SMM605 datasheet(9/23 Pages) SUMMIT

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SMM605

Preliminary Information

Summit Microelectronics, Inc

2064 1.1 09/16/03

APPLICATIONS INFORMATION

DEVICE OPERATION

POWER SUPPLY

The SMM605 can be powered by either an 6V to 14V

input through the 12VIN pin or by a 2.7V to 5.5V input

through the VDD pin (Figure 5). The 12VIN pin feeds

an internal programmable regulator that internally

generates either 5.5V or 3.6V. The internal regulator

must be set to 3.6V if using an 8V supply. 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 SMM605. 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.

VOLTAGE REFERENCE

The SMM605 can operate using either an internal or

external voltage reference, VREF. The internal VREF

is set to 1.25V. Total accuracy with a ±0.1% external

reference is ±0.2% and ±0.5% using the internal

reference.

MODES OF OPERATION

The SMM605 has two basic modes of operation:

supply margining mode and Active DC Output Control

(ADOC

TM). A detailed description of each mode and

feature follows.

ACTIVE DC OUTPUT CONTROL (ADOC)

The SMM605 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 SMM605 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 7, or

an equivalent output voltage feedback adjustment

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

8. Each of the TRIMX pins on the SMM605 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 VMX 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 SMM605 to control the output voltage of

power supply converters to within ±0.2% when using a

±0.1% external voltage reference.

The voltage on the TRIM_CAPX pins is buffered and

applied to the TRIMX pin. The voltage adjustments on

the TRIMX pins cause a slight ripple of less than 1mV

on the power supply voltage. The amplitude of this

ripple is a function of the TRIM_CAPX capacitor and

the trim gain of the converter. Calculation of the

TRIM_CAPX capacitor to achieve a desired minimum

ripple is detailed in Application Note 37.

The pulse of current can be increased to a 10X pulse

of current until the power supply voltages are at their

nominal settings by selecting the programmable Fast

Convergence option. As the name implies, this option

decreases the time required to bring a supply voltage

from the converter’s nominal output voltage to the

Active DC Output Control nominal voltage setting.

The device can be programmed to either enable or

disable the Active DC Control function.

When

disabled or not active, the TRIMX pins on the SMM605

are high impedance inputs. The voltage on the TRIMX

pins are buffered and applied to the TRIM_CAPX pins

charging the capacitor.

This allows a smooth

transition from the converter’s nominal voltage to the

SMM605 controlling that voltage to the Active DC

Control nominal setting.

MONITORING

The SMM605 monitors the VMX pins. The READY pin

is programmable active high/low open drain output

indicates that all VMX pins are at their set point.

SMM605 Datasheet(PDF) 9 Page - Summit Microelectronics, Inc.

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