LM3524DN National Semiconductor, LM3524DN Datasheet - Page 9

• Manufacturer Part Number: LM3524DN
• Description: ENHANCED PWM CONTROLLER, 3524, DIP
• Manufacturer: National Semiconductor

Specifications of LM3524DN

• Frequency: 350kHz
• Power Dissipation Pd: 1W
• Digital Ic Case Style: DIP
• No. Of Pins: 16
• Operating Temperature Range: 0°C To +125°C
• Svhc: No SVHC (15-Dec-2010)
• Operating Temperature Max: 125°C
• Base Number: 3524
• Controller Type: PWM
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Functional Description
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
applied to pin 9 which will override the error amplifier and
force a particular duty cycle to the outputs. An example of
this could be a non-regulating motor speed control where a
variable voltage 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
FIGURE 5.
(Continued)
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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
and −C
proximately 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
resistor, 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.
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sense terminals. Increasing the sense voltage ap-
FIGURE 6.
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