LTC3455/LTC3455-1
PIN FUNCTIONS
FB1 (Pin 1): Feedback Pin for Switcher 1. Set the output
voltage by connecting feedback resistors to this pin.
V
(Pin 10): Max Voltage Pin. This pin is used to
MAX
power the two internal step-down DC/DC converters and
is provided externally to power other devices (i.e. LDOs
or Switchers for LCD bias, white LED backlight drive, etc).
When the LTC3455/LTC3455-1 is on and neither USB or
wallpowerareavailable,aninternalPMOSswitchconnects
PROG (Pin 2): Charge Current Program and Charge Cur-
rent Monitor Pin. Connect a resistor, R
to ground to program battery charge current.
, from this pin
PROG
I
= 1000 • 1.23V / R
this pin to the V
pin. When either USB or wall power
BAT
PROG
BAT
is present, they provide power to this pin, and the battery
charger draws power from this pin. In shutdown, this pin
is discharged to ground to provide output disconnect.
In all modes the voltage on the PROG pin can be used to
measurechargecurrent. PROGhasaweakpull-upcurrent
source to turn the charger off if the pin is left open.
WALLFB(Pin11):WallPowerDetectionPin.Thispinisthe
input to a comparator used to signal the presence of a 5V
wall adapter. A resistor divider taken from the wall adapter
inputisconnectedtothispintotelltheLTC3455/LTC3455-1
when the adapter voltage is high enough to provide power
to the LTC3455/LTC3455-1. When this pin is higher than
1.23V, the battery charger is enabled. The 5V wall adapter
TIMER (Pin 3): Timer Capacitor Pin. Connect a capacitor,
TIMER
cycle termination time. The timer starts when USB or wall
power is first present. The timer period is:
C
, between this pin and ground to set the charge
T
(hours) = C
• (3 hours) / (0.1μF)
TIMER
TIMER
Tie TIMER to ground to disable just the internal timer
function. Tie TIMER to V to use the charger in a con-
is connected to the V
pin through a Schottky diode.
MAX
MAX
Tie WALLFB to ground if a wall adapter is not used.
stant-current-onlymode(whichdisablesthetimer,voltage
amplifier and trickle charge function).
SW2 (Pin 12): Switch Pin for Switcher 2. Minimize the
length of the metal trace connected to this pin. Place the
inductor for Switcher 2 as close to this pin as possible.
CHRG (Pin 4): Open-Drain Charge Status Pin. This pin is
pulled low with an internal N-channel MOSFET whenever
the battery charger is enabled, and is forced into a high
impedance state whenever it is disabled.
HSI (Pin 13): Hot Swap Input Pin. This pin is connected
to the HSO pin through a current-limited PMOS switch.
USBHP (Pin 5): USB High Power Mode Pin. This pin is
used to select the appropriate USB current limit (either
500mA or 100mA). Pull high to select 500mA (high power
mode); low to select 100mA (low power mode).
HSO (Pin 14): Hot Swap Output Pin. This output is used
for memory cards or other devices that would appear as
a short if they were hot-plugged directly to one of the
outputs (typically the 3.3V output). The current out of this
pin is limited to 160mA.
SUSPEND (Pin 6): USB Suspend Pin. When this pin is
pulled high, the internal USB power controller is disabled
and the USB pin current reduces to less than 20μA.
HSON (Pin 15): Hot Swap Enable Pin. This pin turns on
the PMOS that connects the HSI and HSO pins.
SW1(Pin7):SwitchPinforSwitcher1.Minimizethelength
of the metal trace connected to this pin. Place the inductor
for Switcher 1 as close to this pin as possible.
AI (Pin 16): Gain Block Input Pin. This pin is the inverting
input to an amplifier that can be used as a low-battery
detector or as an LDO with the addition of an external
PNP or PMOS. The non-inverting input of the gain block
is connected to the 0.8V internal reference.
USB (Pin 8): USB Supply Pin. Input current into this pin
is limited to either 100mA or 500mA based on the state
of the USBHP pin. The charger and Switcher 1 will remain
alive whenever USB power is present (when USB pin is
above 3.9V and SUSPEND is low).
AO (Pin 17): Gain Block Output Pin. This pin is an open-
drain output, and is pulled low when the AI pin is less
than 800mV. This output can be used as a low-battery
detector, or as an LDO with the addition of an external
PNP or PMOS. This pin can sink up to 1mA.
V
(Pin 9): Battery Input Pin. Bypass this pin with a
BAT
capacitor as close to the device as possible.
3455fc
7
Linear [ Linear ]
