RT9611A Ver la hoja de datos (PDF) - Richtek Technology
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RT9611A Datasheet PDF : 15 Pages
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Application Information
The RT9611A/B is a High frequency, synchronous rectified,
single phase dual MOSFET driver containing Richtek's
advanced MOSFET driver technologies. The RT9611A/B
is designed to be able to adapt from normal MOSFET
driving applications to high performance CPU VR driving
capabilities. The RT9611A/B can be utilized under both
VCC = 5V or VCC = 12V applications which may happen in
different fields of electronics application circuits. In the
efficiency point of view, higher VCC equals higher driving
voltage of UG/LG which may result in higher switching
loss and lower conduction loss of power MOSFETs. The
choice of VCC = 12V or VCC = 5V can be a tradeoff to
optimize system efficiency.
The RT9611A/B are designed to drive both high side and
low side N-MOSFET through external input PWM control
signal. It has power on protection function which held
UGATE and LGATE low before the VCC voltage rises to
higher than rising threshold voltage. After the initialization,
the PWM signal takes the control. The rising PWM signal
first forces the LGATE signal turns low then UGATE signal
is allowed to go high just after a non-overlapping time to
avoid shoot through current. The falling of PWM signal
first forces UGATE to go low. When UGATE and PHASE
signal reach a predetermined low level, LGATE signal is
allowed to turn high.
The PWM signal is acted as “High” if the signal is above
the rising threshold and acted as “Low” if the signal is
below the falling threshold. Any signal level enters and
remains within the shutdown window is considered as “tri-
state” the output drivers are disabled and both MOSFET
gates are pulled and held low. If left the PWM signal floating,
the pin will be kept around 1.8V by the internal divider and
provide the PWM controller with a recognizable level. OD
pin will also turn off both high/low side MOSFETs when
tied to GND.
The RT9611A/B builds in an internal bootstrap power switch
to replace external bootstrap diode, and this can facilitate
PCB design and reduce total BOM cost of the system.
Hence, no external bootstrap diode is required in real
applications.
The difference of the RT9611A and the RT9611B is the
RT9611A/B
propagation delay, tUGATEpdh. The RT9611B has
comparatively large tUGATEpdh to further prevent from shoot
through when high side power MOSFETs are going to be
turned on. The long propagation delay of the RT9611B
sacrifices efficiency for compromise of system safety.
Hence, the RT9611A is usually recommended to be
utilized in performance oriented applications, such as high
power density CPU VR or GPU VR.
Non-overlap Control
To prevent the overlap of the gate drives during the UGATE
pull low and the LGATE pull high, the non-overlap circuit
monitors the voltages at the PHASE node and high side
gate drive (UGATE-PHASE). When the PWM input signal
goes low, UGATE begins to pull low (after propagation
delay). Before LGATE can pull high, the non-overlap
protection circuit ensures that the monitored voltages have
gone below 1.1V. Once the monitored voltages fall below
1.1V, LGATE begins to turn high. For short pulse condition,
if the PHASE pin had not gone high after LGATE pulls
low, the LGATE has to wait for 200ns before pull high. By
waiting for the voltages of the PHASE pin and high side
gate drive to fall below 1.1V, the non-overlap protection
circuit ensures that UGATE is low before LGATE pulls
high.
Also to prevent the overlap of the gate drives during LGATE
pull low and UGATE pull high, the non-overlap circuit
monitors the LGATE voltage. When LGATE go below 1.1V,
UGATE is allowed to go high.
Driving Power MOSFETs
The DC input impedance of the power MOSFET is
extremely high. When Vgs1 or Vgs2 is at 12V or 5V, the
gate draws the current only for few nano-amperes. Thus
once the gate has been driven up to “ON” level, the
current could be negligible.
However, the capacitance at the gate to source terminal
should be considered. It requires relatively large currents
to drive the gate up and down 12V (or 5V) rapidly. It is
also required to switch drain current on and off with the
required speed. The required gate drive currents are
calculated as follows.
Copyright ©2012 Richtek Technology Corporation. All rights reserved.
DS9611A/B-03 June 2012
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
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