RT9017
8
DS9017-05 April 2011www.richtek.com
Applications Information
Like any low-dropout regulator, the external capacitors used
with the RT9017 must be carefully selected for regulator
stability and performance. Using a capacitor whose value
is > 1μF on the RT9017 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 inch 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 LDOs
application. The RT9017 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 > 20mΩ on the
RT9017 output ensures stability. The RT9017 still works
well with output capacitor of other types due to the wide
stable ESR range. Figure 1. shows the curves of allowable
ESR range as a function of load current for various output
capacitor values. 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 inch from the V
OUT
pin of the RT9017
and returned to a clean analog ground.
Thermal Considerations
Thermal protection limits power dissipation in RT9017.
When the operation junction temperature exceeds 165°C,
the OTP circuit starts the thermal shutdown function and
turns the pass element off. The pass element turn on again
after the junction temperature cools by 30°C.
RT9017 lowers its OTP trip level from 165°C to 110°C
when output short circuit occurs (V
OUT
< 0.4V) as shown
in Figure 2. This limits IC case temperature under 100°C
and provides maximum safety to end users when output
short circuit occurs.
Figure 1
Enable Function
The RT9017 features an LDO regulator enable/disable
function. To assure the LDO regulator will switch on, the
EN turn on control level must be greater than 1.2 volts.
The LDO regulator will go into the shutdown mode when
the voltage on the EN pin falls below 0.4 volts. For to
protecting the system, the RT9017 have a quick-discharge
function. If the enable function is not needed in a specific
application, it may be tied to V
IN
to keep the LDO regulator
in a continuously on state.
Figure 2. Short Circuit Thermal Folded Back Protection
when Output Short Circuit Occurs
V
OUT
Short to GND
0.4V
V
OUT
I
OUT
TSD
OTP Trip Point
165 C
°
110 C
°
110 C
°
80 C
°
IC Temperature
Region of Stable C
OUT
ESR vs. Load Current
0.00
0.01
0.10
1.00
10.00
100.00
0 100 200 300 400 500
Load Current (mA)
C
OUT
ESR (Ω)
C
OUT
= 1uF
100
10
1
RT9017-15PB
C
IN
= 1μF, X7R
Unstable Region
Stable Region
Unstable Region (Simulation Verity)
Region of Stable C
OUT
ESR (Ω)
