SMS66
Preliminary Information
APPLICATIONS INFORMATION
POWER-ON SEQUENCING
DEVICE OPERATION
The SMS66 can be programmed to sequence up to six
power supplies in any order. Each of these six
channels (A-F) has an associated open drain PUP
output that, when connected to a converter’s enable
POWER SUPPLY
The SMS66 can be powered by either a 12V input
through the 12VIN pin or by a 3.3V or 5.0V input
through the VDD pin. The 12VIN pin feeds an internal
programmable regulator that internally generates
either 5.5V or 3.6V. 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 SMS66.
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.
pin, controls the turn-on of the converter.
The
channels are assigned sequence positions to
determine the order of the sequence. Any channel
can also be programmed to not take part in the
sequencing in applications with fewer than six
supplies. The polarity of each of the PUPX outputs is
programmable for use with various types of
converters.
Power-on sequencing can be initiated by the
PWR_ON/OFF pin or via I2C control. The polarity of
the PWR_ON/OFF pin is programmable. If hard wired
in its active state the SMS66 will automatically initiate
the Power-on sequence. Otherwise, toggling the
PWR_ON/OFF pin to its active state will initiate the
Power-on sequence. To enable software control of
the sequencing feature, the SMS66 offers an I2C
command to initiate Power-on sequencing while the
PWR_ON/OFF pin is in its inactive state.
MODES OF OPERATION
The SMS66 has three basic modes of operation:
Power-on sequencing mode, monitoring mode, and
Power-off sequencing mode (shown in Figures 4B
through 4E). In addition, there is a forced shutdown
feature. A detailed description of each mode and
feature follows.
Figure 4E SMS66 Sequence-Off Waveforms
Figure 4D: SMS66 Sequence-On Waveforms
Time/Horizontal division = 400mS
Time/Horizontal division = 40mS
Ch 1(500mV/Div) = 3.3V DC-DC converter output (Yellow trace)
Ch 2 (500mV/Div) = 2.5V DC-DC converter output (Blue trace)
Ch 3 (500mV/Div) = 1.8V DC-DC converter output (Purple trace)
Ch 4 (500mV/Div) = 1.5V DC-DC converter output (Green trace)
Ch 1(500mV/Div) = 3.3V DC-DC converter output (Yellow trace)
Ch 2 (500mV/Div) = 2.5V DC-DC converter output (Blue trace)
Ch 3 (500mV/Div) = 1.8V DC-DC converter output (Purple trace)
Ch 4 (500mV/Div) = 1.5V DC-DC converter output (Green trace)
Summit Microelectronics, Inc
2070 1.0 7/16/03
12
SUMMIT [ SUMMIT MICROELECTRONICS, INC. ]
