XRP7659 Datasheet, PDF (7/10 Pages) Exar Corporation – 1.5A 18V1.4MHz Non Synchronous Step-Down Regulator

XRP7 65 9
1 .5 A 1 8 V 1 .4 MHz Non Sy n ch r on ou s St ep - Dow n Reg u lat or
VOUT
1.8 V
2.5 V
3.3 V
5 .0V
5NŸ
100
39
43
47
Table 1: Resistor Selection
5NŸ
82
18.7
14
9.09
SELECTING THE OUTPUT CAPACITOR
The output capacitor C _OUT filters the inductor
current ripple , providing DC to the load. C _OUT
also limits the V _OUT transients arising from a
sudden current load step . A 22 µF ceramic
capacitor is sufficient for most applications.
SELECTING THE INDUCTO R
PCB LAYOUT GUIDELINE S
Select the inductor for inductance L , saturation
current I _sat and DC current I _DC. I _sat and I _DC
should be larger than 2.4A
and 2.2A
Following guidelines will
help safeguard
against EMI related problems .
respectively. This will allow the inductor to
1. Minimize the loop area among C_IN , high -
ZLWKVWDQGDQDFFLGHQWDORYHUOsidReDMGOSFXETQaWnLd DO1. TWoKacHhiev,e &th¶is V, C_IN
OCP get activated . Calculate the inductance
and D1 have to be placed as closed to IC
from:
pins IN and SW as possible. Also the
  _L V_OUT uV_IN V_OUT
V_IN u'I _L uf _s
Æ©,_L is inductor current ripple, nominally set at
30% of I _OUT.
ground return of C _IN and D1 should be
close. Use short and wide traces for
connecting these components.
2. Minimize the loop area among D1, L1 and
C_OUT. Use short and wide traces f or
connecting these components.
3. From the above it follows that the ground
SELECTING THE INPUT C APACITOR
returns of C _IN , D1 and C _OUT should be as
The input capacitor C_IN supplie s the pulsating
input current resulting from fast switching of
the high - side MOSFET . Ceramic capacitors are
close as possible.
4. Route the sensitive FB trace away from
noisy SW.
recommended because they have low ESR / ESL
and can therefore meet the high di/dt
require ment. A 10 µF capacitor is sufficient for
most application s.
© 2012 Exar Corporation
7/ 10
Rev. 1. 2.0