MAX16974EVKIT+ Maxim Integrated Products, MAX16974EVKIT+ Datasheet - Page 16

• Manufacturer Part Number: MAX16974EVKIT+
• Description: Power Management Modules & Development Tools MAX16974 EVAL KIT MAX16974 EVAL KIT
• Manufacturer: Maxim Integrated Products

Specifications of MAX16974EVKIT+

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

the voltage drop across the high-side MOSFET. Current-
mode control eliminates the double pole in the feedback
loop caused by the inductor and output capacitor result-
ing in a smaller phase shift and requiring less elaborate
error-amplifier compensation than voltage-mode control.
A simple single-series resistor (R
are all that is required to have a stable, high-bandwidth
loop in applications where ceramic capacitors are
used for output filtering (Figure 5). For other types of
capacitors, due to the higher capacitance and ESR, the
frequency of the zero created by the capacitance and
ESR is lower than the desired closed-loop crossover fre-
quency. To stabilize a nonceramic output capacitor loop,
add another compensation capacitor (C
GND to cancel this ESR zero.
The basic regulator loop is modeled as a power modulator,
output feedback divider, and an error amplifier. The power
modulator has a DC gain set by g
and zero pair set by R
and its ESR. The following equations approximate the
value for the gain of the power modulator (GAIN
neglecting the effect of the ramp stabilization. Ramp stabi-
lization is necessary when the duty cycle is above 50% and
is internally done for the device.
where R
ing frequency in MHz, L is the output inductance in FH,
and g
In a current-mode step-down converter, the output
capacitor, its ESR, and the load resistance introduce a
pole at the following frequency:
The output capacitor and its ESR also introduce a zero at:
When C
parallel, the resulting C
= ESR
lel combination of alike capacitors is the same as for an
individual capacitor.
High-Voltage, 2.2MHz, 2A Automotive Step-
Down Converter with Low Operating Current
16
f
pMOD
_____________________________________________________________________________________
mc
(EACH)
GAIN
LOAD
OUT
= 3S.
=
f
MOD(DC)
2
is composed of “n” identical capacitors in
/n. Note that the capacitor zero for a paral-
zMOD
= V
π ×
OUT
C
OUT
=
/I
2
LOAD
=
LOUT(MAX)
π ×
OUT
g
×
mc



ESR C
R
, the output capacitor (C
R
= n O C
LOAD
×
LOAD
1
R
×
R
1
LOAD
mc
LOAD
C
OUT
in I, f
+
) and capacitor (C
×
O R
OUT(EACH)
(f
f
SW
SW
+
×
LOAD
F
SW
(f
f
) from COMP to
×
×
SW
SW
L
L)
is the switch-
, with a pole
×
×
+
MOD(DC)
L
L)
ESR
and ESR
OUT



C
),
),
)
The feedback voltage-divider has a gain of GAIN
V
The transconductance error amplifier has a DC gain of
GAIN
amplifier transconductance, which is 1000FS (typ), and
R
A dominant pole (f
capacitor (C
(R
resistor (R
There is an optional pole (f
cancel the output capacitor ESR zero if it occurs near
the crossover frequency (f
1 (0dB)). Thus:
The loop-gain crossover frequency (f
below 1/5th of the switching frequency and much higher
than the power-modulator pole (f
Figure 5. Compensation Network
FB
OUT,EA
OUT,EA
/V
EA(DC)
OUT
R
R
1
2
V
is the output resistance of the error amplifier 50MI.
OUT
). A zero (f
, where V
C
f
pdEA
= g
) and the compensation capacitor (C
C
V
) and the amplifier output resistance
REF
m,EA
=
f
f
zEA
pEA
f
pMOD
FB
2
dpEA
O R
π ×
ZEA
is 1V (typ).
=
=
C
OUT,EA
2
) is set by the compensation
2
) is set by the compensation
C
<<
π ×
C
g
π ×
m
, where the loop gain equals
×
pEA
f
(R
C
C
C
1
1
C
F
, where g
1
OUT,EA
≤
) set by C
pMOD
×
×
f
SW
R
R
5
C
R
C
C
C
C
C
):
+
) should be set
m,EA
R )
C
F
COMP
and R
is the error
C
F
FB
C
C
to
=
).