MP26121 – +28V, 1A Li+ Linear Batt Charger with Flexible NTC Interface

MP26121 Rev. 0.9

www.MonolithicPower.com

8

9/15/2008

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Resistance

The recommended resistance for programming

charging status. When the battery full condition

is met or any other condition prevents the

floating pin.

Timer Operation

The TMR pin is used to set the internal

oscillator frequency,

OSC

TMR

F

F11Hz

C

µ

=×

. The

on-chip timer will start to count down after initial

power-up or every time it is enabled. This timer

will limit the max trickle-charge time to 32768

internal oscillating cycles. If the charger stays in

trickle mode for longer than 32768 cycles, it will

be terminated and a fault will be set by floating

CHG

pin. After fault reporting, the charger can

be re-initiated only by recycling the power

supply or SHDN signal. If the charger

successfully goes through trickle charge within

the allowed time limit, it will start CC charging

and then CV charging. If the total charge time

exceeds 262144 cycles and the battery full has

not been qualified, the charger will be

terminated and a fault will also be set by

oscillation frequency. This function prevents

charging a dead battery for prolonged duration.

The timer function can be disabled by shorting

TMR to ground.

Charger Status Indication

SHDN = High Vin

Fault

Battery Full

Time out Fault Ambient Temperature Fault

In Charging

CHG

HIGH

HIGH

Toggle

HIGH

LOW

ACOK

Negative Thermal Coefficient (NTC) Thermistor

The MP26121 has a built-in NTC resistance

window comparator. If configured as the typical

application circuit as indicated in Figure 1, the

MP26121 can fit most types of NTC resistors

with two extra programming resistors.

NTCH

NTCL

NTCL

NTCH

R

R

R

R

R

×

−

×

×

×

=

416

.

0

108

.

0

308

.

0

T2

()

NTCL

T

T

R

R

R

//

828

.

0

2

1

×

=

For example, for the EWTF03-103 J31 H NTC

resistor, the valid charging temperature range is

from 0°C to 50°C. The MP26121 will cease

Thermal Protection

The

MP26121

has

proprietary

thermal

protection to prevent the IC from overheating.

When in thermal protection mode, the average

charge current will be reduced to prevent the IC

from

overheating.

Operating

in

thermal

protection mode will slow down the charging

process. Lowering the input voltage and

enhancing

thermal

dissipation

to

the

environment can effectively prevent the IC from

going into thermal protection mode.

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