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LD2985 Datasheet(PDF) 12 Page - Unisonic Technologies

Part No. LD2985
Description  VERY LOW DROP AND LOW NOISE VOLTAGE REGULATOR LOW ESR CAP. COMPATIBLE
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Maker  UTC [Unisonic Technologies]
Homepage  http://www.utc-ic.com
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LD2985 Datasheet(HTML) 12 Page - Unisonic Technologies

 
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LD2985
LINEAR INTEGRATED CIRCUIT
UNISONIC TECHNOLOGIES CO., LTD
12 of 15
www.unisonic.com.tw
QW-R102-024.M
REV ERSE CU RREN T T EST CI RCU I T
APPLI CAT I ON I N FORM AT I ON
EXTERNAL CAPACITORS
Like any low-dropout regulator, the UTC 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 soldering input and outputting capacitors as close as possible to the relative pins.
INPUT CAPACITOR
An input capacitor whose value is 1
μF is required with the UTC 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 UTC 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 1
μF for output voltages equal or major than 3.8V, 2.2μF for VO
going from 1.8 ~ 3.3V, and 3.3
μF 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.
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 1
μA. When the inhibit feature is not used, this pin must be tied to Vi to 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 VIH VIL.
Any slew rate can be used to drive the inhibit.
REVERSE CURRENT
The power transistor used in the UTC LD2985 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 VREV voltage is applied on the output, the reverse current measured flows to the GND
across the two feedback resistors. This current typical value is 160
μA. R1 and R2 resistors are implanted type; typical
values are, respectively, 42.6K
Ω and 51.150KΩ.


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