PWM HighSpeed

dsPIC33C CH/CK/CDV dsPIC33E GS dsPIC33F selected

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This block is designed for demanding motor control and power conversion applications requiring precise timing, independent channel control, and high switching frequencies.

When to use:

• High-speed motor control on dsPIC33C/CH/CK or dsPIC33E (GS) devices
• Applications requiring independent time bases per PWM channel
• Multiple ADC trigger outputs per PWM cycle (advanced control)
• Double update mode for asymmetric center-aligned PWM

When NOT to use:

• dsPIC33A devices → use PWM HS FEP for fine edge placement (16× resolution)
• dsPIC30F or standard dsPIC33F/33E → use PWM for standard PWM peripheral
• SAM devices → use TCC PWM or PWM SAM7x

Block Dialog

Block Input and Initialisation Tab

Ports

Block Inputs

Block Outputs

Parameters

This block uses a custom 5-tab GUI dialog. All parameters shown below are visible to users.

Scaling

This block uses uint16 raw values for all inputs (period, duty cycle, phase, trigger). User scaling is required.

⚠️ Important: The block performs no range checking on inputs. Users must clamp values before the block input (e.g., using a Saturation block) to prevent overflow.

Uint Raw Input

• Uint raw: Integer values transfer directly to peripheral registers with no runtime computation—maximum efficiency.

The block creates workspace variables for user scaling:

Fixed Period (period input disabled):

$$\text{DutyCycle}_\text{raw} = \text{DutyCycle}_\text{normalized} \times \text{PWMxmax}$$

DutyCycle_raw = DutyCycle_normalized × PWMxmax

Where DutyCycle_normalized is in the range [0, 1] relative to the fixed Max Period.

Variable Period (period input enabled):

When the period is dynamically controlled via block input, both period and duty cycle use the same scaling:

$$\text{Period}_\text{raw} = \text{Period}_\text{normalized} \times \text{PWMxmax}$$

Period_raw = Period_normalized × PWMxmax

$$\text{DutyCycle}_\text{raw} = \text{DutyCycle}_\text{normalized} \times \text{Period}_\text{raw}$$

DutyCycle_raw = DutyCycle_normalized × Period_raw

⚠️ Constraints:

• Period input must always be < PWMxmax (Max Period in GUI)
• Duty cycle normalizes to the actual period input, not @@PROT_19@@
• If ADC triggers from PWM events and drives the scheduler, changing period alters the control loop sample time

Center-Aligned vs Edge-Aligned

Center-Aligned Mode: The @@PROT_20@@ workspace variable is halved at configuration time because the timer counts both up and down. This applies to all input types (Uint raw, Float).

No runtime division: Since @@PROT_21@@ is already halved, the block passes integer inputs directly to registers without any runtime shift operation. Users simply scale their values to the halved @@PROT_22@@.

Edge-Aligned Mode: The timer counts up only. @@PROT_23@@ represents the full period count. Duty cycle updates take effect at the next period boundary (unless Immediate Update is enabled).

Double Update Mode

When Double Update is enabled (requires Center-Aligned Mode + Independent Period):

• Duty cycle input becomes a 2-element vector: @@PROT_24@@
• First value applied during up-count, second during down-count
• Enables asymmetric PWM waveforms for harmonic reduction

Workspace variables for double update:

• @@PROT_25@@ — Maximum value for high-side (up-count)
• @@PROT_26@@ — Maximum value for low-side (down-count)

Dead Time

• GUI configuration: Specify in seconds (e.g., @@PROT_27@@ for 1 µs)

• Integer block input: Dead time uses a different scaling base (full period, not halved).

  ⚠️ In center-aligned mode, multiply @@PROT_28@@ by 2 for dead time scaling:

$$\text{DeadTime}_\text{raw} = \frac{\text{DeadTime}_s \times 2 \times \text{PWMxmax}}{\text{MaxPeriod}_s}$$

DeadTime_raw = (DeadTime_s × 2 × PWMxmax) / MaxPeriod_s

• Note: Dead time scaling is identical in center-aligned and edge-aligned modes—the factor of 2 compensates for the halved PWMxmax

Output Modes

Device Support

Features

PWM-ADC Synchronization

Synchronizing ADC sampling with PWM switching is essential for accurate current measurement in motor control and power conversion.

Option 3: PWM → ADC → Task (Motor Control Standard)

Configuration using Initial ADC Trigger:

% In PWM HighSpeed GUI, Block Input and Initialisation tab:
Initial_ADC_Trigger = 0;  % Trigger at valley (center-aligned)
% Or for edge-aligned:
Initial_ADC_Trigger = Max_Period / 2;  % Trigger at mid-period

% In ADC block:
Trigger_Source = 'PWM Trigger 1';
Sample_Time = 'Inherited';

Benefits:

• Synchronized current sensing with PWM switching
• Sample when low-side FET is ON (minimal switching noise)
• Control loop rate automatically matches PWM frequency

Best Practices

Usage Examples

Example 1: 3-Phase Motor Control (Complementary Mode)

% Main tab:
PWM_HL_mode = 'Complementary';
Independent_Period = false;      % Master time base
Independent_Duty_Cycle = true;   % Per-channel control
Center_Aligned_Mode = true;
Immediate_Update = false;        % Synchronized updates
Double_Update = false;

% Max Period for 20 kHz PWM:
Max_Period = 1/20000;  % 50 µs

% Dead Time tab:
Dead_Time = 1e-6;      % 1 µs
Alt_Dead_Time = 1e-6;  % 1 µs

Example 2: Asymmetric Center-Aligned (Double Update)

% Main tab:
Independent_Period = true;       % Required for Double Update
Center_Aligned_Mode = true;      % Required for Double Update
Double_Update = true;            % Enable asymmetric PWM

% Duty cycle input becomes [val1 val2] for up/down count
% Use case: Harmonic reduction, EMI optimization

Examples

Programmatic Setup

% Add block to model
add_block('MCHP_Blockset/PWM IO/PWM High Speed', [mdl '/PWM_HS']);

% Configure key parameters
set_param([mdl '/PWM_HS'], 'MaxPeriod_s', '50e-6');
set_param([mdl '/PWM_HS'], 'InitPeriode_s', '50e-6');
set_param([mdl '/PWM_HS'], 'InitDutyCycleP_s', '20e-6');
set_param([mdl '/PWM_HS'], 'PWM1_HL', 'PWMxH & PWMxL output enabled');

Troubleshooting

Double Update Mode Requirements

Double Update requires:

• Independent Period = enabled
• Center Aligned Mode = enabled

If conditions not met, double update is automatically disabled.

Immediate vs. Synchronized Update

• Immediate Update = off (default): Updates at period boundary. Eliminates pulse width glitches. Recommended for motor control.
• Immediate Update = on: Updates immediately. Use for fast transient response but may cause glitches.

References

• dsPIC33F Family Reference Manual
• dsPIC33E/EP Family Reference Manual
• dsPIC33C Family Reference Manual

Related Blocks

• MCHP_PWM - Standard PWM for dsPIC30F/33F/33E
• MCHP_PWM_HighSpeed_Override - Override control for this block
• MCHP_PWM_HS_FEP - PWM with Fine Edge Positioning (dsPIC33A)
• MCHP_MCPWM - Motor Control PWM (advanced fault handling)
• MCHP_ADC - ADC with PWM trigger synchronization