LTC2926CGN View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC2926CGN' PDF : 28 Pages View PDF
LTC2926
APPLICATIO S I FOR ATIO
3.3V MODULE
VIN IN OUT
RX0
SENSE
1.8V MODULE
VIN IN OUT
RX1
SENSE
Q0
Q3
10Ω
Q1
10Ω
MASTER
1.8V
SLAVE1
2.5V MODULE
VIN IN OUT
RX2
SENSE
CMGATE
Q2
10Ω
2.5V
SLAVE2
VIN
0.1µF
RTB1
RTA1
RTB2
RTA2
VIN
10k
FAULT
ON/OFF
RSGATE MGATE RAMP SGATE1 SGATE2
D1
D2
VCC
S1
RAMPBUF
S2
TRACK1
FB1
LTC2926
TRACK2
FB2
RFB1
RFA1
RFB2
VIN
RFA2
FAULT
ON
GND
PGTMR
STATUS/PGI
2926 F07
CPGTMR
10k
STATUS
Figure 7. Typical Application with Master Supply
Ramp Buffer
The RAMPBUF pin provides a buffered version of the RAMP
pin voltage that drives the resistive dividers on the TRACK
pins. When there is no external MOSFET, it sources or sinks
up to 3mA to drive the track resistors even though the
MGATE pin only supplies 10µA (Figure 8). The RAMPBUF
pin also proves useful in systems with an external MOSFET.
If RTBn were directly connected to the MOSFET’s source
(the master output), the servo mechanism of the tracking
cell could potentially drive the master output towards 0.8V
when the MOSFET is off. The ramp buffer prevents this
by eliminating that path for current.
Fault Input/Output
The FAULT pin allows external upstream monitoring circuits
to control and to communicate with the LTC2926. The pin
is driven internally by an N-channel MOSFET pull-down
to GND, and by an 8.5µA pull-up to VCC through a series
diode. Under normal conditions, the MOSFET is off and the
1.8V MODULE
VIN IN OUT
RX1
SENSE
Q1
10Ω
1.8V
SLAVE1
2.5V MODULE
VIN IN OUT
RX2
SENSE
NC
CMGATE
Q2
10Ω
2.5V
SLAVE2
VIN
0.1µF
RTB1
RTA1
RTB2
RTA2
VIN
10k
FAULT
ON/OFF
RSGATE MGATE RAMP SGATE1 SGATE2
D1
D2
VCC
S1
RAMPBUF
S2
TRACK1
FB1
LTC2926
TRACK2
FB2
RFB1
RFA1
RFB2
VIN
RFA2
FAULT
ON
GND
PGTMR STATUS/PGI
2926 F08
CPGTMR
10k
STATUS
Figure 8. Typical Application Without Master Supply
current pulls the FAULT pin voltage high. When an upstream
monitor signal pulls FAULT below 0.5V, the LTC2926’s
internal fault latch is set, which immediately opens the
remote sense switches and cuts off the master and slave
supplies by pulling MGATE, SGATE1 and SGATE2 to GND.
A fault also activates the internal MOSFET pull-down on the
STATUS/PGI pin, which indicates to external downstream
monitoring circuits that the supplies are no longer valid
(see Status Output). Until the fault latch is reset, the sup-
plies stay disconnected and an internal pull-down keeps
the FAULT pin low as a signal to upstream monitors.
Fault latch reset is initiated by bringing the ON pin voltage
below 0.5V, and completed when PGTMR is <0.1V. Reduc-
ing the VCC pin voltage below VCC(UVLO) – ΔVCC(UVLO),
typically 2.35V, also resets the fault latch. After it is
cleared, the fault latch is armed by bringing the ON pin
voltage above 0.6V. No faults can be latched until after
the latch is armed.
The FAULT pin is pulled up by 8.5µA to VCC through a
Schottky diode, which allows the pin to be pulled safely
above the LTC2926’s supply if required. Leave the FAULT
pin unconnected if it is unused.
2926fa
13
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