
PTH08T230W, PTH08T231W
SLTS265L –NOVEMBER 2005–REVISED AUGUST 2011
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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 ×1μF, 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.
Table 3. Input/Output Capacitors(1)
Capacitor Characteristics Quantity
Max Output Bus (2)
Max.
Capacitor Vendor, Ripple
Working Value ESR Physical Input
Type Series (Style) No Turbo-
Current Vendor Part No.
Voltage (µF) at 100 Size (mm) Bus Turbo- Trans
at 85°C
kHz Trans Cap Type(3)
(Irms)
Panasonic
FC (Radial) 25 V 1000 43mΩ1690mA 16 ×15 1 ≥2 N/R(4) EEUFC1E102S
FC (Radial) 25 V 820 38mΩ1655mA 12 ×20 1 ≥1 N/R(4) EEUFC1E821S
FC (SMD) 35 V 470 43mΩ1690mA 16 ×16,5 1 ≥1 N/R(4) EEVFC1V471N
FK (SMD) 35 V 1000 35mΩ1800mA 16 ×16,5 1 ≥2 N/R(4) EEVFK1V102M
United Chemi-Con
PTB, Poly-Tantalum(SMD) 6.3 V 330 25mΩ2600mA 7,3×4,3×2.8 N/R(5) 1 ~ 4 C ≥2(6) 6PTB337MD6TER (VO≤5.1V)(7)
LXZ, Aluminum (Radial) 35 V 680 38mΩ1660mA 12,5 ×20 1 1 ~ 3 N/R(4) LXZ35VB681M12X20LL
PS, Poly-Alum (Radial) 16 V 330 14mΩ5060mA 10 ×12,5 1 1 ~ 3 B ≥2(6) 16PS330MJ12
PS, Poly-Alum (Radial) 6.3 V 390 12mΩ5500mA 8 ×12,5 N/R(5) 1 ~ 2 B ≥1(6) 6PS390MH11 (VO≤5.1V)(7)
PXA, Poly-Alum (SMD) 16 V 330 14mΩ5050mA 10 ×12,2 1 1 ~ 3 B ≥2(6) PXA16VC331MJ12TP
PXA, Poly-Alum (Radial) 10 V 330 14mΩ4420mA 8 ×12,2 N/R(5) 1 ~ 2 B ≥1(6) PXA10VC331MH12
Nichicon, Aluminum
PM (Radial) 25 V 1000 43mΩ1520mA 18 ×15 1 ≥2 N/R(4) UPM1E102MHH6
HD (Radial) 35 V 470 23mΩ1820mA 10 ×20 1 ≥2 N/R(4) UHD1V471HR
Panasonic, Poly-Aluminum 2.0 V 390 5mΩ4000mA 7,3×4,3×4,2 N/R(5) N/R(8) B≥2(6) EEFSE0J391R(VO≤1.6V)(7)
(1) Capacitor Supplier Verification
Please verify availability of capacitors identified in this table. Capacitor suppliers may recommend alternative part numbers because of
limited availability or obsolete products.
RoHS, Lead-free and Material Details
See the capacitor suppliers regarding material composition, RoHS status, lead-free status, and manufacturing process requirements.
Component designators or part number deviations can occur when material composition or soldering requirements are updated.
(2) Additional output capacitance must include the required 200 μF of ceramic type.
(3) Required capacitors with TurboTrans. See the TurboTrans Application information for Capacitor Selection
Capacitor Types:
(a) Type A = (100 <capacitance ×ESR ≤1000)
(b) Type B = (1,000 <capacitance ×ESR ≤5,000)
(c) Type C = (5,000 <capacitance ×ESR ≤10,000)
(4) Aluminum Electrolytic capacitor not recommended for the TurboTrans due to higher ESR ×capacitance products. Aluminum and higher
ESR capacitors can be used in conjunction with lower ESR capacitance.
(5) N/R –Not recommended. The voltage rating does not meet the minimum operating limits.
(6) Required capacitors with TurboTrans. See the TurboTrans Application information for Capacitor Selection
Capacitor Types:
(a) Type A = (100 <capacitance ×ESR ≤1000)
(b) Type B = (1,000 <capacitance ×ESR ≤5,000)
(c) Type C = (5,000 <capacitance ×ESR ≤10,000)
(7) The voltage rating of this capacitor only allows it to be used for output voltage that is equal to or less than 80% of the working voltage.
(8) N/R –Not recommended. The ESR value of this capacitor is below the required minimum when not using TurboTrans.
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