RT9073
11
DS9073-06 June 2017 www.richtek.com
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Copyright 2017 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation.
Application Information
Like any low dropout linear regulator, the RT9073’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 VIN and GND
pins. Any output capacitor meeting the minimum 1mΩ
ESR (Equivalent Series Resistance) and effective
capacitance larger than 1μF 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 RT9073 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 V
IN
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
RT9073 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 :
OUT SNS
R1 + R2
V V (1)
R2
where V
SNS
is determined by the output voltage selections
in the ordering information of RT9073.
When we choose 39kΩ and 15kΩ as R1 and R2
respectively, and select a 0.9V output at SNS pin, the
adjustable output voltage will be set to around 3.24V. Its
Figure 4. Temperature Coefficient of Adjustable Output
Voltage
Output Voltage vs. Temperature
3.20
3.21
3.22
3.23
3.24
3.25
3.26
3.27
3.28
3.29
3.30
-50-25 0 25 50 75100125
Temperature (°C)
Output Voltage (V)
I
LOAD
= 1mA
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.
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
RT9073
1µF
1µF
SNS
R1
56pF/NC
temperature coefficient in Figure 4 is still perfect in such
kind of application.
