Rainbow Electronics MAX15034 User Manual
Page 22
MAX15034
Configurable, Single-/Dual-Output, Synchronous
Buck Controller for High-Current Applications
22
______________________________________________________________________________________
The MAX15034 provides precision average current-limit
programmability while using standard sense resistors
or shunts. Use the equation below to determine the
appropriate V
AVGLIMIT
external reference voltage at
AVGLIMIT:
For example, assuming the desired average current
limit is 18A, and R
SENSE
= 2m
Ω.
where R
SENSE
is determined from maximum load cur-
rent, wattage rating, and circuit parasitics (see above)
and I
LOAD(MAX)
from circuit requirements. V
AVGLIMIT
is
the average current-limit reference voltage selected for
a desired I
LOAD(MAX)
and is set by a resistive voltage-
divider from REG to AGND. See the
Programming the
Average Current Limit
section.
The second current-protection circuit is the hiccup fault
protection as explained in the
Hiccup Fault Protection
section. The average current during a short at the out-
put is given by:
Programming the Average Current Limit
The MAX15034 average current-limit reference voltage
is set by connecting a resistor-divider network from
REG to AGND, the center node is connected to
AVGLIMIT. The resistive divider’s upper resistor, R1, is
connected between REG and the AVGLIMIT. The resis-
tive divider’s lower resistor, R2, is connected between
the AVGLIMIT and AGND.
The resistor-divider values are determined by first,
choosing R2. To minimize reference noise select R2
such that (R1 + R2) < 100k
Ω; a typical value is 10kΩ.
Next, determine R1 from:
From the example above, assuming V
AVGLIMIT
= 1.91V:
A standard value for R1 is 16.2k
Ω. Connect AVGLIMIT
to AGND for default current limit
20 4
.
.
mV
R
SENSE
⎛
⎝⎜
⎞
⎠⎟
R
k
V
V
k
1 10
5
1 91
1
16 18
=
×
−
⎛
⎝⎜
⎞
⎠⎟ =
Ω
Ω
.
.
R
R
V
V
k
V
V
REG
AVGLIMIT
AVGLIMT
1
2
1
10
5
=
Ч
−
⎛
⎝⎜
⎞
⎠⎟
=
Ч
Ω
((
)
[ ]
MAX
V
−
⎛
⎝
⎜
⎞
⎠
⎟
1
I
I
AVG SHORT
LOAD MAX
(
)
(
)
.
=
×
0 0625
V
m
A
mV
mV
V
AVGLIMIT
=
Ч
Ч
(
)
+
=
=
2
36 18
612 5
1910
1 91
Ω
.
.
V
R
m
I
A
AVGLIMIT
SENSE
LOAD MAX
=
Ч
Ч
(
)
+
56
[
]
[ ]
(
)
Ω
6
612 5
. mV
ESL
SENSE RESISTOR (INDUCTIVE)
R
SENSE
V
OUT
LX_
CSP_
MAX15034
CSN_
C2
R1
C1
C3
R2
L
OUT
Figure 10. Inductive Sense Resistor