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PX3511B Schematic ( PDF Datasheet ) - Intersil Corporation

Teilenummer PX3511B
Beschreibung Advanced Synchronous Rectified Buck MOSFET Drivers
Hersteller Intersil Corporation
Logo Intersil Corporation Logo 




Gesamt 10 Seiten
PX3511B Datasheet, Funktion
®
Data Sheet
Advanced Synchronous Rectified Buck
MOSFET Drivers with Protection Features
The PX3511A and PX3511B are high frequency MOSFET
drivers specifically designed to drive upper and lower power
N-Channel MOSFETs in a synchronous rectified buck
converter topology. These drivers combined with the
ISL6595 Digital Multi-Phase Buck PWM controller and
N-Channel MOSFETs form a complete core-voltage
regulator solution for advanced microprocessors.
The PX3511A drives the upper gate to 12V, while the lower
gate can be independently driven over a range from 5V to
12V. The PX3511B drives both upper and lower gates over a
range of 5V to 12V. This drive-voltage provides the flexibility
necessary to optimize applications involving trade-offs
between gate charge and conduction losses.
An adaptive zero shoot-through protection is integrated to
prevent both the upper and lower MOSFETs from conducting
simultaneously and to minimize the dead time. These
products add an overvoltage protection feature operational
before VCC exceeds its turn-on threshold, at which the
PHASE node is connected to the gate of the low side
MOSFET (LGATE). The output voltage of the converter is
then limited by the threshold of the low side MOSFET, which
provides some protection to the microprocessor if the upper
MOSFET(s) is shorted during initial start-up.
These drivers also feature a three-state PWM input which,
working together with Intersil’s multi-phase PWM controllers,
prevents a negative transient on the output voltage when the
output is shut down. This feature eliminates the Schottky
diode that is used in some systems for protecting the load
from reversed output voltage events.
PX3511A, PX3511B
February 26, 2007
FN6462.0
Features
• Dual MOSFET Drives for Synchronous Rectified Bridge
• Adjustable Gate Voltage (5V to 12V) for Optimal Efficiency
• 36V Internal Bootstrap Schottky Diode
• Bootstrap Capacitor Overcharging Prevention
• Supports High Switching Frequency (up to 2MHz)
- 3A Sinking Current Capability
- Fast Rise/Fall Times and Low Propagation Delays
• Three-State PWM Input for Output Stage Shutdown
• Three-State PWM Input Hysteresis for Applications With
Power Sequencing Requirement
• Pre-POR Overvoltage Protection
• VCC Undervoltage Protection
• Expandable Bottom Copper Pad for Enhanced Heat
Sinking
• Dual Flat No-Lead (DFN) Package
- Near Chip-Scale Package Footprint; Improves PCB
Efficiency and Thinner in Profile
• Pb-Free Plus Anneal Available (RoHS Compliant)
Applications
• Core Regulators for Intel® and AMD® Microprocessors
• High Current DC/DC Converters
• High Frequency and High Efficiency VRM and VRD
Related Literature
• Technical Brief TB363 “Guidelines for Handling and
Processing Moisture Sensitive Surface Mount Devices
(SMDs)”
• Technical Brief TB417 for Power Train Design, Layout
Guidelines, and Feedback Compensation Design
1 CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
1-888-INTERSIL or 1-888-468-3774 | Intersil (and design) is a registered trademark of Intersil Americas Inc.
Copyright Intersil Americas Inc. 2006. All Rights Reserved
All other trademarks mentioned are the property of their respective owners.






PX3511B Datasheet, Funktion
Description
PWM
UGATE
PX3511A, PX3511B
tPDHU
tRU
1.18V<PWM<2.36V
tPDLU
tFU
tPDTS
0.76V<PWM<1.96V
tTSSHD
tPDTS
LGATE
tPDLL
tFL tRL
tPDHL
tTSSHD
FIGURE 1. TIMING DIAGRAM
Operation
Designed for versatility and speed, the PX3511A and
PX3511B MOSFET drivers control both high-side and low-
side N-Channel FETs of a half-bridge power train from one
externally provided PWM signal.
Prior to VCC exceeding its POR level, the Pre-POR
overvoltage protection function is activated during initial
startup; the upper gate (UGATE) is held low and the lower
gate (LGATE), controlled by the Pre-POR overvoltage
protection circuits, is connected to the PHASE. Once the
VCC voltage surpasses the VCC Rising Threshold (See
Electrical Specifications), the PWM signal takes control of
gate transitions. A rising edge on PWM initiates the turn-off
of the lower MOSFET (see Timing Diagram). After a short
propagation delay [tPDLL], the lower gate begins to fall.
Typical fall times [tFL] are provided in the Electrical
Specifications section. Adaptive shoot-through circuitry
monitors the LGATE voltage and determines the upper gate
delay time [tPDHU]. This prevents both the lower and upper
MOSFETs from conducting simultaneously. Once this delay
period is complete, the upper gate drive begins to rise [tRU]
and the upper MOSFET turns on.
A falling transition on PWM results in the turn-off of the upper
MOSFET and the turn-on of the lower MOSFET. A short
propagation delay [tPDLU] is encountered before the upper
gate begins to fall [tFU]. Again, the adaptive shoot-through
circuitry determines the lower gate delay time, tPDHL. The
PHASE voltage and the UGATE voltage are monitored, and
the lower gate is allowed to rise after PHASE drops below a
level or the voltage of UGATE to PHASE reaches a level
depending upon the current direction (See next section for
details). The lower gate then rises [tRL], turning on the lower
MOSFET.
6
Adaptive Zero Shoot-Through Deadtime Control
These drivers incorporate an adaptive deadtime control
technique to minimize deadtime, resulting in high efficiency
from the reduced freewheeling time of the lower MOSFETs’
body-diode conduction, and to prevent the upper and lower
MOSFETs from conducting simultaneously. This is
accomplished by ensuring either rising gate turns on its
MOSFET with minimum and sufficient delay after the other
has turned off.
During turn-off of the lower MOSFET, the LGATE voltage is
monitored until it drops below 1.75V, at which time the
UGATE is released to rise after 20ns of propagation delay.
Once the PHASE is high, the adaptive shoot-through
circuitry monitors the PHASE and UGATE voltages during a
PWM falling edge and the subsequent UGATE turn-off. If
either the UGATE falls to less than 1.75V above the PHASE
or the PHASE falls to less than +0.8V, the LGATE is
released to turn on.
Three-State PWM Input
A unique feature of these drivers and other Intersil drivers is
the addition of a shutdown window to the PWM input. If the
PWM signal enters and remains within the shutdown window
for a set holdoff time, the driver outputs are disabled and
both MOSFET gates are pulled and held low. The shutdown
state is removed when the PWM signal moves outside the
shutdown window. Otherwise, the PWM rising and falling
thresholds outlined in the ELECTRICAL SPECIFICATIONS
determine when the lower and upper gates are enabled.
This feature helps prevent a negative transient on the output
voltage when the output is shut down, eliminating the
Schottky diode that is used in some systems for protecting
the load from reversed output voltage events.
In addition, more than 400mV hysteresis also incorporates
into the three-state shutdown window to eliminate PWM
FN6462.0
February 26, 2007

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