LD2980ABM28TR STMICROELECTRONICS [STMicroelectronics], LD2980ABM28TR Datasheet - Page 11

• Manufacturer Part Number: LD2980ABM28TR
• Description: VERY LOW DROP VOLTAGE REGULATORS WITH INHIBIT LOW ESR OUTPUT CAPACITORS COMPATIBLE
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

LD2980 SERIES
APPLICATION NOTES
EXTERNAL CAPACITORS
Like any low-dropout regulator, the LD2980 requires external capacitors for regulator stability. This
capacitor must be selected to meet the requirements of minimum capacitance and equivalent series
resistance. We suggest to solder input and output capacitors as close as possible to the relative pins.
INPUT CAPACITOR
An input capacitor whose value is 1µF is required with the LD2980 (amount of capacitance can be
increased without limit). This capacitor must be located a distance of not more than 0.5" from the input pin
of the device and returned to a clean analog ground. Any good quality ceramic, tantalum or film capacitors
can be used for this capacitor.
OUTPUT CAPACITOR
The LD2980 is designed specifically to work with ceramic output capacitors. It may also be possible to use
Tantalum capacitors, but these are not as attractive for reasons of size and cost. By the way, the output
capacitor must meet both the requirement for minimum amount of capacitance and ESR (equivalent
series resistance) value. The figures 1 and 2 show the allowable ESR range as a function of the output
capacitance. These curves represent the stability region over the full temperature and I
range. Due to
O
the different loop gain, the stability improves for higher output versions and so the suggested minimum
output capacitor value, if low ESR ceramic type is used, is 1µF for output voltages equal or major than
3.8V, 2.2µF for output voltages from 2.85 to 3.3V, and 3.3µF for the other versions. However, if an output
capacitor lower than the suggested one is used, it’s possible to make stable the regulator adding a resistor
in series to the capacitor (see Figure1 & Figure2 to choose the right value according to the used version
and keeping in account that the ESR of ceramic capacitors has been measured @ 100KHz).
IMPORTANT
The output capacitor must maintain its ESR in the stable region over the full operating temperature to
assure stability. Also, capacitor tolerance and variation with temperature must be considered to assure
the minimum amount of capacitance is provided at all times. This capacitor should be located not more
than 0.5" from the output pin of the device and returned to a clean analog ground.
INHIBIT INPUT OPERATION
The inhibit pin can be used to turn OFF the regulator when pulled low, so drastically reducing the current
consumption down to less than 1µA. When the inhibit feature is not used, this pin must be tied to V
to
I
keep the regulator output ON at all times. To assure proper operation, the signal source used to drive the
inhibit pin must be able to swing above and below the specified thresholds listed in the electrical
characteristics section under V
V
. Any slew rate can be used to drive the inhibit.
IH
IL
REVERSE CURRENT
The power transistor used in the LD2980 has not an inherent diode connected between the regulator input
and output. If the output is forced above the input, no current will flow from the output to the input across
the series pass transistor. When a V
voltage is applied on the output, the reverse current measured,
REV
according to the test circuit in figure 19, flows to the GND across the two feedback resistors. This current
typical value is 160µA. R
and R
resistors are implanted type; typical values are, respectively, 42.6 K
1
2
and 51.150 K .
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