BESCHREIBUNG

The LT8648S/LT8648SP synchronous step-down regulator features second generation Silent Switcher architecture designed to minimize EMI emissions while delivering high efficiency at high switching frequencies. This includes the integration of input and boost capacitors to optimize all the fast current loops inside and make it easy to achieve advertised EMI performance by reducing layout sensitivity. This performance makes the LT8648S/ LT8648SP ideal for noise sensitive applications and environments.

The fast, clean, low overshoot switching edges enable high efficiency operation even at high switching frequencies, leading to a small overall solution size. Peak current mode control with a 25ns minimum on-time allows high step down ratios even at high switching frequencies. External compensation via the VC pin allows for fast transient response at high switching frequencies. The VC pin also enables current sharing and a CLKOUT pin enables synchronizing other regulators to the LT8648S/ LT8648SP.

Burst Mode operation enables low standby current consumption, forced continuous mode can control frequency harmonics across the entire output load range, or spread spectrum operation can further reduce EMI emissions.

The LT8648SP package features an exposed back for heat sink attachment, which can be used to significantly improve thermal performance.

 

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

Hohe Effizienz bei hoher Frequenz

Up to 95.5% Efficiency at 1MHz, 12VIN to 5VOUT

Up to 93% Efficiency at 2MHz, 12VIN to 5VOUT

Wide Input Voltage Range: 3V to 42V

15A Output Current

Low Quiescent Current Burst Mode® Operation

100μA IQ Regulating 12VIN to 5VOUT

Ausgangswelligkeit < 10mVP-P

External Compensation: Fast Transient Response and Current Sharing

Fast Minimum Switch On-Time: 25ns

Low Dropout Under All Conditions: 35mV at 1A

Forced Continuous Mode

Einstellbar und synchronisierbar: 200kHz bis 2,2MHz

Output Soft-Start and Power Good

Safely Tolerates High Reverse Current

36-Lead 7mm × 4mm LQFN Package (LT8648S) and Exposed Back Package (LT8648SP)

AEC-Q100 qualifiziert für Automobilanwendungen

 

ANWENDUNGEN

Automobil- und Industriebedarf

Allzweck-Abwärtsregler

 

OPERATION

The LT8648S/LT8648SP 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 0.6V 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 (only in Burst Mode Operation). If overload conditions result in more than 21A flowing through the bottom switch, the next clock cycle will be delayed until switch current returns to a safe level.

The “S” in LT8648S/LT8648SP refers to the second generation silent switcher technology. This technology allows fast switching edges for high efficiency at high switching frequencies, while simultaneously achieving good EMI performance. This includes the integration of ceramic capacitors into the package for VIN and BST. These caps keep all the fast AC current loops small, which improves EMI performance.

The “P” in LT8648SP refers to the fact that the package features an exposed die for heat sink attach. This means heat sinks can be used to significantly improve thermal performance.

If the EN/UV pin is low, the LT8648S/LT8648SP is shut down and draws approximately 6μA from the input. When the EN/UV pin is above 0.98V, the switching regulator will become active.

To optimize efficiencyat light loads, the LT8648S/ LT8648SP operates in Burst Mode operation in light load situations. Between bursts, all circuitry associated with controlling the output switch is shut down, reducing the input supply current to 140μA (BIAS = 0). In a typical application, 100μA (VIN = 12V, BIAS = 5VOUT) will be consumed from the input supply when regulating with no load. The SYNC/MODE pin is tied low to use Burst Modeoperation and can be floated to use forced continuous mode (FCM). If a clock is applied to the SYNC/MODE pin, the part will synchronize to an external clock frequency and operate in FCM.

The LT8648S/LT8648SP can operate in forced continuous mode (FCM) for fast transient response and full frequency operation over a wide load range. When in FCM the oscillator operates continuously and positive SW transitions are aligned to the clock. Negative inductor current is allowed. The LT8648S/LT8648SP can sink current from the output and return this charge to the input in this mode, improving load step transient response.