PTR08100W_15 Datasheet, PDF (9/16 Pages) Texas Instruments – 10-A, 4.5-V to 14-V INPUT, NON-ISOLATED, ADJUSTABLE WIDE-OUTPUT, SWITCHING REGULATOR

PTR08100W
www.ti.com
SLTS284F – AUGUST 2007 – REVISED OCTOBER 2012
Input Capacitor (Required)
The PTR08100W requires a minimum input capacitance of 100 μF. The ripple current rating of the electrolytic
capacitor must be at least 750 mArms. An optional 22-μF X5R/X7R ceramic capacitor is recommended to reduce
the RMS ripple current. Table 3 includes a preferred list of capacitors by vendor.
Input Capacitor Information
The size and value of the input capacitor is determined by the converter’s transient performance capability. The
minimum value assumes that the converter is supplied with a responsive, low-inductance input source. The
source should have ample capacitive decoupling, and be distributed to the converter via PCB power and ground
planes.
Ceramic capacitors should be located as close as possible to the module's input pins, within 0.5 inch (1.3 cm).
Adding ceramic capacitance is necessary to reduce the high-frequency ripple voltage at the module's input. This
reduces the magnitude of the ripple current through the electroytic capacitor, as well as the amount of ripple
current reflected back to the input source. Additional ceramic capacitors can be added to further reduce the RMS
ripple current requirement for the electrolytic capacitor.
The main considerations when selecting input capacitors are the RMS ripple current rating, temperature stability,
and maintaining less than 100 mΩ of equivalent series resistance (ESR).
Regular tantalum capacitors are not recommended for the input bus. These capacitors require a recommended
minimum voltage rating of 2 × (maximum dc voltage + ac ripple). This is standard practice to ensure reliability.
No tantalum capacitors were found to have voltage ratings sufficient to meet this requirement.
When the operating temperature is below 0°C, the ESR of aluminum electrolytic capacitors increases. For these
applications, OS-CON, poly-aluminum, and polymer-tantalum types should be considered.
Output Capacitor (Required)
The PTR08100W requires a minimum 100 μF of non-ceramic output capacitance. Additional non-ceramic, low-
ESR capacitance is recommended for improved performance. See data sheet for maximum capacitance limits.
The required capacitance above the minimum is determined by actual transient deviation requirements. Table 3
includes a preferred list of capacitors by vendor.
Output Capacitor Information
When selecting output capacitors, the main considerations are capacitor type, temperature stability, and ESR.
Ceramic output capacitors added for high-frequency bypassing should be located as close as possible to the
load to be effective. Ceramic capacitor values below 10 μF should not be included when calculating the total
output capacitance value.
When the operating temperature is below 0°C, the ESR of aluminum electrolytic capacitors increases. For these
applications, OS-CON, poly-aluminum, and polymer-tantalum types should be considered.
Designing for Fast Load Transients
The transient response of the dc/dc converter has been characterized using a load transient with a di/dt of
2.5 A/μs. The typical voltage deviation for this load transient is given in the Electrical Characteristics table using
the minimum required value of output capacitance. As the di/dt of a transient is increased, the response of a
converter’s regulation circuit ultimately depends on its output capacitor decoupling network. This is an inherent
limitation with any dc/dc converter once the speed of the transient exceeds its bandwidth capability.
If the target application specifies a higher di/dt or lower voltage deviation, the requirement can only be met with
additional low ESR ceramic capacitor decoupling. Generally, with load steps greater than 100 A/μs, adding
multiple 10-μF ceramic capacitors plus 10 × 1 μF, and numerous high frequency ceramics (≤ 0.1 μF) is all that is
required to soften the transient higher frequency edges. The PCB location of these capacitors in relation to the
load is critical. DSP, FPGA and ASIC vendors identify types, location and amount of capacitance required for
optimum performance. Low impedance buses, unbroken PCB copper planes, and components located as close
as possible to the high frequency devices are essential for optimizing transient performance.
Copyright © 2007–2012, Texas Instruments Incorporated
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