NCV8667 Ver la hoja de datos (PDF) - ON Semiconductor

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componentes Descripción

Fabricante

NCV8667

150 mA LDO Regulator with Enable, Reset and Early Warning

ON Semiconductor 

NCV8667

for selected preset Early Warning options are described by

Equations 1 and 2.

ȡ ǒ Ǔȣ RSI1 RSI2 ) RSI_ext

ȧȢ ȧȤ Vin_EW(th)_Low + 1.1 1 )

RSI2 RSI_ext

) 0.25

(eq. 1)

ȧȡ RSI_ext + 1.1

ȢRSI2

RSI1 RSI2

ǒ Ǔ Vin_EW(th)_Low * 0.25 * 1.1

106ȧȣȤ

(eq. 2)

Where:

RSI1,RSI2 − internal EW divider resistors (see Figure 3)

(select values from Early Warning Preset Options table)

RSI−ext − external resistor connected between SI and GND

(recommended to be selected from 50 kW to 250 W)

If Adjustable Early Warning Threshold option

(NCV8667y0) is used EW threshold is adjusted by external

resistor divider. (See Figure 2) The values for RSI1 and RSI2

are selected for a typical threshold of 1.2 V on the SI pin

according to Equations 3 and 4, where Vin_EW(th) is

demanded value of input voltage at which Early Warning

signal has to be generated. RSI2 is recommended to be

selected in range of 100 kW to 1 MW. The higher are values

of resistors RSI1 and RSI2 the lower is current flowing

through the resistor divider, however this also increases a

delay between Input voltage and SI input voltage caused by

charging SI input capacitance with higher RC constant. The

delay can be lowered by decreasing the resistors values with

consequence of resistor divider current is increased.

ǒ Ǔ Vin_EW(th) + 1.25

1 ) RSI1

RSI2

(eq. 3)

ǒ Ǔ Vin_EW(th)

RSI1 + RSI2

*1

1.2

(eq. 4)

Sense Output

The Sense Output is from an open drain driver with an

internal 30 kW pull up resistor to Vout. Figure 26 shows the

SO Monitor timing waveforms as a result of the circuit

depicted in Figure 1. If the input voltage decreases the output

voltage decreases as well. If the SI input low threshold

voltage is crossed it causes the voltage on the SO output goes

low sending a warning signal to the microprocessor that a

reset signal may occur in a short period of time. TWARNING

is the time the microprocessor has to complete the function

it is currently working on and get ready for the reset

shutdown signal.

V out

V SI

V SI,Low

V RO

V SO

T WARNING

Figure 30. SO Warning Timing Diagram

Sense

Input

V SI,High

V SI,Low

Sense

Output

High

tPSOLH

t

tPSOHL

Low

t

Figure 31. Sense Input to Sense Output Timing Diagram

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