RT9080

11

DS9080-03 October 2016

www.richtek.com

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Copyright 2016 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

Application Information

Like any low dropout linear regulator, the RT9080’s

external input and output capacitors must be properly

selected for stability and performance. Use a 1

μF or larger

input capacitor and place it close to the IC's VIN and GND

pins. Any output capacitor meeting the minimum 1m

Ω

ESR (Equivalent Series Resistance) and effective

capacitance larger than 1

μF requirement may be used.

Place the output capacitor close to the IC's VOUT and

GND pins. Increasing capacitance and decreasing ESR

can improve the circuit's PSRR and line transient response.

Enable

The RT9080 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 0

μA

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.

Adjustable Output Voltage Setting

Because of the small input current at the SNS pin, the

RT9080N 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 50

μA 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 :

OUT

SNS

R1 + R2

V

V

(1)

R2



where VSNS is determined by the output voltage selections

in the ordering information of RT9080N. The maximum

adjustable output voltage can be as high as input voltage

deducted by the dropout voltage.

When we choose 51k

Ω and 16kΩ as R1 and R2

respectively, and select a 0.8V output at SNS pin, the

adjustable output voltage will be set to around 3.35V. Its

temperature coefficient in Figure 4 is still perfect in such

kind of application.

Figure 4. Temperature Coefficient of Adjustable Output

Voltage

Output Voltage vs. Temperature

3.28

3.29

3.30

3.31

3.32

3.33

3.34

3.35

-50

-25

0

25

50

75

100

125

Temperature(°C)

ILOAD = 1mA

The minimum recommended 50

μA 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.

Figure 5. Fine Adjustable Output Voltage Application

Circuit

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 equation2 :

OUT

SNS

SNS

V

V

+ I

R1

(2)



VIN

EN

VOUT

GND

RT9080N

1µF

1µF

SNS

R1

56pF/NC