LM5010 EVAL/NOPB National Semiconductor, LM5010 EVAL/NOPB Datasheet - Page 11

• Manufacturer Part Number: LM5010 EVAL/NOPB
• Manufacturer: National Semiconductor

Specifications of LM5010 EVAL/NOPB

• Lead Free Status / Rohs Status: Compliant

Start-up Regulator (V
Regulation Comparator
The feedback voltage at FB is compared to the voltage at the
Softstart pin (2.5V,
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
culated from the following:
ON
resistor and the input voltage (V
±
2%). In normal operation (the output
CC
)
FIGURE 11. Shutdown Implementation
FIGURE 10. Self Biased Configuration
(Continued)
IN
), cal-
11
The inverse relationship of t
constant frequency as V
quires a high frequency the minimum value for t
consequently R
which limits the maximum duty cycle at minimum V
tolerance for Equation 5 is
1 MHz are possible with the LM5010.
Shutdown
The LM5010 can be remotely shut down by taking the
R
softstart pin is internally grounded, the on-timer is disabled,
and the input current at V
the R
the switch is open, the nominal voltage at R
in Figure 6.
ON
/SD pin below 0.65V. See Figure 11. In this mode the
ON
/SD pin allows normal operation to resume. When
ON
20119918
, is limited by the off-time (265 ns,
20119916
IN
IN
±
is reduced (Figure 7). Releasing
is varied. If the application re-
25%. Frequencies in excess of
ON
vs. V
IN
results in a nearly
ON
/SD is shown
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ON
IN
±
, and
. The
15%)
(5)