Slide 1: Constant-On-Time (COT) Control for FPGA High-Current Power Supplies
Start Time: January 17, 2024 | 5:00 PM CET | 8:00 AM PST | 11:00 AM EST Constant-On-Time (COT) Control for FPGA High-Current Power Supplies Tomas Hudson, Monolithic Power Systems, Inc. January 17, 2024
Slide 2: Agenda
Agenda 1. Peak Current Mode Control Basics 2. Peak Current Mode Control Basics: Subharmonic Oscillation 3. Constant-On-Time (COT) Control 4. COT Advantages and Challenges 5. MPS’s Adaptive COT Control 6. MPS’s COT Power Modules for FPGA 7. Using Power Modules to Simplify Hardware Design
Slide 3: Peak Current Mode Control Basics
Peak Current Mode Control Basics L Fast Loop → Current V + HS Drive VIN CIN COUT Load VOUT Drivers COMP - CC3 Inductor Current PWM Comparator CC2 RFB1 RC1 - Inductor Current - R Drive Q + Clock COMP + S Comp VREF RFB2 CLOCK PWM Peak Current Linear Control t LATCH Mode PWM Circuit Slow Loop → Voltage
Slide 4: Peak Current Mode Control Is Not Sufficient for Certain Applications
Peak Current Mode Control Is Not Sufficient for Certain Applications For applications where fast transient responses are required, current mode control is not fast enough. • Goal: Faster transient response • Thought Process: Transient response can be improved by not waiting for the clock. • Solution
Slide 5: Constant-On-Time (COT) Control
Constant-On-Time (COT) Control For applications where fast transient responses are required, current mode control is not fast enough. • Goal: Faster transient response • Thought Process: Transient response can be improved by not waiting for the clock. • Solution: Use constant-on-time (COT) control t
Slide 6: Constant-On-Time (COT) Control
Constant-On-Time (COT) Control COT control does not use a clock: • When VOUT falls bellow the reference voltage (VREF), the high-side MOSFET turns on • The on time is constant and determined by the one-shot timer, while the off time is variable L + V HS VIN CIN COUT Load VOUT Drive Drivers - VOUT PW
Slide 7: Constant-On-Time (COT) Control
Constant-On- Time (COT) Control Advantages Disadvantages • Excellent load transient performance: • Must generate a slope on FB (e.g. using o About 4x faster compared to fixed- COUT_ESR) frequency current mode • The switching frequency (fSW) is not • Simple architecture does not require constant due
Slide 8: COT Advantages: Fast Transient Response
COT Advantages: Fast Transient Response Vin Ref Turn On FB Driver SW Turn Off Ton Peak Current Mode Control Constant-On-Time GND Gradually change ILOAD the duty cycle I_Load Instantly change the frequency FB FB FB PWM FB PWM CLK Ton Ton Ton Ton
Slide 9: COT Advantages: Fast Transient Response
COT Advantages: Fast Transient Response Peak Current Mode Constant-On-Time 523mV VPK-PK (±8%) 170mV VPK-PK (±2.5%) • 3x faster transient response compared to peak current mode with the same components and set-up: o 12V input, 3.3V output, 0A to 3.5A load step o 1µH LOUT, 2x22µF COUT
Slide 10: Example: Virtex-7
Example: Virtex-7 VCCINT Stability Requirement: 3% (30mV) MPM3695-25 • 3V to 16V VIN Range • Continuous Output Current (IOUT) Up to 20A • Supports PMBus/I2C for Monitoring and Control • COT Control for Fast Transients • 1% Reference Voltage (VREF) across a 0°C to 70°C Temperature Range • VOUT Remote
Slide 11: COT Advantages: Simple Architecture
COT Advantages: Simple Architecture Since COT control does not require a compensator, no time is spent tuning the compensator parameters. C2 C1 R2 C3 FB R1 COMP REF Delay Delay COMP PWM EA RS Power Stage VOUT Current CLK Mode No Delay High-Speed PWM COT Comparator Power Stage VOUT Control
Slide 12: COT Advantages: Transition from Light Loads to Heavy Loads
COT Advantages: Transition from Light Loads to Heavy Loads Due to variable frequency, COT control provides intrinsic pulse-skipping capabilities, enabling a linear transition between light-load operation and continuous conduction mode (CCM). COT Control CMC
Slide 13: Low-Voltage Series: MPM3804, MPM3814C, MPM3824C, MPM3834C
Low-Voltage Series: MPM3804, MPM3814C, MPM3824C, MPM3834C MPM3804 • 2.3V to 5.5V VIN Range • Adjustable Output from 0.6V • 100% Duty Cycle in Dropout • 2.4MHz Switching Frequency (fSW) • Low Profile: 0.9mm • QFN-10 (2mmx2mmx0.9mm) Package • Best-in-Class Efficiency Total Solution Size: 3.7mmx3.7mm 1
Slide 14: COT Challenges: Variable Frequency in Steady State
