CS52845 datasheet(5/6 Pages) CHERRY

部件名	CS52845

功能描述	Current Mode PWM Control Circuit with 50% Max Duty Cycle

PDF	6 Pages

Scroll/Zoom	100%

制造商	CHERRY [Cherry Semiconductor Corporation]

网页	http://www.cherrycorp.com/

标志

5 / 6 page

Setting the Oscillator

The times Tc and Td can be determined as follows:

Grounding

High peak currents associated with capacitive loads neces-

sitate careful grounding techniques. Timing and bypass

capacitors should be connected close to Gnd in a single

point ground.

The transistor and 5kΩ potentiometer are used to sample

the oscillator waveform and apply an adjustable ramp to

Sense.

Vupper

Vlower

ton

toff

ton=tc

toff=tc+2td

Circuit Description:: continued

Substituting in typical values for the parameters in the

above formulas:

VREF = 5.0V, Vupper = 2.7V, Vlower = 1.0V, Id = 8.3mA,

then

tc ≈ 0.5534RTCT

td = RTCT ln

For better accuracy RT should be ≥10kΩ.

)

2.3 - 0.0083 RT

4.0 - 0.0083 RT

(

VCC

Switch

Current

EA Output

Toggle

F/F Output

OSC

RESET

VOSC

Figure 2: Timing Diagram

Figure 3: Duty Cycle parameters.

tc = RTCT ln

td = RTCT ln

)

VREF - IdRT - Vlower

VREF - IdRT - Vupper

(

)

VREF - Vlower

VREF - Vupper

(

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