LTC2926IUFD データシートの表示（PDF） - Linear Technology

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LTC2926IUFD

MOSFET-Controlled Power Supply Tracker

Linear Technology 

LTC2926

PI FU CTIO S GN/UFD Packages

RAMP (Pin 11/ Pin 9): Ramp Buffer Input. Connect the

RAMP pin to the master ramp signal to force the slave

supplies to track it. When the RAMP pin is connected to

the source of an external N-channel MOSFET, the slave

supplies track the MOSFET’s source, the master supply

voltage, as it ramps up and down. When a master supply

is not required, the RAMP pin can be tied directly to the

MGATE pin to form a master ramp voltage. In this configura-

tion, the supplies track the capacitor on the MGATE pin as

it is charged and discharged by the 10µA current source

that is controlled by the ON pin. The RAMP pin is weakly

clamped to VCC + 1V. Do not drive RAMP above VCC with

a low impedance source to avoid sinking large currents

into the pin. Ground the RAMP pin if it is unused.

RAMPBUF (Pin 20/Pin 18): Ramp Buffer Output. The

RAMPBUF pin provides a low impedance buffered ver-

sion of the signal on the RAMP pin. This buffered output

drives the resistive voltage dividers that connect to the

TRACK pins. Limit the capacitance at the RAMPBUF pin

to less than 100pF.

RSGATE (Pin 13/Pin 11): Gate Drive for Internal and

External N-Channel MOSFET Remote Sense Switches. A

remote sense path between a load and the sense input of

its supply generator automatically compensates for voltage

drops across the tracking MOSFET. After the series MOS-

FETs are fully enhanced, a 10µA current pulls up RSGATE.

An internal charge pump guarantees that RSGATE will

pull up to 5.5V above VCC, which ensures that logic-level

N-channel MOSFETs are fully enhanced. When the voltage

at RSGATE exceeds VCC + 4.9V, the STATUS/PGI pull-down

is released. When the ON pin is low, a 10µA current source

pulls RSGATE to GND. Supplies will not track down until

the RSGATE pin voltage falls below 1.23V, which ensures

that the remote sense switches open before the loads are

disconnected. Connect RSGATE to the gates of additional

external N-channel MOSFETs to create more remote sense

switches. Upon a fault condition, the RSGATE pin is pulled

low immediately with 20mA. Optionally connect a capaci-

tor between RSGATE and GND to set the switch-on rate

or to add delay between switch closure and STATUS/PGI

assertion. Leave RSGATE unconnected if it is unused.

SGATE1, SGATE2 (Pins 5, 16/Pins 3, 14): Slave Gate Con-

trollers for External N-Channel MOSFETs. Each SGATE pin

ramps a slave supply by controlling the gate of an external

N-channel MOSFET so that its source terminal follows the

tracking profile set by external resistors and the master

ramp. It is a good practice to add a 10Ω resistor between

this pin and the MOSFET’s gate to prevent high frequency

oscillations. An internal charge pump guarantees that the

SGATE pin voltage will pull up to 5.5V above VCC, which

ensures that logic-level N-channel MOSFETs are fully

enhanced. Leave unused SGATE pins unconnected.

STATUS/PGI (Pin 14/Pin 12): Status Output/Power Good

Input. A 10µA current pulls up STATUS/PGI when MGATE,

SGATE1 and SGATE2 are fully enhanced, and the remote

sense switches are closed, otherwise an internal N-channel

MOSFET pulls down STATUS/PGI. If the STATUS/PGI pin

is pulled below 1V after the power-good time-out delay

(see PGTMR pin description), the fault latch is set, and

MGATE, SGATE1, SGATE2 and RSGATE are all pulled low

immediately. An internal charge pump guarantees that the

STATUS/PGI pin voltage will pull up to 5.5V above VCC.

An external pull-up resistor may be added to limit the

STATUS/PGI voltage to logic levels. Leave the STATUS/PGI

pin unconnected if it is unused.

TRACK1, TRACK2 (Pins 2, 19/Pins 20, 17): Tracking Con-

trol Inputs. A resistive voltage divider between RAMPBUF

and each TRACK pin determines the tracking profile of

each supply channel. Each TRACK pin pulls up to 0.8V,

and the current supplied at TRACK is mirrored at FB. The

TRACK pins are capable of supplying at least 1mA when

VCC = 2.9V. They may be capable of supplying up to 10mA

when the supply is at 5.5V, so care should be taken not to

short this pin for extended periods. Limit the capacitance

at the TRACK pins to less than 25pF. Leave unused TRACK

pins unconnected.

VCC (Pin 1/Pin 19): Positive Voltage Supply. Operating

range is from 2.9V to 5.5V. An undervoltage lockout resets

the part when the supply is below 2.4V. VCC should be

bypassed to GND with a 0.1µF capacitor.

2926fa

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