LTC3455_15 Datasheet, PDF(7/28 Page) Linear Technology – Dual DC/DC Converter with USB Power Manager and Li-Ion Battery Charger

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LTC3455_15 Datasheet, PDF (7/28 Pages) Linear Technology – Dual DC/DC Converter with USB Power Manager and Li-Ion Battery Charger

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LTC3455/LTC3455-1

PIN FUNCTIONS

FB1 (Pin 1): Feedback Pin for Switcher 1. Set the output

voltage by connecting feedback resistors to this pin.

PROG (Pin 2): Charge Current Program and Charge Cur-

rent Monitor Pin. Connect a resistor, RPROG, from this pin

to ground to program battery charge current.

IBAT = 1000 â¢ 1.23V / RPROG

In all modes the voltage on the PROG pin can be used to

measure charge current. PROG has a weak pull-up current

source to turn the charger off if the pin is left open.

TIMER (Pin 3): Timer Capacitor Pin. Connect a capacitor,

CTIMER, between this pin and ground to set the charge

cycle termination time. The timer starts when USB or wall

power is ï¬rst present. The timer period is:

TTIMER (hours) = CTIMER â¢ (3 hours) / (0.1Î¼F)

Tie TIMER to ground to disable just the internal timer

function. Tie TIMER to VMAX to use the charger in a con-

stant-current-only mode (which disables the timer, voltage

ampliï¬er and trickle charge function).

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.

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).

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 20Î¼A.

SW1 (Pin 7): Switch Pin for Switcher 1. Minimize the length

of the metal trace connected to this pin. Place the inductor

for Switcher 1 as close to this pin as possible.

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).

VBAT (Pin 9): Battery Input Pin. Bypass this pin with a

capacitor as close to the device as possible.

VMAX (Pin 10): Max Voltage Pin. This pin is used to

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

wall power are available, an internal PMOS switch connects

this pin to the VBAT pin. When either USB or wall power

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.

WALLFB (Pin 11): Wall Power Detection Pin. This pin is the

input to a comparator used to signal the presence of a 5V

wall adapter. A resistor divider taken from the wall adapter

input is connected to this pin to tell the LTC3455/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

is connected to the VMAX pin through a Schottky diode.

Tie WALLFB to ground if a wall adapter is not used.

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.

HSI (Pin 13): Hot Swap Input Pin. This pin is connected

to the HSO pin through a current-limited PMOS switch.

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.

HSON (Pin 15): Hot Swap Enable Pin. This pin turns on

the PMOS that connects the HSI and HSO pins.

AI (Pin 16): Gain Block Input Pin. This pin is the inverting

input to an ampliï¬er 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.

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.

3455fc

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