PS700 datasheet(8/38 Pages) MICROCHIP

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PS700

DS21760F-page 8

 2004 Microchip Technology Inc.

3.1.8

CHARGE/DISCHARGE TIME

COUNTERS

The Charge Time Counter (CTC) will increment at the

rate of 2 counts every second as long as a negative

voltage is measured at the SR pin. The CTC can

thereby maintain a time count representing the total

time that charge current has flowed into the battery.

The Discharge Time Counter (DTC) will increment at

the rate of 2 counts every second as long as a positive

voltage is measured at the SR pin. The DTC can

thereby maintain a time count representing the total

time that discharge current has flowed from the battery.

3.1.9

GENERAL PURPOSE

ACCUMULATORS

There are two general purpose accumulators, TA and

VC2A. For typical applications, these accumulators

have been assigned specific functions. The user can

redefine the use of these accumulators to fit the design

requirements.

TA can be used to accumulate results from the ITres or

ETres registers. Accumulation to TA must be enabled

in the Accumctrl register bit “AccT”. The selection for

accumulation of the values represented by the internal

or external thermistor is also determined in the

Accumctrl register bit “tsel”.

VC2A can be used to accumulate results from VC2res.

Accumulation in VC2A must be enabled in the

Accumctrl register bit “AccV”. The value stored in

VC2res corresponds to the measurement as defined in

the A/D Control register VC2ctrl. This function is

utilized if the VC2 pin is configured as an independent

A/D input and not connected to the cell stack.

The “Accum” bit in the Accumctrl register must be

enabled for accumulation to occur in TA and VC2A.

3.1.10

GENERAL PURPOSE TIMERS

There are two general purpose timers that are enabled

by accumulation in the TA and VC2A accumulators.

TAT is used to maintain a time count during accumula-

tion in the TA register. This timer increments at a

frequency of 2 counts every second.

VC2T is used to maintain a time count during

accumulation

the

VC2A

This

timer

increments at a frequency of 2 counts every second.

3.2

Power Modes

The PS700 has four operational power modes: Run,

Sample, Sample-Sleep and Shelf-Sleep. Each con-

sumes power according to the configuration settings as

described in the following sections.

3.2.1

RUN MODE

During Run mode, the PS700 performs continuous A/D

conversion cycles per the programming of the A/D

conversion cycle documented in Section 3.1.1 “A/D

Conversion Cycle”. As described above, during each

cycle, between 1 and 8 conversions are performed and

the accumulators/time counters are updated as

programmed by the user.

Run mode is entered following a Power-on Reset when

the pack voltage (VPACK) applied on the VC1 pin rises

above the VPOR threshold. Run mode can also

be entered from the Sample, Sample-Sleep and

Shelf-Sleep modes as described below.

The PS700 will remain in Run mode as long as the pack

voltage is above the VPOR threshold and the Sample,

Sample-Sleep and Shelf-Sleep modes are not active.

3.2.2

SAMPLE MODE

In Sample mode, A/D measurements are not continu-

ously performed as in Run mode. Instead, they are

performed at a user selectable rate. The purpose of

Sample mode is to reduce power consumption during

periods of low rate charge or discharge. The power

advantage of Sample mode comes from the reduction

in frequency of A/D measurements.

Sample mode is entered by programming the “Samp”

bit = 1 in the A/D Configuration register. The PS700 will

remain in Sample mode as long as “Samp” bit = 1 and

the VC1 voltage is above the VPOR threshold and the

Sample-Sleep and Shelf-Sleep modes are not active.

Run mode will be resumed when the Samp bit is

cleared to ‘0’.

The Sample mode rate is selected using the “SampDiv”

bits within the A/D Configuration register. The sample

interval is 2**(SampDiv) * 0.5 sec. The possible sample

rate intervals are as follows.

TABLE 3-6:

SAMPLE RATE INTERVALS

In Sample mode, much of the analog circuitry remains

on. Therefore, the power savings are not as great as in

Sample-Sleep mode (described below). Refer to

Section 6.0 “Electrical Characteristics” for a specifi-

cation of the amount of current consumed in Sample

mode.

“SampDiv”

Sample Interval

Value = 0

0.5s

Value = 1

1.0s

Value = 2

2.0s

Value = 3

4.0s

Value = 4

8.0s

Value = 5

16.0s

Value = 6

32.0s

Value = 7

64.0s

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