説明

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.

 

特徴

サイレント・スイッチャー2のアーキテクチャ

あらゆるPCBで超低EMIエミッションを実現

PCBレイアウトの感度を排除

内部バイパス・コンデンサが放射EMIを低減

オプションのスペクトラム拡散変調

高周波での高効率

1MHzで最大96%効率、12VIN～5VOUT

2MHzで最大95%効率、12VIN～5VOUT

広い入力電圧範囲：3.4V〜42V

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

最大連続6A、ピーク出力7A

超低静止電流バーストモード®動作

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

出力リップル < 10mVP-P

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

Robust High VOUT Operation (LT8640SA/LT8643SA)

Safely Tolerates High Reverse Current

高速最小スイッチ・オン時間：30ns

あらゆる条件下で低ドロップアウト：1Aで100mV

強制連続モード

調整および同期可能：200kHz～3MHz

出力ソフトスタートとトラッキング

4mm×4mm小型24ピンLQFNパッケージ

自動車用AEC-Q100認定

 

アプリケーション

自動車・産業用品

 

オペレーション

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.

FBピンの電圧を監視しているコンパレータは、出力電圧がセットポイントから±8%（代表値）以上変動した場合、またはフォルト状態が存在する場合、PGピンをローレベルにプルします。

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.