CS2842A Ver la hoja de datos (PDF) - ON Semiconductor

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componentes Descripción

Fabricante

CS2842A

Off−Line Current Mode PWM Control Circuit with Undervoltage Lockout

ON Semiconductor 

CS2842A, CS3842A, CS2843A, CS3843A

ǒ Ǔ tc + RTCT

ln

VREF * Vlower

VREF * Vupper

ǒ Ǔ td + RTCT

ln

VREF * IdRT * Vlower

VREF * IdRT * Vupper

Substituting in typical values for the parameters in the

above formulas:

VREF = 5.0 V

Vupper = 2.7 V

Vlower = 1.0 V

Id = 8.3 mA

tc ≈ 0.5534RTCT

ǒ Ǔ td + RTCT

ln

2.3 * 0.0083RT

4.0 * 0.0083RT

The frequency and maximum duty cycle can be

determined using the Typical Performance Characteristic

graphs.

Grounding

High peak currents associated with capacitive loads

necessitate careful grounding techniques. Timing and

bypass capacitors should be connected close to GND pin in

a single point ground.

The transistor and 5.0 kΩ potentiometer, shown in the test

circuit, are used to sample the oscillator waveform and apply

and adjustable ramp to Sense.

VREF

OSC

GND

Timing Parameters

Vupper

Vlower

tc

Sawtooth Mode

Large RT (≈ 10 kΩ)

Triangular Mode

Small RT (≈ 700 kΩ)

RT

CT

td

VOSC

Internal Clock

VOSC

Internal Clock

Figure 7. Oscillator Timing Network and

Parameters

http://onsemi.com

7

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