Datasheet

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Designing for Load Transients
PTH04070W
SLTS227B – SEPTEMBER 2004 – REVISED OCTOBER 2007
The transient response of the dc/dc converter has been characterized using a load transient with a di/dt of
1 A/ μ s. The typical voltage deviation for this load transient is given in the data sheet specification table using the
optional 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 output
capacitor decoupling. In these cases, special attention must be paid to the type, value, and ESR of the
capacitors selected.
If the transient performance requirements exceed those specified in the data sheet, the selection of output
capacitors becomes more important. Review the minimum ESR in the characteristic data sheet for details on the
capacitance maximum.
Table 3. Recommended Input/Output Capacitors
CAPACITOR CHARACTERISTICS QUANTITY
85 ° C
CAPACITOR VENDOR/
EQUIVALENT
VENDOR
WORKING MAXIMUM PHYSICAL
COMPONENT
VALUE SERIES INPUT OUTPUT
NUMBER
VOLTAGE RIPPLE SIZE
SERIES
( μ F) RESISTANCE BUS
(1)
BUS
(V) CURRENT (mm)
(ESR) ( Ω )
(I
rms
) (mA)
Panasonic WA (SMT) 10 120 0.035 2800 8 × 6.9 1 ≤ 4
(1)
EEFWA1A121P
(2)
FC (SMT) 25 47 0.400 230 8 × 6.2 1 1
(1)
EEVFC1E470P
(2)
Panasonic SL SP-cap(SMT) 6.3 47 0.018 2500 7.3 × 4.3 1 ≤ 3 EEFCD0J470R
6.3 56 0.009 3000 7.3 × 4.3 1 ≤ 2 EEFSL0J560R
United Chemi-con PXA (SMT) 10 47 0.031 2250 6.3 × 5.7 1 1 PXA10VC470MF60TP
FS 10 100 0.040 2100 6.3 × 9.8 1 ≤ 5 10FS100M
LXZ 16 100 0.250 290 6.3 × 11.5 1 1 LXZ16VB101M6X11LL
MVZ (SMT) 16 100 0.440 230 6.3 × 5.7 1 1 MVZ16VC101MF60TP
Nichicon UWG (SMT) 16 100 0.400 230 8 × 6.2 1 1 UWG1C101MCR1GS
F559(Tantalum) 10 100 0.055 2000 7.7 × 4.3 1 ≤ 5 F551A107MN
PM 10 100 0.550 210 6 × 11 1 1 UPM1A101MEH
Sanyo Os-con\ POS-Cap SVP 10 68 0.025 2400 7.3 × 4.3 1 ≤ 5 10TPE68M
(SMT) 6.3 47 0.074 1110 5 × 6 1 ≤ 5 6SVP47M
SP 10 56 0.045 1710 6.3 × 5.0 1 ≤ 5 10SP56M
AVX Tantalum TPS (SMD) 10 47 0.10 1100 7.3L × 4.3W 1 ≤ 5 TPSD476M010R0100
10 47 0.060 > 412 × 4.1H 1 ≤ 5 TPSB476M010R0500
Kemet T520 (SMD) 10 68 0.060 >1200 7.3L × 5.7W 1 ≤ 5 T520V686M010ASE060
AO-CAP 6.3 47 0.028 >1100 × 4.0H 1 ≤ 3 A700V476M006AT
Vishay/Sprague 594D/595D 10 68 0.100 >1000 7.3L × 6.0W 1 ≤ 5 594D686X0010C2T
(SMD) 10 68 0.240 680 × 4.1H 1 ≤ 5 595D686X0010C2T
94SL 16 47 0.070 1550 8 × 5 1 ≤ 5 94SL476X0016EBP
TDK Ceramic X5R 6.3 22 0.002 >1400 1210 case ≥ 2
(3)
≤ 3 C3225X5R0J226KT/MT
Murata Ceramic X5R 6.3 22 0.002 >1000 3225 mm ≥ 2
(3)
≤ 3 GRM32ER61J223M
Kemet 6.3 22 0.002 >1000 ≥ 2
(3)
≤ 3 C1210C226K9PAC
TDK Ceramic X5R 6.3 47 0.002 >1400 1210 case ≥ 1 ≤ 3 C3225X5R0J476KT/MT
Murata Ceramic X5R 6.3 47 0.002 >1000 3225 mm ≥ 1 ≤ 3 GRM32ER60J476M/6.3
Kemet 6.3 47 0.002 >1000 ≥ 1 ≤ 3 C1210C476K9PAC
(1) A ceramic capacitor is required on both the input and the output. An electrolytic capacitor can be added to the output for improved
transient response.
(2) An optional through-hole capacitor available.
(3) A total capacitance of 44 μ F is an acceptable replacement for a single 47- μ F capacitor.
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