Manual

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
= 2mΩ.
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) < 100kΩ; a typical value is 10kΩ.
Next, determine R1 from:
From the example above, assuming V
AVGLIMIT
= 1.91V:
A standard value for R1 is 16.2kΩ. Connect AVGLIMIT
to AGND for default current limit
20 4.
.
mV
R
SENSE
⎛
⎝
⎜
⎞
⎠
⎟
Rk
V
V
k110
5
191
11618=× −
⎛
⎝
⎜
⎞
⎠
⎟
=ΩΩ
.
.
RR
V
V
k
V
V
REG
AVGLIMIT
AVGLIMT
12 1
10
5
=× −
⎛
⎝
⎜
⎞
⎠
⎟
=×Ω
(()
[]
MAX
V
−
⎛
⎝
⎜
⎞
⎠
⎟
1
II
AVG SHORT LOAD MAX() ()
.=×0 0625
VmAmV
mV V
AVGLIMIT
=××
()
+
==
2 36 18 612 5
1910 1 91
Ω .
.
VRmIA
AVGLIMIT SENSE LOAD MAX
=× ×
()
+56 [ ] [ ]
()
Ω 6612 5.m
V
ESL
SENSE RESISTOR (INDUCTIVE)
R
SENSE
V
OUT
LX_
CSP_
MAX15034
CSN_
C2
R1
C1
C3
R2
L
OUT
Figure 10. Inductive Sense Resistor