SMM665B datasheet(13/30 Pages) SUMMIT

13 / 30 page

SMM665B

Preliminary Information

Summit Microelectronics, Inc

2089 1.1 10/20/04

APPLICATIONS INFORMATION

DEVICE OPERATION

POWER SUPPLY

The SMM665B can be powered by either a 12V input

through the 12VIN pin or by a 3.3V or 5.0V input

through the VDD pin. The 12VIN pin feeds an internal

programmable regulator that internally generates

either 5.5V or 3.6V. A voltage arbitration circuit allows

the device to be powered by the highest voltage from

either the regulator output or the VDD input. This

voltage arbitration circuit continuously checks for these

voltages to determine which will power the SMM665B.

The resultant internal power supply rail is connected to

the VDD_CAP pin that allows both filtering and hold-

up of the internal power supply. To ensure that the

input voltage is high enough for reliable operation, an

under voltage lockout circuit holds the controlled

supplies off until the UVLO thresholds are met.

MODES OF OPERATION

The SMM665B has four basic modes of operation

(shown in Figures 5 through 8): Power-on cascade

sequencing mode, ongoing operations-monitoring

mode, supply margining mode and Power-off cascade

sequencing mode. In addition, there are two features:

ADOC and forced shutdown which can be used during

monitoring and margining mode. A detailed description

of each mode and feature follows.

ACTIVE DC OUTPUT CONTROL (ADOC

TM)

The SMM665B can actively control the DC output

voltage of bricks or DC/DC converters that have a trim

pin during monitoring and margining mode.

The

converter may be an off-the shelf compact device, or

may be a “roll your own” circuit on the application

board. In either case, the SMM665B dramatically

improves voltage accuracy (down to 0.2%) by

implementing closed-loop ADOC active control. This

utilizes the DC-DC’s “trim” pin as shown in Figure 12,

or an equivalent output voltage feedback adjustment

“VADJ” or “FB” node in a user’s custom circuit, Figure

13. Each of the TRIMX pins on the SMM665B is

connected to the trim input pins on the power supply

converters. A sense line from the channel’s point-of-

load connects to the corresponding VM input. The

ADOC function cycles through all six channels (A-F)

every 1.7ms making slight adjustments to the voltage

on the associated TRIMX output pins based on the

voltage inputs on the VMX pins.

These voltage

adjustments allow the SMM665B to control the output

voltage of power supply converters to within ±0.2%

when using a ±0.1% external voltage reference.

Figure 7 - Waveform shows four SMM665B channels

exhibiting Sequence-on to Nominal voltage, Margin

High or Low, Nominal voltage and then sequence-off

Ch 1 = 2.5V DC-DC converter output (Yellow trace)

Ch 2 = 1.8V DC-DC converter output (Blue trace)

Ch 3 = 1.5V DC-DC converter output (Purple trace)

Ch 4 = 1.2V DC-DC converter output (Green trace

Figure 8 - Waveform shows two SMM665B channels

Sequencing-on to Nominal voltage, Margin High and

Low, and then sequence-off. Channel 3 and 4 shows

the RST and HEALTHY signals.

Ch 1 = 2.5V DC-DC converter output (Yellow trace)

Ch 2 = 1.5V DC-DC converter output (Blue trace)

Ch 3 = RST signal output (Purple trace)

Ch 4 = HEALTHY signal output (Green trace

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