MIC68400 Datasheet, PDF (13/15 Pages) Micrel Semiconductor – 4A Sequencing LDO with Tracking and Ramp Control™

Micrel, Inc.
Tracking Configurations
Normal Tracking
In normal tracking the Slave RC pin is driven from the
Master output. The internal control buffering assures
that the output of the Slave is always slightly above
the Master to guarantee that the Slave properly
regulates (based on its own internal reference) if
Master and Slave are both fixed voltage devices of the
same output voltage. The schematic and plot below
show a 1.2 volt device tracking a 1.8 volt device
through the entire turn-on / turn-off sequence. Note
that since the RC pin will overdrive the target voltage
(to assure proper regulation) the ramp down delay is
longer than the POR delay during turn-on.
MIC68400
Fixed voltage versions of MIC68400 have two internal
voltage dividers: one for setting the output voltage and
the other for driving the tracking circuitry. Adjustable
parts have up to two external dividers: one from
output to SNS (to set the output voltage) and one from
the output to the Slave RC pin (in tracking
configurations). Also, the RC pin in fixed parts
operates at the same voltage as the output, whereas
the RC pin in adjustable parts operates at the 0.5V
reference. To setup a normal tracking configuration,
the divider driving the Slave RC pin is the same ratio
(or nearly the same – if both Master and Slave are set
to the same output voltage, the Slave RC divider
should be adjusted 2% to 4% higher) as the divider
driving the Slave SNS pin. This is shown below.
Fixed Voltage Devices
Adjustable Voltage devices
September 2007
13
M9999-090607-C