lm2991qml National Semiconductor Corporation, lm2991qml Datasheet - Page 9

• Manufacturer Part Number: lm2991qml
• Description: Lm2991qml Negative Low Dropout Adjustable Regulator
• Manufacturer: National Semiconductor Corporation

Application Hints
using resistors lower than 100 kΩ makes the adjust pin
current negligible. For example, neglecting the adjust pin
current, and setting R2 to 100 kΩ and V
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).
Typical Applications
V
*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 10Ω over the same operating temperature range as the regulator.
O
= V
Ref
(1 + R2/R1)
(Continued)
OUT
Fully Isolated Post-Switcher Regulator
to −5V, results in
9
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.
20158701
www.national.com
20158706