Details

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BUY uc3845ad https://www.utsource.net/itm/p/8640832.html

Parameter	Symbol	Min	Typ	Max	Unit	Description
Supply Voltage	Vcc	15	30		V	Operating supply voltage range
Start-Up Current	Istrt		1.2		mA	Current required to start the oscillator
Operating Current	Icc	1.5	3.5	6.0	mA	Typical operating current at Vcc = 30V
Error Amplifier Input Offset	Vos	-5	0	+5	mV	Maximum input offset voltage of the error amplifier
Error Amplifier Input Bias	Iib	10	20	30	nA	Input bias current of the error amplifier
Error Amplifier Gain	Aea	50	70	90	dB	Open-loop gain of the error amplifier
Compensation Pin Leakage	Icl	-10	0	+10	nA	Leakage current at the compensation pin
Soft-Start Capacitance	Css				pF	Capacitance for soft-start control
Frequency Set Resistor	Rfset				kΩ	Resistor to set the switching frequency
Minimum Off Time	Toffmin	2.5			μs	Minimum off time of the PWM output
Maximum Duty Cycle	Dmax	95			%	Maximum duty cycle of the PWM output
Overcurrent Protection	Iocp		1.0		A	Overcurrent protection threshold
Thermal Shutdown	Tsd	150			°C	Temperature at which thermal shutdown occurs
Operating Temperature Range	Topr	-40		125	°C	Operating temperature range

Instructions for UC3845AD:

1. Supply Voltage (Vcc):

   • Connect the Vcc pin to a power supply between 15V and 30V.
   • Ensure the supply is stable and within the specified range to avoid damage or erratic behavior.

2. Start-Up Current (Istrt):

   • The IC requires a minimum of 1.2mA to start the oscillator. Ensure the power supply can provide this current.

3. Operating Current (Icc):

   • The typical operating current is 3.5mA at Vcc = 30V. Design the power supply to handle this current.

4. Error Amplifier:

   • Connect the inverting and non-inverting inputs of the error amplifier to the appropriate feedback and reference voltages.
   • Use a compensation network (typically RC) to stabilize the loop and ensure proper operation.

5. Soft-Start:

   • Connect a capacitor (Css) between the soft-start pin and ground to control the startup time and reduce inrush current.

6. Frequency Set:

   • Connect a resistor (Rfset) between the frequency set pin and ground to set the desired switching frequency.

7. Overcurrent Protection:

   • Connect the overcurrent protection (OCP) pin to a sense resistor that monitors the current through the power switch.
   • The IC will shut down if the current exceeds the threshold (1.0A).

8. Thermal Shutdown:

   • The IC will automatically shut down if the temperature exceeds 150°C to prevent damage.
   • Ensure proper heat sinking and ventilation to keep the temperature within safe limits.

9. Operating Temperature:

   • The IC is designed to operate between -40°C and 125°C. Ensure the ambient temperature is within this range.

10. Layout Considerations:

    • Use short, wide traces for high-current paths to minimize inductance and resistance.
    • Place decoupling capacitors close to the Vcc and ground pins to filter out noise.

11. Testing and Debugging:

    • Monitor the output waveform and adjust the compensation network as needed to achieve stable operation.
    • Use an oscilloscope to verify the switching frequency and duty cycle.

By following these instructions, you can ensure reliable and efficient operation of the UC3845AD in your power supply design.

(For reference only)