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Designing for Load Transients
PTN04050A
SLTS250 – SEPTEMBER 2005
The transient response of the dc/dc converter has been characterized using a load transient with a di/dt of
1 A/µs. The typical voltage deviation for this load transient is given in the data sheet specification table using the
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 of
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
(µF) RESISTANCE BUS BUS
(V) CURRENT (mm)
(ESR) ( Ω )
(I
rms
) (mA)
Panasonic FC( Radial) 25 180 0.117 555 8 X 11 1 1 EEUFC1E181
Panasonic FC (SMD) 25 100 0.30 450 8 X 10,2 1 1 EEVFC1E101P
PXA16VC151MJ80TP (V
O
≤ 13
United Chemi-Con PXA (SMD) 16 150 0.026 3430 10 X 7,7 1 1
V)
PS 25 100 0.020 4320 10 X 12,5 1 1 25PS100MJ12
LXZ 25 100 0.250 290 6,3 X 11,5 1 1 LXZ25VB101M6X11LL
MVY(SMD) 35 100 0.300 450 8 X 10 1 1 MVY35VC101MH10TP
Nichicon UWG (SMD) 50 100 0.300 500 10 X 10 1 1 UWG1H101MNR1GS
F559 (Tantalum) 10 100 0.055 2000 7,7 X 4,3 1 1
(1)
F551A107MN (V
O
≤ 5 V)
HD 25 100 0.130 405 6,3 X 11 1 1 UHD1E101MER
Sanyo Os-Con SVP (SMD) 20 100 0.024 2500 8 X 12 1 1 20SVP100M
16SP100M
SP 16 100 0.032 2890 10 X 5 1 1
(1)
(V
O
≤ 14 V)
7,3L X 4,3W TPSV107M020R0085
20 100 0.085 1543 1 ≤ 1
(1)
X 4,1H (V
O
≤ 10 V)
AVX Tantalum TPS (SMD)
TPSE107M020R0200
20 100 0.200 > 817 1 ≤ 1
(1)
(V
O
≤ 10 V)
GRM32ER60J107M
Murata X5R Ceramic 6.3 100 0.002 >1000 3225 1 ≤ 1
(1)
(V
O
≤ 5.5 V)
C3225X5R0J107MT
TDK X5R Ceramic 6.3 100 0.002 >1000 3225 1 ≤ 1
(1)
(V
O
≤ 5.5 V)
GRM32ER61C476M
Murata X5R Ceramic 16 47 0.002 >1000 3225 2 ≤ 2
(1)
(V
o
≤ 13.5 V)
C1210C476K9PAC
Kemet X5R Ceramic 6.3 47 0.002 >1000 3225 2 ≤ 2
(1)
(V
O
≤ 5.5 V)
C3225X5R0J476MT
TDK X5R Ceramic 6.3 47 0.002 >1000 3225 2 ≤ 2
(1)
(V
O
≤ 5.5 V)
GRM422X5R476M6.3
Murata X5R Ceramic 6.3 47 0.002 >1000 3225 2 ≤ 2
(1)
(V
O
≤ 5.5 V)
C3225X5R1E2265KT/MT
TDK X5R Ceramic 16 22 0.002 >1000 3225 5 ≤ 5
(1)
(V
O
≤ 14 V)
Murata X7R Ceramic 25 22 0.002 >1000 3225 5 ≤ 5 GRM32ER61C226K
C1210C226K3PAC
Kemet X7R Ceramic 16 22 0.002 >1000 3225 5 ≤ 5
(1)
(V
O
≤ 14 V)
(1) The maximum voltage rating of the capacitor must be selected for the desired set-point voltage (V
O
). To operate at a higher output
voltage, select a capacitor with a higher voltage rating.
10
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