SMB214C datasheet(16/26 Pages) SUMMIT

16 / 26 page

SMB214A/B/C

Summit Microelectronics, Inc

2128 2.0 6/20/2008

APPLICATIONS INFORMATION (CONTINUED)

POWER OFF SEQUENCING

The SMB214A/B/C 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

power-off

command

issued

the

SMB214A/B/C 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.

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 MONITORING

Both products 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

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 SMB214A/B/C can be programmed

to respond in one of three ways, perform: a power-off

operation, a force-shutdown operation and-or it can

trigger the nRESET/HEALTHY pin.

DYNAMIC VOLTAGE MANAGEMENT

In addition to the nominal voltage settings, the

SMB214A/B/C have six additional voltage settings.

These are ideal for situations where a core voltage

needs to be reduced for power conservation.

The dynamic voltage control 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 bits for each

channel that adjust the output voltages to one of the 7

set points after a volatile I2C write command.

When all channels are at their voltage setting, a bit is set in

the dynamic voltage control status registers.

SOFT START

The SMB214A/B/C provide a 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.

HIGH VOLTAGE OPERATION

While the SMB214 has a maximum input voltage of

6.0V, the controller can operate to much higher

voltages by using the circuit shown in Figure 6. By

inserting a capacitor (C1) in series with the HSDRV

gate signal, the HSDRV pin is isolated from the 12V

supply, and the AC coupling capacitor acts as a level

translator transferring the 0-5V signal from the HSDRV

pin to a 12V-to-7V (12V-5V=5V) signal at the gate of

the PFET. When the gate stops switching, the

capacitor becomes an open circuit, and the fate will be

pulled high by R1, turning off the output. The schottky

diode and the pull-up resistor are used for DC

restoration and as a pull-up, respectively. Since the

converter runs directly from the input supply (Example:

12V), the efficiency is consistent with that of a

synchronous converter.

–

VREF

COMP1

Vout

Vout= Vref* (1 + R2/R1)

Soft-Start Slew Rate=SRref* (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 I

2C interface

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