RT9094A
Application Information
The RT9094A is a low dropout regulator that features soft-
start capability. It provides EN and PGOOD for easily
system sequence control, and built-in over current &
thermal protection for safe operation.
Power Up Sequence Requirement
The RT9094A supports power on the input VIN, VBIAS,
and EN pins in any order without damage the device.
Generally, connecting the ENand VINfor most application
is acceptable, as long as VIN and VEN is greater than the
EN threshold (typ. = 1.1V) and the input ramp rate of VIN
and VBIAS is faster than the output settled soft-start ramp
rate. If the VIN/BIAS input source ramp rate is slower
than the output settled soft-start time, the output will track
the input supply ramp up level and minus the dropout
voltage until it reaches the settled output voltage level.
For the other case, If EN is connected with VBIAS, and
the provided VIN is present before VBIAS, the output soft-
start will as programmed. While VBIAS and VEN are
present before VIN is applied also the settled soft-start
time has expired, then VOUT tracks VIN ramp up. If the
soft-start time has not expired, output tracks VINramp up
until output reaches the value set by the charging soft-
start capacitor.
Dropout Voltage
Because of two power supply inputs VIN and VBIAS and
one VOUT regulator output, there are twoDropout voltages
specified. The first is the VINDropout voltage is the voltage
difference (VIN − VOUT) when VOUT starts to decrease
by percent specified in the Electrical Characteristics table.
The second, VBIAS dropout voltage is the voltage
difference (VBIAS − VOUT) when VINand VBIAS pins are
joined together and VOUT starts to decrease. This option
allows the device to be used in applications where an
auxiliary bias voltage is not available or low dropout is not
required. In these applications, VBIAS is suggested be
1.8V above VOUT and attention on power rating and
thermal is needed.
Input, Output, and Bias Capacitor Selection
Thermal Considerations
The device is designed to be stable for all available types
and values of output capacitors ≥ 2.2μF. The device is
also stable with multiple capacitors in parallel, which can
be of any type or value. The capacitance required on the
VINand VBIAS pins strongly depends on the input supply
source impedance. To counteract any inductance in the
input, the minimum recommended capacitor for VIN is 1μF
and minimum recommended capacitor for VBIAS is 0.1μF.
If VIN and VBIAS are connected to the same supply, the
recommended minimum capacitor for VBIAS is 4.7μF. Good
quality, low ESR capacitors should be used on the input;
ceramic X5R and X7R capacitors are preferred. These
capacitors should be placed as close the pins as possible
for optimum performance.
Thermal protection limits power dissipation in the
RT9094A. When power dissipation on the pass element
(PDIS = (VIN − VOUT) x IOUT ) is too high and raises the
junction operation temperature over 160°C, the OTP circuit
starts the thermal shutdown function and turns the pass
element off. The pass element turns on again after the
junction temperature cools down by 20°C.
The output is shorted to ground when there is short circuit
at the output. This procedure can reduce the chip
temperature and provide maximum safety to end users
when output short circuit occurs.
The junction temperature should never exceed the
absolute maximum junction temperature TJ(MAX), listed
under Absolute Maximum Ratings, to avoid permanent
damage to the device. The maximum allowable power
dissipation depends on the thermal resistance of the IC
package, the PCB layout, the rate of surrounding airflow,
and the difference between the junction and ambient
temperatures. The maximum power dissipation can be
calculated using the following formula :
Adjusting the Output Voltage
The output voltage of the RT9094A is adjustable from 0.8V
to 3.6V by external voltage divider resisters as shown in
Typical Application Circuit. R1 and R2 can be calculated
the output voltage. In order to achieve the maximum
accuracy specifications, R2 should be ≤ 4.99kΩ.
Copyright 2022 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
DS9094A-00 January 2022
www.richtek.com
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