LTC4155 datasheet(13/52 Pages) LINER

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LTC4155

4155fc

PIN FUNCTIONS

USBGT to energize the external transistors. If the input

voltage exceeds VOVLO, USBGT will be pulled to GND to

disable the pass transistors and protect the LTC4155 from

high voltage.

Power detected on WALLSNS is prioritized over USBSNS.

If power is detected on both WALLSNS and USBSNS, by

default, only WALLGT will receive drive for its pass tran-

sistors. See the Operations section for further information

about programmable priority.

USBGT (Pin 9): Overvoltage Protection and Priority Mul-

tiplexer Gate Output. Connect USBGT to the gate pins of

two source-connected external N-channel MOSFET pass

transistors. One drain of the transistors should be con-

nected to VBUS and the other drain should be connected

to a low priority DC input connector. In the absence of an

overvoltage condition, this pin is driven from an internal

charge pump capable of creating sufficient overdrive to fully

enhance the pass transistors. If an overvoltage condition

is detected, USBGT is brought rapidly to GND to prevent

damage to the LTC4155. USBGT works in conjunction with

USBSNS to provide this protection. USBGT also works in

conjunction with WALLSNS to determine power source

prioritization. See the Operation section.

OVGCAP (Pin 10): Overvoltage Protection Capacitor

Output. A 0.1μF capacitor should be connected from

OVGCAP to GND. OVGCAP is used to store charge so

that it can be rapidly moved to WALLGT or USBGT. This

feature provides faster power switchover when multiple

inputs are supported by the end product.

WALLGT (Pin 9): Overvoltage Protection and Priority Mul-

tiplexer Gate Output. Connect WALLGT to the gate pins of

two source-connected external N-channel MOSFET pass

transistors. One drain of the transistors should be con-

nected to VBUS and the other drain should be connected

to a high priority input connector. In the absence of an

overvoltage condition, this pin is driven from an internal

charge pump capable of creating sufficient gate drive to fully

enhance the pass transistors. If an overvoltage condition

is detected, WALLGT is brought rapidly to GND to prevent

damage to the LTC4155. WALLGT works in conjunction

with WALLSNS to provide this protection. WALLGT also

works in conjunction with USBSNS to determine power

source prioritization. See the Operation section.

VC (Pin 12): Compensation Pin. A 0.047μF ceramic ca-

pacitor on this pin compensates the switching regulator

control loops.

VOUTSNS (Pin 13): Output Voltage Sense Input. Connecting

VOUTSNS directly to the VOUT bypass capacitor ensures that

VOUT regulates at the correct level.

NTCBIAS (Pin 14): NTC Thermistor Bias Output. Connect a

bias resistor between NTCBIAS and NTC, and a thermistor

between NTC and GND. The value of the bias resistor should

usually be equal to the nominal value of the thermistor.

NTC (Pin 15): Input to the Negative Temperature Coefficient

Thermistor Monitoring Circuit. The NTC pin connects to

a negative temperature coefficient thermistor, which is

typically copackaged with the battery, to determine if the

battery is too warm or too cold to charge or if the battery

is dangerously hot. If the battery’s temperature is out of

range, charging is paused until the battery temperature re-

enters the valid range. A low drift bias resistor is required

from NTCBIAS to NTC and a thermistor is required from

NTC to ground. The thermistor’s temperature reading is

continually digitized by an analog to digital converter and

may be read back at any time via the I2C port.

BATSNS (Pin 16): Battery Voltage Sense Input. For proper

operation, this pin must always be connected to the battery.

For fastest charging, connect BATSNS physically close to

the Lithium-Ion cell’s positive terminal. Depending upon

available power and load, a Li-Ion battery connected to

the BATSNS pin will either be charged from VOUT or will

deliver system power to VOUT via the required external

P-channel MOSFET transistor.

BATGATE (Pin 17): Battery Charger and Ideal Diode Am-

plifier Control Output. This pin controls the gate of an

external P-channel MOSFET transistor used to charge the

Lithium-Ion cell and to provide power to VOUT when the

system load exceeds available input power. The source of

the P-channel MOSFET should be connected to CHGSNS

and the drain should be connected to BATSNS and the

battery.

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