CS2844LDR14 View Datasheet(PDF) - Cherry semiconductor

Part Name

Description

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CS2844LDR14

IES Current Mode PWM Control Circuit with 50% Max Duty Cycle

Cherry semiconductor 

VOSC

OSC

RESET

Toggle

F/F Output

EA Output

Switch

Current

VCC

IO

VO

Figure 2: Timing Diagram

Vupper

Vlower

ton

toff

td

tC

ton = tC

toff = tC+2td

Figure 3: Duty Cycle parameters.

Circuit Description: continued

Setting the Oscillator

The times Tc and Td can be determined as follows:

( ) tc = RTCT ln

VREF - Vlower

VREF - Vupper

( ) td = RTCT ln

VREF - IdRT - Vlower

VREF - IdRT - Vupper

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

2.3 - 0.0083 RT

4.0 - 0.0083 RT

For better accuracy RT should be ≥10kΩ.

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.

5

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