TPS7A39
www.ti.com.cn
ZHCSGP0A –JULY 2017–REVISED SEPTEMBER 2017
8.2.2.4 Application Curves
0
-20
0
-20
-40
-40
-60
-60
-80
-80
-100
-120
-140
-160
-180
-200
-100
-120
-140
-160
-180
-200
100
1k
10k
100k
100
1k
10k
100k
Frequency (Hz)
Frequency (Hz)
fIN = 1 kHz, VPP = 10.0 V
fIN = 1 kHz, VPP = 10.0 V
图 79. FFT Using 5-V and 0-V Supply Rails
图 80. FFT Using 5.2-V and –0.2-V Supply Rails
9 Power-Supply Recommendations
The input supply for the LDO must be within the recommended operating conditions. The input voltage must
provide adequate headroom in order for the device to have a regulated output. Place the 10-µF input capacitors
as close to the device as possible. If the input supply is noisy, additional input capacitors can help improve the
output noise performance.
10 Layout
10.1 Layout Guidelines
Layout is a critical part of good power-supply design. There are several signal paths that conduct fast-changing
currents or voltages that can interact with stray inductance or parasitic capacitance to generate noise or degrade
the power-supply performance. To help eliminate these problems, bypass the IN pin to ground with capacitors.
Tie the GND pin directly to the thermal pad under the device. The thermal pad must be connected to any internal
PCB ground planes using multiple vias directly under the device.
Every capacitor must be placed as close as possible to the device and on the same side of the PCB as the
regulator itself.
Do not place any of the capacitors on the opposite side of the PCB from where the regulator is installed. The use
of vias and long traces is strongly discouraged because these circuits can impact system performance
negatively, and even cause instability.
10.1.1 Board Layout Recommendations to Improve PSRR and Noise Performance
To improve ac performance (such as PSRR, output noise, and transient response), TI recommends that the
board be designed with separate ground planes for VIN and VOUT, with each ground plane star connected only at
the GND pin of the device. In addition, the ground connection for the bypass capacitor must connect directly to
the GND pin of the device.
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