SMM151 datasheet(2/23 Pages) SUMMIT

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SMM151/152

Preliminary Datasheet

Summit Microelectronics, Inc

2131 2.1 8/15/2008

The SMM151 and SMM152 are capable of margining the

DC output voltage of LDOs or DC/DC converters that

use a trim/adjust pin. The Margin function is

programmable over a standard 2-wire I

2C serial data

interface and is used to set the margin low/high DC

output voltages. The devices are also capable of

monitoring the differential output voltage and the input

current of DC/DC converters, thereby providing real-time

power information to the system.

In margining mode the user communicates with the

SMM151/152 via the I

2C serial data bus to select the

desired values for margining. This allows the part to

margin the supplies up or down to these set values

either through asserting the MUP and MDN pins or by

writing to the margin register directly. The margin high

and margin low voltage settings can range from 0.3V to

VDD around the converter’s nominal output voltage

setting depending on the specified margin range of the

DC-DC converter and/or system components, usually

±10%.

When the SMM151/152 receive the command to margin,

the TRIM output will begin adjusting the supply to the

selected margin voltage. This is accomplished by

incrementing (or decrementing) an internal counter

based on the digital comparison between the voltage

margin target value and that read by the ADC from the

VM+ - VM- differential input. This operation is repeated

until the 2 values are equal, after which the

SMM151/152 hold the TRIM output pin at the voltage

required to maintain the margin setting. An I

2C command

or de-assertion of the MUP/MDN pin will return the TRIM

output pin to a high impedance state thus allowing the

converter to return to its nominal operating voltage.

The SMM151 and SMM152 sense converter input

current using a sense resistor connected in series with

the converter supply whose terminals are connected to

the CS+ and CS- pins. The internal ADC, also used for

measuring the converter’s output voltage, is used to

measure the converter’s input current using the voltage

dropped across the current sense resistor RS (see

Figure 1).

The SMM151/152 have 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 internal

reference (VREF: 0.5V or 1.25V). 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.

The SMM152 also provides four programmable general-

purpose inputs/outputs. The power-on state of these

I/Os is determined via non-volatile (NV) memory. Volatile

programming allows the user to select the logic level

(HIGH or LOW) of each I/O, which can also be read via

a status register.

Programming of the SMM151/152 is performed over the

industry standard I

2C 2-wire serial data interface. A

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.

GENERAL DESCRIPTION

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