MIC68220_10 Datasheet, PDF (15/17 Pages) Micrel Semiconductor – Dual 2A LDO Regulator

Micrel
Tracking Configurations
Normal Tracking
In normal tracking the Slave RC pin is driven from the
Master output. 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.
Fixed Voltage Devices
MIC68220
Fixed voltage versions of MIC68220 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.
Adjustable Voltage devices
September 2010
15
M9999-092310-C