PAC1932SLASH3SLASH4 datasheet(19/62 Pages) MICROCHIP

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DS20005850C-page 19

PAC1932/3/4

4.1

Detailed Description

A high-voltage multiplexer connects the input pins to

the VBUS and VSENSE amplifiers. The amplifier outputs

are sampled simultaneously for each channel,

converted by 16 bit ADCs and processed for gain and

offset error correction. After each conversion, VBUS

and VSENSE are multiplied together to give VPOWER.

An internal oscillator and digital control signals control

the two ADCs and the mux. The mux sequentially

connects each channel’s amplifiers to the ADC inputs.

The PAC1932/3/4 measures the source-side voltage,

VBUS, and the voltage VSENSE across an external

current sense resistor, RSENSE.

4.1.1

INITIAL OPERATION AND ACTIVE

STATE

After POR and a start-up sequence, the device is in

the Active state and begins sampling the inputs

sequentially. Voltage and current are sampled for all

active channels and power is calculated and

accumulated. All active channels are sampled at 1024

samples/second by default. Sample rates of 256, 64 or

eight samples/second may be programmed over I2C

or SMBus. If the SLOW pin is asserted the sample rate

is eight samples per second. For sampling rates lower

than 1024 samples/second, the device is in Sleep

mode for a portion of the conversion cycle, which

results in lower power dissipation. If fewer than four

channels are active, power is also reduced.

To read accumulator data and reset the accumulators,

the REFRESH command is used. To read the voltage,

current, power and accumulator data without resetting

the accumulators, the REFRESH_V command is

used. Changes to the Control register (01h) are

activated

sending

either

REFRESH

REFRESH_V. When a new value is written to the

Control register (01h), the new values take effect at

the end of the next round-robin sampling cycle

following the next REFRESH or REFRESH_V

command.

4.1.2

REFRESH COMMAND

The master sends the REFRESH command after

changing the Control register and/or before reading

accumulator data from the device. The master controls

the accumulation period in this manner.

The readable registers for the VBUS, VSENSE, Power,

accumulator outputs and accumulator count are

updated by the REFRESH command and the values

will be static until the next REFRESH command.

These readable registers will be stable within 1 mS

from sending the REFRESH command, and may be

read by the master at any time up until the next

REFRESH command is sent. The internal accumulator

values and accumulator count will be reset by the

REFRESH command, but the sampling of the inputs,

data conversion and power integration is not

interrupted and will continue as determined by the

settings in the Control register.

Changes written to the control and configuration

registers take effect 1 mS after a REFRESH command

is sent. Any new commands written within this 1 mS

window will be ignored and NACKed to indicate that

they are ignored.

The values for VBUS and VSENSE measurement results

and Power calculation results respond to the

REFRESH command in the same fashion as the

accumulators and accumulator count. The readable

registers will be stable within 1 mS from sending the

REFRESH command and may be read by the master

at any time. The internal values continue to be

updated according to the sampling plan determined by

the settings in the Control register. The results that are

sent to the readable registers for VBUS, VSENSE and

Power are the values from the most recent complete

conversion cycle. See Register 6-1 REFRESH

Command (Address 00h).

4.1.3

REFRESH_G COMMAND

The REFRESH_G is identical in every respect to the

REFRESH command, but it is used with the I2C

General Call address (0000 000). This allows the

system to issue a REFRESH command to all of the

PAC1932/3/4 devices in the system with a single

command. Then the data from this REFRESH_G

command may be read device-by-device to capture a

snapshot of the system power and energy for all

devices. See Register 6-12 REFRESH_G Command

(Address 1Eh). Note that the REFRESH_G command

can also be used with a valid Slave address but in this

case only the device with this Slave address will

receive the command. In other words it has the same

properties as the REFRESH command with the

possibility of being compatible with the I2C General

Call address.

4.1.4

REFRESH_V COMMAND

If the user wants to read VSENSE and VBUS results, the

most recent Power calculation, and/or the accumulator

values and count without resetting the accumulators,

the REFRESH_V command may be sent. Sending the

REFRESH_V command and waiting 1 mS ensures that

the

VSENSE, VBUS, Power, accumulator and

accumulator count values will be stable when read by

the master. The sampling of the inputs, data conversion

and power integration are not interrupted and will

continue as determined by the settings in the Control

remain stable until the next REFRESH or REFRESH_V

command. The internal accumulator values and

accumulator count are unaffected by the REFRESH_V

command.

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