MC44608_06 Datasheet, PDF (10/15 Pages) ON Semiconductor – Few External Components Reliable and Flexible SMPS Controller

MC44608
EQUATION 7
dBM +
ȧȡȢ ^{1 )}
IccS) IG
Istup
1
ǒ ǒ kS_ńStup ) kS_ńL
ǓǓ ^Istup
IccL) Ipin3
ȧȣȤ
EQUATION 8
dBM +
È¡
ǒ Ǔ _ȧȧȥ 1 )
k1
)
IG
Istup
È¢
1
È¡
ȧȧȧ_{kSńStup ) (kSńL}
È¢
ȣȣ
ǒ Ǔ ^k2)
1
Ipin3
Istup
)^{ȧȧȧȧȧȦ}
ȤȤ
where: k1 = I_ccs/I_stup
k2 = I_ccL/I_stup
k_S/Stup = (V_stup−UVLO2)/(V_stup−UVLO1)
k_S/L = (UVLO1−UVLO2)/(V_stup−UVLO1)
PULSED MODE CURRENT SENSE CLAMPING LEVEL
Equations 9, 10, 11 and 12 allow the calculation of the Rcs value for the desired maximum current peak value during the
SMPS standby mode.
EQUATION 9
Ipkstby +
Vcs–th * (Rcs
RS
Ics)
where: V_cs−th is the CS comparator threshold
I_cs is the CS internal current source
R_S is the sensing resistor
R_cs is the resistor connected between pin 2 and R_S
EQUATION 10
Ipkstby + Vcs–th
ǒ Ǔ 1 * Rcs
Ics
Vcs–th
RS
EQUATION 11
Ipkstby + Vcs–th
1 * (Rcs Ycs–stby )
RS
where: Y_cs−stby = I_cs/V_cs−th
Taking into account the circuit propagation delay (dt_cs) and the Power Switch reaction time (dt_ps):
EQUATION 12
ƪ Ipkstby + Vcs–th
ƫ 1 * (Rcs Ycs–stby )
RS
) ^Vin
(dtcs ) dtps)
Lp
http://onsemi.com
10