Summary of Synchronous Step-Down Switching Regulator
The LT3690 is a high-efficiency, adjustable frequency monolithic buck switching regulator capable of handling input voltages from 3.9V to 36V with a maximum output current of 4A. It features an integrated 30mΩ synchronous switch, eliminating the need for an external catch diode, and utilizes current mode topology for stability. The device includes robust protection mechanisms like thermal shutdown and short-circuit sensing, along with low ripple Burst Mode operation for efficiency at light loads.
Parts used in the LT3690 Project:
- LT3690 Monolithic Buck Switching Regulator
- Resistor Divider for UVLO Pin Configuration
- 4mm × 6mm QFN Package with Exposed Pads
Description
The LT3690 is an adjustable frequency monolithic buck switching regulator that accepts input voltages up to 36V. A high efficiency 90mΩ switch is included on the device along with the boost diode and the necessary oscillator, control, and logic circuitry. The internal synchronous power switch of 30mΩ increases efficiency and eliminates the need for an external Schottky catch diode.
Current mode topology is used for fast transient response and good loop stability. Shutdown reduces input supply current to less than 1μA. The low ripple Burst Mode maintains high efficiency at low output currents while keeping output ripple below 15mV in typical applications.
The LT3690 features robust operation and is easily configurable. Using a resistor divider on the UVLO pin provides a programmable undervoltage lockout. A power good flag signals when VOUT reaches 90% of the programmed output voltage. Protection circuitry senses the current in the power switches to protect the LT3690 against short-circuit conditions. Frequency foldback and thermal shutdown provide additional protection. The LT3690 is available in a 4mm × 6mm QFN package with exposed pads for low thermal resistance.
Features
- Wide Input Range:
– Operation from 3.9V to 36V
– Overvoltage Lockout Protects Circuits Through 60V Transients - 4A Maximum Output Current
- Integrated 30mΩ N-Channel Synchronous Switch
- Low Ripple (<15mVP-P) Burst Mode® Operation:
IQ = 70μA at 12VIN to 3.3VOUT - Programmable Input Undervoltage Lockout
- 0.8V Feedback Reference Voltage
- Output Voltage: 0.8V to 20V
- Programmable and Synchronizable Oscillator
(170kHz to 1.5MHz) - Soft-Startup and Output Voltage Tracking
- Short-Circuit Robust
- Power Good Flag
- Small Thermally Enhanced 4mm × 6mm QFN Package
For more detail: Synchronous Step-Down Switching Regulator
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What is the maximum output current of the LT3690?
The device supports a maximum output current of 4A. -
Does the LT3690 require an external Schottky catch diode?
No, the internal synchronous power switch eliminates the need for an external Schottky catch diode. -
How does the LT3690 maintain efficiency at low output currents?
It uses low ripple Burst Mode operation which keeps output ripple below 15mV while maintaining high efficiency. -
Can the oscillator frequency be adjusted on the LT3690?
Yes, the oscillator is programmable and synchronizable within a range of 170kHz to 1.5MHz. -
What happens if the input voltage exceeds 60V transients?
An overvoltage lockout feature protects the circuits through transients up to 60V. -
How can you configure the undervoltage lockout on this device?
You can use a resistor divider on the UVLO pin to provide a programmable undervoltage lockout.
