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SI91843DT-25-T1 Fiches technique(PDF) 9 Page - Vishay Siliconix |
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SI91843DT-25-T1 Fiches technique(HTML) 9 Page - Vishay Siliconix |
9 / 9 page Si91841/3 Vishay Siliconix Document Number: 71447 S-40592—Rev. C, 29-Mar-04 www.vishay.com 9 BLOCK DIAGRAM Si91841/3 VIN Reference − + Thermal Sensor Shutdown Control GND VOUT Reverse Polarity Protection Current Limit SD BP Si91841 Only DETAILED DESCRIPTION The Si91841/3 is a low-noise, low drop-out and low quiescent current linear voltage regulator, packaged in a small footprint Thin SOT23-5 package. The Si91841/3 can supply loads up to 300 mA. As shown in the block diagram, the circuit consists of a bandgap reference error, amplifier, p-channel pass transistor and feedback resistor string. An external bypass capacitor connected to the BP pin reduces noise at the output. Additional blocks, not shown in the block diagram, include a precise current limiter, reverse battery and current protection and thermal sensor. Thermal Overload Protection The thermal overload protection limits the total power dissipation and protects the device from being damaged. When the junction temperature exceeds 150_, the device turns the p-channel pass transistor off. Reverse Battery Protection The Si91841/3 has a battery reverse protection circuitry that disconnects the internal circuitry when VIN drops below the GND voltage. There is no current drawn in such an event. When the SD pin is hardwired to VIN, the user must connect the SD pin to VIN via a 100-kW resistor if reverse battery protection is desired. Hardwiring the SD pin directly to the VIN pin is allowed when reverse battery protection is not desired. Noise Reduction An external 10-nF bypass capacitor at BP is used to create a low pass filter for noise reduction. The start-up time is fast, since a power-on circuit pre-charges the bypass capacitor. After the power-up sequence the pre-charge circuit is switched to standby mode in order to save current. It is therefore not recommended to use larger bypass capacitor values than 50 nF. When the circuit is used without a capacitor, stable operation is guaranteed. Auto-Discharge/No-Discharge For Si91841 only, VOUT has an internal 100-W (typ.) discharge path to ground when the SD pin is low. The Si91843 does not have a discharge path when the SD pin is low. Stability The circuit is stable with only a small output capacitor equal to 6 nF/mA (= 1 mF @ 150 mA). Since the bandwidth of the error amplifier is around 1−3 MHz and the dominant pole is at the output node, the capacitor should be capacitive in this range, i.e., for 150-mA load current, an ESR <0.4 W is necessary. Parasitic inductance of about 10 nH can be tolerated. |
Numéro de pièce similaire - SI91843DT-25-T1 |
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Description similaire - SI91843DT-25-T1 |
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