MAX8855ETJ+ Maxim Integrated Products, MAX8855ETJ+ Datasheet - Page 15

• Manufacturer Part Number: MAX8855ETJ+
• Description: IC REG STP DWN DUAL 5A 32-TQFN
• Manufacturer: Maxim Integrated Products
• Type: Step-Down (Buck)r

Specifications of MAX8855ETJ+

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 2
• Voltage - Output: 0.6 ~ 3.24 V
• Current - Output: 5A
• Frequency - Switching: 500kHz ~ 2MHz
• Voltage - Input: 2.35 ~ 3.6 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 32-TQFN Exposed Pad
• Power - Output: 2.76W
• Output Current: 5 A
• Input Voltage: 2.35 V to 3.6 V
• Supply Current: 2.8 mA
• Switching Frequency: 2 MHz
• Mounting Style: SMD/SMT
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

These equations are based on the assumptions that C9
>> C10, and R4 >> R8, which are true in most applica-
tions. Placement of these poles and zeros is deter-
mined by the frequencies of the double pole and ESR
zero of the power stage transfer function. It is also a
function of the desired closed-loop bandwidth. Figure 5
shows the pole zero cancellations in the type III com-
pensation design.
The following section outlines the step-by-step design
procedure to calculate the required compensation com-
ponents. Begin by setting the desired output voltage as
described in the Setting the Output Voltage section.
The crossover frequency f
bandwidth of the regulator) should be between 10%
and 20% of the switching frequency, f
crossover frequency results in a faster transient
response. Too high of a crossover frequency can result
in instability. Once f
from the following equation:
Figure 5. Pole Zero Cancellations in Compensation Design
f
f
f
P
P
Z
______________________________________________________________________________________
2
3
2
C
_
_
_
EA
EA
EA
is chosen, calculate C9 (in farads)
=
=
=
2
2
2
Dual, 5A, 2MHz Step-Down Regulator
C
π
π
π
POWER-STAGE TRANSFER FUNCTION
×
×
×
(or closed-loop, unity-gain
COMPENSATION TRANSFER FUNCTION
R
R
R
1
7
1
8
1
4
×
×
×
C
C
C
10
11
11
S
. A higher
DOUBLE POLES
FIRST AND SECOND ZEROS
FREQUENCY
where V
crossover frequency in Hertz, R4 is the upper feedback
resistor (in ohms), R
tance and the internal switch on-resistance, and R
the output load resistance (V
Due to the underdamped nature of the output LC double
pole, set the two zero frequencies of the type III com-
pensation less than the LC double-pole frequency to
provide adequate phase boost. Set the two zero fre-
quencies to 80% of the LC double-pole frequency.
Hence:
Set the third compensation pole, f
which yields:
C
IN
R
7
11
is the input voltage in volts, f
=
=
0 8
C
0 8
.
SECOND POLE
9
OPEN-LOOP GAIN
.
1
×
=
1
×
C
2
R
R
L
9
π
4
8
×
is the sum of the inductor resis-
×
=
×
THIRD POLE
f
C
C
L C
2 5
×
L C
O
.
×
R
C
×
OUT
×
4
11
×
ESR
O
×
V
O
R
R
IN
⎛
⎜
⎝
/I
×
L
1
×
L
OUT
(
+
+
R
(
+
R
R
R
O
R
R
O
P3_EA
O
).
O
L
O
+
+
⎞
⎟
⎠
ESR
ESR
, at f
)
)
C
Z_ESR
is the
O
15
is
,