AN2390 datasheet(8/42 Pages) STMICROELECTRONICS

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Theory of operation

AN2390

8/42

Once the battery is saturated, its voltage is still monitored to prevent the battery from

discharging completely. If the battery voltage drops below VTRI, charging restarts until VF is

reached again. Charge time is reset when trickle charging starts.

1.3

Slot management

In the demo, there are two different kinds of slots for charging Li-ion and NiMH battery

chemistries to show that it can support wide range of batteries. But the positive terminal of

one slot is shorted to the positive slot of another battery and similarly for the negative

terminals. So the system can support charging of only one battery at a time. Hence you

must take care to connect only one battery at a time to the charger. Otherwise the batteries

will be shorted together.

1.4

Man-machine interface

The charger periodically checks for battery presence so no button is needed to start or stop

charging. An LED is used to indicate the charge status as listed in Table 3..

A reset button is also included on the evaluation board to manually reset the application.

Table 2.

NiMH Charge parameters used in the evaluation board

Symbol

Meaning

Value

Unit

VMAX

Max Battery Voltage

1.7/Cell

VTRI

Trickle Charge Voltage

1.0V/Cell

VFAIL

Battery Failure Voltage

0.9/Cell

ICONST

Constant Charge Current

1000

ITRICKLE_1

Initial Trickle Charging Current

250

ISAT

Battery Saturation Current

IFAIL

Short Circuit Current

1200

tINITIAL

Initial Delay

minutes

tFAIL

Battery Failure Time

tEXP

Charge Expire Time

tFAST

Fast Charging Time

Table 3.

LED slot status color code

LED output

Charging status

OFF

No battery in the slot

Flashing @ 1 Hz

Charging ongoing

Flashing @ 2 Hz

Problem in charging

Battery Present/ Charging Complete

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