COT Challenges: Variable Frequency in Steady State L + HS ESR Since there is no clock, the COT VIN Load CIN Drivers COUT VOUT converter’s fSW heavily depends on VIN, VOUT, and ILOAD. - PWM Comparator RFB1 A stable fSW at steady state (stable ILOAD) - VFB may be difficult due to variations in VIN, S
Slide 15: MPS Solution: Adaptive COT Control
MPS Solution: Adaptive COT Control L + HS ESR Adaptive COT control uses the conversion VIN CIN Load Drivers COUT VOUT ratio (VOUT/VIN) to adjust the one-shot timer that sets the on time (tON). - PWM Comparator RFB1 This enables a steady fSW during steady - S VFB state, without affecting the converte
Slide 16: COT Challenge: Stability Is Dependent on ESR
COT Challenge: Stability Is Dependent on ESR COT control compares the feedback voltage to a set reference voltage. The feedback voltage ripple has two main components: 1. ESR ripple: Directly proportional to the inductor current (IL), with no delay/phase difference 2. VCAP ripple: Caused by charging
Slide 17: COT Challenge: Stability Is Dependent on ESR
COT Challenge: Stability Is Dependent on ESR If the ESR ripple dominates, the VOUT ripple is in If the VCAP ripple dominates, the VOUT ripple is phase with IL, and the circuit operates correctly. out of phase with IL, and the circuit can enter subharmonic oscillation. Duty Duty ESR ripple ESR ripple
Slide 18: MPS Solution: Current Ripple Injection
MPS Solution: Current Ripple Injection Option 1: Use COUT with sufficient ESR L + HS IC ESR VIN CIN + Load VOUT Duty Drivers COUT VC - - ESR ripple PWM Comparator tDELAY RFB1 Capacitor ripple - S Drive Q + R Reference Total ripple RFB2 PWM Latch VC One-Shot Timer VIN VOUT PWM Circuit
Slide 19: MPS Solution: Current Ripple Injection
MPS Solution: Current Ripple Injection Option 2: Add an external ramp L + HS IC ESR VFB’ PWM VIN CIN + Load VOUT VREF DriversConstant- COUT on Time VC one shot VREF - L - VOUT COMP RAMP FBCOMP EN VRAMP SET VFB VFB’ IL PWM Comparator RESR R1 RFB1 VRAMP - ∑ VFB PWM S C Drive + R2 Q R Reference IL RFB2
Slide 20: MPS Solution: Current Ripple Injection
MPS Solution: Current Ripple Injection Option 3: Use the RC circuit to generate a slope voltage and ensure that the FB ripple is in phase with IL L + HS IC ESR VIN CIN RSLOPE CSLOPE + Load VOUT Duty Drivers VC COUT - - VSLOPE VSLOPE PWM Comparator RFB1 ESR ripple - VFB S Capacitor ripple Drive Q + R
Slide 21: MPM3695-100: 100A Power Module
MPM3695-100: 100A Power Module Key Advantages: • 3V to 16V VIN Range • 0.5V to 3.3V VOUT Range • 100A of Continuous Current (60A for 3.3V VOUT) • Parallel Up to 800A Available in a BGA (15mmx30mmx5.18mm) Package Small Size and Easy to Use Fast Transients and Min COUT Diagnostics and Reliability ● Ve
Slide 22: Save Up to 50% on External Components
Save Up to 50% on External Components PLACEHOLDER
Slide 23: Auto-Interleaving COT
Auto-Interleaving COT • MPS scalable power modules allow for up to 8-phase operation • Active current balancing ensures equal current across all outputs • Automatic master/slave detection and phase counting via the TAKE pin
Slide 24: COT Challenge: DC Offset Error
COT Challenge: DC Offset Error ESR ripple Capacitor ripple Total ripple Total ripple VOUT VREF VOUT VCOMP Duty • Add an integrator to compensate the ½ (VOUT ripple) influence • The voltage loop is a slow-speed loop, which is used for DC regulation only • Does not impact transient speed
Slide 25: MPS's Adaptive COT Control
MPS’s Adaptive COT Control Advantages Disadvantages • Excellent load transient performance: • Must generate a slope on FB (e.g. using o About 4x faster compared to fixed- COUT_ESR) frequency current mode • fSW is not constant due to variations in the • Simple architecture does not require off time c
Slide 26: MPS's COT Power Modules for FPGA
MPS’s COT Power Modules for FPGA 10A 20A 30A 50A 100A+ MPM3695-10 MPM3690-20A/B MPM3690-30A/B MPM3690-50A/B MPM3698/99 3.3V to 16V, 10A, 4V to 16V, A: Dual 13A, 4V to 16V, A: Dual 18A, 4V to 16V, 25A, 4.5V to 16V/3V to 16V, Multiple 0.5V to 5V VOUT, B: Single 26A, 500kHz to B: Single 36A, 500kHz to
Slide 27: MPS Power Module: Key Advantages
MPS Power Module: Key Advantages Monolithic Power Stage Customized, Soft Improved EMI Performance Saturation Inductor Wide Temperature MeshConnectTM Range Passives Packaging Technology MPM38111 MP2152 x 2 Module Layout Optimized for EMI: • Small Solution Size • Smaller Switch Node • Simplified Board