|
XR76121 Datasheet, PDF (13/18 Pages) Exar Corporation – PowerBloxTM 20A Synchronous Step-Down COT Regulators | |||
|
◁ |
VIN Ã [tON â (2.5 Ã 10-8)]
RON =
3.45 Ã 10-10
Applications InformVaOtUiTon (Continued)
OvercurrenttOPNro=teVcItNioxn1.(0O6CxPf x) Eff.
If the load current exceeds the programmed overcurrent
threshold IOCP for four consecutive switching cycles,
the regulator enters the hiccup mode of operation.
I(nhihccicucpuptimmeooduet)th. eFoMl1lOo.0wS6ViFOxnEUgf TTxtEhgfeaf.theâiscca[(u2rep.5tutÃimr1ne0e-od8)uoxtfVfaINfo]sro1ft1-s0tmarst
iTshaettreemgupltaetdoR.rOIwNf il=Ol rCePmapienrsinisht(si3c,.c4h5uipcÃcm1u0po-1d0t)eimuenotuiltlowaidll
repeat.
current
is reduced below the programmed IOCP. In order to program
overcurrent protection use the following equation:
(IOCP + (0.5 Ã âIL))
RLIM =
ILIM
+ 0.16kâ¦
RDS
Where:
â â RLIM is resistor value in k⦠for programming IOCP
â â IOCP is the overcurrent value to be programmed
â â ÎIL is thRe1 =peRa2kx-to-Vp0Oe.U6aTk iând1uctor current ripple
â â ILIM/RDS is the minimum value of the parameter
specified in the tabulated data
â â
â â
I0L.I1M6/Rkâ¦DSCaSc=Sc1o=4ut.nS5tSusAxfo/mr10â¦O0.6µCVAP
comparator
offset
The above equation is for worst-case analysis and
Ï sfoarfeagugairvdesnaCRgFaLFiInM=s,t2wpxrilel mxbaRet11uhxrei5ghOxefCLrCPt.hTanypitchaalt
value of IOCP,
predicted by
the above equation. Graph of calculated IOCP vs. RLIM is
compared to typical IOCP in Figures 23.
SIf hthoert-oCuitrpcuutitfvLPoClrt=oagteec2tdxiroÏonpxs(âS1bLCexPloC)wOU6T0% of its programmed
value (i.e., FB drops below 0.36V), the regulator will enter
hiccup mode. Hiccup mode will persist until short-circuit
is
of
resmofot-vsetadr.t.RTFhHFe=icSc2uCxpPÏ
c1ircuit becomes active at
mx foxdCeFFand short-circuit
the end
recovery
waveform is shown in Figure 16.
Over Temperature Protection (OTP)
OTP triggers at a nominal controller temperature of 138°C.
The gates of the switching FET and the synchronous FET
are turned off. When controller temperature cools down to
123°C, soft-start is initiated and regular operation resumes.
RON = VIN Ã [tON â (2.5 Ã 10-8)]XR76121
3.45 Ã 10-10
Overvoltage Protection (OVPVO)UT
TothnheeVvoOouUlttTpaugotef OtahVtePVreftSOugRNnNuOcS=lNatiot=opVnrIiN.nVdIOxeNtt1oVÃe.P0c[a6ttOsnixsNafOanxâcVE(oh2fPfvi..e5evtrÃehvdro1e0ltsb-a8h)yg]oecldocmovnpodaltiartiiongnge
set at 1.2 x VREF. When VS3N.4S5 Ãv1o0l-t1a0 ge exceeds the
OVP threshold, an internal overvoltage signal asserts after
1tTcuauhrpsneas(ctlyooitpwonirc-tsahuilde)n.etTliol hFwViEs-RSsTOOiNdNtVOSer=ePNmFv=sEoai1glTitV.nna0IsaNag6VlneOxxlodaUf1ndtVTx.ca0rOhEo6(ltUs3ofepfxT.o.4ssf5daoxâbiÃssfEfesc[f1(tlfeh2oh.0.rawe-5t1rs0)Ãgh1eiPg1.G10ht-5-h8Os)eixOxdVeDoIVNuF]RltoEpEwTuF..t,
Then low-side FET turns off to prevent complete discharge
of VOUT. The high-side and low-side FETs remain latched
off until VIN or EN is recycled. In order to use this feature,
connect VSNS
the application
ctoRirLcVIMuOit=U. TUw(sIOeitCh1tPh.0a+e6VIr(LsOx0eIaUM.fs5mTxisÃEetofâfr.rIeLds)â)iivs[itd(+o2e.r05r.d1Ãai6vs1kiâ¦d0s-eh8)roxwvVanINlu]ine
that was used for pRroOgNra=mmingRVDOSU(T3..45 Ã 10-10)
Programming the Output Voltage
Use a voltage divider as shown in Figure 1 to program the
output voltage VOUT.
R1R=LIRM2=x
(IVOOCUPT+
0.6
(0.5
IâLI1M
RDS
Ã
âIL))
+ 0.16kâ¦
The recommended value for R2 is 2kâ¦.
Programming thCeSSS o=fttS-SStxart100.6µVA
Place a capacitor CSS between the SS and AGND pins to
Ï poforflolotgSwrSai,nmgcatehlqceuuslaaottifeot-nsCt:thFRaF1ert==.reIR2nq2xuoxirrdexedVRr0O11.tcU6oxaT5pparâxocf1gLitCraanmcea
soft-start time
CSS from the
fLCCS=S
=2tSxSÏx
x
110µA
â0L.6xVCOUT
PXoFuirRget7up-B6rue1ti.a21sT15y.ShptaiacsratltuhppeRreFc-FCabF=piFaas=2bixs2litÏtaxyrxÏ1ttufoxxpRsC1t1wFaFxart5vuepxfofLirnCmtos
a pre-charged
are shown in
MThaeximstuemadAy-lslotawteablvfeLoCVlt=aogltea2gxreiÏpRpxilpeâ1pLlaextCaOtfUeFTeBdbPainck pin FB
(VFB,RIPPLE) must not exceed 50mV in order for the regulator
to function correctly. If VFB,RIPPLE is larger than 50mV then
Ï kCeOeUpTtahnedV/oFrBL,RsIPhPoLuElRdbFFbeel=oiwn2c5xre0amxs1Vfe.xdCaFsF necessary in order to
REV1A
13/18
|
▷ |