RT9182ACE RICHTEK [Richtek Technology Corporation], RT9182ACE Datasheet - Page 7

• Manufacturer Part Number: RT9182ACE
• Description: DUAL, LOW-NOISE, 200mA LDO REGULATOR
• Manufacturer: RICHTEK [Richtek Technology Corporation]

Applications Information
Capacitor Selection and Regulator Stability
Like
capacitors used with the RT9182 must be carefully
selected for regulator stability and performance.
Using a capacitor whose value is > 1µF on the
RT9182 input and the amount of capacitance can be
increased without limit. The input capacitor must be
located a distance of not more than 0.5" from the
input pin of the IC and returned to a clean analog
ground. Any good quality ceramic or tantalum can be
used for this capacitor. The capacitor with larger
value and lower ESR (equivalent series resistance)
provides better PSRR and line-transient response.
The output capacitor must meet both requirements
for minimum amount of capacitance and ESR in all
LDO applications (see Fig.1). The RT9182 is
designed specifically to work with low ESR ceramic
output capacitor in space-saving and performance
consideration. Using a ceramic capacitor whose
value is at least 1µF with ESR is > 5mΩ on the
RT9182 output ensures stability. The RT9182 still
works well with output capacitor of other types due to
the wide stable ESR range. Output capacitor of larger
capacitance can reduce noise and improve load-
transient response, stability, and PSRR. The output
capacitor should be located not more than 0.5"
from the V
clean analog ground.
Note that some ceramic dielectrics exhibit large
capacitance and ESR variation with temperature. It
may be necessary to use 2.2µF or more to ensure
stability at temperatures below -10°C in this case.
Also, tantalum capacitors, 2.2µF or more may be
needed to maintain capacitance and ESR in the
stable region for strict application environment.
Tantalum capacitors maybe suffer failure due to
surge current when it is connected to a low-
impedance source of power (like a battery or very
large capacitor). If a tantalum capacitor is used at the
input, it must be guaranteed to have a surge current
DS9182-02 April 2002
any
OUT
low-dropout
pin of the RT9182 and returned to a
regulator,
the
external
Preliminary
rating
manufacture.
Use a 10nF bypass capacitor at BP pin for low output
voltage noise. The capacitor, in conjunction with an
internal resistor, which connects bypass pin and the
band-gap reference, creates a low-pass filter for
noise reduction. Increasing the capacitance will
slightly decrease the output noise, and it is almost
independent of the start-up time. The capacitor
connected to the bypass pin for noise reduction must
have very low leakage. This capacitor leakage
current causes the output voltage to decline by a
proportional amount to the current.
Load-Transient Considerations
The RT9182 load-transient response graphs show
two components of the output response: a DC shift
from the output impedance due to the load current
change, and the transient response. The DC shift is
quite small due to the excellent load regulation of the
IC. Typical output voltage transient spike for a step
change in the load current from 0mA to 50mA is tens
mV, depending on the ESR of the output capacitor.
Increasing
decreasing the ESR attenuates the overshoot.
0.001
0.01
100
0.1
10
1
Region of Stable C
0
sufficient
the
40
output
for
Load Current (mA)
80
the
OUT
capacitor’s
Fig. 1
ESR vs. Load Current
application
120
www.richtek-ic.com.tw
C
RT9182
OUT
C
OUT
160
value
= 4.7µF
= 1µF
by
and
200
the
7