DESCRIPTION

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.

 

CARACTÉRISTIQUES

Architecture de Silent Switcher 2

Émissions EMI extrêmement faibles sur n'importe quel circuit imprimé

Élimine la sensibilité de l'agencement des circuits imprimés

Les condensateurs de dérivation internes réduisent les interférences électromagnétiques rayonnées

Modulation à spectre étalé en option

Rendement élevé à haute fréquence

Up to 96% Efficiency at 1MHz, 12VIN to 5VOUT

Up to 95% Efficiency at 2MHz, 12VIN to 5VOUT

Wide Input Voltage Range: 3.4V to 42V

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

6A Maximum Continuous, 7A Peak Output

Ultralow Quiescent Current Burst Mode® Operation

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

Ondulation de sortie < 10mVP-P

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

Robust High VOUT Operation (LT8640SA/LT8643SA)

Safely Tolerates High Reverse Current

Fast Minimum Switch On-Time: 30ns

Low Dropout Under All Conditions: 100mV at 1A

Mode continu forcé

Adjustable and Synchronizable: 200kHz to 3MHz

Démarrage progressif et suivi de la sortie

Small 24-Lead 4mm × 4mm LQFN Package

Qualification AEC-Q100 pour l'automobile

 

Applications

Fournitures automobiles et industrielles

 

FONCTIONNEMENT

The LT8640S/LT8643S/LT8640SA/LT8643SA 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 LT8640S/ LT8643S/LT8640SA/LT8643SA can sink current from the output and return this charge to the input in this mode, improving load step transient response.

To improve EMI, the LT8640S/LT8643S/LT8640SA/ LT8643SA can operate in spread spectrum mode. This feature varies the clock with a triangular frequency modulation of +20%. For example, if the LT8640S/LT8643S/ LT8640SA/LT8643SA’s frequency is programmed to switch at 2MHz, spread spectrum mode will modulate the oscillator between 2MHz and 2.4MHz. The SYNC/MODE pin should be tied high to INTVCC (~3.4V) or an external supply of 3V to 4V to enable spread spectrum modulation with forced continuous mode.

To improve efficiency across all loads, supply current to internal circuitry can be sourced from the BIAS pin when biased at 3.3V or above. Else, the internal circuitry will draw current from VIN. The BIAS pin should be connected to VOUT if the LT8640S/LT8643S/LT8640SA/LT8643SA output is programmed at 3.3V to 25V.

The VC pin optimizes the loop compensation of the switching regulator based on the programmed switching frequency, allowing for a fast transient response. The VC pin also enables current sharing and a CLKOUT pin enables synchronizing other regulators to the LT8643S/LT8643SA.

Les comparateurs qui surveillent la tension de la broche FB mettent la broche PG à l'état bas si la tension de sortie varie de plus de ±8% (typique) par rapport au point de consigne, ou si une condition de défaut est présente.

The oscillator reduces the LT8640S/LT8643S/LT8640SA/ LT8643SA’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 or overcurrent conditions. When a clock is applied to the SYNC/ MODE pin, the SYNC/MODE pin is floated, or held DC high, the frequency foldback is disabled and the switching frequency will slow down only during overcurrent conditions.