TDA5147CH 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
Preliminary specification
TDA5147CH
FUNCTIONAL DESCRIPTION
Spindle drivers
The spindle section (see Fig.2) contains both the low and
high side drivers (configured as H bridges) for a
three-phase DC brushless motor. Back EMF (Electro
Motive Force) sensing of the commutation rate
(pin SENWIS) is an output to an external digital ASIC
circuit. This circuit should provide the input commutation
control as well. Consequently, all speed control, start-up
routine and commutation control will be generated by the
external 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 depends solely on the duty factor.
The pole location of this first order low-pass filter is
controlled by an external capacitor at pin SPWMFLT.
Dynamic braking is possible only during non power-down
situations and must be initiated by the digital circuit.
A 3- level mode line (pin SMODE1) allows for:
• Induction sensing in pre-start-up (SMODE1 = 0.5V_CC5
or high impedance)
• PWM control during start-up (SMODE1 = 0 V)
• Linear control (SMODE1 = V_CC5).
SENSING MODE
The induction sensing mode can be used to sense the
rotor position and to spin-up with high current.
To sense the rotor position, one of the BEMF sensor
outputs (pin SENWIS) will be shared with the voltage
comparator that is used for the induction sensing function.
Prior to start-up each phase is 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.
In cases where the spindle motor requires more current to
spin-up, the sensing mode is used with the exception that
the output SENWIS is ignored. The output drivers are
operated in saturation in the sensing mode, so the motor
current is only limited by the power supply. This condition
of induction sense mode can be used to overcome the
head friction and must only be used 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, because
saturation reduces the power dissipation during start-up.
When the spindle current reaches the value destined by
the duty factor of the signal at pin SIPWM, a one-shot is
fired. The output of the one-shot remains HIGH for the
programmed off-time (t_off) set by the RC-network at
pin SPWMTC. The one-shot is not retriggerable for
approximately 10% of the off-time, giving a minimum for
the on-time of 0.1t_off. During the off-time, the lower spindle
output drivers are switched off. The on-time of the drivers
is determined by the charging time of the coil current.
The turn-off time follows: t_off = R × C _ln(2)
With R = 68 kΩ and C = 220 pF, t_off = 10.4 µs
The minimum on-time is: 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 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^{---SP---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----.-1-3---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--}
The duty factor is arranged so that at 100%, the voltage
SPWMFLT = 1.74 V and at a 5% duty factor
SPWMFLT = 0 V. This is to ensure that at 0% duty factor
the current will be zero (allowances for circuit tolerances).
The input decoder is driven by three lines which define the
windings to be energized. The input decoder must then
translate these lines to six lines to drive the six output
drivers. The truth table is given in Table 1. The status of
each block in the spindle drive section during the possible
modes of operation is given in Table 4
1997 Jul 09
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