ADP5350ACBZ-1-R7 datasheet(22/63 Pages) AD

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ADP5350

Data Sheet

Rev. B | Page 22 of 63

CHARGER MODES

Input Current Limit

The ADP5350 features a programmable input current limit,

from 100 mA to 1500 mA, via the ILIM[3:0] I2C bits, which

ensures compatibility with the USB limits requirements listed in

Table 11. The current limit defaults to 100 mA to allow

compatibility with a USB host or hub that is not configured.

This input current limit resets to the 100 mA default value

during every power cycle on VBUSx to protect the USB port.

When the input current limit feature is used, the available input

current may be too low for the charger to meet the programmed

charging current, ICHG, and the rate of charge is reduced. In this

case, the VBUS_ILIM flag is set.

When connecting an improper voltage level to VBUSx, the dc-

to-dc regulator shuts down, the ISOFET turns on, and the high

voltage blocking part is in a state wherein it draws only 1.3 mA

(typical) of current until VVBUSx reaches the VVBUS_OV_FALL level.

The ADP5350 always monitors the VVBUSx voltage when there is

a proper USB power connection. The VBUSOK bit, Bit 3 in

VVBUS_OV and VVBUSOK, which can be programmed to be masked

to the PGOOD pin via the VBUSOK_MASK bit in Register 0x37.

The default setting of the VBUSOK_MASK is programmed via a

factory fuse trim.

Trickle Charge Mode

A deeply discharged Li-Ion cell may exhibit a very low cell

voltage, making it unsafe to charge the cell at high current rates.

The ADP5350 charger uses a trickle charge mode to reset the

battery pack protection circuit and lift the cell voltage to a safe level

for fast charging. A cell with a voltage below VTRK_DEAD is

charged with the trickle mode current, ITRK_DEAD. During trickle

charge mode, the CHARGER_STATUS[3:0] bits are set.

During trickle charging, the ISOS node is regulated to VISOS_TRK

by the dc-to-dc regulator and the battery isolation FET is off,

which means the battery is isolated from the system power supply.

The enable of the trickle charging function is controlled via the

I2C EN_TRK bit.

Trickle Charge Mode Timer

The duration of trickle charge mode is monitored to ensure the

battery is revived from its deeply discharged state. If trickle

charge mode runs for longer than 60 minutes without the cell

voltage reaching VTRK_DEAD, a fault condition is assumed and the

charging stops. The battery isolation FET turns on and the dc-

to-dc regulator stops working. The fault condition is asserted in

the CHARGER_STATUS register, allowing the user to initiate

the fault recovery procedure specified in the Fault Recovery

section.

Weak Charge Mode (Constant Current)

When the battery voltage exceeds VTRK_DEAD but is less than VWEAK,

the charger switches to weak charge mode and the ISOS node is

regulated to VISOS_FC by turning on the battery isolation FET.

In weak charge mode, the battery charges with the programmed

ICHG current from the ISOS node through the isolation FET and

trickle charge current, ITRK_DEAD. Due to the VBUSx input current

limit, the real ICHG charge current from the ISOS node may be less

than the programmed value. The system load can also share the

current from the ISOS node. However, the trickle charge current,

ITRK_DEAD, remains on to charge the battery in weak charge mode.

Fast Charge Mode (Constant Current)

When the battery voltage exceeds VTRK_DEAD and VWEAK, the

charger switches to fast charge mode, charging the battery with

the constant current, ICHG. During fast charge mode (CC), the

CHARGER_STATUS[3:0] bits are set.

During CC mode, other features may prevent the current, ICHG,

from reaching its full programmed value. Isothermal charging

mode or input current limiting for USB compatibility may affect

the value of ICHG under certain operating conditions. The

voltage on ISOS is regulated to stay at VISOS_FC by the battery

isolation FET when VISOB < VISOS_FC.

Fast Charge Mode (Constant Voltage)

As the battery charges, its voltage rises and approaches the termi-

nation voltage, VTRM. The ADP5350 charger monitors the voltage

on the BSNS pin to determine when charging ends. However,

the internal ESR of the battery pack combined with PCB and

other parasitic series resistances creates a voltage drop between

the sense point at the BSNS pin and the cell terminal itself. To

compensate for this and ensure a fully charged cell, the ADP5350

enters a constant voltage charge mode when the BSNS voltage

reaches the termination voltage. The ADP5350 reduces charge

current gradually as the cell continues to charge, maintaining a

voltage of VTRM on the BSNS pin. During fast charge mode

(constant voltage), the CHARGER_STATUS[3:0] bits are set.

Fast Charge Mode Timer

The duration of fast charge mode is monitored to ensure that

the battery is charging correctly. If the fast charge mode runs for

longer than tCHG without the voltage at the BSNS pin reaching

VTRM, a fault condition is assumed and charging stops. The battery

isolation FET remains on, and the dc-to-dc regulator shuts down.

The fault condition is asserted on the CHARGER_STATUS reg-

ister, allowing the user to initiate the fault recovery procedure

specified in the Fault Recovery section.

If the fast charge mode runs for longer than tCHG, and VTRM is

reached on the BSNS pin but the charge current is not yet below

IEND, charging stops by turning the battery isolation FET off, but

the system voltage is maintained at VISOS_TRK by the dc-to-dc

regulator. No fault condition is asserted in this circumstance,

and the ADP5350 transitions to charge complete status.

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