PM6675 Datasheet, PDF (20/47 Pages) STMicroelectronics – Very fast load transient response using constant on-time control loop

Device description
PM6675
Figure 8. "Virtual-ESR" network
T NODE
VOLTAGE
∆V1
COMP PIN
VOLTAGE
VREF
∆V2
t
t
COMP
+ ^VREF
I=gm(V1-Vr)
RINT CINT
-
PWM
Comparator
CFILT
gm
T
+ _RFb1
R1
Vr
V1
R
C
VSNS
RFb2
OUTPUT
VOLTAGE
ESR
∆V
COUT
t(s) ^t
duc _{The ripple on the COMP pin is the sum of the output voltage ripple and the triangular ripple}
ro generated by the Virtual-ESR Network. In fact the Virtual-ESR Network behaves like a
P another equivalent series resistor R_VESR.
te A good trade-off is to design the network in order to achieve an R_VESR given by:
ole Equation 10
- ^{Obs RVESR}
=
V_RIPPLE
∆I_L
− ESR
t(s) where ∆I_L is the inductor current ripple and V_RIPPLE is the total ripple at the T node, chosen
c _{greater than approximately 20mV.}
du _{The new closed-loop gain depends on CINT. In order to ensure stability it must be verified}
ro that:
P _{Equation 11}
Obsolete^where:
C_INT
>
g_m
2π ⋅ f_Z
⋅
Vr
Vout
Equation 12
f_Z
=
1
2π ⋅ C_out ⋅ R_TOT
and:
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