LM5009EVAL National Semiconductor, LM5009EVAL Datasheet - Page 8

• Manufacturer Part Number: LM5009EVAL
• Description: BOARD EVALUATION LM5009
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM5009EVAL

• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 10V
• Current - Output: 150mA
• Voltage - Input: 12 ~ 95V
• Regulator Topology: Buck
• Frequency - Switching: 240Hz
• Board Type: Fully Populated
• Utilized Ic / Part: LM5009
• Lead Free Status / RoHS Status: Not applicable / Not applicable
• Power - Output: -
• Lead Free Status / Rohs Status: Not Compliant

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The output voltage (V
sistors as shown in
as follows:
This regulator regulates the output voltage based on ripple
voltage at the feedback input, requiring a minimum amount of
ESR for the output capacitor C2. A minimum of 25mV of ripple
voltage at the feedback pin (FB) is required for the LM5009.
In cases where the capacitor ESR is too small, additional se-
ries resistance may be required (R3 in
For applications where lower output voltage ripple is required
the output can be taken directly from a low ESR output ca-
pacitor, as shown in
the load regulation.
High Voltage Start-Up Regulator
The LM5009 contains an internal high voltage startup regu-
lator. The input pin (VIN) can be connected directly to line
voltages up to 95 Volts, with transient capability to 100 volts.
The regulator is internally current limited at 9.5mA. Upon
power up, the regulator sources current into the external ca-
pacitor at VCC (C3). When the voltage on the VCC pin reach-
es the under-voltage lockout threshold of 6.3V, the buck
switch is enabled.
In applications involving a high value for V
dissipation in the V
age can be diode connected to the VCC pin. Setting the
voltage between 8V and 14V shuts off the internal regulator,
reducing internal power dissipation. See
required into the VCC pin is shown in the Typical Performance
Characteristics.
FIGURE 2. Low Ripple Output Configuration
V
OUT
CC
Figure
Figure
OUT
regulator is a concern, an auxiliary volt-
= 2.5 x (R1 + R2) / R2
) is programmed by two external re-
1. The regulation point is calculated
2. However, R3 slightly degrades
Figure
Figure
IN
, where power
1).
3. The current
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(1)
8
Regulation Comparator
The feedback voltage at FB is compared to an internal 2.5V
reference. In normal operation (the output voltage is regulat-
ed), an on-time period is initiated when the voltage at FB falls
below 2.5V. The buck switch will stay on for the programmed
on-time, causing the FB voltage to rise above 2.5V. After the
on-time period, the buck switch will stay off until the FB volt-
age again falls below 2.5V. During start-up, the FB voltage
will be below 2.5V at the end of each on-time, resulting in the
minimum off-time. 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 2.875V
reference. If the voltage at FB rises above 2.875V the on-time
pulse 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 Generator and Shutdown
The on-time for the LM5009 is determined by the R
and is inversely proportional to the input voltage (Vin), result-
ing in a nearly constant frequency as Vin is varied over its
range. The on-time equation is:
R
V
This requirement limits the maximum frequency for each ap-
plication, depending on V
The LM5009 can be remotely disabled by taking the RON/SD
pin to ground. See
is between 1.7V and 5V, depending on Vin and the value of
the R
IN
ON
) greater than 250 ns, for proper current limit operation.
should be selected for a minimum on-time (at maximum
ON
resistor.
FIGURE 3. Self Biased Configuration
T
ON
= 1.25 x 10
Figure
IN
4. The voltage at the RON/SD pin
and V
-10
x R
OUT
ON
.
/ V
IN
ON
resistor,
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