参数资料
型号: ISL6323IRZ
厂商: Intersil
文件页数: 26/36页
文件大小: 0K
描述: IC HYBRID CTRLR PWM MONO 48-QFN
标准包装: 43
应用: 控制器,AMD SVI
输入电压: 5 V ~ 12 V
输出数: 2
输出电压: 最高 2V
工作温度: -40°C ~ 85°C
安装类型: 表面贴装
封装/外壳: 48-VFQFN 裸露焊盘
供应商设备封装: 48-QFN(7x7)
包装: 管件
ISL6323
Finally, the resistive part of the upper MOSFET is given in
Equation 26 as P UP(4) .
Gate Drive Voltage Versatility
The ISL6323 provides the user flexibility in choosing the
? I M ?
I P-P
P UP ( 4 ) ≈ r DS ( ON ) ? ? ------ ? ? d + ----------
2
? N ? 12
2
(EQ. 26)
gate drive voltage for efficiency optimization. The controller
ties the upper and lower drive rails together. Simply applying
a voltage from 5V up to 12V on PVCC sets both gate drive
C BOOT_CAP ≥ --------------------------------------
Δ V BOOT_CAP
Q GATE = ------------------------------------ ? N Q1
The total power dissipated by the upper MOSFET at full load
can now be approximated as the summation of the results
from Equations 23, 24, 25 and 26. Since the power
equations depend on MOSFET parameters, choosing the
correct MOSFETs can be an iterative process involving
repetitive solutions to the loss equations for different
MOSFETs and different switching frequencies.
Internal Bootstrap Device
All three integrated drivers feature an internal bootstrap
Schottky diode. Simply adding an external capacitor across
the BOOT and PHASE pins completes the bootstrap circuit.
The bootstrap function is also designed to prevent the
bootstrap capacitor from overcharging due to the large
negative swing at the PHASE node. This reduces voltage
stress on the boot to phase pins.
The bootstrap capacitor must have a maximum voltage
rating above PVCC + 4V and its capacitance value can be
chosen from Equation 27:
Q GATE
(EQ. 27)
Q G1 ? PVCC
V GS1
rail voltages simultaneously.
Package Power Dissipation
When choosing MOSFETs it is important to consider the
amount of power being dissipated in the integrated drivers
located in the controller. Since there are a total of three
drivers in the controller package, the total power dissipated
by all three drivers must be less than the maximum
allowable power dissipation for the QFN package.
Calculating the power dissipation in the drivers for a desired
application is critical to ensure safe operation. Exceeding the
maximum allowable power dissipation level will push the IC
beyond the maximum recommended operating junction
temperature of +125°C. The maximum allowable IC power
dissipation for the 7x7 QFN package is approximately 3.5W
at room temperature. See “Layout Considerations” on
page 33 for thermal transfer improvement suggestions.
When designing the ISL6323 into an application, it is
recommended that the following calculations is used to
ensure safe operation at the desired frequency for the
selected MOSFETs. The total gate drive power losses,
P Qg_TOT , due to the gate charge of MOSFETs and the
integrated driver ’s internal circuitry and their corresponding
average driver current can be estimated with Equations 28
and 29, respectively.
P Qg_Q1 = --- ? Q G1 ? PVCC ? f SW ? N Q1 ? N PHASE
where Q G1 is the amount of gate charge per upper MOSFET
at V GS1 gate-source voltage and N Q1 is the number of
control MOSFETs. The Δ V BOOT_CAP term is defined as the
allowable droop in the rail of the upper gate drive.
1.6
P Qg_TOT = P Qg_Q1 + P Qg_Q2 + I Q ? VCC
3
2
P Qg_Q2 = Q G2 ? PVCC ? f SW ? N Q2 ? N PHASE
(EQ. 28)
I DR = ? --- ? Q G1 ? N
1.4
1.2
3
? 2
Q1
?
+ Q G2 ? N Q2 ? ? N PHASE ? f SW + I Q
(EQ. 29)
20nC
1.0
0.8
0.6
0.4
0.2
0.0
0.0 0.1
Q GATE = 100nC
50nC
0.2 0.3 0.4 0.5
0.6
0.7
0.8
0.9
1.0
Where, P Qg_Q1 is the total upper gate drive power loss and
P Qg_Q2 is the total lower gate drive power loss; the gate
charge (Q G1 and Q G2 ) is defined at the particular gate to
source drive voltage PVCC in the corresponding MOSFET
data sheet; I Q is the driver total quiescent current with no load
at both drive outputs; N Q1 and N Q2 are the number of upper
and lower MOSFETs per phase, respectively; N PHASE is the
number of active phases. The I Q *VCC product is the
quiescent power of the controller without load on the drives.
Δ V BOOT_CAP (V)
FIGURE 17. BOOTSTRAP CAPACITANCE vs BOOT RIPPLE
VOLTAGE
26
FN9278.5
May 17, 2011
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