LTC2926CGN View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC2926CGN' PDF : 28 Pages View PDF
LTC2926
APPLICATIO S I FOR ATIO
through the power good timeout period, a fault and retry
will subsequently occur.
To ensure a consistent power good timeout period, the
LTC2926 requires the PGTMR pin voltage to fall below 0.1V
for the fault latch reset to complete. The ON pin needs to be
held low for only 10µs to initiate fault reset; it is allowed to
go high while the timing capacitor on PGTMR discharges
to 0.1V (see Functional Block Diagram).
When a resistive voltage divider drives the ON and FAULT
pins together, include the contribution of IFAULT(UP) when
choosing the resistor values (Figure 10a). When a logic
output drives both pins, up to 30kΩ of series resistance
may be added to limit the output current while the fault
pull-down is active (Figure 10b).
VIN
RONB
VON
RONA
VCC
ON
VCC
IFAULT(UP)
LTC2926
VON
=
RONA
RONA + RONB
•
VIN
+ (RONA || RONB) • IFAULT(UP)
FAULT
FAULT LATCH
QS
GND
R
RSERIES
IOUT
(a)
VIN
VCC
ON
VCC
IFAULT(UP)
LTC2926
LIMIT IOUT WITH RSERIES
RSERIES ≤ 30kΩ
FAULT
FAULT LATCH
QS
GND
R
2926 F10
(b)
Figure 10. Fault Retry Configurations, (a) Resistive Voltage
Divider and (b) Logic Driven
Automatic Remote Sense Switching
The LTC2926 provides integrated remote sense switches
that solve the problem of voltage drops in the external series
MOSFETs that control supply ramping. A switch creates
a feedback path from a slave supply output to the slave
supply generator sense input that allows the generator
to compensate for the I • R drop across the controlling
MOSFET (see, for example, Figure 6). After the supply
ramping is complete, but before the internal pull-down
releases the STATUS/PGI pin, the two integrated remote
sense switches are closed.
For applications that require more than two remote sense
switches, connect the RSGATE pin to the gates of additional
external N-channel MOSFETs. An internal charge pump
guarantees that RSGATE will reach VCC + 5.5V, which al-
lows full enhancement of logic-level MOSFETs with source
or drain voltages up to VCC.
The switches are open when supply ramping has not
completed to avoid creating a power path between the
supply generator and the load. When the remote sense
switches are open, the supply generator’s sense input must
be connected locally to its output through a resistor that
is much larger than the remote sense switch resistance
of 10Ω (max); a 100Ω resistor is adequate for most ap-
plications as in Figure 7.
Some supply modules have built-in resistors of 10Ω or
less between their out and sense pins, which may require
a lower switch resistance. Choose an external N-channel
MOSFET with an RDS(on) that is at most 1/10 the module
out-to-sense resistance, but that is still much larger than
the RDS(on) of the power path MOSFET.
If neither external remote sense switches nor a sta-
tus activation delay is required, leave the RSGATE pin
unconnected.
2926fa
15
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