5.4 Analog Functionality

Table 5-3. Internal Op Amp Parameters
Op Amp #	Analog Function	Passive Components	Design Equations
2	Low-pass filter	R2, R3, R5, R6, C13, C14, C17	$R 2 = R 3 = R 5 = R 6 = R$ $C 13 = C 17 = C$ $R 1 = R 7$ $C o m m o n - \mod e f_{- 3 d B} ≅ \frac{1}{2 π R C}$ $D i f f e r e n t i a l - \mod e f_{- 3 d B} ≅ \frac{1}{2 π (2 R) (\frac{C}{2} + C 14)}$ $D i f f e r e n t i a l a m p l i f i e r g a i n ≅ \frac{R 7}{2 R}$
	Reference voltage bias	R1, R7
	Differential amplifier input	R2, R3, R5, R6
	Differential amplifier feedback	R1

$D i f f e r e n t i a l a m p l i f i e r g a i n = \frac{30 k Ω}{2 * 1 k Ω} = 15$

$D i f f e r e n t i a l \mod e f_{- 3 d B} ≅ \frac{1}{2 π (2 * 1 k Ω) (\frac{56 p F}{2} + 56 p F)} ≅ 948 K H z$

${C o m m o n - \mod e f}_{- 3 d B} ≅ \frac{1}{2 π (1 k Ω) (56 p F)} ≅ 2.8 M H z$

$C u t o f f {f r e q u e n c y}_{- 3 d B} = \frac{1}{2 π (30 k ∥ 2 k + 300) 10 n F} ≅ 7321 H z$

$30 d e g r e e p h a s e s h i f t f r e q u e n c y = \frac{\tan (30)}{2 π (30 k ∥ 2 k + 300) 10 n F} = 4226 H z$

Thus, the theoretical maximum speed of the motor will be:

$4226 H z * 60 ≅ 253560 e R P M$

$M e c h a n i c a l R P M = e R P M / P o l e p a i r s$