MAX15034 Datasheet, PDF (22/25 Pages) Maxim Integrated Products – Configurable, Single-/Dual-Output, Synchronous Buck Controller for High-Current Applications

Configurable, Single-/Dual-Output, Synchronous
Buck Controller for High-Current Applications
LX_
MAX15034
SENSE RESISTOR (INDUCTIVE)
L_OUT
ESL
R_SENSE
V_OUT
R1
C1
CSP_
C2
CSN_
R2
C3
Figure 10. Inductive Sense Resistor
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:
( ) ^VAVGLIMIT ^{= 56 × R}SENSE^{[mΩ] × I}LOAD(MAX)^{[A] + 612.5mV}
For example, assuming the desired average current
limit is 18A, and R_SENSE = 2mΩ.
V_AVGLIMIT = (2mΩ × 36 × 18A) + 612.5mV
= 1910mV = 1.91V
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:
I_AVG(SHORT) = 0.0625 × I_LOAD(MAX)
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:
R1
=
R2
×
⎛
⎝⎜
V_REG
V_AVGLIMIT
⎞
− 1_⎠⎟
=
10kΩ
×
⎛
⎜
⎝
5V
V_AVGLIMT(MAX) [V]
−
⎞
1_⎟
⎠
From the example above, assuming V_AVGLIMIT = 1.91V:
R1 =
10kΩ
×
⎛ ^5V
⎝⎜ _1.91V
− 1^{⎞⎠⎟}
=
16.18kΩ
A standard value for R1 is 16.2kΩ. Connect AVGLIMIT
to AGND for default current limit
⎛
⎝⎜
20.4mV
R_SENSE
⎞
⎠⎟
.
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