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Higher values, lower cost ceramic capacitors are now becoming available in smaller case sizes. Their high ripple current, high
voltage rating and low ESR make them ideal for switching regulator applications. However, care must be taken when these
capacitors are used at input and output. When a ceramic capacitor is used at the input and the power is supplied by a wall
adapter through long wires, a load step at the output can induce ringing at the input, VIN. At best, this ringing can couple to
the output and be mistaken as loop instability. At worst, a sudden inrush of current through the long wires can potentially
cause a voltage spike at VIN large enough to damage the part.
Output Rectifier Diode
The output rectifier diode supplies the current to the inductor when the high‐side switch is off. To reduce losses due to the
diode forward voltage and recovery times, use a Schottky diode.
Choose a diode whose maximum reverse voltage rating is greater than the maximum input voltage, and whose current rating
is greater than the maximum load current.
Choose a rectifier who’s maximum reverse voltage rating is greater than the maximum input voltage, and who’s current
rating is greater than the maximum load current.
Checking Transient Response
The regulator loop response can be checked by looking at the load transient response. Switching regulators take several
cycles to respond to a step in load current. When a load step occurs, VOUT immediately shifts by an amount equal to ΔILOAD (ESR)
also begins to charge or discharge COUT generating a feedback error signal for the regulator to return VOUT to its steady‐state
value. During this recovery time, VOUT can be monitored for overshoot or ringing that would indicate a stability problem.
Table 1. Suggested Inductors for Typical Application Circuit
Component Supplier
COILTRONICS
MAGLAYERS
TOKO
Series
DR73‐4R7
MSCH‐5750C‐4R67M
A916CY‐4R7M
Dimensions (mm)
6.0 x 7.6 x 3.5
5.7 x 5.0 x 4.7
6.2 x 6.2 x 3.5
Table 2. Suggested Capacitors for CIN and COUT
Component Supplier
Part No.
Capacitance (uF)
Case Size
1206
1206
1200
1200
MURATA
TDK
MURATA
TDK
GRM31CR61E106K
C3225X5R1E106K
GRM32ER71C226M
C3225X5R1C226M
10
10
22
22
Table 3. Schottky Rectifier Selection Guide
2A Load Current
VIN (Max.)
Part No.
Vendor
B320
SK33
SS32
Diodes, Inc. (www.diodes.com)
Pan Jit International (www.panjit.com.tw)
General Semiconductor (www.gensemi.com)
Diodes, Inc. (www.diodes.com)
20V
26V
B330
B340L
SK33
MBRD330
Diodes, Inc. (www.diodes.com)
Diodes, Inc. (www.diodes.com)
On Semiconductor (www.onsemi.com)
Fairchild Semiconductor (www.fairchildsemi.com)
General Semiconductor (www.gensemi.com)
SS33
DS‐RS6508A‐05 February, 2010
www.Orister.com
ORISTER [ ORISTER CORPORATION ]
