Overview
The L5991, produced by STMicroelectronics, is a primary controller IC designed for use in power supply applications, particularly in flyback topologies. It features a current-mode control PWM with a switching frequency that can be set up to 1 MHz. The device is known for its low start-up current of less than 120 µA and high-current output drive suitable for power MOSFETs up to 1 A. The L5991 also includes a standby function that optimizes power consumption under light load conditions, making it efficient for various power supply designs.
Key Specifications
| Parameter | Min. | Typ. | Max. | Unit |
|---|---|---|---|---|
| VCC Supply Voltage (ICC < 50mA) | - | - | Self-limit | V |
| IOUT Output Peak Pulse Current | - | - | 1.5 A | A |
| VREF Output Voltage | 4.925 | 5.0 | 5.075 | V |
| Line Regulation | 2.0 | - | 10 mV | mV |
| Load Regulation | 2.0 | - | 10 mV | mV |
| Temperature Stability | 0.4 | - | mV/°C | mV/°C |
| VCCON Startup Voltage | 14 | 15 | 16 | V |
| VCCOFF Minimum Operating Voltage | 9 | 10 | 11 | V |
| Iop Operating Current | 9 | 13 | - | mA |
| Iq Quiescent Current (After turn on) | 7.0 | 10 | - | mA |
| Switching Frequency | - | - | Up to 1 MHz | Hz |
Key Features
- Current-mode control PWM with switching frequency up to 1 MHz
- Low start-up current (< 120 µA)
- High-current output drive suitable for power MOSFETs (up to 1 A)
- Fully latched PWM logic with double pulse suppression
- Programmable duty cycle (100% and 50% maximum duty cycle limit)
- Standby function with programmable soft start
- Primary overcurrent fault detection with re-start delay
- PWM UVLO with hysteresis
- In/Out synchronization
- Latched disable
- Internal 100ns leading edge blanking of current sense
- Accurate voltage reference (5V ± 1.5%)
Applications
The L5991 is primarily used in power supply applications, especially in flyback topologies. It is suitable for a wide range of power supply designs, including:
- Switch-mode power supplies
- Flyback converters
- DC-DC converters
- Power adapters
- Industrial power supplies
Q & A
- What is the maximum switching frequency of the L5991?
The maximum switching frequency of the L5991 is up to 1 MHz.
- What is the start-up current of the L5991?
The start-up current of the L5991 is less than 120 µA.
- What is the output drive capability of the L5991?
The L5991 has a high-current output drive suitable for power MOSFETs up to 1 A.
- Does the L5991 have a standby function?
Yes, the L5991 includes a standby function that optimizes power consumption under light load conditions.
- What is the voltage reference output of the L5991?
The voltage reference output of the L5991 is 5V ± 1.5%.
- Can the duty cycle of the L5991 be programmed?
Yes, the duty cycle of the L5991 can be programmed to 100% and 50% maximum duty cycle limit.
- Does the L5991 have overcurrent protection?
Yes, the L5991 features primary overcurrent fault detection with re-start delay.
- How is the switching frequency set on the L5991?
The switching frequency can be set using resistors (RA and RB) and a capacitor (CT) connected to the oscillator pins.
- Is synchronization possible with the L5991?
Yes, the L5991 supports in/out synchronization.
- What is the purpose of the internal 100ns leading edge blanking on the L5991?
The internal 100ns leading edge blanking is used to mask the current sense signal during the leading edge of the PWM pulse.
