TDA5147K Datasheet, PDF (8/32 Pages) NXP Semiconductors – 12 V Voice Coil Motor VCM driver and spindle motor drive combination chip

Philips Semiconductors
12 V Voice Coil Motor (VCM) driver and
spindle motor drive combination chip
Product specification
TDA5147K
FUNCTIONAL DESCRIPTION
Spindle drivers
The spindle section contains both the low and high side
drivers (configured as H bridges) for a three-phase DC
brushless motor. Back EMF (BEMF) sensing of the
commutation rate needs to be output to an external digital
ASIC circuit. This digital circuit also provides the input
commutation control. Consequently, all speed control,
start-up routine and commutation control will be generated
by the digital circuit.
The SIPWM signal from the digital circuit is used to control
the spindle current. This PWM signal is internally filtered.
The output of this filter is duty factor dependent only. The
filter characteristics is that of a 1-pole low-pass filter, with
the pole location being controlled by the external capacitor
connected to pin SPWMFLT.
Dynamic braking is possible only during non power-down
situations and must be initiated by the digital circuit.
SMODE1
A 3-state level mode line (SMODE1) has been included to
allow for;
1. An induction sensing algorithm in pre-start-up (V_CCA1).
2. PWM control during start-up (0.5V_CCA1).
3. Linear control (0 V).
SENSING MODE
The induction sensing mode is used for two purposes.
Firstly one of the BEMF sensor outputs (SENWIS) will be
shared with the voltage comparator that is used for the
induction sensing function. Prior to start-up each phase
can be excited for a short period of time. The current from
each coil can be monitored via the multiplexed output
(SENWIS). By comparing the rise times of each phase the
rotor position can be determined.
Secondly, in situations where the spindle motor requires
more current to spin-up, this mode is used with the
exception that the output SENWIS is ignored. Since, in the
induction sense mode, the output drivers are operated in
saturation mode, the motor current is limited only by the
power supply. This condition of induction sense mode can
be used to overcome the head friction and must be used
only when needed.
PWM MODE
The PWM mode is normally used during the start-up
phase. Maximum drive voltage is applied to the low drivers
to obtain high start-up torque. The purpose of the PWM
mode is to drive the low drivers into saturation (saturation
reduces the power dissipation in the TDA5147K during
start-up).
When the spindle current reaches the programmed set
current (SIPWM) value, a one-shot is fired. The output of
the one-shot remains high for the programmed off-time
(t_off) set by the capacitor/resistor network at the SPWMTC
pin. The one-shot is not retriggerable for approximately
10% of the off-time, this gives a minimum of (10% t_off)
time-on. During the off-time, the lower spindle output
drivers are switched off. The on-time of the drivers is not
fixed but is determined by the charging time of the coil
current to reach the program set current.
The turn-off time is calculated by the equation:
t_off = R × C_ln(2)
Where R = 68 kΩ and C = 220 pF, t_off = 10.4 µs.
The minimum on-time can be calculated by the equation:
t_on= ^C----I-V---
LINEAR MODE
The linear mode is used when the motor is near to its
intended speed. It can also be used at start-up, but higher
power dissipation will occur. In the linear mode the linear
drivers are controlled by a sensing amplifier. A Miller
network is used to obtain soft switching on the lower
drivers. This prevents large voltage spikes on the motor
coils when the lower drivers are switching. The high drivers
are switched into the linear (resistive) region.
The transconductance gain of the low driver current to filter
voltage can be calculated as follows:
G_m
=
V-----_S^---_P^--I-_W^-c--o--_M^-i-l--_F^---_L^---_T^{- =}
R--1---_s^-



V---V--_S^--S-_P^{---IW-S----EM---N-}_F^---HL---_T^-



=
-R-1---_s-
=
15--
=
A/V
For a 100% duty factor at SIPWM, the nominal voltage at
SPWMFLT = 1.74 V. The calculated coil current for a
100% duty factor (sense resistors R_s = 0.33 Ω) is:
I_coil = _{0----.-13----3--} × ^15-- × 1.74 = 1.05 A
Referencing to the duty factor, the coil current is:
I_coil = _R--1---s- = ^15-- × 1.74 × ^{0----%--1----0-d--0-u---t--y--} = -R-1---_s- (0.348) × ^{0----%--1----0-d--0-u---t--y--}
1996 Jul 26
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