MAX1980ETP+ Maxim Integrated Products, MAX1980ETP+ Datasheet - Page 21

• Manufacturer Part Number: MAX1980ETP+
• Description: IC CNTRLR QUICK-PWM 20-TQFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX1980ETP+

• Pwm Type: Controller
• Number Of Outputs: 1
• Frequency - Max: 550kHz
• Duty Cycle: 50%
• Voltage - Supply: 4 V ~ 28 V
• Buck: Yes
• Boost: No
• Flyback: No
• Inverting: No
• Doubler: No
• Divider: No
• Cuk: No
• Isolated: No
• Operating Temperature: 0°C ~ 85°C
• Package / Case: 20-TQFN Exposed Pad
• Frequency-max: 550kHz
• Input Voltage: 4 V to 28 V
• Mounting Style: SMD/SMT
• Maximum Operating Temperature: + 100 C
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Current Limit Design Example
For the typical application circuit shown in Figure 1 V
= 12V, V
= 50A, L = 0.6µH, R
= 3mΩ.
1) Determine the peak-to-peak inductor current and
2) Determine the master’s current-limit threshold from
3) Determine the slave’s current-limit threshold:
R
the valley current limit:
the valley current limit and low-side MOSFETs’ max-
imum on-resistance over temperature:
Now select the resistive-divider values (R
in Figure 5) to set the appropriate voltage at the
master’s ILIM input:
Selecting R
value for R
Select the resistive-divider values (R
Figure 5) to set the appropriate voltage at the
slave’s ILIM input:
Selecting R
value for R
B
Driver Disable for Multiphase DC-DC Converter
R
=
D
I
∆I
LIMIT VALLEY



V
=
INDUCTOR
V
10 130
ITHS
OUT



ITH(MASTER)
R
10 42
(
A
x
20
≥
20
=
= 1.3V, f
x
µ
A
1 5
A



D
B
A
.
:
:
µ
10 130
mV
A
m x
= 30.1kΩ ±1% provides the following
= 100kΩ ±1% provides the following
=
)
mV
______________________________________________________________________________________
=
Ω
x
12
DS(ON)(MAX)






2



1 3
to
V x
50
V
SW
≥ 21.8A
.
to



2



130
A
mV
V x
10 130
6



300
= 300kHz,



10 42
m
-
x
10
mV
(
−
Ω
12



10
kHz x
1
x
µ



1
2
✕
V
A
µ
x
+
x
6mΩ = 130mV
mV
A
-
= 6mΩ, R
100
mV
1 3
6 4
6 4
.
.
0 6
.

 =

.
Quick-PWM Slave Controller with
V
A
k
η
A

 =

)
µ
Ω

 ≈


 =

= 2, I
H
65
21
≈
42
=
21 8
k to
54
k to
C
DS(ON)(MIN )
Ω
6 4
Ω
mV
.
LOAD(MAX)
k
.
and R
A
Ω
A
A
130
and R
42
k
k
D
Ω
Ω
IN
in
B
4) Determine R
5) Finally, verify that that the total bias currents do not
When unadjusted, the on-resistance variation of the
low-side MOSFETs results in a maximum current-limit
variation (∆I
where A
MAX1980 to adjust the master’s current-limit threshold
results in a maximum current-limit variation less than
the peak-to-peak inductor current:
As shown in Figure 6, the resulting current-limit varia-
tion of the master is dramatically reduced. For the
above example, this control scheme reduces the cur-
rent-limit variation from 21.7A (unadjusted) to less than
6.4A (adjusted).
The output filter capacitor must have low enough ESR to
meet output ripple and load-transient requirements, yet
have high enough ESR to satisfy stability requirements.
In CPU V
the output is subject to large load transients, the output
capacitor selection typically depends on how much
ESR is needed to prevent the output from dipping too
low under a load transient. Ignoring the sag due to
finite capacitance:
Unadjusted I
exceed the 50µA maximum load of the master’s ref-
erence:
I



BIAS TOTAL
R
30 1
RDS
R
LIMIT
CORE
C
.
(
LIMIT
k
Adjusted ∆I
=
Ω
= R



≤
2
+
converters and other applications where
10 42
V
LIMIT
(
∆
113
53 6
) determined by the following equation:
R
DS(ON)(MAX)
LIMIT
)
x
ESR
.
2
=
k
Output Capacitor Selection
V
k



(Figure 5) from the above equation:
Ω
Ω
54
mV
6
=
≤

 =

m
LIMIT
//
V
k
∆
100
Ω
ITHM HIGH
Ω
I
-
36
LOAD MAX
1
-
+



V
3
µ
k
(
STEP
≤ ∆I
(
m
x
100
/R
Ω
A
30 1
Ω
(
)
DS(ON)(MIN)
2
x m
INDUCTOR
k
. Ω
V
)



Ω
3
k
R
)
//
DS ON MAX
Ω
34 8
A
≈
(
RDS
113
≈
.
35
)(
k
Ω
−
k
. Using the
k
1
Ω
)
Ω

 +

)



21