ST7MC1 datasheet(277/308 Pages) STMICROELECTRONICS

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ST7MC1/ST7MC2

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MOTOR CONTROL CHARACTERISTICS (Cont’d)

12.12.3 Input Stage (Current Feedback Comparator + Sampling)

Notes:

1. The comparator accuracy depends on the environment. In particular, the following cases may reduce the accuracy of

the comparator and must be avoided:

– Negative injection current on the I/Os close to the comparator inputs

– Switching on I/Os close to the comparator inputs

– Negative injection current on not used comparator input (MCCFI0 or MCCFI1)

– Switching with a high dV/dt on not used comparator input (MCCFI0 or MCCFI1)

These phenomena are 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 ouput chang-

es.

Example: When CFF=0 (detection is based on a single detection), MCO outputs are turned OFF at the 4th clock cycle

after comparator commutation, i.e. there is a variation of (1/fmtc) or (4 / fPERIPH) depending on the case.

Symbol

Parameter

Conditions

Min

Typ

Max

Unit

VIN

Comparator input voltage range

VSSA - 0.1

VDD + 0.1

Voffset

Comparator offset error

40 1)

Ioffset

Input offset current

µA

tpropag

Comparator propagation

delay 1)

100

tstartup

Start-up filter duration 2)

Time waited before sampling

when comparator is turned

ON, i.e. CKE=1 or DAC=1

(with fPERIPH = 4MHz)

µs

tsampling Digital sampling delay

Time needed to turn OFF the

MCOs when comparator out-

put rises (CFF=0)

4 / f MTC (see Figure 155)

Time between a comparator

toggle (current loop event)

and bit CL becoming set

(CFF=0)

2 / f MTC (see Figure 155)

Time needed to turn OFF the

MCOs when comparator out-

put rises (CFF=x)

(1+x) * (4 / fPERIPH) + (3 / fmtc)

(see Figure 156)

Time between a comparator

toggle (current loop event)

and bit CL becoming set

(CFF=x)

(1+x) * (4 / fPERIPH) + (1 / fmtc)

(see Figure 156)

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