PXD20RM Datasheet, PDF (1436/1628 Pages) Freescale Semiconductor, Inc – PXD20 Microcontroller

The maximum time span which the timer can cover depends on the clock frequency F of the main clock.
The maximum delay D covered by the counter is D = MCSDTO[TOUT]* F. Due to sampling and syn-
chronization of the feedback signal, the value of MCSDTO[TOUT] must always be larger than 2.
The two synchronizer stages imply also, that a a short-circuit with a duration of less than or equal to 2 clock
cycles cannot be detected.
Two special cases shall be highlighted:
• Static short-circuit to ground and PWM signal = 1 see Figure 41-35: In this case, the enable of the
short-circuit detector starts the sampling process and the interrupt bit is set MCSDTO[TOUT]+1
cycles after enabling the short-circuit detector
• Static short-circuit to VDD and PWM signal = 0 see Figure 41-36: In this case. the enable of the
short-circuit detector starts the sampling process and the interrupt bit is set MCSDTO[TOUT]+3
cycles after enabling the short-circuit detector due to the synchronizer which has been cleared
during disable of the short-circuit detector
CLK
EN
PWM=1
FB_sample =0
FB at pin=0
Counter
3
3
3
2
1
0
0
MCSDIn[SDIF[sd ]] interrupt flag
T_sample
T_diff
PWM
FB at pin
FB_Sample
:Sample and synchronization delay
:Delay between FB at pin and the internal PWM signal
:Signal from motor controller
:This is the signal directly after the input driver of the pad s ignal
:Pad signal after sampling and synchronization
Figure 41-35. Static Short-circuit, PWM signal always at 1 and FB always at 0, MCSDTO[TOUT]=3
41-36
PXD20 Microcontroller Reference Manual, Rev. 1
Preliminary—Subject to Change Without Notice
Freescale Semiconductor