参数资料
型号: LM10506TME
厂商: NATIONAL SEMICONDUCTOR CORP
元件分类: 电源管理
英文描述: 1-CHANNEL POWER SUPPLY SUPPORT CKT, PBGA34
封装: 0.40 MM PITCH, MICRO SMD-34
文件页数: 17/34页
文件大小: 1020K
代理商: LM10506TME
19.2.6 Internal Synchronous Rectification
While in PWM mode, the bucks use an internal NFET as a
synchronous rectifier to reduce the rectifier forward voltage
drop and the associated power loss. Synchronous rectifica-
tion provides a significant improvement in efficiency whenev-
er the output voltage is relatively low compared to the voltage
drop across an ordinary rectifier diode.
19.2.7 Bypass-FET Operation on Buck 1 and Buck 2
There is an additional bypass FET used on Buck 1. The FET
is connected in parallel to High Side FET and inductor. Buck
2 has no extra bypass FET – it uses High Side FET (PFET)
for bypass operation. If Buck 1 input voltage is greater than
3.5V (2.6V for Buck 2), the bypass function is disabled. The
determination of whether or not the Buck regulators are in
bypass mode or standard switching regulation is constantly
monitored while the regulators are enabled. If at any time the
input voltage goes above 3.5V (2.6V for Buck 2) while in by-
pass mode, the regulators will transition to normal operation.
When the bypass mode is enabled, the output voltage of the
buck that is in bypass mode is not regulated, but instead, the
output voltage follows the input voltage minus the voltage
drop seen across the FET and DCR of the inductor. The volt-
age drop is a direct result of the current flowing across those
resistive elements. When Buck 1 transitions into bypass
mode, there is an extra FET used in parallel along with the
high side FET for transmission of the current to the load. This
added FET will help reduce the resistance seen by the load
and decrease the voltage drop. For Buck 2, the bypass func-
tion uses the same high side FET.
30166211
19.2.8 Low Dropout Operation
The device can operate at 100% duty cycle (no switching;
PMOS switch completely on) for low dropout support. In this
way the output voltage will be controlled down to the lowest
possible input voltage. When the device operates near 100%
duty cycle, output voltage ripple is approximately 25 mV.
The minimum input voltage needed to support the output volt-
age:
V
IN_MIN=VOUT+ILOAD*(RDSON_PFET+RIND), where
I
LOAD = Load Current
R
DSON_PFET = Drain to source resistance of PFET (high
side) switch in the triode region
R
IND = Inductor resistance
www.national.com
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LM10506
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