Overview
The L5991A is a primary controller IC developed by STMicroelectronics, designed for implementing offline or DC-DC power supply applications. It is built using the BCD60II technology and features a current-mode control PWM with a switching frequency up to 1 MHz. The device is characterized by its low start-up current of less than 120 µA and high-current output drive suitable for power MOSFETs (up to 1 A). It includes a fully latched PWM logic with double pulse suppression and programmable duty cycle limits.
Key Specifications
| Parameter | Min. | Typ. | Max. | Unit |
|---|---|---|---|---|
| VCC Supply Voltage (ICC < 50mA) | - | - | Self-limit | V |
| Output Peak Pulse Current | - | - | 1.5 A | A |
| VREF Output Voltage (Tj = 25°C, IO = 1mA) | 4.925 | 5.0 | 5.075 | V |
| Line Regulation (VCC = 12 to 20V, Tj = 25°C) | 2.0 | - | 10 mV | mV |
| Load Regulation (IO = 1 to 10mA, Tj = 25°C) | 2.0 | - | 10 mV | mV |
| Temperature Stability | 0.4 mV/°C | - | - | mV/°C |
| Startup Voltage (L5991A) | 7.8 | - | 8.4 | V |
| Minimum Operating Voltage (L5991A) | 7.6 | - | 8.2 | V |
| UVLO Hysteresis (L5991A) | 0.5 | - | 0.8 | V |
| Start-Up Current Before Turn-on | 40 | 75 | 120 µA | µA |
| Operating Current (CT = 1nF, RT = 13.3kΩ, CO = 1nF) | 9 | 13 | - | mA |
| Quiescent Current (After turn-on, CT = 1nF, RT = 13.3kΩ, CO = 0nF) | 7.0 | 10 | - | mA |
Key Features
- Current-mode control PWM with switching frequency up to 1 MHz
- Low start-up current of less than 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 limits (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 and latched disable
- Internal 100ns leading edge blanking of current sense
- Accurate voltage reference (5V ± 1.5%) with external circuit capability
- Standby function optimized for flyback topology, reducing power losses under light load conditions
Applications
- Offline or DC-DC power supply applications
- Flyback converters
- Off-line autoranging battery chargers
- Constant power and constant current mode applications
- High-efficiency power supply systems requiring low start-up current and high-current output drive
Q & A
- What is the maximum switching frequency of the L5991A?
The maximum switching frequency of the L5991A is up to 1 MHz.
- What is the start-up current of the L5991A before turn-on?
The start-up current before turn-on is between 40 µA and 120 µA.
- What is the output voltage reference of the L5991A?
The output voltage reference (VREF) is 5V ± 1.5%.
- Does the L5991A have a standby function?
Yes, the L5991A has a standby function optimized for flyback topology, which reduces power losses under light load conditions.
- What is the maximum output peak pulse current of the L5991A?
The maximum output peak pulse current is 1.5 A.
- How is the switching frequency set in the L5991A?
The switching frequency can be set using resistors (RA and RB) and a capacitor (CT) connected to the oscillator pin (RCT).
- Does the L5991A support synchronization?
Yes, the L5991A supports in/out synchronization and can operate in master or slave mode.
- What is the purpose of the VREF pin in the L5991A?
The VREF pin provides an accurate voltage reference (5V ± 1.5%) that can deliver some mA to an external circuit.
- How does the L5991A handle overcurrent protection?
The L5991A features primary overcurrent fault detection with a re-start delay.
- What is the quiescent current of the L5991A after turn-on?
The quiescent current after turn-on is between 7.0 mA and 10 mA.
