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ADP1050

Data Sheet

Clock Generation and Stretching

The ADP1050 is always a PMBus slave device in the overall system;

therefore, the device never needs to generate the clock, which is

done by the master device in the system. However, the PMBus

slave device is capable of clock stretching to put the master in a

wait state. By stretching the SCL signal during the low period, the

slave device communicates to the master device that it is not

ready and the master device must wait.

Conditions in which the PMBus slave device stretches the SCL

line low include the following:

•

The master device is transmitting at a higher baud rate

than the slave device.

•

The receive buffer of the slave device is full and must be

read before continuing. This prevents a data overflow

condition.

•

The slave device is not ready to send data that the master

has requested.

Note that the PMBus slave device can stretch the SCL line only

during the low period. Also, whereas the I2C specification allows

indefinite stretching of the SCL line, the PMBus specification

limits the maximum time that the SCL line can be stretched, or

held low, to 25 ms. After this time period, the slave device must

release the communication lines and reset its state machine.

Start and Stop Conditions

Start and stop conditions involve serial data transitions when the

serial clock is at a logic high level. The PMBus slave device moni-

tors the SDA and SCL lines to detect the start and stop conditions

and transitions its internal state machine accordingly. Typical

start and stop conditions are shown in Figure 45.

SCL

SDA

START

STOP

Figure 45. Start and Stop Conditions

GENERAL CALL SUPPORT

The PMBus slave is capable of decoding and acknowledging

a general call address. The PMBus slave device responds to both

its own address and the general call address (0x00). The general

call address enables all devices on the PMBus to be written to

simultaneously.

Note that all PMBus commands must start with a slave address,

with the R/W bit cleared to 0 and followed by the command code.

This is also true when using the general call address to communi-

cate with the PMBus slave device.

10-BIT ADDRESSING

The ADP1050 does not support 10-bit addressing as defined in

the I2C specification.

FAST MODE

Fast mode, with a data rate of 400 kbps, uses essentially the

same mechanics as the standard mode of operation; the electrical

specifications and timing are most affected. The PMBus slave is

capable of communicating with a master device operating in fast

mode or in standard mode, which has a data rate of 100 kbps.

FAULT CONDITIONS

The PMBus protocol provides a comprehensive set of fault

conditions that must be monitored and reported. These fault

conditions can be grouped into two major categories:

communication faults and monitoring faults.

Communication faults are error conditions associated with the

data transfer mechanism of the PMBus protocol. Monitoring

faults are error conditions associated with the operation of the

ADP1050, such as output overvoltage protection. These fault

conditions are described in detail in the Power Monitoring,

Flags, and Fault Responses section.

TIMEOUT CONDITIONS

The SMBus specification includes three clock stretching

specifications related to timeout conditions.

A timeout condition occurs if any single SCL clock pulse is held

low for longer than the minimum tTIMEOUT value of 25 ms. Upon

detecting the timeout condition, the PMBus slave device has 10 ms

to abort the transfer, release the bus lines, and be ready to accept

a new start condition. The device that is initiating the timeout must

hold the SCL clock line low for at least the maximum tTIMEOUT

value of 35 ms, guaranteeing that the slave device is given enough

time to reset its communication protocol.

DATA TRANSMISSION FAULTS

Data transmission faults occur when two communicating devices

violate the PMBus communication protocol, as specified in the

PMBus Power System Management Protocol Specification

(Revision 1.2, September 6, 2010). See the specification for

more details on each fault conditions.

Corrupted Data, Packet Error Checking (PEC)

Packet error checking is not supported by the ADP1050.

Sending Too Few Bits

Transmission is interrupted by a start or stop condition before

a complete byte (eight bits) has been sent. This function is not

supported; any transmitted data is ignored.

Reading Too Few Bits

Transmission is interrupted by a start or stop condition before

a complete byte (eight bits) has been read. This function is not

supported; any received data is ignored.

Rev. A | Page 40 of 92

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