MAX8686ETL+ Maxim Integrated Products, MAX8686ETL+ Datasheet - Page 18

• Manufacturer Part Number: MAX8686ETL+
• Description: IC BUCK SYNC ADJ 25A 40TQFN
• Manufacturer: Maxim Integrated Products
• Type: Step-Down (Buck)r

Specifications of MAX8686ETL+

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 0.7 ~ 5.5 V
• Current - Output: 25A
• Frequency - Switching: 300kHz ~ 1MHz
• Voltage - Input: 4.5 ~ 20 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 40-TQFN Exposed Pad
• Power - Output: 4W
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Single/Multiphase, Step-Down,
DC-DC Converter Delivers Up to 25A Per Phase
The peak current-limit threshold (V
a resistor connected from ILIM to GND. An internal
10µA current source flows through this resistor to set a
voltage that is 61 times higher than the current-limit
threshold. For example, a 300kΩ resistor sets the cur-
rent-limit threshold at (10µA x 300kΩ)/61 or 49mV:
where R
sponds to the peak voltage across the sensing element
(inductor resistance or current-sense resistor).
This allows a maximum average DC output current of
(ILIM):
where R
resistor and I
To ensure maximum output current, use the minimum
value of V
values at the highest expected operating temperature.
The DC resistance of the inductor’s copper wire has a
+0.38%/°C temperature coefficient.
When using a sense resistor, the current through the
sense resistor sets a voltage compared with the peak
current limit.
To provide a more efficient and lower cost design, the
current can be measured through the inductor using a
DCR method (voltage across the DC resistance of the
inductor) as shown in Figure 5.
An RC circuit is connected across the inductor. The RC
time constant is set to be 1.1 to 1.2 times the inductor
time constant (L/R
4.7µF range, and then calculate R1 from:
R2 is added in some applications to scale down the
current signal. R2 and LIR should be selected to meet
the following condition.
18
______________________________________________________________________________________
I
OUT MAX
DC
ILIM
N
_
TH
is the DC resistance of the inductor or sense
V
is in kilohms, V
P-P
TH
from each setting and the maximum R
Setting the Peak Current Limit
is the peak-to-peak inductor current.
x
=
I
LIM
DC
⎛
⎜
⎝
V
R
1
CS
1
+
). Pick the value of C1 in the 1µF to
=
=
+
LIR
R
R
2
−
V
1 2
DC
TH
DC
.
V
⎞
⎟
⎠
CS
TH
x R
x L
−
x C
−
I
P P
is in millivolts, and corre-
1
DC
=
2
1
−
10
x
CS+
x R
R
61
1
R
ILIM
- V
+ 2 2
2
R
CS-
≤
) is set by
45
mV
DC
In the multiphase converter, the phases are interleaved
to reduce the output voltage ripple. The master starts
conduction at the beginning of the FREQ ramp. The
phase delay time, t
of slaves from the master. Determine the phase delay
time as follows:
where X is the number of the slave (X = 1 to 5 for 6
phase converters) f
phase in kilohertz, and N is the total number of phases.
Calculate the phase voltage of each slave from:
where C
FREQ (see the Setting the Switching Frequency sec-
tion). For better jitter immunity, V
ed between 0.3V and 2.5V.
Then determine resistor-divider for each slave.
Preselect more than 10kΩ for phase resistor RX5 (X = 2
to 6, R25, R35, R45, R55, and R65) in Figure 4, and cal-
culate RX4 (R24, R34, R44, R54, and R64) as follows:
The input capacitor reduces the peak current drawn
from the power source and reduces the noise and volt-
age ripple on the input DC voltage bus caused by the
circuit’s switching. The input capacitors must meet the
Figure 5. Current Sense Using the Inductor’s DC Resistance
FREQ
MAX8686
V
PHASEX
RX
is the total capacitance (in picofarads) at
t
PHASEX
4
Calculating the Phase Voltage
=
PHASE
RX
SW
CS+
CS-
=
LX
5
t
=
PHASEX
is the switching frequency per
×
f
, is the conduction delay time
SW
5 4
.
R1
x
V V
V
C
X
10
x
PHASE X
−
FREQ
PHASE
C1
L1
R2
5
3
PHASE X
Input Capacitor
x
x N
10
( )
8
should be limit-
( )
−
30
V
OUT