RS6507 Datasheet, PDF (7/10 Pages) Orister Corporation – 3A, 20V, 400KHz DC/DC Asynchronous Step‐Down Converter

Page No. : 7/10
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, V_IN. 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 V_IN 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, V_OUT immediately shifts by an amount equal to ΔI_{LOAD (ESR)}
also begins to charge or discharge C_OUT generating a feedback error signal for the regulator to return V_OUT to its steady‐state
value. During this recovery time, V_OUT can be monitored for overshoot or ringing that would indicate a stability problem.
Table 1. Suggested Inductors for Typical Application Circuit
Component Supplier
MAGLAYERS
SUMIDA
TOKO
Series
MSCDRI‐124‐150M
CDRH104R
D104C
Dimensions (mm)
12 x 12 x 5.0
10.1 x 10 x 3.0
10 x 10 x 4.3
Table 2. Suggested Capacitors for C_IN and C_OUT
Component Supplier
Part No.
MURATA
GRM31CR61E106K
TDK
C3225X5R1E106K
MURATA
GRM32ER71C226M
TDK
C3225X5R1C226M
Capacitance (uF)
10
10
22
22
Case Size
1206
1206
1210
1210
Table 3. Schottky Rectifier Selection Guide
V_IN (Max.)
20V
26V
Part No.
B320
SK33
SS32
B330
B340L
SK33
MBRD330
SS33
3A Load Current
Vendor
Diodes, Inc. (www.diodes.com)
Pan Jit International (www.panjit.com.tw)
General Semiconductor (www.gensemi.com)
Diodes, Inc. (www.diodes.com)
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)
DS‐RS6507‐02 February, 2010
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