LTC2926IUFD View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC2926IUFD' PDF : 28 Pages View PDF
LTC2926
APPLICATIO S I FOR ATIO
MASTER
SLAVE2
SLAVE1
LARGE τL = RLCL
RL ≈ RFB
500mV/DIV
5ms/DIV
2926 F24
Figure 24. Tracking Effects of Weak Resistive Load
Under worst-case conditions, FB pin voltages may reach
the maximum clamp voltage of 2.4V. To limit the slave
voltage offset to below 100mV, choose RFB ≥ 23 • RL.
Add a resistor in parallel with the load to strengthen weak
resistive loads as required.
Start-Up Delays
Often power supplies do not start up immediately when
their input supplies are applied. If the LTC2926 tries to ramp
up these power supplies as soon as the input supply is
present, the start-up of the outputs may be delayed, which
defeats the tracking circuit. Make sure the ON pin does not
initiate ramp-up until all supply sources are available.
RAMP Pin Clamp
The RAMP pin is weakly clamped to the VCC pin. When
MGATE and RAMP are tied together their pin voltages will
not exceed VCC + 1V. If the RAMP pin is driven by a low
impedance source that can exceed VCC, include a series
resistor to limit the current to <20µA. Use 50kΩ per source
volt above VCC.
Layout Considerations
Be sure to place a 0.1µF bypass capacitor as near as pos-
sible to the supply pin of the LTC2926.
To minimize the noise on the slave supplies’ outputs, keep
the traces connecting the FB pins of the LTC2926 and the
feedback nodes of the slave supplies’ resistive voltage
dividers as short as possible. In addition, do not route
those traces next to signals with fast transitions times.
To get the best compensation of the series I • R drops
of the external MOSFETs, make sure the supply output
nodes and the supply generator sense connections use
Kelvin-sensing. The feedback resistive voltage divider
should Kelvin-sense the slave supply output node for
accuracy, as well.
SUPPLY
MODULE
Q1
OUT
100Ω
SENSE
KELVIN-SENSE 10Ω
CONNECTIONS
GND
D1 SGATE1 S1
KELVIN-SENSE
CONNECTIONS
MINIMIZE
TRACE
LENGTH
LTC2926
MINIMIZE RFB
TRACE LENGTH
VCC
FB1
0.1µF
GND
RFA
SLAVE
LOAD
KELVIN-SENSE
CONNECTIONS
2926 F25
Figure 25. Layout Considerations
2926fa
25
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