UC3845D Fairchild Semiconductor, UC3845D Datasheet - Page 7

• Manufacturer Part Number: UC3845D
• Description: IC CTLR PWM CURR MODE 14-SOIC
• Manufacturer: Fairchild Semiconductor

Specifications of UC3845D

• Pwm Type: Current Mode
• Number Of Outputs: 1
• Frequency - Max: 500kHz
• Duty Cycle: 50%
• Voltage - Supply: 8.2 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: 14-SOIC (3.9mm Width), 14-SOL
• Frequency-max: 500kHz
• Duty Cycle (max): 50 %
• Output Voltage: 4.90 V to 5.10 V
• Output Current: 1000 mA
• Mounting Style: SMD/SMT
• Switching Frequency: 500 KHz
• Operating Supply Voltage: 30 V
• 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
• Other names: UC3845DFS

Shutdown of the UC3842 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 SCR 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)
CC
below the lower UVLO threshold. At this point the reference turns off, allowing the SCR to reset.
Temperature ( C)
Temperature ( C)
UC3842/UC3843
Figure 9. Slope Compensation
T
, forms a filter with R2 to suppress the leading edge switch
Figure 11. Temperature Drift (Ist)
Temperature ( C)
UC3842/UC3843/UC3844/UC3845
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