参数资料
型号: ISL6620IRZ
厂商: Intersil
文件页数: 8/10页
文件大小: 0K
描述: IC SYNC RECT MOSFET DRVR 10-DFN
标准包装: 100
配置: 高端和低端,同步
输入类型: PWM
延迟时间: 40ns
电流 - 峰: 2A
配置数: 1
输出数: 2
高端电压 - 最大(自引导启动): 36V
电源电压: 4.5 V ~ 5.5 V
工作温度: -40°C ~ 85°C
安装类型: 表面贴装
封装/外壳: 10-VFDFN 裸露焊盘
供应商设备封装: 10-DFN(3x3)
包装: 管件
产品目录页面: 1248 (CN2011-ZH PDF)
ISL6620, ISL6620A
LVCC
C GD
D
In addition, connecting the thermal pad of the DFN package
to the power ground through a via, or placing a low noise
copper plane underneath the SOIC part is recommended for
high switching frequency, high current applications. This is to
R HI2
R LO2
G
R L2
R G2
C GS
C DS
Q2
improve heat dissipation and allow the part to achieve its
full thermal potential.
Upper MOSFET Self Turn-on Effects at Start-up
S
FIGURE 4. TYPICAL LOWER-GATE DRIVE TURN-ON PATH
Application Information
MOSFET and Driver Selection
The parasitic inductances of the PCB and of the power
devices’ packaging (both upper and lower MOSFETs) can
cause serious ringing, exceeding the device’s absolute
maximum ratings. The negative ringing at the edges of the
PHASE node could increase the bootstrap capacitor voltage
through the internal bootstrap diode, and in some cases, it
may overstress the upper MOSFET driver. Careful layout,
proper selection of MOSFETs and packaging, as well as the
driver can minimize such unwanted stress.
The selection of D 2 -PAK, or D-PAK packaged MOSFETs, is
a much better match (for the reasons discussed) for the
ISL6620A. Low-profile MOSFETs, such as Direct FETs and
multi-source leads devices (SO-8, LFPAK, PowerPAK), have
low parasitic lead inductances and can be driven by either
ISL6620 or ISL6620A (assuming proper layout design). The
ISL6620, missing the 3 Ω integrated BOOT resistor, typically
yields slightly higher efficiency than the ISL6620A.
Should the driver have insufficient bias voltage applied, its
outputs are floating. If the input bus is energized at a high
dV/dt rate while the driver outputs are floating, due to self
coupling via the internal C GD of the MOSFET, the gate of the
upper MOSFET could momentarily rise up to a level greater
than the threshold voltage of the device, potentially turning
on the upper switch. Therefore, if such a situation could
conceivably be encountered, it is a common practice to
place a resistor (R UGPH ) across the gate and source of the
upper MOSFET to suppress the Miller coupling effect. The
value of the resistor depends mainly on the input voltage’s
rate of rise, the C GD /C GS ratio, as well as the gate-source
threshold of the upper MOSFET. A higher dV/dt, a lower
C DS /C GS ratio, and a lower gate-source threshold upper
FET will require a smaller resistor to diminish the effect of
the internal capacitive coupling. For most applications, the
integrated 20k Ω resistor is sufficient, not affecting normal
performance and efficiency.
The coupling effect can be roughly estimated using Equation 5,
which assumes a fixed linear input ramp and neglects the
clamping effect of the body diode of the upper drive and the
bootstrap capacitor. Other parasitic components, such as lead
inductances and PCB capacitances, are also not taken into
account. Figure 5 provides a visual reference for this
phenomenon and its potential solution.
– V
?
---------------------------------- ?
? dV ?
V GS_MILLER = ------- ? R ? C rss ? 1 – e dt
iss ?
------ ? R ? C
Layout Considerations
FA good layout helps reduce the ringing on the switching
node (PHASE) and significantly lower the stress applied to
the output drives. The following advice is meant to lead to an
dV
DS
dt ? ?
? ?
? ?
(EQ. 5)
optimized layout:
? Keep decoupling loops (VCC-GND and BOOT-PHASE) as
R = R UGPH + R GI
C rss = C GD
C iss = C GD + C GS
short as possible.
? Minimize trace inductance, especially on low-impedance
lines. All power traces (UGATE, PHASE, LGATE, GND,
VCC) should be short and wide, as much as possible.
? Minimize the inductance of the PHASE node. Ideally, the
UVCC
BOOT
C BOOT
C GD
VIN
D
source of the upper and the drain of the lower MOSFET
should be as close as thermally allowable.
? Minimize the current loop of the output and input power
DU
DL
UGATE
G
R GI
C DS
trains. Short the source connection of the lower MOSFET
to ground as close to the transistor pin as feasible. Input
capacitors (especially ceramic decoupling) should be
PHASE
C GS
S
Q UPPER
placed as close to the drain of upper and source of lower
MOSFETs as possible.
FIGURE 5. GATE TO SOURCE RESISTOR TO REDUCE
UPPER MOSFET MILLER COUPLING
8
FN6494.0
April 25, 2008
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