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LM2991S-NOPB 数据表(PDF) 8 Page - Texas Instruments

部件名 LM2991S-NOPB
功能描述  LM2991 Negative Low Dropout Adjustable Regulator
Download  19 Pages
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制造商  TI [Texas Instruments]
网页  http://www.ti.com
标志 TI - Texas Instruments

LM2991S-NOPB 数据表(HTML) 8 Page - Texas Instruments

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LM2991
SNVS099H – MAY 1999 – REVISED JUNE 2013
www.ti.com
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
(1)
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 error due to 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. The
impedance of the voltage source driving the ON/OFF pin should be low enough to source the ON/OFF pin input
current to meet the OFF threshold voltage level, 100 µA maximum at 2.4V.
If the ON/OFF function is not needed, the pin should be connected to Ground. The ON/OFF pin should not be
left floating, as this is not an ensured operating condition.
See the Adjustable Current Sink Application, Figure 21.
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.
Thermal Shutdown
The LM2991 has an internally set thermal shutdown point of typically 160°C, with approximately 10°C of
hysteresis. This thermal shutdown temperature point is outside the specified Operating Rating range, above the
Absolute Maximum Ratings, and is intended as a safety feature for momentary fault conditions only. Continuous
operation near the thermal shutdown temperature should be avoided as it may have a negative affect on the life
of the device.
8
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Copyright © 1999–2013, Texas Instruments Incorporated
Product Folder Links: LM2991


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