ST7MC1 datasheet(273/308 Pages) STMICROELECTRONICS

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ST7MC1/ST7MC2

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MOTOR CONTROL CHARACTERISTICS (Cont’d)

12.12.2 Input Stage (comparator + sampling)

Note:

1. The comparator accuracy is dependent of the environment. The offset value is given for a comparison done with all

digital I/Os stable. Negative injection current on the I/Os close to the inputs may reduce the accuracy. In particular care

must be taken to avoid switching on I/Os close to the inputs when the comparator is in use. This phenomenon is even

more critical when a big external serial resistor is added on the inputs.

2. This filter is implemented to wait for comparator stabilization and avoid any wrong information during start-up.

3. This delay represents the number of clock cycles needed to generate an event as soon as the comparator output

or MCO outputs change.

Example: In tachogenerator mode, this means that capture is performed on the 4th clock cycle after comparator commu-

tation., i.e. there is a variation of (1/fmtc) or (1 / fSCF) depending on the case.

Symbol

Parameter

Conditions

Min

Typ

Max

Unit

VIN

Comparator input volt-

age range

VSSA - 0.1

VDD + 0.1

Voffset

Comparator offset error

40 1)

Ioffset

Input offset current

µA

tpropag

Comparator propagation

delay

100

tstartup

Start-up filter duration2)

Time waited before sampling when com-

parator is turned ON, i.e. CKE=1 or

DAC=1 (with fPERIPH = 4MHz)

µs

tsampling Digital sampling delay

Time needed to generate a capture in

tachogenerator mode as soon as the MCI

input toggles

4 / fmtc

Time needed to capture MTIM in MZREG

(BEMF) when sampling during PWM sig-

nal OFF time as soon as MCO becomes

3 / fmtc (see Figure 150)

Time needed to set/reset the HST bit

when sampling during PWM signal OFF

time as soon as MCO becomes ON

(BEMF)

1 / fmtc (see Figure 150)

Time needed to generate Z event (MTIM

captured in MZREG) as soon as the com-

parator toggles (when sampling at fSCF)

1 / fSCF + 3 / fmtc (see Figure 151)

Time needed to generate D event (MTIM

captured in MDREG) as soon as the com-

parator toggles

1 / fSCF + 3 / fmtc (see Figure 151)

Time needed to set/reset the HST bit

when sampling during PWM signal ON

time after a delay (DS>0) as soon as

MCO becomes ON

Delay programmed in DS bits

(MCONF) +1 / fmtc

(see Figure 152)

Time needed to generate Z event (MTIM

in MZREG) when sampling during PWM

signal ON time after a delay (DS>0) as

soon as MCO becomes ON

Delay programmed in DS bits

(MCONF)

+ 3 / fmtc

(see Figure 152)

Time needed to generate Z event (MTIM

captured in MZREG) when sampling dur-

ing PWM signal ON time at fSCF after a

delay (DS>0)

Delay programmed in DS bits

(MCONF)

+ 1 / fSCF + 3 / fmtc

(see Figure 152)

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