Datasheet

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Designing for Load Transients
PTN78000A
SLTS246B–APRIL 2005 – REVISED JANUARY 2006
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
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 t ransient 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)
FC( Radial) 35 100 0.117 550 8 × 11,5 ≥1 1 EEUFC1H181
FC (SMD) 35 100 0.015 670 10 × 10,2 ≥1
(1)
1 EEVFC1V101P
PXA16VC180MF60 (V
I
,|V
O
|<
United Chemi-Con PXA (SMD) 16 180 0.016 4360 8 × 12 ≥1
(1)
≤ 1
14 V)
PS 25 100 0.020 4300 8 × 10,5 ≥1
(1)
≤ 1 10FS100M (V
I
,|V
O
|<22V)
LXZ 50 100 0.220 485 8 × 12,5 ≥1 1 LXZ50VB101M8X12LL
MVY50VC101M10X10TP
MVY(SMD) 50 100 0.300 500 10 × 10 ≥11
(|V
O
| ≤ 5V)
Nichicon UWG (SMD) 50 100 0.300 500 10 × 10 ≥1 1 UWG1H101MNR1GS
F550 (Tantalum) 10 100 0.055 2000 7.7 × 4,3 N/R
(1)
≤ 3
(2)
F551A107MN (|V
O
| ≤ 5V)
HD 50 120 0.072 979 10 × 12,5 ≥1 1 UHD1H101MPR
Sanyo Os-Con SVP (SMD) 20 100 0.024 2500 8 × 12 ≥1
(1)
≤ 1 20SVP100M (V
I
,|V
O
| ≤ 16 V)
SP 16 100 0.032 2890 10 × 5 ≥ 1
(1)
≤ 1 16SP100M (V
I
,|V
O
| ≤ 14 V)
7,3 L × 4,3 TPSV107M020R0085
20 100 0.085 1543 N/R
(3)
≤ 2
W × 4,1 H (|V
O
| ≤ 10 V)
AVX Tantalum TPS (SMD)
TPSE107M020R0200
20 100 0.200 > 817 N/R
(3)
≤ 2
(|V
O
| ≤ 10 V)
GRM32ER61C476M
Murata X5R Ceramic 16 47 0.002 >1000 3225 1
(1)
≤ 2
(|V
o
|~V
I
≤ 13.5 V)
GRM422X5R476M6.3
Murata X5R Ceramic 6.3 47 0.002 >1000 3225 N/R
(1)
≤ 2
(|V
O
| ≤ 5.5 V)
C3225X7R1E225KT/MT
TDK X7R Ceramic 25 2.2 0.002 >1000 SMD ≥ 4
(4)
1
(|V
O
| ≤ 20 V)
GRM32RR71E225K
Murata X7R Ceramic 25 2.2 0.002 >1000 3225 ≥ 4
(4)
1
(|V
O
| ≤ 20 V)
C1210C225K3RAC
Kemet X7R Ceramic 25 2.2 0.002 >1000 3225 ≥ 4
(4)
1
(|V
O
| ≤ 20 V)
12103C225KAT2A
AVX X7R Ceramic 25 2.2 0.002 >1000 3225 ≥ 4
(4)
1
(|V
O
| ≤ 20 V)
Murata X7R Ceramic 50 4.7 0.002 >1000 3225 ≥ 2 1 GRM32ER71H475KA88L
TDK X7R Ceramic 50 2.2 0.002 >1000 ≥ 4 1 C3225X7R1H225KT
Murata Radial Through-hole 50 2.2 0.004 >1000 ≥ 4 1 RPER71H2R2KK6F03
(1) 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 the next higher voltage rating.
(2) 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.
(3) Not recommended (N/R). The voltage rating does not meet the minimum operating limits in most applications.
(4) The maximum rating of the ceramic capacitor limits the regulator's operating input voltage to 20 V. Select a alternative ceramic
component to operate at a higher input voltage.
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