KA3844B Fairchild Semiconductor, KA3844B Datasheet - Page 7

• Manufacturer Part Number: KA3844B
• Description: IC CONTROLLER PWM SMPS 8-DIP
• Manufacturer: Fairchild Semiconductor

Specifications of KA3844B

• Pwm Type: Current Mode
• Number Of Outputs: 1
• Frequency - Max: 500kHz
• Duty Cycle: 50%
• Voltage - Supply: 11.5 V ~ 30 V
• Buck: No
• Boost: No
• Flyback: No
• Inverting: No
• Doubler: No
• Divider: No
• Cuk: No
• Isolated: No
• Operating Temperature: 0°C ~ 70°C
• Package / Case: 8-DIP (0.300", 7.62mm)
• Frequency-max: 500kHz
• Duty Cycle (max): 50 %
• Output Current: 1000 mA
• Mounting Style: Through Hole
• Switching Frequency: 500 KHz
• Supply Current: 17 mA
• Maximum Operating Temperature: + 70 C
• Fall Time: 35 ns
• Minimum Operating Temperature: 0 C
• Rise Time: 45 ns
• Synchronous Pin: No
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Shutdown of the KA3842B can be accomplished by two methods; either raise pin 3 above 1V or pull pin 1 below a voltage
two diode drops above ground. Either method causes the output of the PWM comparator to be high (refer to block diagram).
The PWM latch is reset dominant so that the output will remain low until the next clock cycle after the shutdown condition at
pins 1 and/or 3 is removed. In one example, an externally latched shutdown may be accomplished by adding an SOR which
will be reset by cycling V
A fraction of the oscillator ramp can be resistively summed with the current sense signal to provide slope compensation for
converters requiring duty cycles over 50%. Note that capacitor, C
spikes.
Figure 10. Temperature Drift (Vref)
Figure 12. Temperature Drift (Icc)
TEMPERATURE ( C)
TEMPERATURE ( C)
CC
below the lower UVLO threshold. At this point the reference turns off, allowing the SCR to reset.
Figure 9. Slope Compensation
T
, forms a filter with R2 to suppress the leading edge switch
Figure 11. Temperature Drift (Ist)
TEMPERATURE ( C)
KA3842B/KA3843B/KA3844B/KA3845B
7