Rainbow Electronics MAX15034 - 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