HA17431FP datasheet(16/20 Pages) RENESAS

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HA17431 Series

REJ03D0678-0300 Rev.3.00 Apr 03, 2007

Page 16 of 19

In Figure 3, the following formulas are obtained:

Gain

G1 = G0 ≈ 50 dB to 60 dB (determined by shunt regulator)

G2 =

Corner frequencies

f1 = 1/(2π C1 G0 R3)

f2 = 1/(2π C1 R5)

G0 is the shunt regulator open-loop gain; this is given by the reciprocal of the reference voltage fluctuation

∆Vref/∆V

KA, and is approximately 50 dB.

3. Practical Example

Consider the example of a photocoupler, with an internal light emitting diode VF = 1.05 V and IF = 2.5 mA, power

supply output voltage V2 = 5 V, and bias resistance R2 current of approximately 1/5 IF at 0.5 mA. If the shunt

regulator VK = 3 V, the following values are found.

R1 =

5V – 1.05V – 3V

2.5mA + 0.5mA

= 316(

Ω) (330Ω from E24 series)

R2 =

1.05V

0.5mA

= 2.1(k

Ω) (2.2kΩ from E24 series)

Next, assume that R3 = R4 = 10 kΩ. This gives a 5 V output. If R5 = 3.3 kΩ and C1 = 0.022 µF, the following

values are found.

G2 = 3.3 kΩ / 10 kΩ = 0.33 times (–10 dB)

f1 = 1 / (2 × π × 0.022 µF × 316 × 10 kΩ) = 2.3 (Hz)

f2 = 1 / (2 × π × 0.022 µF × 3.3 kΩ) = 2.2 (kHz)

HA17431FP 데이터시트(PDF) 16 Page - Renesas Technology Corp