RT9078
Application Information
adjustable output voltage will be set to around 3.35V. Its
temperature coefficient in Figure 4 is still perfect in such
kind of application.
Like any low dropout linear regulator, the RT9078’s
external input and output capacitors must be properly
selected for stability and performance. Use a 1μF or larger
input capacitor and place it close to the IC's VINandGND
pins. Any output capacitor meeting the minimum 1mΩ
ESR (Equivalent Series Resistance) and capacitance larger
than 1μF requirement may be used. Place the output
capacitor close to the IC's VOUT andGNDpins. Increasing
capacitance and decreasing ESR can improve the circuit's
PSRR and line transient response.
Output Voltage vs. Temperature
3.35
3.34
3.33
3.32
3.31
3.30
Enable
The RT9078 has an EN pin to turn on or turn off the
regulator, When the EN pin is in logic high, the regulator
will be turned on. The shutdown current is almost 0μA
typical. The EN pin may be directly tied to VIN to keep the
part on. The Enable input is CMOS logic and cannot be
left floating.
3.29
ILOAD = 1mA
75 100 125
3.28
-50
-25
0
25
50
Temperature (°C)
Figure 4. Temperature Coefficient ofAdjustable Output
Voltage
Adjustable Output Voltage Setting
The minimum recommended 50μA in the resistor divider
makes the application no longer an ultra low quiescent
LDO. Figure 5 is another fine adjustable output voltage
application can keep the LDO still operating in low power
consumption. The fine tune range is recommended to be
less than 50mV (R1 ≤ 91kΩ) in order to keep a good
temperature coefficient of the output voltage.
Because of the small input current at the SNS pin, the
RT9078N with SNS pin also can work as an adjustable
output voltage LDO. Figure 3 gives the connections for
the adjustable output voltage application. The resistor
divider from VOUT to SNS sets the output voltage when
in regulation.
The voltage on the SNS pin sets the output voltage and is
determined by the values of R1 and R2. In order to keep
a good temperature coefficient of output voltage, the values
of R1 and R2 should be selected carefully to ignore the
temperature coefficient of input current at the SNS pin. A
current greater than 50μA in the resistor divider is
recommended to meet the above requirement. The
adjustable output voltage can be calculated using the
formula given in equation 1 :
RT9078N
VIN
EN
VOUT
SNS
1µF
R1
1µF
56pF/NC
GND
Figure 5. Fine Adjustable Output Voltage Application
Circuit
R1 + R2
VOUT
VSNS
(1)
R2
There isn't extra current consumption in the above
application. But the temperature coefficient of output
voltage will be degraded by the input current at SNS pin.
If the tuning range is larger than 50mV, a compensation
capacitor (56pF) is required to keep the stability of output
voltage. The fine adjustable output voltage is calculated
using the formula given in equation 2 :
where VSNS is determined by the output voltage selections
in the ordering information of RT9078N. The maximum
adjustable output voltage can be as high as input voltage
deducted by the dropout voltage.
When we choose 51kΩ and 16kΩ as R1 and R2
respectively, and select a 0.8V output at SNS pin, the
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is a registered trademark of Richtek Technology Corporation.
DS9078-08 June 2017
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