CS51221 Ver la hoja de datos (PDF) - Cherry semiconductor

Número de pieza

componentes Descripción

Fabricante

CS51221

Enhanced Voltage Mode PWM Controller

Cherry semiconductor 

COMP

Application Information: continued

VOUT

VIN(LOW). Otherwise, two voltage dividers have to be used

to program OV and UV separately.

Ier

R1

-

FB

Ri

+

+- 1.27

R2

VIN

R1

R2

R3

VUV

Figure 11. OV/UV Monitor Divider.

VOV

Figure 10. The design of feedback voltage divider has to consider the

error amplifier input current.

Design voltage dividers for OV and UV detection

In Fig.11, the voltage divider uses three resistors in series

to set OV and UV threshold seen from the input voltage.

The values of the resistors can be calculated from the fol-

lowing three equations, where the third equation is

derived from OV hysteresis requirement.

( ) VIN(LOW) ×

R2 + R3

R2 + R3 + R1

= 1V

(A)

( ) VIN(HIGH) ×

R3

R2 + R3 + R1

= 2V

(B)

12.5µA × (R1 + R2) = VHYST

(C)

where

VLINE(LOW), VLINE(HIGH) = input voltage OV and UV threshold

VHYST = OV hysteresis seen at VIN

It is self-evident from equation A and B that to use this

design, VIN(HIGH) has to be two times greater than

11

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