參數(shù)資料
型號(hào): LM5010
廠商: National Semiconductor Corporation
元件分類: 基準(zhǔn)電壓源/電流源
英文描述: RADIATION HARDENED HIGH EFFICIENCY, 5 AMP SWITCHING REGULATORS
中文描述: 抗輻射高效,5安培開關(guān)穩(wěn)壓器
文件頁數(shù): 11/19頁
文件大小: 453K
代理商: LM5010
Start-up Regulator (V
CC
)
(Continued)
Regulation Comparator
The feedback voltage at FB is compared to the voltage at the
Softstart pin (2.5V,
±
2%). In normal operation (the output
voltage is regulated) an on-time period is initiated when the
voltage at FB falls below 2.5V. The buck switch stays on for
the on-time causing the FB voltage to rise above 2.5V. After
the on-time period the buck switch stays off until the FB
voltage falls below 2.5V. Bias current at the FB pin is less
than 5 nA over temperature.
Over-Voltage Comparator
The feedback voltage at FB is compared to an internal 2.9V
reference. If the voltage at FB rises above 2.9V the on-time
is immediately terminated. This condition can occur if the
input voltage, or the output load, change suddenly. The buck
switch will not turn on again until the voltage at FB falls below
2.5V.
ON-Time Control
The on-time of the internal switch (see
Figure 5
) is deter-
mined by the R
resistor and the input voltage (V
IN
), cal-
culated from the following:
(5)
The inverse relationship of t
vs. V
results in a nearly
constant frequency as V
is varied. If the application re-
quires a high frequency the minimum value for t
ON
, and
consequently R
, is limited by the off-time (265 ns,
±
15%)
which limits the maximum duty cycle at minimum V
. The
tolerance for Equation 5 is
±
25%. Frequencies in excess of
1 MHz are possible with the LM5010.
Shutdown
The LM5010 can be remotely shut down by taking the
R
/SD pin below 0.65V. See
Figure 11
. In this mode the
softstart pin is internally grounded, the on-timer is disabled,
and the input current at V
IN
is reduced (
Figure 7
). Releasing
the R
ON
/SD pin allows normal operation to resume. When
the switch is open, the nominal voltage at R
ON
/SD is shown
in
Figure 6
.
20119916
FIGURE 10. Self Biased Configuration
20119918
FIGURE 11. Shutdown Implementation
L
www.national.com
11
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