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MP9447 Datasheet(PDF) 13 Page - Monolithic Power Systems

No. de Pieza. MP9447
Descripción  High-Efficiency, Fast-Transient, 5A, 36V Synchronous, Step-Down Converter
Descarga  19 Pages
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Fabricante  MPS [Monolithic Power Systems]
Página de inicio  http://www.monolithicpower.com
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MP9447 Datasheet(HTML) 13 Page - Monolithic Power Systems

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MP9447–HIGH-EFFICIENCY, FAST-TRANSIENT, SYNCHRONOUS, STEP-DOWN CONVERTER
MP9447 Rev. 1.2
www.MonolithicPower.com
13
1/5/2016
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2016 MPS. All Rights Reserved.
UVLO Protection
The
MP9447
has
under-voltage
lock-out
protection (UVLO). When the input voltage is
higher than the UVLO rising threshold voltage,
the MP9447 will be powered up. It shuts off when
the input voltage is lower than the UVLO falling
threshold voltage. This is non-latch protection.
Floating Driver and Bootstrap Charging
An external bootstrap capacitor power the
floating-power-MOSFET
driver.
A
dedicated
internal regulator charges and regulates the
bootstrap capacitor voltage to ~5V. When the
voltage between the BST and SW nodes drops
below regulation, a PMOS pass transistor
connected from VIN to BST turns on. The
charging current path is from VIN, BST and then
to SW. The external circuit should provide
enough voltage headroom to facilitate charging.
As long as VIN is significantly higher than SW, the
bootstrap capacitor remains charged. When the
HS-FET is ON, VIN≈VSW so the bootstrap
capacitor cannot charge.
When the LS-FET is ON, VIN−VSW reaches its
maximum for fast charging. When there is no
inductor current, VSW=VOUT so the difference
between VIN and VOUT can charge the bootstrap
capacitor.
At higher duty cycles, the bootstrap-charging
time is shorter so the bootstrap capacitor may not
charge sufficiently. In case the internal circuit has
insufficient voltage and time to charge the
bootstrap capacitor, the bootstrap capacitor
voltage will drop low. When VBST−VSW drops
below 2.3V, the HS-FET turns OFF. A UVLO
circuit allows the LS-FET to conduct and refresh
the charge on the bootstrap capacitor. Once
bootstrap capacitor voltage is charged, the HS-
FET can turn on again and the part resumes
normal switching. With this bootstrap refreshing
function, MP9447 is able to work on the low drop-
out mode.
Thermal Shutdown
The MP9447 uses thermal shutdown. The
junction temperature of the IC is internally
monitored. If the junction temperature exceeds
the threshold value (typically 165°C), the
converter shuts off. This is a non-latched
protection. There is about 25°C hysteresis. Once
the junction temperature drops to about 140°C, it
initiates a SS.


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