BESCHREIBUNG

The LT8609S is a compact, high efficiency, high speed synchronous monolithic step-down switching regulator that consumes only 1.7µA of non-switching quiescent current. The LT8609S can deliver 2A of continuous current with peak loads of 3A (<1sec) to support applications such as GSM transceivers which require high transient loads. Top and bottom power switches are included with all necessary circuitry to minimize the need for external components. Low ripple Burst Mode operation enables high efficiency down to very low output currents while keeping the output ripple below 10mVP-P. A SYNC pin allows synchronization to an external clock, or spread spectrum modulation of switching frequencies for low EMI operation. Internal compensation with peak current mode topology allows the use of small inductors and results in fast transient response and good loop stability. The EN/UV pin has an accurate 1V threshold and can be used to program VIN undervoltage lockout or to shut down the LT8609S reducing the input supply current to 1µA. A capacitor on the TR/SS pin programs the output voltage ramp rate during start-up while the PG flag signals when VOUT is within ±8.5% of the programmed output voltage as well as fault conditions. The LT8609S is available in a small 16-lead 3mm × 3mm LQFN package.

 

FEATURES

Silent Switcher 2 Architecture

Ultra-niedrige EMI-Emissionen auf jeder Leiterplatte

Eliminiert die Empfindlichkeit des PCB-Layouts

Interne Bypass-Kondensatoren reduzieren die abgestrahlte EMI

Optionale Spread Spectrum Modulation

Wide Input Voltage Range: 3.0V to 42V

Ultralow Quiescent Current Burst Mode® Operation:

<2.5µA IQ Regulating 12VIN to 3.3VOUT

Output Ripple <10mVP-P

High Efficiency 2MHz Synchronous Operation:

>93% Efficiency at 1A, 12VIN to 5VOUT

2A Maximum Continuous Output, 3A Peak Transient Output

Fast Minimum Switch-On Time: 45ns

Einstellbar und synchronisierbar: 200kHz bis 2,2MHz

Allows Use of Small Inductors

Low Dropout

Betrieb im Spitzenstrommodus

Internal Compensation

Ausgang Soft-Start und Tracking

Small 16-Lead 3mm × 3mm LQFN Package

AEC-Q100 qualifiziert für Automobilanwendungen

 

ANWENDUNGEN

General Purpose Step Down

Low EMI Step Down

 

OPERATION

The LT8609S is a monolithic constant frequency current mode step-down DC/DC converter. An oscillator with frequency set using a resistor on the RT pin turns on the internal top power switch at the beginning of each clock cycle. Current in the inductor then increases until the top switch current comparator trips and turns off the top power switch. The peak inductor current at which the top switch turns off is controlled by the voltage on the internal VC node. The error amplifier servos the VC node by comparing the voltage on the VFB pin with an internal 0.774V reference. When the load current increases it causes a reduction in the feedback voltage relative to the reference leading the error amplifier to raise the VC voltage until the average inductor current matches the new load current.  When the top power switch turns off the synchronous power switch turns on until the next clock cycle begins or inductor current falls to zero. If overload conditions result in excess current flowing through the bottom switch, the next clock cycle will be delayed until switch current returns to a safe level.

The oscillator reduces the LT8609S’s operating frequency when the voltage at the FB pin is low. This frequency foldback helps to control the inductor current when the output voltage is lower than the programmed value which occurs during start-up. When a clock is applied to the SYNC pin the frequency foldback is disabled. Frequency foldback is only enabled when the SYNC pin is tied to ground.

 

ANWENDUNGSINFORMATIONEN

Achieving Ultralow Quiescent Current

To enhance efficiency at light loads, the LT8609S enters into low ripple Burst Mode operation, which keeps the output capacitor charged to the desired output voltage while minimizing the input quiescent current and minimizing output voltage ripple. In Burst Mode operation the LT8609S delivers single small pulses of current to the output capacitor followed by sleep periods where the output power is supplied by the output capacitor. While in sleep mode the LT8609S consumes 1.7μA.