RT9193
8DS9193-17 January 2016www.richtek.com
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Applications Information
Like any low dropout regulator, the external capacitors
used with the RT9193 must be carefully selected for
regulator stability and performance. Using a capacitor
whose value is >1μF on the RT9193 input and the a mount
of capacitance can be increased without limit. The input
ca pacitor 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 ca pa citor . The ca pacitor 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 a pplication.
The RT9193 is designed specifically to work with low ESR
cera mic output capacitor in space-saving and performance
consideration. Using a ceramic ca pa citor whose value is
at least 1μF with ESR is >1mΩ on the RT9193 output
ensures stability . The RT9193 still works well with output
ca pacitor 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 capa citor of larger capa citance can reduce noise
and improve load transient response, stability , and PSRR.
The output ca pacitor should be located not more than 0.5
inch from the VOUT pin of the RT9193 and returned to a
clean analog ground.
Figure 1
Bypass Capa citor and Low Noise
Connecting a 22nF between the BP pin and GND pin
significantly reduces noise on the regulator output, it is
critical that the ca p acitor conne ction between the BP pin
and GND pin be direct and PCB tra ces should be as short
as possible. There is a relationship between the bypass
capacitor value and the LDO regulator turn on time. DC
leakage on this pin can affect the LDO regulator output
noise and voltage regulation performance.
Enable Function
The RT9193 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 RT9193 have a quick-discharge
function. If the enable function is not needed in a specific
a pplication, it may be tied to VIN to keep the LDO regulator
in a continuously on state.
Thermal Considerations
Thermal protection limits power dissipation in RT9193.
When the operation junction temperature exceeds 165°C,
the OTP circuit starts the thermal shutdown function turn
the pass element off. The pass element turn on again
after the junction temperature cools by 30°C.
For continue operation, do not exceed absolute maximum
operation junction temperature 125°C. The power
dissipation definition in device is :
PD = (VIN − VOUT) x IOUT + VIN x IQ
The maximum power dissipation depends on the thermal
resistance of IC package, PCB layout, the rate of
surroundings airflow and temperature difference between
junction to a mbient. The maximum power dissipation ca n
be calculated by following formula :
PD(MAX) = ( TJ(MAX) − TA ) /θJA
Where TJ(MAX) is the maximum operation junction
temperature 125°C, TA is the ambient temperature and
the θJA is the junction to ambient thermal resistance.
Region of Stable COUT ESR vs. Load Current
0.001
0.01
0.1
1
10
100
0 50 100 150 200 250 300
Load Current (mA)
COUT ESR ( )
Instable
Stable
RT9193-15xU5
CIN = COUT = 1μF, X7R
Ω