SMM150
Preliminary Information
GENERAL DESCRIPTION
The SMM150 is 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
2
C serial data interface and is
used to set the margin low/high DC output voltages.
In margining mode the user communicates with the
SMM150 via the I
2
C 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 SMM150 receives 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 input. This operation is repeated until the 2 values
are equal, after which the SMM150 holds the TRIM
output pin at the voltage required to maintain the
margin setting. An I
2
C 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 SMM150 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 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.
Programming of the SMM150 is performed over the
industry standard I
2
C 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.
Summit Microelectronics, Inc
2075 2.6 05/13/05
2
SUMMIT [ SUMMIT MICROELECTRONICS, INC. ]
