SMM151 datasheet(10/23 Pages) SUMMIT

10 / 23 page

SMM151/152

Preliminary Datasheet

Summit Microelectronics, Inc

2131 2.1 8/15/2008

DEVICE OPERATION

POWER SUPPLY

The SMM151 and SMM152 can be powered by a 2.7V

to 5.5V input to the VDD pin (Figure 1). See Figure 6

as an example.

VOLTAGE REFERENCE

The SMM151/152 use an internal voltage reference,

VREF with a level of 1.25V. Total accuracy of VREF is

±1.0% over temperature and supply variations.

MODES OF OPERATION

The SMM151/152 have four basic modes of operation:

under-voltage (UV) and over-voltage (OV) monitoring

mode, differential output voltage sensing mode, input

current monitoring mode and supply margining mode.

A detailed description of each mode and feature

follows and can also be found in Application Note 68.

A flow diagram is shown in Figure 5.

MARGIN MODE

The SMM151/152 can control margining of a DC/DC

converter that has a trim pin or any regulator having

access to its feedback node. The TRIM pin on the

SMM151 is connected to the trim input pin on the

power supply converter. Sense lines from the

converter’s point-of-load connects to the VM+ and VM-

inputs. The margin function begins upon an I

command or assertion of the MUP/MDN pins. The

TRIM pin is driven by a DAC whose input is

incremented or decremented every 200µs based on

the digital comparison of the margin target value and

the actual converter output voltage. The voltage on the

TRIM output will continue increasing (decreasing) until

the converter’s output voltage equals the target margin

voltage. This voltage adjustment allows the SMM151

and SMM152 to control the margined output voltage of

the power supply converter to within ±1.0% in an

open-loop manner.

The converter is held at the margin voltage until the

SMM151 receives an I

2C command or the respective

MUP/MDN pin is de-asserted. When not margining,

the TRIM pin on the SMM151/152 is in a high

impedance state. The voltage on the TRIM pin is

buffered and applied to the ADC at the beginning of a

margin cycle to ensure the converter is margined from

its nominal setpoint. This allows a smooth transition

from

the

converter’s

nominal

voltage

the

SMM151/152 controlling that margin voltage to the

margin target setting. After margining high, low or

nominal, issuing a margin Off command will cause the

trim pin to go high impedance. The part margin time

from Off to High or Off to Low is specified as a typical

according to the equation:

TMARG_UPDATE = (X)(1.8ms) where:

X=step number of possible 256 and 1 step = 10mV

The Active Margin Command Delay Time using the

MUP and MDN pins is shown in Figure 4.

DC/DC

Supply

GND

SMM151

MPU/D/EN

Total Margin Delay Time

Margin

N/H/L

ADC_DAC ADC/DAC

Sample/

Conversion time

1.8ms

MARGIN_UPDATE

MARGIN - Internal

Programmable Active

Margin Delay Time

Turn on Time

ADC_DAC ADC/DAC

Sample/

Conversion time

Figure 4 – Margin Delay Time

APPLICATIONS INFORMATION

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