DESCRIPCIÓN

The LT8640S/LT8643S/LT8640SA/LT8643SA 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 bypass 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 LT8640S/LT8643S/LT8640SA/LT8643SA ideal for noisesensitive applications and environments. Peak current mode control with a 30ns minimum on-time allows high step-down ratios even at high switching frequencies. The LT8643S/LT8643SA has external compensation to enable current sharing and fast transient response at high switching frequencies. Burst Mode operation enables ultralow 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.

 

CARACTERÍSTICAS

Silent Switcher 2 Architecture

Emisiones EMI ultrabajas en cualquier placa de circuito impreso

Elimina la sensibilidad del diseño de la placa de circuito impreso

Los condensadores de bypass internos reducen la radiación EMI

Modulación de espectro ensanchado opcional

Alta eficiencia a alta frecuencia

Hasta 96% Eficiencia a 1MHz, 12VIN a 5VOUT

Hasta 95% Eficiencia a 2MHz, 12VIN a 5VOUT

Amplio rango de tensión de entrada: 3,4 V a 42 V

Output Voltage Range: 0.97V to 10V(LT8640S/LT8643S); 0.97V to (VIN – 0.5V) (LT8640SA/LT8643SA)

Salida continua máxima de 6 A, pico de 7 A

Funcionamiento en modo ráfaga® con corriente de reposo ultrabaja

2.5μA IQ Regulating 12VIN to 3.3VOUT (LT8640S/LT8640SA)

Ondulación de salida < 10mVP-P

External Compensation: Fast Transient Response and Current Sharing (LT8643S/LT8643SA)

Robust High VOUT Operation (LT8640SA/LT8643SA)

Safely Tolerates High Reverse Current

Tiempo mínimo de conexión rápida: 30 ns

Baja caída en todas las condiciones: 100mV a 1A

Modo continuo forzado

Ajustable y sincronizable: de 200 kHz a 3 MHz

Arranque progresivo y seguimiento de la salida

Encapsulado LQFN pequeño de 24 conductores de 4 mm × 4 mm

Cualificación AEC-Q100 para automoción

 

Aplicaciones

Suministros industriales y de automoción

 

OPERACIÓN

The LT8640S/LT8643S/LT8640SA/LT8643SA 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 0.97V 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 more than 10A flowing through the bottom switch, the next clock cycle will be delayed until switch current returns to a safe level.

The “S” in LT8640S/LT8643S/LT8640SA/LT8643SA 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, BST, and INTVCC (see Block Diagram). These caps keep all the fast AC current loops small, which improves EMI performance.

If the EN/UV pin is low, the LT8640S/LT8643S/LT8640SA/ LT8643SA is shut down and draws 1μA from the input. When the EN/UV pin is above 1V, the switching regulator will become active.

To optimize efficiency at light loads, the LT8640S/LT8643S/ LT8640SA/LT8643SA 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 1.7μA (LT8640S/ LT8640SA) or 230μA (LT8643S/LT8643SA with BIAS = 0). In a typical application, 2.5μA (LT8640S/LT8640SA) or 120μA (LT8643S/LT8643SA with BIAS = 5VOUT) will be consumed from the input supply when regulating with no load. The SYNC/MODE pin is tied low to use Burst Mode operation 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.