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参数资料
| 型号： | LT3724MPFE#TR |
| 厂商： | LINEAR TECHNOLOGY CORP |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHING CONTROLLER, 225 kHz SWITCHING FREQ-MAX, PDSO16 |
| 封装： | 4.40 MM, PLASTIC, TSSOP-16 |
| 文件页数： | 2/26页 |
| 文件大小： | 309K |
| 代理商： | LT3724MPFE#TR |
LT3724
10
3724fd
OPERATIONS
either the start of the next cycle or until the bootstrapped
capacitor is fully charged.
MOSFET Driver
The LT3724 contains a high speed boosted driver to turn
on and off an external N-channel MOSFET switch. The
MOSFET driver derives its power from the boost capacitor
which is referenced to the SW pin and the source of the
MOSFET. The driver provides a large pulse of current to
turn on the MOSFET fast and minimize transition times.
Multiple MOSFETs can be paralleled for higher current
operation.
To eliminate the possibility of shoot through between the
MOSFET and the internal SW pull-down switch, an adap-
tive nonoverlap circuit ensures that the internal pull-down
switch does not turn on until the gate of the MOSFET is
below its turn on threshold.
Low Current Operation (Burst Mode Operation)
To increase low current load efficiency, the LT3724 is
capable of operating in Linear Technology’s proprietary
BurstModeoperationwheretheexternalMOSFEToperates
intermittently based on load current demand. The Burst
Mode function is disabled by connecting the BURST_EN
pin to VCC and enabled by connecting the pin to SGND.
When the required switch current, sensed via the VC pin
voltage, is below 15% of maximum, Burst Mode operation
is employed and that level of sense current is latched onto
the IC control path. If the output load requires less than
this latched current level, the converter will overdrive the
output slightly during each switch cycle. This overdrive
condition is sensed internally and forces the voltage on the
VC pin to continue to drop. When the voltage on VC drops
150mV below the 15% load level, switching is disabled,
and the LT3724 shuts down most of its internal circuitry,
reducing total quiescent current to 100A. When the
converter output begins to fall, the VC pin voltage begins
to climb. When the voltage on the VC pin climbs back to
the 15% load level, the IC returns to normal operation and
switching resumes. An internal clamp on the VC pin is set
at 100mV below the output disable threshold, which limits
the negative excursion of the pin voltage, minimizing the
converter output ripple during Burst Mode operation.
During Burst Mode operation, the VIN pin current is 20A
and the VCC current is reduced to 80A. If no external drive
is provided for VCC,allVCCbiascurrentsoriginatefromthe
VIN pin, giving a total VIN current of 100A. Burst current
can be reduced further when VCC is driven using an output
derived source, as the VCC component of VIN current is
then reduced by the converter duty cycle ratio.
Start-Up
The following section describes the start-up of the supply
and operation down to 4V once the step-down supply is
up and running. For the protection of the LT3724 and the
switching supply, there are internal undervoltage lockout
(UVLO) circuits with hysteresis on VIN, VCC and VBOOST,
as shown in the Electrical Characteristics table. Start-up
and continuous operation require that all three of these
undervoltage lockout conditions be satisfied because
the TG MOSFET driver is disabled during any UVLO fault
condition.Instartup,formostapplications,VCCispowered
from VIN through the high voltage linear regulator of the
LT3724. This requires VIN to be high enough to drive the
VCC voltage above its undervoltage lockout threshold.
VCC, in turn, has to be high enough to charge the BOOST
capacitor through an external diode so that the BOOST
voltage is above its undervoltage lockout threshold. There
is an NPN switch that pulls the SW node to ground each
cycle during the TG power MOSFET off-time, ensuring the
BOOST capacitor is kept fully charged. Once the supply
is up and running, the output voltage of the supply can
backdrive VCCthroughanexternaldiode.Internalcircuitry
disables the high voltage regulator to conserve VIN supply
current. Output voltages that are too low or too high to
backdriveVCCrequireadditionalcircuitrysuchasavoltage
doubler or linear regulator. Once VCC is backdriven from
a supply other than VIN, VIN can be reduced to 4V with
normal operation maintained.
(Refer to Functional Diagram)
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相关代理商/技术参数 |
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| LT3726EGN | 制造商:Linear Technology 功能描述: |
| LT373L | 制造商:未知厂家 制造商全称:未知厂家 功能描述:Optoelectronic |
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