3V LDO Output Pin. This pin provides
a regulated, always-on, 3.3V supply voltage. LDO3V3
gets its power from V
OUT
. It may be used for light loads
such as a watchdog microprocessor or real time clock.
A 1µF capacitor is required from LDO3V3 to ground. If
the LDO3V3 output is not used it should be disabled by
connecting it to V
OUT
.
CLPROG (Pin 2): USB Current Limit Program and Moni-
tor Pin. A resistor from CLPROG to ground determines
the upper limit of the current drawn from the V
BUS
pin.
A fraction of the V
BUS
current is sent to the CLPROG pin
when the synchronous switch of the PowerPath switching
regulator is on. The switching regulator delivers power until
the CLPROG pin reaches 1.188V. Several V
BUS
current limit
settings are available via user input which will typically
correspond to the 500mA and 100mA USB specifications.
A multilayer ceramic averaging capacitor or R-C network
is required at CLPROG for filtering.
NTC (Pin 3): Input to the Thermistor Monitoring Circuits.
The NTC pin connects to a battery’s thermistor to deter-
mine 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 re-enters the valid range. A low drift bias resistor
is required from V
BUS
to NTC and a thermistor is required
from NTC to ground. If the NTC function is not desired,
the NTC pin should be grounded.
SW1 (Pin 4): Power Transmission Pin for (Buck) Switch-
ing Regulator 1.
V
IN1
(Pin 5): Power Input for (Buck) Switching Regula-
tor 1. This pin will generally be connected to V
OUT
. A 1µF
MLCC capacitor is recommended on this pin.
FB1 (Pin 6): Feedback Input for (Buck) Switching Regula-
tor 1. When regulator 1’s control loop is complete, this
pin servos to 1 of 16 possible set-points based on the
commanded value from the I
2
C serial port. See Table 4.
FB3 (Pin 7): Feedback Input for (Buck-Boost) Switching
Regulator 3. When regulator 3’s control loop is complete,
this pin servos to 1 of 16 possible set-points based on the
commanded value from the I
2
C serial port. See Table 4.
V
C3
(Pin 8): Output of the Error Amplifi er and Voltage
Compensation Node for (Buck-Boost) Switching Regula-
tor 3. External Type I or Type III compensation (to FB3)
connects to this pin. See Applications Information section
for selecting buck-boost compensation components.
SWAB3 (Pin 9): Switch Node for (Buck-Boost) Switching
Regulator 3. Connected to internal power switches A and B.
External inductor connects between this node and SWCD3.
DV
CC
(Pin 10): Logic Supply for the I
2
C Serial Port.
V
IN3
(Pin 11): Power Input for (Buck-Boost) Switching
Regulator 3. This pin will generally be connected to V
OUT
. A
1µF (min) MLCC capacitor is recommended on this pin.
V
OUT3
(Pin 12): Regulated Output Voltage for (Buck-Boost)
Switching Regulator 3.
Switching Regulator 3 Step
Response (0mA to 300mA)
Start-Up Sequencing with SEQ = 0V
V
IN1
= V
IN2
= V
IN3
= 4.2V
All Outputs Loaded with 5mA
100µs/DIV
V
OUT3
100mV/DIV
AC
COUPLED
300mA
0
I
OUT3
200mA/
DIV
3556 G35
V
IN3
= 3.8V
V
OUT3
= 3.3V
200µs/DIV
V
OUT3
= 3.3V
ENALL
V
OUT2
= 1.8V
V
OUT1
= 1.6V
1V/DIV
3556 G36
TYPICAL PERFORMANCE CHARACTERISTICS