LD2985 ST Microelectronics, LD2985 Datasheet - Page 9

• Manufacturer Part Number: LD2985
• Description: VERY LOW DROP AND LOW NOISE VOLTAGE REGULATOR LOW ESR CAP. COMPATIBLE / WITH INHIBIT FUNCTION
• Manufacturer: ST Microelectronics

Figure 13 : Load Transient
V
EXTERNAL CAPACITORS
Like any low-dropout regulator, the LD2985 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 LD2985 (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 LD2985 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 E.S.R. (equivalent
series resistance) value. Due to the different loop gain, the stability improves for higher output versions
and so the suggested minimum output capacitor value, if low E.S.R. ceramic type is used, is 1µF for
output voltages equal or major than 3.8V, 2.2µF for V
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.
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
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
O
=2.5V, I
O
=0 to 50mA, no C
I
, C
O
=10 F, t
IH
s
=t
V
f
=2ns
IL
. Any slew rate can be used to drive the inhibit.
O
Figure 14 : Load Transient
V
O
going from 1.8 to 3.3V, and 3.3µF for the other
=2.5V, I
O
=0 to 50mA, no C
I
, C
O
=4.7 F, t
LD2985 SERIES
s
=t
f
=2ns
9/13
I
to