L9374TRLF datasheet(38/80 Pages) STMICROELECTRONICS

38 / 80 page

Circuit description

L9374LF

38/80

DocID025414 Rev 1

4.5.4

Current controller diagnostic performance

The maximum output value from the current controller is 1FF. This values is only reached if

the measured current does not reach the commanded current. If this maximum value

extends for more than tCNR (8ms typ, Table 18.) the Current Not Reachable flag (CNRx,

5.2.4) is set. The PWM controller contains the check for this condition (for details see

section 4.6.1: Current not reachable detection(Q3 and Q4 only):).

A set CNRx flag indicates that the load regulation is out of control and resets the ISAT value.

This forces the ALU to re-learn a new ISAT value returning the system to a stable dynamic

performance.

The ISAT register can be monitored by the master

C to determine if it is on the positive or

negative limit. This will indicate if the current controller is out of range and that the current

precision can not be assured.

4.6

PWM generator

The PWM Generator converts a Duty Cycle Set Point value into a PWM signal for each

Output Driver. The duty cycle setpoint can be derived from either a direct SPI command

(through the Set-Point Controller directly) or through the Current Controller.

The PWM-generator (Figure 23) provides a 4 kHz PWM duty cycle (f_Qx) depending on the

value of the 9 bit control variable. A 9-Bit ring counter counts with a frequency of fCLK

(2 MHz). The ring counter output is compared to the control variable. If the value of the

counter is lower than the control variable the output f_Qx is high turning on the output Qx. If

the value of the counter is equal or higher to the output f_Qx is low turning off the output Qx.

The counter can be reset by either a counter overflow at '1F4(Hex)' (→ 500(10)), or by a

SYNC_TRIG command. The control variable value is changed only when the counter

passes through zero.

Figure 23. PWM control block diagram

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