PS700 datasheet(4/38 Pages) MICROCHIP

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PS700

DS21760F-page 4

 2004 Microchip Technology Inc.

2.0

ARCHITECTURAL OVERVIEW

The PS700 contains a complete analog “front-end” for

battery monitoring as well as digital logic for control, mea-

surement accumulation, timing and communications.

Major functions within the PS700 include:

• Voltage Regulator

• Precision Time Base

• Temperature Sensor

• 512-Byte EEPROM Memory

• 32-Byte RAM Memory

• Analog-to-Digital (A/D) Converter

• 32-bit Accumulators/Timers

•SMBus/I2C Communications Interface

Figure 1-1 is a block diagram of the internal circuitry of

the PS700. Figure 1-2 is a schematic diagram that

depicts the PS700 in a typical single cell Lithium Ion

application. The function of each of the blocks listed

above is summarized in the following sections.

2.1

Internal Voltage Regulator

The PS700 incorporates an internal voltage regulator

that supports 1 or 2-cell series lithium pack configura-

tions. The internal regulator draws power directly from

the VC1 input. No other external components are

required to regulate internal supply voltage.

2.2

Precision Time Base

The integrated precision time base is a highly accurate

RC oscillator that provides precise timing for the sigma-

delta A/D and for the on-chip elapsed time counters

without the need for an external crystal. This time base

trimmed

during

manufacturing

nominal

frequency of 131,072 Hz.

2.3

Temperature Sensor

An integrated temperature sensor is provided that can

eliminate the need for an external thermistor. As an

option, a connection is provided for an external

thermistor for applications where the battery pack is

physically located at a distance away from the PS700.

2.4

EEPROM Memory

512 bytes of EEPROM memory are incorporated for

storage

nonvolatile

parameters,

such

PowerSmart® 3D cell models for use with host driver

firmware. An initialization block is reserved within the

EEPROM array for values that are loaded into PS700

registers following a power-on condition.

2.5

RAM Memory

32 bytes of general purpose RAM memory are

provided for storage of temporary parameters.

2.6

A/D Converter

The PS700 incorporates an integrating sigma-delta

A/D converter together with an analog mux that has

inputs for charge and discharge current, cell and pack

voltages, the on-chip temperature sensor and an off-

chip thermistor. The converter can be programmed to

perform a conversion with resolutions of 8 to 15 bits plus

sign while utilizing either a ±340 mV or a ±170 mV

reference.

2.7

32-Bit Accumulators/Timers

The PS700 incorporates four 32-bit accumulators and

four 32-bit elapsed time counters. The Discharge

Current Accumulator (DCA) and the Charge Current

Accumulator (CCA) are intended to record discharge

and charge capacity values. The Discharge Time

Counter (DTC) and the Charge Time Counter (CTC)

are intended to maintain the total discharge time and

charge time. Accumulated charge and discharge

values can be used to determine state of charge of the

battery as well as cycle count information. With

information provided by the elapsed time counters,

average charge and discharge currents over an

extended period of time can be calculated.

2.8

SMBus/I2C Communications

Interface

The communications port for the PS700 is a 2-wire

industry standard SMBus/I2C interface. All commands,

status and data are read or written from the host

system via this interface.

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