LM3524DM National Semiconductor, LM3524DM Datasheet - Page 9

• Manufacturer Part Number: LM3524DM
• Description: IC, REGULATING PWM, 16-SOIC
• Manufacturer: National Semiconductor

Specifications of LM3524DM

• Primary Input Voltage: 40V
• No. Of Outputs: 1
• Output Voltage: 18V
• Output Current: 200mA
• No. Of Pins: 16
• Operating Temperature Range: 0°C To +125°C
• Power Dissipation Pd: 1W
• Termination Type: SMD
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

The output of the amplifier, or input to the pulse width modu-
lator, can be overridden easily as its output impedance is very
high (Z
to pin 9 which will override the error amplifier and force a par-
ticular duty cycle to the outputs. An example of this could be
a non-regulating motor speed control where a variable volt-
age was applied to pin 9 to control motor speed. A graph of
the output duty cycle vs the voltage on pin 9 is shown in Figure
5.
The duty cycle is calculated as the percentage ratio of each
output's ON-time to the oscillator period. Paralleling the out-
puts doubles the observed duty cycle.
The amplifier's inputs have a common-mode input range of
1.5V–5.5V. The on board regulator is useful for biasing the
inputs to within this range.
O
5 MΩ). For this reason a DC voltage can be applied
FIGURE 5.
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CURRENT LIMITING
The function of the current limit amplifier is to override the
error amplifier's output and take control of the pulse width.
The output duty cycle drops to about 25% when a current limit
sense voltage of 200 mV is applied between the +C
−C
mately 5% results in a 0% output duty cycle. Care should be
taken to ensure the −0.7V to +1.0V input common-mode
range is not exceeded.
In most applications, the current limit sense voltage is pro-
duced by a current through a sense resistor. The accuracy of
this measurement is limited by the accuracy of the sense re-
sistor, and by a small offset current, typically 100 μA, flowing
from +CL to −CL.
OUTPUT STAGES
The outputs of the LM3524D are NPN transistors, capable of
a maximum current of 200 mA. These transistors are driven
180° out of phase and have non-committed open collectors
and emitters as shown in Figure 6.
L
sense terminals. Increasing the sense voltage approxi-
FIGURE 6.
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L
and