SMM205

Preliminary Information

Summit Microelectronics, Inc

2069 1.4 6/23/03

2

GENERAL DESCRIPTION

The SMM205 is capable of controlling and margining

the DC output voltage of LDOs or DC/DC converters

that use a trim/adjust pin and to automatically change

the level using a unique Active DC Output Control

(ADOC). The ADOC function is programmable over a

standard 2-wire I

used to set the nominal DC output voltage as well as

the margin high and low settings. The part actively

controls the programmed set levels to maintain tight

control over load variations and voltage drops at the

point of load. The margin range will vary depending on

the supply manufacturer and model but the normal

range is 10% adjustment around the nominal output

setting. However, the SMM205 has the capability to

margin from VREF_CNTL to VDD.

The user can set the desired voltage settings

(nominal, margin high and margin low) into the EE

memory array for the device. Then, volatile registers

are used to select one of these settings. The registers

are accessed over the I

In normal operation, Active DC Output Control is set to

adjust the nominal output voltage of one or two

trimmed converters.

Typical converters have

±2%

accuracy ratings for their output voltage. Using the

Active DC Output Control feature of the SMM205 can

increase the accuracy to

±0.2%. This high accuracy

control of a converter output voltage is extremely

important in low voltage applications where deviations

in power supply voltage can result in lower system

performance.

Active DC Output Control may be

turned off by de-selecting the function in the Control

Select Register. Active DC Output Control can also be

used for margining a supply during system test.

When the SMM205 receives the command to margin

the Active DC Output Control will adjust the supply to

the selected margin voltage. Once the supply has

reached its margined set point the Ready bit in the

status register will set and the READY pin will go

active. If Active DC Control is disabled a margined

supply can return to its nominal voltage by writing to

the margin command register.

In order to obtain maximum accuracy the SMM205

requires an external voltage reference. An external

reference with ±0.1% accuracy will enable an overall

±0.2% accuracy for the device. A configuration option

also exists so that an internal voltage reference can be

used, but with less accuracy. Total accuracy using the

internal reference is ±0.5%. The SMM205 can be

powered from either a 12V or 8V input via an internal

regulator, or the VDD input (Figure 3).

The SMM205 has two additional input pins and one

additional output pin. The input pins, COMP1 and

COMP2, are high impedance inputs, each connected

to

a

comparator

and

compared

against

the

VREF_CNTL input or the internal reference (VREF).

Each comparator can be independently programmed

to monitor for UV or OV. When either of the COMP1

or COMP2 inputs are in fault the open-drain FAULT#

output will be pulled low. A configuration option exists

to disable the FAULT# output during margining.

Programming of the SMM205 is performed over the

industry standard I

status register is available to read the state of the part,

and a Write Protect (WP#) pin is available to prevent

writing to the configuration registers and EE memory.

Figure 2 – Example Power Supply Margining using the SMM205. The waveform on the left is margin nominal

to high from 2.5V to 2.8V and 1.8V to 2.1V. The waveform on the right is margin nominal to low from 2.5V to

2.2V and 1.8V to 1.5V. The bottom waveform is the READY signal indicating when margining is complete.