DCP010505B_15 Datasheet, PDF (18/30 Pages) Texas Instruments – Unregulated DC/DC Converter Modules

DCP010505B, DCP010512B, DCP010515B, DCP012405B, DCP010505DB, DCP010507DB
DCP010512DB, DCP010515DB, DCP011512DB, DCP011515DB, DCP012415DB
SBVS012F – DECEMBER 2000 – REVISED OCTOBER 2015
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9.2.3 Detailed Design Procedure
9.2.3.1 Input Capacitor
For all 5-V and 15-V input voltage designs, select a 2.2-μF low-ESR ceramic input capacitor to ensure a good
startup performance. 24-V input applications require only 0.47-μF of input capacitance.
9.2.3.2 Output Capacitor
For any DCP01B design, select a 1.0-μF low-ESR ceramic output capacitor to reduce output ripple.
9.2.3.3 SYNC_IN Pin
In a stand-alone application, leave the SYNC_IN pin floating.
9.2.4 PCB Design
The copper losses (resistance and inductance) can be minimized by the use of mutual ground and power planes
(tracks) where possible. If that is not possible, use wide tracks to reduce the losses. If several devices are being
powered from a common power source, a star-connected system for the track must be deployed. Do not connect
the devices in series, because that type of connection cascades the resistive losses. The position of the
decoupling capacitors is important. They must be as close to the devices as possible in order to reduce losses.
See the PCB Layout section for more details.
9.2.5 Decoupling Ceramic Capacitors
All capacitors have losses because of internal equivalent series resistance (ESR), and to a lesser degree,
equivalent series inductance (ESL). Values for ESL are not always easy to obtain. However, some
manufacturers provide graphs of frequency versus capacitor impedance. These graphs typically show the
capacitor impedance falling as frequency is increased (as shown in Figure 35). In Figure 35, X_C is the reactance
due to the capacitance, X _L is the reactance due to the ESL, and f₀ is the resonant frequency. As the frequency
increases, the impedance stops decreasing and begins to rise. The point of minimum impedance indicates the
resonant frequency of the capacitor. This frequency is where the components of capacitance and inductance
reactance are of equal magnitude. Beyond this point, the capacitor is not effective as a capacitor.
Z
X_C
X_L
0
f₀
Frequency (Hz)
Figure 35. Capacitor Impedance vs Frequency
X_C = X_L
when
• f₀
(1)
However, there is a 180° phase difference resulting in cancellation of the imaginary component. The resulting
effect is that the impedance at the resonant point is the real part of the complex impedance, namely, the value of
the ESR. The resonant frequency must much higher than the 800-kHz switching frequency of the device.
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Product Folder Links: DCP010505B DCP010512B DCP010515B DCP012405B DCP010505DB DCP010507DB
DCP010512DB DCP010515DB DCP011512DB DCP011515DB DCP012415DB