MIC68200 Datasheet, PDF (14/15 Pages) Micrel Semiconductor – 2A Sequencing LDO with Tracking and Ramp Control

Micrel, Inc.
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
V_IN = 2.5V
MIC68200-1.8YML
IN
U1 OUT
EN
1nF
EN
RC
Master ^SNS
1nF _DLY
GND POR
10K
1K
1.5K
VOUT1
4.7µF
MIC68200-1.2YML
IN
U2 OUT
EN _Slave SNS
RC
NC _{DLY GND POR}
VOUT2
4.7µF
POR
MIC68200
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
V_IN = 3.3V
EN
3nF
1nF
MIC68200YML
IN
U1 ^OUT
EN _Master SNS
RC
DLY GND POR
10KΩ
10.0K
2.5K
VOUT1
4.7µF
MIC68200YML
IN
U2 ^OUT
EN _Slave SNS
RC
NC _{DLY GND POR}
10.0K
3.83K
VOUT2
4.7µF
POR
Final Note on Tracking
The MIC68200 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 it may prevent complete shutdown of the
MIC68200. This will cause no damage, but some Q current will remain and may cause concern in 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 MIC68200 will shutdown when the tracking voltage gets near zero. In no case can the
MIC68200 enter the tracking mode unless EN is pulled high.
July 2006
14
M9999-071206
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