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參數(shù)資料
| 型號： | 45IZ |
| 廠商： | Intersil Corporation |
| 英文描述： | 5V or 12V Single Synchronous Buck Pulse-Width Modulation (PWM) Controller |
| 中文描述： | 單5V或12V同步降壓脈寬調(diào)制（PWM）控制器 |
| 文件頁數(shù)： | 6/16頁 |
| 文件大?。?/td> | 302K |
| 代理商： | 45IZ |
www.DataSheet4U.com
14
FN6305.3
November 15, 2006
BOOTSTRAP Considerations
Figure 11 shows the upper gate drive (BOOT pin) supplied by
a bootstrap circuit from VCC. The boot capacitor, CBOOT,
develops a floating supply voltage referenced to the PHASE
pin. The supply is refreshed to a voltage of VCC less the boot
diode drop (VD) each time the lower MOSFET, Q2, turns on.
Check that the voltage rating of the capacitor is above the
maximum VCC voltage in the system; a 16V rating should be
sufficient for a 12V system. A value of 0.1F is typical for
many systems driving single MOSFETs.
If VCC is 12V, but VIN is lower (such as 5V), then another
option is to connect the BOOT pin to 12V, and remove the
BOOT cap (although, you may want to add a local cap from
BOOT to GND). This will make the UGATE VGS voltage
equal to (12V - 5V = 7V). That should be high enough to
drive most MOSFETs, and low enough to improve the
efficiency slightly. Do NOT leave the BOOT pin open, and try
to get the same effect by driving BOOT through VCC and the
internal diode; this path is not designed for the high current
pulses that will result.
For low VCC voltage applications where efficiency is very
important, an external BOOT diode (in parallel with the
internal one) may be considered. The external diode drop
has to be lower than the internal one; the resulting higher
VG-S of the upper FET will lower its rDS(ON). The modest
gain in efficiency should be balanced against the extra cost
and area of the external diode.
For information on the Application circuit, including a
complete Bill-of-Materials and circuit board description, can
be found in Application Note AN1257.
+VCC
ISL6545
GND
LGATE/OCSET
UGATE
PHASE
BOOT
VCC
+VIN
VG-S ≈ VCC - VD
VG-S ≈ VCC
CBOOT
Q1
Q2
+
-
FIGURE 11. UPPER GATE DRIVE BOOTSTRAP
VCC
+ VD -
ISL6545, ISL6545A
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