MP2615

– 2A, 1- CELL OR 2- CELL LI-ION BATTERY CHARGER

MP2615 Rev. 1.0

www.MonolithicPower.com

13

1/16/2014

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© 2014 MPS. All Rights Reserved.

Charge Full Termination and Auto-Recharge

When the charge current drops below the

phase, the charger will stop charging and the

CHGOK

pin becomes open drain. The timer will

also be reset and turned off. Once the battery

voltage decreases below the recharge threshold

(4.0V/Cell

while

connect

SEL-pin

to

AGND), recharging will automatically kick in and

the timer restarts a new charge cycle.

COT Charge Mode

The MP2615 uses the floating ground method to

drive

the

high-side

MOSFET

of

the

buck

converter. During the off-time of the high-side

MOSFET, the BST capacitor is recharged and

the voltage across it is used as the HS-MOS gate

drive. Thus a minimum off-time 200ns is required

to maintain sufficient voltage at BST capacitor.

When200ns minimum off-time is achieved due to

large duty cycle, the MP2615 will enter COT

(constant off-time) charge mode. In this mode of

operation,

switching

frequency

is

slightly

decreased in order to achieve 99% duty cycle.

Charge Status Indication

The MP2615 has two open-drain status outputs,

CHGOK

pin and ACOK pin. The ACOK pin

goes low when the input voltage is 300mV larger

than battery voltage and over the under voltage

the

status

of

the

charge

cycle.

Table

1

ACOK according to the status of charge.

Table 1: Charging Status Indication

ACOK

CHGOK

Charger Status

Low

Low

In charging

Low

High

impedance

End of charge;

NTC fault;

Timer out:

Thermal shutdown;

High

impedance

High

impedance

Safety Timer Operation

The MP2615 has an internal safety timer to

terminate charging during time out. The capacitor

is used to set the internal oscillator period,

P

TMR

T (seconds)

0.46 C

(uF)



(1)

This timer limits the max trickle charge time to

8192 internal oscillating periods. If the charger

stays in trickle charge mode for longer than the

max oscillating periods, it will be terminated and

timer-out fault. If charge cycle successfully goes

through trickle charge within the allowed time

limit, it enters into the CC charge mode and the

timer continues to count the oscillating periods.

When the battery is charged full, the timer turns

off and clears the counter, waiting for the auto-

recharge to restart.

If the charge time during CC/CV mode exceeds

49152 oscillating periods and the battery full has

not been qualified, the charger will be terminated

and a timer-out fault is also indicated by floating

fault state and the on-chip safety timer restarts

counting when one of the following conditions

occurs:



The battery voltage falls below the auto-



A power-on-reset (POR) event occurs;



EN pin is toggled.

The timer can be disabled by pulling TMR-pin to

AGND.

Thus, the trickle mode charge time is:

Trickle_tmr

TMR

t

(minutes)

62.8 C

(uF)



(2)

time is about 30 minutes.

The CC/CV mode charge time is:

Total_tmr

TMR

t

(hours)

6.28 C

(uF)



(3)

time is 2.95 hours.