XR79206EL-F Datasheet, PDF (12/20 Pages) Exar Corporation – 40V, 6A Synchronous Step-Down COT Power Module

Applications Information (Continued)
Programming the On-Time
The on-time t_ON is programmed via resistor R_ON according
to following equation:
VIN × [tON – (2.5 × 10^-8)]
RON =
2.95 x 10^-10
A graph of t_ON vs. R_ON, using the above equation,
is compared to typical test data in Figure 5. The graph
shows that
within 3%.
ca_ROlc_tNu_Ol_N=at₌e_Vd_INVI×Nda_[×tt_Oa_1NV.0O–m_6UxT(a_2ft_.c_5×h_×Ee_fs_1f.0-8t₎y_]pical
test
data
The t_ON corresponding to^2.9a⁵ p^x a¹r⁰t^-i¹c⁰ular set of operating
conditions can be calculated based on empirical data from:
Where:
VOUT
1.06 x f × Eff.
V^–_O[U(2T.5 ^{× 10-8) × VIN]}
RON =
tON
=
VINVI×N([2×t.O91N5.0×–⁶
1x(20f.^-₅¹Ã—⁰_{×)Ef1f.0-8)]}
RON =
2.95 x 10^-10
■■
fnomisina_Rtl_Lh_IIMe_OU=T1d_.0e^(6IOs_Vxi^COr^Pe_{Uf ×T}d⁺
(0_s.5_w×_itc∆_hIL_in))_g
IELfIfM. ^{– [(2.5 ×}
frequency
+100^-8.)1×6kVΩIN]
at
■■ Enoffm. iis^R_n^O_at^N_lhIe⁼_OUc_To_tOn_Nve₌rte_VIr_NRe_(×2Df_.f^S91ic_5V.0i_Oe_×6Un_xT1c_0fy-_×10c_)Eo_fr_f.responding to
Substituting for t_ON in the first equation we get:
RLRIMFB=11.=0(6IROVFxOCBPUf2×T+×ERI(L0fDIfM..S5V0_–^{O×.6U[∆}V(T2I.L5^{–))×1}+_100-8.)1×6kVΩIN]
RON =
(2.95 × 10^-10)
VN_I^o_N^w, VR_OOUNT,cfaann^RbdFeBE^1cfaf=.l(C^cuIROS^usFCSliBan_P=2^tg+^et×td^S(h0Sei.ⁿ5×Va^0t×O^e.b^6Uro1∆^V0mT0v^.I6Lµes^V)–A)eo¹qf uoapteiorant.inAgt
conditions
V_IN = 24V,
f = 500kHz,RLI_OIMU=_T = 6A an_ILd_IMusing the+ e0f.1fi6ckieΩncy numbers
from Figure 22 we get the _Rfo_Dl_Slowing R_ON:
V_OUT (V)
12.0
π ^CF_E^FC_f⁼_{fS. S(}2_%=×)
1
tSS××RFB1010f_.6µx(_Vk^A5H^xZ)^fLC
RFB1 = R9_F4_B2 ×
VOUT
0.6V
7–010
R_ON (kΩ)
56.3
5.0
90
500
33.5
3.3
1.8
ππ ^fLCCFF=C=_{88S07S22=×xtSS×x×}^√R1FL1B10x10.C6µx_55VOA005U₀₀^Tx fLC
22.2
12.4
fLCR=FF
CFF =
=
2
2
x
π^x
2×π
π
x
×
11
x
√
f x CFF
L1x COUT
RFB1 x 5 x
fLC
XR79206
VIN × [tON – (2.5 × 10^-8)]
RON =
2.95 x 10^-10
Overcurrent Protection (OCP)
IttfhhretehsehmolooldaddulIe_Ocu_Cr_{PerenntfteOot rNrse=}xfocteu_VheIreNd_×scho₁tin_V.hc_{0Osec6eUuxTcppuf}rot_×ivgmEerfao_f.mdsemwietocdhf _{ionvogepreccruyarctriloeenns.t,}
In hiccup mode the MOSFET gates are turned off for 110ms
(hiccup timeout). Following the hiccup timeout a soft-start
is attempted. If
The module will
rOe₁^Cm_.0^P₆a^Vi_xOnp^Ufei_×Tnrs_Ehi_f^si_fc_.^{tsc–,uph[(2imc.5cou×}dpe^10tui-m8n^{) et×}ilo^VluoIN^ta]dwicllurrerepnetaits.
orevdeurccuerdrebne^Rt^OlopNwro=ttehcetiopnrougsraem⁽t²hm^.e^9e5fdo^×llI¹o^O0w^C-1i^P0n^{).gIneqourdaetior} nto: ^program
(IOCP + (0.5 × ∆IL))
RLIM =
ILIM
+ 0.16kΩ
RDS
Where:
■■
■■
R_LIM
I_OCP
is
is
trhe^Res^FiBsot1voe^=rrvcRauFlBrur²een^×int vka^VΩ0Ol^.u^{6UfeVoTrtop–rbo1}egrparmogmrainmgmI^Oe^Cd^P
■■ ΔI_L is the peak-to-peak inductor current ripple
■■ I_LIM/R_DS = 2.4µA/mΩ is the minimum value of the
■■
parameter specified in the
0.16kΩ account^Cs^SSfo⁼r O^tSC^S P^×
ta₁b₀u_µAlated data
co⁰m^.6p^Varator offset
The above equation is for worst-case analysis and
safeguards against premature OCP. Typical value of I_OCP,
π ^{ftcohoremaapbagoreivvdeenteoqRtuyLapItiM}_ci^Co,aFnlFw.I=_O^iGl_C^l 2^r_P^ab×^peinhFh×^oiiggfR^huc_F^er1Baer₁^lc9x^tuh.l5^aax^tnef^d_L^t_C^{hIaOtCPprvesd.icRteLdIM}
by
is
Short-Circuit Protection (SCP)
If the output voltage drops below 60% of its programmed
vuaanftletuilresP,htGhoOert-OMcDiorcdauusiltes_{fLiewsCrti=rlsleehmnig2otehvx}r.e_πhdi_x.c√cS₁u_LCpxPmCOcoiUdrc_Teu.iHt ibceccuopmweilsl
persist
active
Over Temperature Protection (OTP)
OTP triggers at a nominal controller temperature of 150°C.
The gate
turned off.
oWf shwenitchc_Rio_Fn_{Fngt=roF2llEex}Tr_πtxae¹n_fmxdp_CeFsr_Fyantucrherocnoooulss
FET are
down to
135°C, soft-start is initiated and operation resumes.
RFF
fLC =
=
2
2
x
x
π
π
x
1
x1f x CFF
√ L x COUT
REV1B
12/19