TDA5345HT

Features:

· Single chip voice coil and spindle motor drivers:
· Complementary outputs (Nmos & Pmos): No step-up converter needed
· On-chip isolation switch to allow synchronous rectification at power-down
· Suited for ramp load operation
· Register based architecture: on-chip serial interface
· Temperature shut down protection
· Linear 3.3 V regulator using one external NPN transistor
· Power monitor circuitrymonitoring the 5 V supply
· 1 axis shock sensor amplifier
· Switched capacitor regulator (-3 V) using 2 external capacitors and 2 external shottky diodes
· All main internal functions can be independently put in Sleep mode
· Small low profile package: TQFP64 (1.2 mm high).


Pinout




Specifications

SYMBOL	PARAMETER	CONDITIONS	MIN.	MAX.	UNIT
VDD5A/D	+5 V supplies	indefinite time period	- 0.3	5.5	V
VDD5A/D	+5 V supplies	see note1	- 0.3	7	V
VPeakVCM	VCM drive output voltage	Inductance connected to VCM+ and VCM-	-0.5	VDD5 + 0.5	V
IPeakVCM	VCM drive output peak current	peak < 0.5 s		1.0	V
VPeakSpin	spindle drive output voltage	Inductance connected to SpinMotA, B & C.	-0.5	VDD5 + 0.5	V
IPeakSpin	spindle drive output peak current	peak < 0.5 s		2.0	A
Vi	other pins	I < 1 mA	-0.5	VDD5 + 0.5	V
Ptot	total Power dissipation				W
Tstor	IC storage temperature
Tj(max)	junction temperature		-	+140

Description

The TDA5345HT is a combination of a voice coil motor and a spindle motor driver, designed for 5 V high performance portable small form factor hard disk drives. Communications with the micro-controller take place through a 16-bit 3-wire uni-directional serial port. Power dissipation is a major concern in portable drives, therefore each main function can be individually put in sleep mode whenTDA5345HT is not used, to save as much power as possible. The serial port and the power monitor are the only functions which remain always active.

The TDA5345HT integrates a spindle driver and the commutation logic that drives a three-phase brushless, sensorless DC motor in full wave mode. Commutations are generated from the internal back-EMF sensing circuitry from start-up to the running mode. An internal speed loop combining FLL and PLL technics makes sure that the spindle reaches the right speed, programmed through the serial port. The 6-bit DAC TDA5345HT is used to limit the Start-up current by limiting the voltage on the speed loop filter. To reduce acoustical noise and current noise on both power supply and ground, the fly-back pulse leading edge slew-rate is controlled. 4 different slope values are programmable.
To prevent internal parasitic effects, positive and negative fly-back pulses are clamped by the output power transistors themselves: lower NMOS transistors are turned ON to limit the negative fly-back pulses just below ground while upper PMOS limit the positive fly-backs just above the power supply. This active limitation of TDA5345HT is still active at power down during the VCM retract. In this way, an efficient back-EMF rectification is obtained (no diodes losses).

The VCM driver is a linear transconductance amplifier; TDA5345HT is a true AB class with a 8 mA quiescent current. It means that there is absolutely no crossover distortion. An external compensation network of TDA5345HT is used to set the loop bandwidth and ensure the loop stability. With common VCM characteristics, the bandwidth can go up to 40 kHz. To prevent internal parasitic effects, positive and negative fly-back pulses are clamped by the output power transistors themselves.

An on-chip 12-bit DAC TDA5345HT is used to generate the VCM amplifier input voltage. This a signed converter, with an output range of [1.25 V ; 1.75 V] when the low gain is selected and an output range of [0.5 V ; 2.5 V] when the high gain is selected. The all VCM transconductance works then around a 1.5 V reference (available on one pin). It is possible to add an external notch filter between the 12-bit DAC output and the VCM loop intput. An other 6-bit DAC TDA5345HT is used to cancel the Vcm loop offsets. An additional Vcm back-EMF amplifier is provided to monitor the actuator speed when ramp loading. A ramp unload circuitry is included as well. TDA5345HT can be activated through the serial bus (SoftRetract) or automatically initiated in case of temperature shut down or at power-down. The ramp unload sequence is made of 3 steps : brake, slow retract and then full power. The retract steps duration is set by means of internal programmable counters, clocked by the spindle back-EMF. In case of power down, this sequence is followed by a spindle brake. The three spindle lower power NMOS are switched fully ON together.

The linear 3.3 V DC-DC converter is designed to drive an external power NPN that will supply the 3.3 V chips. TDA5345HT can be enabled or disabled by hardware, using the external Reg3v3On pin.

The switched capacitor -3 V regulator is designed to supply a very clean negative voltage to the PreAmp IC in the drive. The shock sensor amplifier TDA5345HT is intended to be connected to an external 1 axis shock sensor. The window comparator threshold TDA5345HT is programmable through the serial bus.

An internal circuitry TDA5345HT provides either an analog or a digital information about the junction temperature. These two informations can be selected through the serial bus. When the analog output is selected, the voltage is proportional to the internal chip temperature. When the digital output is selected, TDA5345HT indicates that the temperature exceeds 145 °C. An internal thermal shut down mode is initiated when the temperature is higher than 160 °C: the 3 spindle outputs are disabled while the vcm is immediately retracted.

The power monitor circuitry monitors the 5V power supply. The Power On Reset PORN output is driven low when the 5 V supply is below 4.1 V. This threshold can be changed by an external resistor divider. Once the power supplies of TDA5345HT is above its threshold, the Power On Reset output goes high after a delay that is set by an external capacitor. A second output, called Power Fault (active HIGH), indicates that the 5 V power supply is below 4.2 V when high. There is no delay between the supply crossing the threshold and the PowerFault output change.