SA56202 Datasheet, PDF (10/24 Pages) NXP Semiconductors – One-chip motor driver

Philips Semiconductors
SA56202
One-chip motor driver
I_LIM can be chosen to be a fraction of this maximum current I_MAX. By making the ratio
between R_LIM (connected to pin 10) and R_REF (connected to pin 8) this same fraction, I_LIM
is programmed as expressed in the following formula:
I_LIM
=
-^R----^L---^I-^M---
R_REF
×
I_MAX
So by choosing I_LIM, R_LIM needs to be: R_LIM = -_II--_M-^L---^IA--^M-_X-- × R_REF
Figure 8 shows the limit current as a function of R_LIM with R_REF = 47 kΩ.
100
I_LIM
(% of I_MAX)
80
001aaa434
60
40
20
0
0
10
20
30
40
50
R_LIM (kΩ)
Fig 8. Limit current I_LIM as a function of external resistor R_LIM.
During accelerating and braking the motor current will not exceed I_LIM. I_LIM also sets the
transconductance gain I_LIM/V_VINREF of the spindle driver.
7.5 Programming R_EMF
The back-EMF voltage is internally regenerated. The ratio between R_EMF and R_REF is
used to scale the internal EMF regeneration. The value of external resistor R_EMF depends
on the type of motor (k-factor and number of pole pairs N_PP) and the motor supply voltage
V_DD(SPN). The following formula should be used to determine the R_EMF resistor:
R_EMF = -^k----^×-_N----²_P---^._P-⁶---_×--^×---_V-¹---⁰-_D---^3D---^×-₍--_S--^R_P---_N-^R---₎^E----^F- with k in units Nm/A.
7.6 FG generator
The raw zero-crossings of the Hall sensors are first filtered and debounced before being
passed to the FG generator. The FG generator toggles its output at every filtered Hall
zero-crossing. For three Hall sensors this means that the motor frequency is linked to the
FG frequency by: f _motor = ₃-----_×-^F----_NG-----_P---_P-
9397 750 12772
Preliminary data sheet
Rev. 01 — 19 July 2004
© Koninklijke Philips Electronics N.V. 2004. All rights reserved.
10 of 24