XR76121ELMTR-F Datasheet, PDF (14/19 Pages) Exar Corporation – PowerBlox 20A Synchronous Step-Down COT Regulators

(IOCP + (0R.5DS× ∆IL))
RLIM =
tON =
RILDIVMSOUT
+ 0.16kΩ
VIN x 1.06 x f x Eff.
XR76121
Applications_R1In₌f_Ro₂r_xma^V0t^Oi_.U6o^Tn_–(C₁ ontinued)
F_pCThe_haae_elcsd_fuee-_lF_aeo_tdmer_-fw_aCora_rFgwr_FiRnd_af1rrC_Cdo=wRSma_chOSRp_ae2Nt=a_phnxc_=aetSi_ct_Sfuio_otVsoxr_10lOlir.o.n(_U06CC_{wgT61V0FFi0Oxn.FF6–cµUgf})_{ViAeTsx1erEau(q3fmsfu..4eai5cdt–i×oto[on1(2u:s0.te-51p0t)×utht1e0c-n8a)epxcaVecIsNits]oarrsy.}
CSS =
CFF
tSS
=2
x
10µA
0.61V
x π x R1
(IOCP +
x(05.5x×fL_{∆C IL))}
Where f_LC, th^Ce^FRFL=o^IMu₂t⁼p_xu_πt
calculated from: _{fLC =}
2
x
x
1
f_Ril₁te_xr
15RIL^{dDIxMoSfLuCble-pole+}
π x √ L x COUT
0_f._r1_e6_qk_uΩ_ency
is
fLC =
1
2 x π x √ L x COUT
YdAsheootlueouralmddmibnuseestetptpheuerstfeeo_Resfr_FRfmtRFe^Fm_1c=e^F_(at=adi⁼_nv2n_{Raedu2x2n/fcoπ}a_{xdxarcπxpi1}tfaua_fxVn^1xrc_0Ofeelio_.CxtU6rca_{Fo’TCesnFpFscF–seDtar1}CacryonrsCrdiee_Fesn_FrpatcotairnnendgsibpneocgnuatsrodvejVeus_{OtsetUestTtdo).}
in
In
order to get a
applications
wc^{CrhiSteiScrae=lltyoSS}udta^xpmutp^10e0v^.6dµo^VAlttraagnesierinptplloeadisrelesspsontshea.n
about 3mV, such as when a large number of ceramic
π ^COUT
from
aacrreospsartahlelel^{CeinFddF,u=ict} t₂^iosr_x.neT_x^che_Res₁₁^s_xcai₅rrcy_xut_fi_L^ot_Caunsde
ripple injection
corresponding
calculations are explained in the Exar design note.
π ^Feed-Forward
R_FF is required
C_FF, functions
s^RwimehfLseiClⁱan^s=r^tCoto^FrF2(a^RixsFh^{Fuig)xshe√1dL}f.re^xRqCFuO^FeU^,nT^{incycopnojluenacntiodnawddiths}
gain margin to the frequency response. Calculate R_FF from:
Thermal Design
Proper thermal design is critical in controlling device
temperatures and in achieving robust designs. There are
a number of factors that affect the thermal performance.
One key factor is the temperature rise of the devices in
the package, which is a function of the thermal resistances
of the devices inside the package and the power
being dissipated.
The thermal resistance of the XR76121 is specified in
the Operating Ratings section of this datasheet. The θ_JA
thermal resistance specification is based on the XR76121
evaluation board operating without forced airflow. Since the
actual board design in the final application will be different,
the thermal resistances in the final design may be different
from those specified.
The package thermal derating curves for the XR76121 are
shown in Figures 5 and 6. These correspond to input voltage
of 12V and 5V, respectively. The package thermal derating
curves for the XR76121 are shown in Figures 9 and 10.
RFF
=
2
xπ
1
xf
x
CFF
Where f is the switching frequency.
If R_FF is greater than 0.1 x R1, then instead of C_FF/R_FF, use
ripple injection circuit as described in Exar design note.
REV1A
14/18