SMB218 View Datasheet(PDF) - Summit Microelectronics
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Description
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SMB218 Datasheet PDF : 37 Pages
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PLEASE NOTE: The SMB118 has entered End-of-Life.
SMB118/218
APPLICATIONS INFORMATION (CONTINUED)
individually irrespective of the state of other channels.
In this mode, the enable signal has complete control
over the channel, and all sequencing is ignored. In
Manual mode, channels will not be disabled in the
event of a UV/OV fault on any output or the VBATT pin.
FORCE-SHUTDOWN
When a battery fault occurs, a UV/OV is detected on
any output, or an I2C force-shutdown command is
issued, all channels will be immediately disabled,
ignoring sequence positions or power off delay times.
SEQUENCE TERMINATION TIMER
At the beginning of each sequence position, an internal
programmable timer will begin to time out. When this
timer has expired, the SMB118 and SMB218 will
automatically perform a force-shutdown operation. This
timer is user programmable with a programmable
sequence termination period (tPST) of 50, 100, 200 ms;
this function can also be disabled.
POWER OFF SEQUENCING
The SMB118 and SMB218 have a power-off
sequencing operation. During a power off operation, the
supplies will be powered off in the reverse order they
where powered on in. During the power off sequencing,
all enables are ignored.
When a power-off command is issued the devices will
set the sequence position counter to the last sequence
position and disable that channel without soft-start
control; once off, the power off delay for the channel(s)
in the next to last sequence position will begin to
timeout, after which that channel(s) will be disabled.
This process will continue until all channels have been
disabled and are off. The programmable
If a channel fails to turn off within the sequence
termination period, the sequence termination timer will
initiate a force shutdown, if enabled.
INPUT AND OUTPUT VOLTAGE MONITORING
The SMB118 and SMB218 monitor all outputs for
under-voltage (UV) and over-voltage (OV) faults. The
monitored levels are user programmable, and may be
set at 5, 10, 15, and 20 percent of the nominal output
voltage.
The VBATT pin is monitored for two user
programmable UV settings. The VBATT UV settings
are programmable from 2.55V to 3.45V in 150mV
increments.
Once the UV/OV voltage set points have been violated,
the SMB118 and SMB218 can be programmed to
sequence off the supplies (POWER OFF), turn off all
supplies simultaneously (FORCE SHUTDOWN), assert
the nRESET/HEALTHY pin, or take no action.
SOFT START
The SMB118 and SMB218 provide a programmable
soft-start function for all PWM outputs. The soft-start
control limits the slew rate that each output is allowed
to ramp up without the need for an external capacitor.
The soft start slew rate is proportional to the product of
the output voltage and a slew rate reference. This
global reference is programmable and may be set to
400, 200, 100, 67, 50, 33, 25, and 20 Volts per second.
The slew rate control can also be disabled on any
channel not requiring the feature.
DYNAMIC VOLTAGE MANAGEMENT
The SMB118 and SMB218 have two additional voltage
set points, dynamic voltage control high and low
settings. Together with the nominal voltage setting,
three pre-determined voltage levels can be used. The
three voltage levels are ideal for situations where a
core voltage needs to be reduced for power
conservation.
The dynamic voltage control high and low settings have
the same voltage range as the controllers’ nominal
output voltage. These settings are stored in the non-
volatile configuration registers and can be set by a write
to volatile configuration registers. The dynamic voltage
control command registers contain two bits for each
channel that adjust the output voltages to the high, low
or nominal set point after a volatile I2C write command.
A seven level dynamic voltage control option is
available for channel 3. When enabled, seven level
dynamic voltage control allows channel 3 to be
dynamically modified to one of seven pre-determined
voltage levels. This transition is made by means of a
volatile I2C write command.
When all channels are at their voltage setting, a bit is
set in the dynamic voltage control status registers.
Note: Configuration writes or reads of registers
should not be performed while dynamic voltage
management.
Vout
R2
COMP1
+
R1 VREF –
Soft-Start Slew Rate=SRref* (1 + R2/R1)
Vout= Vref* (1 + R2/R1)
Figure 5 – The output voltage is set by the voltage
divider. The VREF voltage is programmable from 0
to 1.0 volt in 4mV increments via the I2C interface
Summit Microelectronics, Inc
2107 3.0 10/15/2008
19
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