MAX1956ETI Maxim Integrated Products, MAX1956ETI Datasheet - Page 20

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

Specifications of MAX1956ETI

• 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

another high-frequency pole (f
response. This pole should be greater than 100 times
the error-amplifier zero frequency in order to have neg-
ligible impact on the phase margin. This pole also
should be less than half the switching frequency for
effective decoupling:
Select a value for f
then solve for C
With two converters in proximity, there is a potential for
crosstalk between the converters. Crosstalk can be
managed by board layout and high-frequency filtering,
which can be inserted by adding a high-frequency pole
in the feedback network. To do so and minimize effect
on phase margin, add capacitors C7 and C8 (Figure 5)
with a pole frequency of:
Set the poles above ~4 to 5 times the crossover fre-
quency.
Below is a numerical example to calculate the compen-
sation values used in the typical application circuit of
Figure 5:
V
V
V
V
I
C
ESR = 0.008Ω / 2 = 0.004Ω
L = 0.3µH
g
f
1.6V to 5.5V Input, 0.5% Accurate, Dual
180° Out-of-Phase Step-Down Controllers
20
OUT(MAX)
SW
IN
RAMP
OUT
FB
mEA
OUT
f
PMOD
= 3V (the midpoint of the input voltage range)
= 600kHz
= 0.8V
______________________________________________________________________________________
= 1.8V
= 2mS
= 2 x 680µF
= 1V
f
f
PFB1
PFB2
=
=
= 25A
2
2
π
π
= (R2 + R3) / (2π x R2 x R3 x C8)
×
×
= (R4 + R6) / 2π x R4 x R6 x C7)
100f
F
using the following equation:
L
0 3 10
C
1
.
×
PHF
F
ZEA
C
×
=
OUT
2π
< f
in the range given above, and
-
1
6
×
PHF
×
R
1360 10
C
PHF
1
< 0.5f
×
) to the error-amplifier
×
f
PHF
SW
-
6
=
7 879
.
kHz
Pick the crossover frequency (f
f
Select f
the bandwidth is high enough for good transient
response.
The power-modulator gain at f
Pick R
Output Voltage section).
Select R
Select C
capacitor value).
Select f
A summary of feedback divider and compensation
components follows:
R
R
R
C
C
Select f
f
C
C
ZESR
X
Y
C
C
F
C
C
< f
= 8.06kΩ
= 10kΩ
= 33pF
= 18kΩ
= 6800pF
F
=
SW
=
G
2
=
=
X
π
PHF
PHF
C
MOD fc
2
29 3
2
/5:
C
= 8.06kΩ, then R
C
×
π
π
= 100kHz (this meets the criteria above), and
.
= 18kΩ (nearest standard resistor value).
R
R
= 6800pF (rounded up to the next standard
×
×
in the range 100f
= 250kHz, and then solve for C
C
kHz
( )
C
R
C
5
×
C
=
157.6kHz < f
OUT
=
1
f
=
=
PMOD
1
29.3kHz < f
×
g
0 002
3
1
V
mEA
.
f
PHF
RAMP
×
V
×
IN
ESR
29 3
=
×
×
=
.
2
( .
1 8
0 8
G
7 879
×
Y
π
2
kHz
=
.
.
V
MOD fc
π
×
PHF
f
C
= 10kΩ (see the Setting the
OUT
ZEA
(
ZESR
2
18
f
×
PMOD
×
π
< 120kHz
C
×
.
18
kHz
k
×
( )
0636
< 300kHz
C
Ω
< f
is:
100
1360 10
k
) in the range f
×
5
×
Ω
PHF
)
)
×
1
f
2
7 879
2
kHz
C
×
.
=
V
250
×
17 6 Ω
< 0.5f
FB
1
=
kHz
.
kHz
0 0477
-
F
6
k
.
:
SW
×
=
=
0 004
5620
. Hence:
.
33
ZESR
pF
pF
<