Datenblatt-Suchmaschine für elektronische Bauteile |
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LM2991QML Datenblatt(PDF) 9 Page - Texas Instruments |
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LM2991QML Datenblatt(HTML) 9 Page - Texas Instruments |
9 / 15 page LM2991QML www.ti.com SNVS392A – MARCH 2006 – REVISED OCTOBER 2011 MINIMUM LOAD A minimum load current of 500 μA is required for proper operation. The external resistor divider can provide the minimum load, with the resistor from the adjust pin to ground set to 2.4 k Ω. SETTING THE OUTPUT VOLTAGE The output voltage of the LM2991 is set externally by a resistor divider using the following equation: VOUT = VREF x (1 + R2/R1) − (IADJ x R2) where VREF = −1.21V. The output voltage can be programmed within the range of −3V to −24V, typically an even greater range of −2V to −25V. The adjust pin current is about 60 nA, causing a slight error in the output voltage. However, using resistors lower than 100 k Ω makes the adjust pin current negligible. For example, neglecting the adjust pin current, and setting R2 to 100 k Ω and VOUT to −5V, results in an output voltage error of only 0.16%. ON/OFF PIN The LM2991 regulator can be turned off by applying a TTL or CMOS level high signal to the ON/OFF pin (see Adjustable Current Sink Application). FORCING THE OUTPUT POSITIVE Due to an internal clamp circuit, the LM2991 can withstand positive voltages on its output. If the voltage source pulling the output positive is DC, the current must be limited to 1.5A. A current over 1.5A fed back into the LM2991 could damage the device. The LM2991 output can also withstand fast positive voltage transients up to 26V, without any current limiting of the source. However, if the transients have a duration of over 1 mS, the output should be clamped with a Schottky diode to ground. Typical Applications VO = VRef (1 + R2/R1) *Required if the regulator is located further than 6 inches from the power supply filter capacitors. A 1 μF solid tantalum or a 10 μF aluminum electrolytic capacitor is recommended. **Required for stability. Must be at least a 10 μF aluminum electrolytic or a 1 μF solid tantalum to maintain stability. May be increased without bound to maintain regulation during transients. Locate the capacitor as close as possible to the regulator. The equivalent series resistance (ESR) is critical, and should be less than 10 Ω over the same operating temperature range as the regulator. Copyright © 2006–2011, Texas Instruments Incorporated Submit Documentation Feedback 9 Product Folder Links: LM2991QML |
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