AN901 Datasheet, PDF (14/25 Pages) STMicroelectronics – Electromagnetic compatibility

AN901
gm_fb = _g----_m-----_e---_a---_---_R-^g---^m5-----_-^e_---^a_R-----₆----_---+-----₁--
Equation 36.
» ^{gmea is}
R_O,gmfb
the error amplifier transconductance.
R_INT. If R5 and R6 are chosen such
For
that
the Si884xx/Si886xx, gm_ea
their parallel resistance is
s^u1ffxic1i0e^-n³t,lyRla^INr^Tge^r1t0h0ank^Ω1,⁄
and
gm_ea,
Equation 36 simplifies to:
gm_p is given by:
gm_fb  _---_R-----₅----¹_--_--_R-----₆----_
Equation 37.
gm_p  ₁----₀-----_--ⁿ--_R-----₁----₂-
« ^{Equation 38.}
Typically, R_LOAD (R5 + R6) and the DC gain in P-mode simplifies to:
A_{DC P}  – ¹----⁰----^---1---0_R---³--₅--^---_--ⁿ---_R--^--₁--^R--₂---^L---^O----^A---^D--
Equation 39.
Notice that the DC gain of P mode is proportional to R_LOAD and inversely proportional to R5. At heavy loads (small
R_LOAD), a very large R5 could significantly increase the output voltage error as the DC gain reduces. Conversely, a
very small R5 increases power consumption and gm_fb variability due to higher dependency on gm_ea, which can
significantly vary more than 1/(R5||R6) over temperature or from part to part. The total duration of this mode is
approximately 7 ms.
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