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Operational Description of HRPWM

Table 6. SFO Library Routines (continued)

Function Description

MEP steps per TBCLK = MEP_ScaleFactor[n] * (100/50) =66 * 2 = 132

(1)

Constraints when using this function:

SFO_MepDis(n) can be used with SYSCLKOUT from 50 MHz to maximum SYSCLK frequency. MEP

diagnostics logic uses SYSCLKOUT not TBCLK and hence SYSCLKOUT restriction is an important constraint.

SFO_MepDis(n) function does not require a starting Scale Factor value. Additionally, TBCLK must equal

SYSCLKOUT.

When to use

If one of the ePWM modules is not used in HRPWM mode, then it can be dedicated to run the SFO diagnostics

for the modules that are running HRPWM mode. Here the single MEP_ScaleFactor value obtained can be

applied to other ePWM modules. This assumes that all HRPWM module’s MEP steps are similar but may not be

identical.

The ePWM module that is not active in HRPWM mode is still fully operational in conventional PWM mode and

can be used to drive PWM pins. The SFO function only makes use of the MEP diagnostics logic.

The other ePWM modules operating in HRPWM mode incur only a 3-cycle minimum duty limitation.

SFO_MepEn(n) Scale Factor Optimizer with MEP Enabled

This routine runs slower as the calibration logic is used concurrently while HRPWM capabilities are being used

by the ePWM module.

If SYSCLKOUT = TBCLK = 100 MHz and assuming MEP steps size is 150 ps

Typical value at 100 MHz = 66 MEP steps per unit TBCLK (10 ns)

The function returns a value in the variable array:

MEP_ScaleFactor[n]

(2)

= Number of MEP steps/SYSCLKOUT

= Number of MEP steps/TBCLK

Constraints when using this function:

SFO_MepEn(n) function is restricted to be used with SYSCLKOUT of 60 MHz maximum SYSCLK frequency.

MEP diagnostics logic uses SYSCLKOUT not TBCLK and hence SYSCLKOUT restriction is an important

constraint. SFO_MepEn(n) function does require a starting Scale Factor value.MEP_ScaleFactor[0] needs to be

initialized to a typical MEP step size value. Additionally, TBCLK must equal SYSCLKOUT.

NOTE: SFO_MepEn(n) only supports the following HRPWM configuration:

• HRCNFG[HRLOAD] = 0 (load on CTR = ZERO)

• HRCNFG[EDGMODE] = 10 (falling edge MEP control)

SFO_MepEn(n)_V5B.lib includes an SFO_MepEn(n)_V5(n) function which

does not have this limitation.

When to use

If the application requires all ePWM modules to have HRPWM capability (i.e., MEP is operational), then the

SFO_MepEn(n) function can run for each of the active ePWM modules with HRPWM capability.

• In the above case, a 6-cycle MEP inactivity zone exists at the start of the PWM period. See Section 2.3.3

on duty cycle range limitation.

• It is also possible to run the SFO_MepEn(n) function for only one ePWM module and to use the SFO return

value for the other modules. In this case only one ePWM module incurs the 6-cycle limitation, and

remaining modules incur only a 3-cycle minimum duty limitation. See “Duty cycle limitation” section. This

assumes that all HRPWM module’s MEP steps are similar but may not be identical.

(2)

n is the ePWM module number on which the SFO function operates.

e.g., n = 1, 2, 3, or 4 for the F2808. Check your device data manual for device configurations.

Both routines can be run as background tasks in a slow loop requiring negligible CPU cycles. In most

applications only one of these routines will be needed. However, if the application has free HRPWM

resources then both the routines could be used. The repetition rate at which an SFO function needs to be

executed depends on the applications operating environment. As with all digital CMOS devices

temperature and supply voltage variations have an effect on MEP operation. However, in most

applications these parameters vary slowly and therefore it is often sufficient to execute the SFO function

once every 5 to 10 seconds or so. If more rapid variations are expected, then execution may have to be

performed more frequently to match the application. Note, there is no high limit restriction on the SFO

function repetition rate, hence it can execute as quickly as the background loop is capable.

SPRU924F– April 2005– Revised October 2011 High-Resolution Pulse Width Modulator (HRPWM)

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