Datasheet

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Designing for Load Transients
PTH08000W
SLTS248B – JUNE 2005 – REVISED FEBRUARY 2008
Table 3. Recommended Input/Output Capacitors
(1)
CAPACITOR CHARACTERISTICS QUANTITY
85 ° C
CAPACITOR VENDOR/
EQUIVALENT
VENDOR
WORKING MAXIMUM PHYSICAL
COMPONENT
VALUE SERIES INPUT OUTPUT
NUMBER
VOLTAGE RIPPLE SIZE
SERIES
(µF) RESISTANCE BUS
(2)
BUS
(V) CURRENT (mm)
(ESR) ( Ω )
(I
RMS
) (mA)
Panasonic WA (SMT) 20 150 0.026 3700 10 × 10,2 1 ≤ 2 EEFWA1D151P
FC (SMT) 25 220 0.150 670 10 × 10,2 1 1 EEVFC1E221P
Panasonic SL 6.3 47 0.018 2500 7,3 × 4,3 N/R
(3)
≤ 3 EEFCD0J470R
SP-cap(SMT) 6.3 120 0.007 3500 7,3 × 4,3 N/R
(3)
≤ 1 EEFSD0J121R
United Chemi-con
PXA (SMT) 16 150 0.026 3400 10 × 7,7 1 ≤ 2 PXA16VC151MJ80TP
PS 25 100 0.020 4300 10 × 12,5 1 ≤ 2 25PS100MJ12
LXZ 35 220 0.180 760 10 × 12,5 1 1 LXZ35VB221M10X12LL
MVY (SMT) 35 333 0.150 670 10 × 10 1 1 MVY35VC331MJ10TP
Nichicon UWG (SMT) 35 100 0.150 670 10 × 10 1 1 UWG1V101MNR1GS
F559(Tantalum) 10 100 0.055 2000 7,7 × 4,3 N/R
(4)
≤ 3 F551A107MN
HD 25 220 0.072 760 8 × 11,5 1 1 UHD1E221MPR
Sanyo Os-con\ POS-Cap 10 68 0.025 2400 7,3 × 4,3 N/R
(4)
≤ 2 10TPE68M
SVP (SMT) 20 150 0.020 4320 10 × 12,7 1 ≤ 1 20SVP150M
SP 20 120 0.024 3110 8 × 10,5 1 ≤ 2 20SP120M
AVX Tantalum TPS (SMD) 35 47 0.100 1430 7,3 × 4,3 × 4,1 2 ≤ 4 TPSV476M035R0100
25 47 0.100 1150 7,3 × 4,3 × 4,1 2 ≤ 4 TPSE476M025R0100 (V
I
<13V)
Kemet T520 (SMD) 10 100 0.025 > 2000 7,3 × 5,7 × 4 N/R
(4)
≤ 1 T520V107M010ASE025
AO-CAP 6.3 100 0.018 > 2900 7,3 × 5,7 × 4 N/R
(4)
≤ 1 A700V107M006AT
Vishay/Sprague 35 47 0.280 > 1000 7,3 × 6 × 4,1 2 ≤ 5 595D476X0035R2T
594D/SVP(SMD) 20 100 0.025 3200 8 × 12 1 ≤ 2 94SVP107X0020E12
94SS 20 150 0.030 3200 10 × 10,5 1 ≤ 2 94SS157X0020FBP
Murata Ceramic X5R 16 47 0.002 > 1400 3225 1
(5)
≤ 3 GRM32ER61C476M
TDK ceramic X5R 6.3 47 0.002 > 1400 3225 N/R
(4)
≤ 3 C3225X5R0J476MT (V
O
<5.5V)
Kemet Ceramic X5R 6.3 47 0.002 > 1400 3225 N/R
(4)
≤ 3 C1210C476K9PAC (V
O
<5.5V)
TDK Ceramic X7R 25 10 0.002 > 1400 3225 1
(5)
≤ 4 C3225X7R1E106K
Murata Ceramic X5R 25 10 0.002 > 1400 1
(5)
≤ 4 GRM32DR61E106KA12
Kemet 16 10 0.002 > 1400 1
(5)
≤ 4 C1210C106M4PAC
TDK Ceramic X7R 25 2.2 0.002 > 1400 3225 1 1 C3225X7R1E225KT/MT
Murata Ceramic X7R 25 2.2 0.002 > 1400 1 1 GRM32RR71J225KC01L
Kemet 25 2.2 0.002 > 1400 1 1 C1210C225K3RAC
(1) Check with capacitor manufacturers for availability and lead-free status.
(2) The voltage rating of the input capacitor must be selected for the desired operating input voltage range of the regulator. To operate the
regulator at a higher input voltage, select a capacitor with a higher voltage rating.
(3) Not Recommended (N/R). The voltage rating of this capacitor does not meet the minimum operating limit in most applications.
(4) Not Recommended (N/R). The voltage rating of this capacitor does not meet the minimum operating limit in most applications.
(5) Ceramic capacitors can be used to complement electrolytic types at the input bus by reducing high-frequency ripple current.
The transient response of the dc/dc converter has been characterized using a load transient with a di/dt of 1A/µs.
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.
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