MIC68220_10 Datasheet, PDF (16/17 Pages) Micrel Semiconductor – Dual 2A LDO Regulator

Micrel
Ratiometric Tracking
Ratiometric tracking allows independent ramping
speeds for both regulators so that the regulation
voltage is reached at the same time. This is
accomplished by adding a resistor divider between the
Master output pin and the Slave RC pin. The divider
should be scaled such that the Slave RC pin reaches
or exceeds the target output voltage of the Slave as
the Master reaches its target voltage.
Fixed Voltage Devices
MIC68220
Ratiometric tracking may be used with adjustable
parts by simply connecting the RC pins of the Master
and Slave. Use a single RC capacitor of twice the
normal value (since twice the current is injected into
the single RC cap). Alternatively, adjustable parts
may use ratiometric tracking in a manner similar to
standard tracking, with the tracking divider changed to
the same resistor ratio driving the Master Adj/Sns pin.
Adjustable Voltage Devices
Final Note on Tracking
The MIC68220 does not fully shutdown until the output load is discharged to near zero. If RC is driven from an
external source in a tracking configuration, and the external source does not go to zero on shutdown, then it may
prevent complete shutdown of the MIC68220. This will not cause damage, but some Q current will remain and may
cause concern in a battery operated portable equipment. Also, when RC is driven in tracking mode, pulling EN low
will not cause the output to drop. Maintaining low EN in tracking mode simply means that the MIC68220 will
shutdown when the tracking voltage gets near zero. In no case can the MIC68220 enter the tracking mode unless
EN is pulled high.
September 2010
16
M9999-092310-C