SLUSEY7B December   2022  – December 2024 TPSM82816

PRODMIX  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Device Comparison Table
  6. 5 Pin Configuration and Functions
  7. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Typical Characteristics
  8. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Precise Enable (EN)
      2. 7.3.2 Output Discharge
      3. 7.3.3 COMP/FSET
      4. 7.3.4 MODE/SYNC
      5. 7.3.5 Spread Spectrum Clocking (SSC)
      6. 7.3.6 Undervoltage Lockout (UVLO)
      7. 7.3.7 Power-Good Output (PG)
      8. 7.3.8 Thermal Shutdown
    4. 7.4 Device Functional Modes
      1. 7.4.1 Pulse Width Modulation (PWM) Operation
      2. 7.4.2 Power Save Mode Operation (PSM)
      3. 7.4.3 100% Duty-Cycle Operation
      4. 7.4.4 Current Limit and Short-Circuit Protection
      5. 7.4.5 Soft Start / Tracking (SS/TR)
  9. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Setting the Output Voltage
        2. 8.2.2.2 Feedforward Capacitor
        3. 8.2.2.3 Input Capacitor
        4. 8.2.2.4 Output Capacitor
      3. 8.2.3 Application Curves
    3. 8.3 System Examples
      1. 8.3.1 Voltage Tracking
      2. 8.3.2 Synchronizing to an External Clock
    4. 8.4 Power Supply Recommendations
    5. 8.5 Layout
      1. 8.5.1 Layout Guidelines
      2. 8.5.2 Layout Example
        1. 8.5.2.1 Thermal Consideration
  10. 9 Device and Documentation Support
    1. 9.1 Device Support
      1. 9.1.1 Third-Party Products Disclaimer
    2. 9.2 Documentation Support
      1. 9.2.1 Related Documentation
    3. 9.3 Receiving Notification of Documentation Updates
    4. 9.4 Support Resources
    5. 9.5 Trademarks
    6. 9.6 Electrostatic Discharge Caution
    7. 9.7 Glossary
  11. 10Revision History
  12. 11Mechanical, Packaging, and Orderable Information

7.3.3 COMP/FSET

This pin allows the user to set three different parameters independently:

  • Internal compensation settings for the control loop (two settings available)
  • The switching frequency in PWM mode from 1.8 MHz to 4 MHz
  • Enable / disable spread spectrum clocking (SSC)

A resistor from COMP/FSET to GND changes the compensation as well as the switching frequency. The change in compensation allows the user to adopt the device to different values of output capacitance. The resistor must be placed close to the pin to keep the parasitic capacitance on the pin to a minimum. The compensation setting is sampled at the start-up of the converter, so a change in the resistor during operation only has an effect on the switching frequency, but not on the compensation.

To save external components, the pin can also be directly tied to VIN or GND to set a pre-defined switching frequency or compensation. Do not leave the pin floating.

The switching frequency has to be selected based on the maximum input voltage in the application and the output voltage to meet the specifications for the minimum on time.

Example: VIN = 5.5 V, VOUT = 1 V

Equation 1. f S w , m a x = V O U T V I N   ×   t O N , m i n =   1   V 5.5   V   ×   67   n s   = 2.71   M H z

The compensation range has to be chosen based on the effective minimum capacitance used. The capacitance can be increased from the minimum value as given in Table 7-1, up to the maximum of 470 µF in both compensation ranges. If the capacitance of an output changes during operation, for example when load switches are used to connect or disconnect parts of the circuitry, the compensation has to be chosen for the minimum capacitance on the output. If the output capacitance exceeds 72 µF × V / VOUT[V], use the second compensation setting to get the best load transient response. If the output capacitance only exceeds 32 µF × V / VOUT[V], use the first compensation setting. Compensating for large output capacitance but having too little effective capacitance on the output can lead to instability.

The switching frequency for the different compensation setting is determined by the following equations.

For compensation (comp) setting 1 with spread spectrum clocking (SSC) disabled:

Equation 2. RCF[kΩ] = 18  MHz × kΩ fS [MHz]

For compensation (comp) setting 1 with spread spectrum clocking (SSC) enabled:

Equation 3. R C F [ k Ω ] = 60   M H z × k Ω f S [ M H z ]

For compensation (comp) setting 2 with spread spectrum clocking (SSC) disabled:

Equation 4. R C F [ k Ω ] = 180   M H z × k Ω f S [ M H z ]
Table 7-1 Switching Frequency and Compensation
COMPENSATIONRCFSWITCHING FREQUENCYMINIMUM OUTPUT
CAPACITANCE
For smallest output capacitance
(comp setting 1)
SSC disabled		10 kΩ ... 4.5 kΩ1.8 MHz (10 kΩ) ... 4 MHz (4.5 kΩ)
according to Equation 2

32 µF × V / VOUT[V]

For smallest output capacitance
(comp setting 1)
SSC enabled		33 kΩ ... 15 kΩ1.8 MHz (33 kΩ) ... 4 MHz (15 kΩ)
according to Equation 3		32 µF × V / VOUT[V]
For best transient response
(larger output capacitance)
(comp setting 2)
SSC disabled		100 kΩ ... 45 kΩ1.8 MHz (100 kΩ) ... 4 MHz (45 kΩ)
according to Equation 4		72 µF × V / VOUT[V]
For smallest output capacitance
(comp setting 1)
SSC disabled		Tied to GNDInternally fixed 2.25 MHz32 µF × V / VOUT[V]
For best transient response
(larger output capacitance)
(comp setting 2)
SSC enabled		Tied to VINInternally fixed 2.25 MHz72 µF × V / VOUT[V]

The minimum output capacitance required for stability depends on the output voltage as stated in Table 7-1. Refer to Output Capacitor for further details on the output capacitance required depending on the output voltage.

A too-high resistor value for RCF is decoded as "tied to VIN" and a value below the lowest range is decoded as "tied to GND". The minimum output capacitance in Table 7-1 is for capacitors close to the output of the device. If the capacitance is distributed, a lower compensation setting can be required.