PT8A2707 Datasheet, PDF(6/26 Page) Pericom Semiconductor Corporation – Charger Controller with Fuel-Guage & LCD/LED Display

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PT8A2707-12/17-19

Charger Controller

with Fuel-Guage & LCD/LED Display

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Function description (refer to Flow Chart)

1. Battery Voltage Definitions:

Item

No-Power value

Battery-Low value

Max VB

Table 3: Battery Voltage Definition

General Setting

Suggested Value

0.9V-1.0V/cell

1.8-2V for 2cells battery pack

1.0V-1.1V/cell

2.0-2.2V for 2cells battery pack

1.65V-1.7V/cell

3.3-3.4V for 2cells battery pack

Remark

Adjustable externally,

please refer to

âapplication instructionâ

2. Charging Mechanism (cord is connected but motor is off)

When a cord is detected, pre-charge begins. If the battery voltage is higher than Battery-Low threshold (usually set between

0.95V-1.1V/cell) and the battery pack temperature is less than 45ï°C, fast-charge starts. Otherwise, the battery will be kept in

pre-charge status until its voltage is higher than the preset Battery-Low value or a 3 minutes time-out is reached to enter fast-

charge mode. If battery temperature is found increasing to 55ï°C during pre-charge state, battery charging is stopped (DC/DC

cuts power) to enter cool down state. Nevertheless, pre-charge will continue in any case until the battery temperature is

cooled down below 45ï°C.

When entering fast-charge mode, if the battery voltage is below a preset voltage level (usually set at about 1.3V-1.4V/cell,

measured with charging current), a start-up timer is effective to avoid false triggering of -ÎV and dT/dt to have early fast-

charge termination. During the start-up time, -ÎV and dT/dt detections are ignored but maximum temperature of 55ï°C will

always be observed to stop fast-charge. The start-up timer is dependent to the external fast-charge timer setting as tabled

below. The dT/dt data is valid for battery temperature in range of 35ï°C to 55ï°C.

Table 4: Start-up Time

Timer

Tmax (User programmable externally)

Start-up timer for inhibiting

tmax/20

negative ïV and dT/dt

tmax (min)

Start-up time (s)

measurement

180

270

150

450

Fast charge mode is terminated when any one of the following conditions meet:

1) Minus-delta-V Detection (-ïV): The battery pack voltage is sampled by high precision A/D converter every 10s, with 0.5s

sampling time. For each sampling interval (0.5s), the charging current is cut down. Averaging is performed on the collected

data and the result is stored into registers after passing through high-order digital filter. The minus-delta-V is qualified when a

voltage drop of about 5mV/cell from the maximum voltage recorded. The second minus-delta-V is qualified when a voltage

drop of about 5mV/cell after the first minus-delta-V has been qualified. Every minus-delta-V happened, fuel-gauge increased

one level up, and so and so until fuel-gauge is full.

Table 5: Sample Description

Bypass Start-up timer

VB > 2.6V (measured by sampling)

VB sampling period (tp)

10s

VB sampling time

0.5s (fast-charging inhibition)

BT sampling period (tp)

10s (time-multiplexing with VB sampling)

tp=0.5s

VB measurement

BT measurement

2) Maximum Battery Voltage Detection: When the averaged battery pack voltage reaches a preset maximum voltage limit

(usually set about 1.6V-1.7V/cell) during the charging interval, fast-charge in terminated.

3) Battery Temperature Detection (Max. Temp and dT/dt): The PT8A2707-12/2717-19 employs thermistor(NTC) as battery

temperature sensor. When the battery temperature reaches 55ï°C, fast-charge is terminated and the battery will then go to cool

down mode; or the rate of temperature change (dT/dt) reaches preset value, fast-charge is terminated and the battery will then

be under trickle-charge mode at a rate of 1/10 of the fast-charge current. If NTC is not employed, the pin âVTâ should be

biased at an equivalent voltage as for 10ï°C-20ï°C or else the PT8A2707-12/2717-19 determines the NTC is opened and will

stop all charging activity forever.

12-07-0005

PT0268-1 07/05/12

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