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TDA5345HT Datasheet, PDF (20/44 Pages) NXP Semiconductors – 5 V spindle & VCM driver combo
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Philips Semiconductors
5 V spindle & VCM driver combo
Preliminary specification
TDA5345HT
The error amplifier compares the VcmDacOut(49) input command and the VcmSenseOut(18) sense amplifier output
signal to generate the control voltage of the power drivers.
IVCM
23
VcmSenseInP
VcmSenseInM 22
+
SENSE
AMPLIFIER
G=3
-
VcmRef
18
19
RFB
VcmCompensIn
+
ERROR
- AMP
VcmCompensOut
to the power
17
drivers
VcmInput
Rin
20
Fig.12 VCM transconductance gain schematic.
V-----c---m------D-----a----c---O---R--u---i-tn---–-----V----c----m-----R-----e----f= -V----c---m------S----e----n----s----e--R-O---F--u-B---t---–-----V----c----m-----R-----e----f= 3-----×-----R-----s--e-R--n---Fs---eB----×-----I-V----C---M--
(6)
Finally, the transconductance gain of the VCM loop is given by the following equation:
GVCM [ (A) ⁄ (V) ] = V-----c---m------D-----a----c---O-I--V--u-C---t-M--–-----V----c----m-----R-----e----f = -R-R---F-i--nB-- × -3----×-----R---1--s--e---n---s---e- = -R----s0---e-.-4-n--s---e-
(7)
VCM 12-bit resistive ladder DAC:
The VCM loop input voltage is provided by an internal signed 12-bit resistive ladder DAC. The output voltage is a linear
function of the input code written in register #7 (low gain) or register #8 (high gain), bits [11:0] :
Table 10 Dac12 output voltage versus the input code (1 LSB = 125 µV) when writing in register #7 :
INPUT CODE
DAC12 VOLTAGE
(7FF)H
(000)H
(FFF)H
(800)H
1.732 V -1 LSB
1.482 V
1.482 V -1 LSB
1.232 V
Table 11 Dac12 output voltage versus the input code (1 LSB = 500 µV) when writing in register #8 :
INPUT CODE
(7FF)H
(000)H
(FFF)H
(800)H
DAC12 VOLTAGE
2.482 V - 1LSB
1.482 V
1.482 V -1 LSB
0.482 V
Warning : at power up, the 12-bit DAC needs to be programmed so that it is in a defined state.
VCM back-EMF amplifier
To prevent any actuator crash on the disk when a ramp load is used, an internal VCM back-EMF amplifier is build to
monitor the actuator speed. Indeed, the VCM back-EMF is a picture of the actuator speed. The voltage across the VCM
motor is divided in several contributions:
1999 June 10
20
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