ST715PUR(2014) 查看數據表（PDF） - STMicroelectronics
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ST715PUR Datasheet PDF : 24 Pages
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Output voltage selection for adjustable version
ST715
5
Output voltage selection for adjustable version
The ST715 features an adjustable output voltage due to two external resistors connected as
a voltage divider to the FB pin as shown in Figure 4. The output voltage is set by the
following equation:
Equation 1
VOUT = VFB (1 + R1/R2)
where typically VFB = 1.2 V. Choose R2 ≥ 5 kΩ to optimize the quiescent current, accuracy,
and high-frequency power supply rejection. The resistor selection is given by the following
equation:
Equation 2
R1 = R2 x (VOUT/VFB - 1)
5.1
External capacitor requirements
A 0.1 µF or a larger input bypass capacitor, connected between IN and GND and located
close to the device, is recommended. In this manner, the transient response and noise
rejection of the power supply, as a whole, improve. A higher value of the input capacitor may
be necessary if large, fast-rise-time load transients are present in the application and if the
device is several inches far from the power source.
The ST715 requires an output capacitor connected between OUT and GND to stabilize the
internal control loop. Any capacitor, (including ceramic and tantalum) with a value higher
than 0.47 µF, stabilizes this loop.
5.2
Power dissipation and junction temperature
For a reliable operation, junction temperature should not exceed 125 °C. This limits the
power dissipation the regulator can handle in any application. To guarantee that the junction
temperature is within acceptable limits, calculate the maximum allowable dissipation,
PD(max), and the dissipation, PD, which must be less than or equal to PD(max).
The maximum power dissipation limit is given by the following equation:
Equation 3
PD(max) = (TJMAX - TA) / RthJA
where:
TJMAX is the maximum allowable junction temperature
RthJA is the thermal resistance junction-to-ambient for the package
TA is the ambient temperature
The regulator dissipation is calculated by the following equation:
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