HDP01-0512N Datasheet, PDF (5/6 Pages) STMicroelectronics – HARD DISK DRIVE POWER SUPPLY PROTECTION

HDP01-0512N
The ITSM value as a function of the pulse duration tp for the HDP01 device is given on the figure 1 of this
datasheet.
In the case the supply cables of the +12V and +5V are reversed, the +5V (PL5) internal protection of the
HDP01-512N immediately shorts circuits +5V rail and ensures on efficient protection of the electronic mod-
ule.
ABOUT THE +12V PROTECTION
The +12V internal protection (PL12 termination) eliminates all transients appearing on the +12V supply rail.
In normal conditions (region 4 of figure A.3) its leakage current is 1µA maximum at 12V @ 25°C. When a
surge occurs on the +12V rail, the overvoltage is clamped (region 5) and the electronic module connected
to this rail is protected.
Fig. A.3: Current and voltage characteristic of the
+12V protection.
I
The clamping voltage (Vcl) is depending on several
5
parameters which are :
- current induced by the transient (Ipp)
- ambient temperature effect (αT)
- breakdown voltage of the protection (VBR)
4
- dynamic resistance of the protection (Rd)
V
V_CL
To evaluate the clamping voltage appearing on the +12V rail when a transient occurs, the next formula is
needed :
Vcl = VBRmax + Rd*IPP
with a typical Rd equals to 2.5Ω
IPP is the peak current given by the transient which is :
IPP = (Vtransient - Vcl)/Rs
⇒ Vtransient = peak voltage of the transient
⇒ Rs is the series resistance of the surge generator.
If, for example, we consider a 50V combined surge 1.2/50µs - 8/20µs, as defined by the standard
IEC1000-4-5, the Vcl is calculated as:
Vcl = 16 + 2.5*IPP and IPP = (50 - Vcl) / 42 RS = 42 Ω (generator impedance)
then it comes up with Vcl = 17.9V and IPP = 0.7A
The impact of the temperature on the clamping voltage can be considered as to be :
Vcl(T°C) = Vcl(25°C) * (1 + αT(T°C-25°C)) where T°C is the ambient temperature for which the module shall
run.
The HDP01-0512N +12V protection has a power dissipation capability that is given in the figure 2 of this
datasheet named "Peak pulse power versus exponential pulse duration". This figure is necessary to deter-
mine if the power involved in the +12V protection does not exceed the maximum power the HDP01 +12V
protection can support. For example, considering the last calculation where Vcl=17.9 and IPP=0.7A, the
peak power is in that case 12.5W (Vcl*IPP) for a 20µs exponential surge duration. If we compare this value
to the curve of figure 2, then we see the dissipated power is much lower than the +12V protection limit
(200W @ 20µs) this tells us the +12V protection of the HDP01-0512N can easily withstand such a 12.5W
surge.
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