lp2980im5-1.8 National Semiconductor Corporation, lp2980im5-1.8 Datasheet - Page 11

• Manufacturer Part Number: lp2980im5-1.8
• Description: Ic Reg Ldo Micropower Sot23-5
• Manufacturer: National Semiconductor Corporation

At higher values of load currents (using a 2.2 µF output ca-
pacitor), the stable ESR window gets very narrow. It is likely
that a Tantalum capacitor would not be a good choice for a
design that must be robust enough for mass production. In-
stead, a 2.2 µF capacitor with very low ESR (either ceramic
or film) should be used with a 2Ω external resistor placed in
series to provide the ESR.
4.7 µF Output Capacitor
If a 4.7 µF capacitor is used, the stable range of ESR values
for 50 mA operation is approximately 0.6Ω to 6Ω. Because of
the reduced ESR values of the new Tantalum, it is possible
to find 4.7 µF Tantalum capacitors with ESR values at or be-
low 0.6Ω. To ensure a stable design, it is recommended that
an external resistor (value about 0.5Ω) be added in series with
the 4.7 µF Tantalum to provide adequate minimum ESR.
At values of load current
enough that Tantalum can be used without external resis-
tance for added ESR.
Another acceptable configuration for 50 mA operation is to
use a ceramic or film 4.7 µF capacitor (which has very low
ESR) with an external 2Ω resistor in series.
10 µF Output Capacitor
50 mA operation using a 10 µF output capacitor requires an
ESR in the range of approximately 0.4Ω to 7Ω. As stated pre-
viously, it is possible that solid Tantalum capacitors can be
found with ESR values near to or below 0.4Ω. An external
resistor in series with the Tantalum (value of about 0.5Ω) is
recommended to assure unconditional stability.
At values of load current
enough that Tantalum can be used without external resis-
tance for added ESR.
Another acceptable configuration for 50 mA operation is to
use a ceramic or film 10 µF capacitor (which has very low
ESR) with an external 2Ω resistor in series.
15 µF Output Capacitor
The stable ESR range (for 50 mA load current) using a 15 µF
output capacitor is approximately 0.1Ω to 10Ω. It is extremely
unlikely that a 15 µF Tantalum capacitor would be found with
≤
≤
20 mA, the ESR range is wide
20 mA, the ESR range is wide
101091 Version 6 Revision 1
Print Date/Time: 2008/12/05 10:23:42
11
an ESR below 0.1Ω, so no external resistance is required with
a Tantalum.
As before, another acceptable configuration for 50 mA oper-
ation is to use a ceramic or film 15 µF capacitor with an
external 2Ω resistor in series.
ON/OFF INPUT OPERATION
The LP2980 is shut off by pulling the ON/OFF input low, and
turned on by pulling it high. If this feature is not to be used,
this pin should be tied to V
times.
To ensure proper operation, the signal source used to drive
the ON/OFF input must be able to swing above and below the
specified turn-on/turn-off voltage thresholds (see Electrical
Characteristics).
It is also important that the turn-on (and turn-off) voltage sig-
nals applied to the ON/OFF input have a slew rate which is
not less than 40 mV/µs.
CAUTION: The regulator output state can not be guaranteed
if a slow-moving AC (or DC) signal is applied that it is in the
range between the turn-on/turn-off voltage thresholds speci-
fied in the Electrical Characteristics section.
REVERSE INPUT/OUTPUT VOLTAGE
The PNP power transistor used as the pass element in the
LP2980 has an inherent diode connected between the regu-
lator output and input. During normal operation (where the
input voltage is higher than the output) this diode is reverse-
biased.
However, if the output is pulled above the input, this diode will
turn ON and current will flow into the regulator output. In such
cases, a parasitic SCR can latch which will allow a high cur-
rent to flow into V
damage the part.
In any application where the output may be pulled above the
input, an external Schottky diode must be connected from
V
verse voltage across the LP2980 to 0.3V (see Basic Applica-
tion Circuit).
IN
to V
OUT
(cathode on V
IN
(and out the ground pin), which can
IN
IN
, anode on V
to keep the regulator on at all
OUT
), to limit the re-
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