Datasheet

TPS40400

SLUS930B –APRIL 2011– REVISED OCTOBER 2011

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APPLICATION INFORMATION

PMBus

General Description

Timing and electrical characteristics of the PMBus can be found in the PMB Power Management Protocol

Specification, Part 1, revision 1.1 available at http://pmbus.org. The TPS40400 supports both the 100 kHz and

400 kHz bus timing requirements. The TPS40400 does not stretch pulses on the PMBus when communicating

with the master device.

Communication over the TPS40400 device PMBus interface can either support the Packet Error Checking (PEC)

scheme or not. If the master supplies CLK pulses for the PEC byte, it is used. If the CLK pulses are not present

before a STOP, the PEC is not used.

The TPS40400 supports a subset of the commands in the PMBus 1.1 specification. Most all of the controller

parameters can be programmed using the PMBus and stored as defaults for later use. All commands that require

data input or output use the literal format. The exponent of the data words is fixed at a reasonable value for the

command and altering the exponent is not supported. Direct format data input or output is not supported by the

TPS40400. See the SUPPORTED COMMANDS section for specific details.

The TPS40400 also supports the SMBALERT response protocol. The SMBALERT response protocol is a

mechanism by which a slave (the TPS40400) can alert the bus master that it wants to talk. The master

processes this event and simultaneously accesses all slaves on the bus (that support the protocol) through the

alert response address. Only the slave that caused the alert acknowledges this request. The host performs a

modified receive byte operation to get the slave’s address. At this point, the master can use the PMBus status

commands to query the slave that caused the alert. For more information on the SMBus alert response protocol,

see the System Management Bus (SMBus) specification.

The TPS40400 contains non-volatile memory that is used to store configuration settings and scale factors. The

settings programmed into the device are not automatically saved into this non-volatile memory though. The

STORE_DEFAULT_ALL command must be used to commit the current settings to non-volatile memory as

device defaults. The settings that are capable of being stored in non-volatile memory are noted in their detailed

descriptions.

Setting up the Controller – Hardware Connections

The TPS 40400 is an analog controller, meaning that it uses traditional analog circuitry to control the output of

the converter. Many of the operating parameters are set using the PMBus interface. This section describes how

to set the controller parameters in an application.

Output voltage. The output voltage is set in a very similar to the way to a traditional analog controller using a

voltage divider from the output to the feedback (FB) pin. The output voltage must be divided down to the nominal

reference voltage of 600mV. Figure 17 shows the typical connections for the controller. The voltage at the load

can be sensed using the unity gain differential voltage sense amplifier. This provides better load regulation for

output voltages lower than 5V nominal (see electrical specifications for the maximum output voltage of the

differential sense amplifier). For output voltages above this level, connect the output voltage directly to the

junction of R1 and C1, leave DIFFO open do not connect the VSNS inputs to the output voltage. In this case, it is

also recommended to connect VSNS+ to BP3 and VSNS- to GND. If desired the differential amplifier may also

be used elsewhere in the overall system as a voltage buffer provided the electrical specifications are not

exceeded

Product Folder Link(s) :TPS40400