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参数资料
| 型号： | ISL6426CB |
| 厂商： | INTERSIL CORP |
| 元件分类： | 稳压器 |
| 英文描述： | Triple 3-Input Positive-NAND Gates 14-SOIC -40 to 85 |
| 中文描述： | SWITCHING CONTROLLER, 770 kHz SWITCHING FREQ-MAX, PDSO16 |
| 封装： | PLASTIC, MS-012-AC, SOIC-16 |
| 文件页数： | 6/18页 |
| 文件大小： | 541K |
| 代理商： | ISL6426CB |
14
threshold level before the complementary MOSFET is turned
on.
Bootstrap Component Selection
External bootstrap components, a diode and capacitor, are
required to provide sufficient gate enhancement to the upper
MOSFET. The internal MOSFET gate driver is supplied by
the external bootstrap circuitry as shown in Figure 9. The
boot capacitor, CBOOT, develops a floating supply voltage
referenced to the PHASE pin. This supply is refreshed each
cycle, when DBOOT conducts, to a voltage of CPVOUT less
the boot diode drop, VD, plus the voltage rise across
QLOWER.
Just after the PWM switching cycle begins and the charge
transfer from the bootstrap capacitor to the gate capacitance
is complete, the voltage on the bootstrap capacitor is at its
lowest point during the switching cycle. The charge lost on
the bootstrap capacitor will be equal to the charge
transferred to the equivalent gate-source capacitance of the
upper MOSFET as shown:
where QGATE is the maximum total gate charge of the upper
MOSFET, CBOOT is the bootstrap capacitance, VBOOT1 is
the bootstrap voltage immediately before turn-on, and
VBOOT2 is the bootstrap voltage immediately after turn-on.
The bootstrap capacitor begins its refresh cycle when the gate
drive begins to turn-off the upper MOSFET. A refresh cycle
ends when the upper MOSFET is turned on again, which
varies depending on the switching frequency and duty cycle.
The minimum bootstrap capacitance can be calculated by
rearranging the previous equation and solving for CBOOT.
Typical gate charge values for MOSFETs considered in
these types of applications range from 20 to 100nC. Since
the voltage drop across QLOWER is negligible, VBOOT1 is
simply VCPVOUT - VD. A schottky diode is recommended to
minimize the voltage drop across the bootstrap capacitor
during the on-time of the upper MOSFET. Initial calculations
with VBOOT2 no less than 4V will quickly help narrow the
bootstrap capacitor range.
For example, consider an upper MOSFET is chosen with a
maximum gate charge, Qg, of 100nC. Limiting the voltage
drop across the bootstrap capacitor to 1V results in a value
of no less than 0.1
F. The tolerance of the ceramic capacitor
should also be considered when selecting the final bootstrap
capacitance value.
A fast recovery diode is recommended when selecting a
bootstrap diode to reduce the impact of reverse recovery
charge loss. Otherwise, the recovery charge, QRR, would
have to be added to the gate charge of the MOSFET and
taken into consideration when calculating the minimum
bootstrap capacitance.
ISL6406
GND
LGATE
UGATE
PHASE
BOOT
VIN
NOTE:
VG-S VCC
CBOOT
DBOOT
QUPPER
QLOWER
+
-
FIGURE 9. UPPER GATE DRIVE BOOTSTRAP
VG-S VCC -VD
+
VD
-
CPVOUT
ISL6426
QGATE
CBOOT VBOOT1 VBOOT2
–
()
×
=
CBOOT
QGATE
VBOOT1 V
–
BOOT2
-----------------------------------------------------
=
ISL6406, ISL6426
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相关代理商/技术参数 |
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|---|---|
| ISL6426CR | 制造商:Rochester Electronics LLC 功能描述:- Bulk 制造商:Intersil Corporation 功能描述: |
| ISL6426CV | 制造商:Rochester Electronics LLC 功能描述:- Bulk 制造商:Intersil Corporation 功能描述: |
| ISL6426IB | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
| ISL6426IB-T | 制造商:Rochester Electronics LLC 功能描述:- Tape and Reel |
| ISL6426IR | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
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