TDA5345HT Datasheet, PDF (19/44 Pages) NXP Semiconductors – 5 V spindle & VCM driver combo

Philips Semiconductors
5 V spindle & VCM driver combo
Preliminary specification
TDA5345HT
When the 6-bit DAC is used for the spindle, the LSB current is set externally, by means of a 33 kΩ resistor (to have a
very good absolute accuracy). The Spindle Current limit is then set by 31 steps of 20 mA. Please note that only the
positive codes of the 6-bit DAC can be used, so only (2⁵ - 1) = 31 steps can be defined.
Table 8 Spindle Start-up current limit according to the spindle 6-bit DAC code :
INPUT CODE
000000
000001
011111
SPINDLE START-UP CURRENT
0 mA
20 mA
620 mA
When the 6-bit DAC is used for the VCM section, the LSB current is set by an internal resitor to have a good matching
with the 2 internal resistors used to set the VCM loop Gain. The VCM current offset is set by steps of :
I_{VCMOffset (LSB)} = ^{1----.--6-R--1--}_S-3---_e--^â‹-_n--1_s---_e^0----–--³- ( A)
(4)
Table 9 VCM current offset according to the spindle 6-bit DAC code (assuming that R_Sense = 1 Ω, 1 LSB = 1.613 mA) :
INPUT CODE
VCM OFFSET CURRENT
011111
000000
1111111
100001
100000
+50 mA
0 µA
-1.613 mA
-50 mA
-50 mA
VCM driver
The VCM is a linear, AB class type with both low-side and high-side drivers configured as a H-bridge. The zero-current
reference voltage for the VCM loop is internally set at Vdd5/2=2.5 V. The sense resistor R_sense enables the VCM current
to be measured through the sense amplifier. The gain of the sense amplifier is internally set to typically 3. The output
VcmSenseOut is given by the following equation:
VcmSenseOut= 3 × (VcmSenseInP – VcmSenseInM) + VcmRef
(5)
Figure 14 presents the VCM sense amplifier.
VcmRef
18
I_VCM
23
VcmSenseInP
R
3R
+
R = 10 kΩ
22
VcmSenseInM
1999 June 10
R
-
3R
Fig.11 VCM sense amplifier
19