ER3125QI Datasheet, PDF (25/30 Pages) Altera Corporation – MOSFET for Synchronous Buck or Boost Buck Converter

Page 25
Equation 28 shows that the system is a single order system. Therefore, a simple type II compensator can be easily used
to stabilize the system. A type III compensator is needed to expand the bandwidth for current mode control in some
cases.
R2
C1
R3
C3
VCOMP
VO
VREF
R1
RBIAS
FIGURE 31. TYPE III COMPENSATOR
A compensator with 2 zeros and 1 pole is recommended for this part, as shown in Figure 31. Its transfer function is
expressed as Equation 29:
A_v(S)=
v-ˆ--_{c---o---m-----p- =}
vˆ _O
-S---R----1₁---C----₁-
⎝⎛_---1-----⁺_{------ω----⎝⎛--c-S---1-z}^-----_1--+--⎠⎞_---⎝⎛_{-ω-----1S-c-----p--}⁺_{--⎠⎞---ω}^-------_c-S----z^------₂^---⎠⎞_--
(EQ. 29)
where,
ω_cz1 = _R----2--1--C---₁- , ω_cz2 = -₍--R----₁----₊---1--R----₃---₎--C----₃-, ω_cp= -R---₃--1-C----₃-
Compensator design goal:
Loop bandwidth f_c:
⎛
⎝
14--
to
1--1--0-^⎠⎞
f_s
w
Gain margin: >10dB
Phase margin: 45°
May 2014 Altera Corporation
10040
Enpirion Power Datasheet ER3125QI 2.5A Regulator with Integrated High-Side MOSFET for
Synchronous Buck or Boost Buck Converter
May 28, 2014
Rev A