MAX1956ETI-T Maxim Integrated Products, MAX1956ETI-T Datasheet - Page 19

• Manufacturer Part Number: MAX1956ETI-T
• Description: DC/DC Switching Controllers
• Manufacturer: Maxim Integrated Products

Specifications of MAX1956ETI-T

• Number Of Outputs: 2
• Output Voltage: 0.8 V to 4.95 V
• Input Voltage: 1.6 V to 5.5 V
• Package / Case: TQFN EP-28
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

must compensate for this gain drop and phase shift in
order to achieve a stable high-bandwidth closed-loop
system.
The basic regulator loop consists of a power modulator,
an output feedback divider, and an error amplifier. The
power modulator has DC gain set by V
double pole set by the inductor and output capacitor
and a single zero set by the output capacitor (C
and its ESR. Equations that define the power modulator
follow:
The DC gain of the power modulator:
where V
because of the inductor and output capacitor is:
The zero frequency because of the output capacitor’s
ESR is:
The output capacitor is usually composed of several
same-value capacitors connected in parallel. With n
capacitors in parallel, the output capacitance is:
The total ESR is:
The ESR zero (f
capacitors is the same as that of an individual capacitor.
The feedback divider has a gain of G
where V
The transconductance error amplifier has DC gain
G
EA(dc)
FB
of 80dB. A dominant pole is set by the com-
RAMP
is 0.8V.
f
ZESR
f
PMOD
G
= 1V. The double-pole frequency
ZESR
C
MOD DC
______________________________________________________________________________________
OUT
ESR
180° Out-of-Phase Step-Down Controllers
=
(
=
2π
) for a parallel combination of
1.6V to 5.5V Input, 0.5% Accurate, Dual
=
= ×
2π
×
)
n C
ESR
=
ESR C
LC
V
1
EACH
n
RAMP
1
EACH
V
OUT
×
IN
OUT
IN
FB
/V
= V
RAMP
FB
, with a
/V
OUT
OUT
)
,
pensation capacitor (C
tance (R
A zero is set by the compensation resistor and the
compensation capacitor:
The total closed-loop gain must equal unity at the
crossover frequency, where the crossover frequency
should be higher than f
to cross over at unity gain. Also, the crossover frequency
should be less than or equal to 1/5 the switching
frequency:
The loop-gain equation at the crossover frequency is:
where:
The compensation resistor (R
where g
Because of the underdamped (Q > 1) nature of the out-
put LC double pole, the error amplifier compensation
zero should be approximately 0.2 f
good phase boost. C
A small capacitor (C
to GND to provide high-frequency decoupling. C
G
MOD(fc)
mEA
O
≅ 5MΩ), and the compensation resistor (R
R
= 2mS.
V
C
V
OUT
f
= G
PEA
G
FB
=
C
EA(fc)
f
C
ZEA
g
MOD(DC)
=
mEA
f
=
×
ZESR
F
C
2π
2π
) also can be added from COMP
=
ZESR
G
= g
is calculated from:
C
EA fc
×
2π
×
×
<
), the amplifier-output resis-
C
mEA
R
V
( )
f
×
, so that the -1 slope is used
C
V
C
✕
FB
C
OUT
C
C
5
<
×
(f
×
1
) is calculated from:
1
C
×
✕
PMOD
×
(
f
f
R
SW
PMOD
×
5
G
R
G
O
MOD fc
C
R
MOD fc
+
, and
C
)
R
2
PMOD
C
( )
/ (f
( )
)
ESR
= 1
to provide
✕
f
C
F
)
adds
C
19
):