SMB110

Preliminary Information

Summit Microelectronics, Inc

2099 2.3 3/1/2005

22

APPLICATIONS INFORMATION (CONTINUED)

voltage, which varies from 1.0 – 2.0V in 8 mV

increments

LDO STANDBY VOLTAGE

The SMB110 has an internal 3.3 volt Low Dropout

(LDO) linear regulator. While the battery voltage is

above the UV2 level this supply is powered from the

LDO_SUPPLY pin, however, when the battery voltage

drops below the UV2 level the LDO supply voltage will

be routed to the battery through an internal analog

multiplexer. The LDO will continue to be supplied by the

battery until the latched UV2 pin is released. The LDO

will be disabled once the Battery voltage falls below the

UV2 level.

SOFT START

The SMB110 provides 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; see Figure 5.

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.

R1

COMP1

VREF

R1

R2

COMP1

VOUT

R2

1.0V

Vout

VREF_OUT

CHANNEL 0

CHANNELS 1 TO 3

R1 AND R2 INTERNAL

FOR CHANNELS 2 AND 3

+

–

+

–

Figure 6: The output voltage is set by the resistor divider. The resistor divider is internal for all buck channels.

VREF is programmable from 0 to 1.0V in 4 mV increments and VREF_OUT is programmable from 1.0 to 2.0V in 8

mV increments. All voltage references are programmable via the I