ADP5065ACBZ-1-R7 datasheet(18/40 Pages) AD

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ADP5065

Data Sheet

Rev. D | Page 18 of 40

Weak Charge Mode (Constant Current)

When the battery voltage exceeds VTRK_DEAD but is less than

VWEAK, the charger switches to the intermediate charge mode.

During the weak charge mode, the battery voltage is too low to

allow the full system to power-up. Due to the low level of the

battery, the USB transceiver cannot be powered and, therefore,

cannot enumerate for more current from a USB host.

Consequently, the USB limit remains at 100 mA.

The system microcontroller may or may not be powered by the

charger output voltage (VISO_SFC) depending upon the amount of

current required by the microcontroller and/or the system

architecture. In this case, the battery charge current (ICHG_WEAK)

cannot be increased above 20 mA to ensure the microcontroller

can still operate (if doing so) nor increased above the 100 mA

USB limit. Thus, set the battery charging current as follows:

•

Set the default 20 mA via the linear trickle charger branch (to

ensure that the microprocessor remains alive if powered by

the main switching charger output, ISO_Sx). Any residual

current on the main switching charger output, ISO_Sx, is

used to charge the battery at up to the preprogrammed

level in the I2C for ICHG (fast charge current limit) or ILIM

(input current limit).

•

During weak current mode, other features may prevent the

actual programmed weak charging current from reaching

its full programmed value. Isothermal charging mode or

input current limiting for USB compatibility may affect the

programmed weak charging current value under certain

operating conditions. During weak charging, the ISO_Sx

node is regulated to VISO_SFC by the battery isolation FET.

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 (constant

current), the CHARGER_STATUS register is set.

During constant current 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 oper-

ating conditions. The voltage on ISO_Sx is regulated to stay at

VISO_SFC by the battery isolation FET when VISO_B < VISO_SFC.

Fast Charge Mode (Constant Voltage)

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

nation voltage, VTRM. The ADP5065 charger monitors the voltage

on the BAT_SNS pin to determine when charging should end.

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 BAT_SNS pin and the cell terminal

itself. To compensate for this and ensure a fully charged cell, the

ADP5065 enters a constant voltage charging mode when the

termination voltage is detected on the BAT_SNS pin. The

ADP5065 reduces charge current gradually as the cell continues to

charge, maintaining a voltage of VTRM on the BAT_SNS pin. During

fast charge mode (constant voltage), the CHARGER_ STATUS

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 BAT_SNS pin

reaching VTRM, a fault condition is assumed and charging stops.

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 has

been reached on the BAT_SNS pin but the charge current has

not yet fallen below IEND, charging stops. No fault condition is

asserted in this circumstance and charging resumes as normal if

the recharge threshold is breached.

Watchdog Timer

The ADP5065 charger features a programmable watchdog timer

function to ensure charging is under the control of the

processor. The watchdog timer starts running when the

ADP5065 charger determines that the processor should be

operational, that is, when the processor sets the RESET_WD bit

for the first time or when the battery voltage is greater than the

weak battery threshold, VWEAK. When the watchdog timer has

been triggered, it must be reset regularly within the watchdog

timer period, tWD.

If the watchdog timer expires without being reset while in

charger mode, the ADP5065 charger assumes there is a software

problem and triggers the safety timer, tSAFE. For more infor-

mation see the Safety Timer section.

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