MAX8543 MAXIM [Maxim Integrated Products], MAX8543 Datasheet - Page 20

• Manufacturer Part Number: MAX8543
• Description: Step-Down Controllers with Prebias Startup, Lossless Sensing, Synchronization, and OVP
• Manufacturer: MAXIM [Maxim Integrated Products]

Step-Down Controllers with Prebias Startup,
Lossless Sensing, Synchronization, and OVP
2) If the resulting value of R
To set the constant current limit for the latch-up mode,
only R
the current-limit threshold at 1.2 times the maximum-
rated output current:
Similarly, I
current at maximum load, R
resistance of the low-side MOSFET at the highest oper-
ating junction temperature.
Peak inductor current-limit threshold (V
possible settings through ILIM (MAX8543) or ILIM1
(MAX8544) as shown in
current limit is calculated as:
where R
the value of the optional current-sense resistor.
Note that V
variation of ±0.1 x V
maximum output current, use the minimum value of V
from each setting, and the maximum R
highest expected operating temperature. The DC resis-
tance of the inductor’s copper wire has a +0.22%/°C
temperature coefficient.
Table 3. ILIM Current-Limit Threshold
Settings
20
1/3 V
2/3 V
V
V
ILIM
0
VL
increase P
lower R
es the efficiency and results in a lower short-circuit
current.
VL
VL
______________________________________________________________________________________
ILIM
GND
Voltage-divider:
100kΩ from ILIM/ILIM1 to GND
200kΩ from ILIM/ILIM1 to VL
Voltage-divider:
200kΩ from ILIM/ILIM1 to GND
100kΩ from ILIM/ILIM1 to VL
VL
DC
R
ILIM
VALLEY
is used. The equation for R
ILIM
DS(ON)
is either the DC resistance of the inductor or
ILIM CONNECTION
RECOMMENDED
FB
is a logic-level setting, and can allow a
=
or choose a low-side MOSFET with a
1 2
I
. The latter is preferred as it increas-
LIM
.
is the value of the inductor valley
VL
×
=
without affecting V
I
R
VALLEY
V
Table
DC
TH
DS(ON)
1
−
µ
ILIM
A
I
3 below. The resulting
P P
2
×
−
Peak Current Limit
is the maximum on-
is negative, either
R
127.5
170.0
(mV)
MIN
38.5
85.0
V
DS ON
TH
DC
ILIM
(
TH
TH
values at the
)
(mV)
. To ensure
TYP
V
100
150
200
below sets
) has four
50
TH
115.0
172.5
230.0
MAX
(mV)
56.5
V
TH
TH
To use the DC resistance of the output inductor for cur-
rent sensing, an RC circuit is added (see Figure 7). The
RC time constant is set to be twice the inductor (L / R
time constant. Pick the value of R4 in the range of 470Ω
to 2kΩ, and then calculate the capacitor value from: C9
= 2L / (R
R4 to the CS- connection to minimize input-offset error.
The equivalent current-sense resistance is equal to the
DC resistance of the inductor (R
To use a current-sense resistor, connect the resistor as
shown in Figure 8. Since most current-sense resistors
have inductance, the RC circuit is also required
and is calculated in the same manner as inductor
current sensing. Place C11 close to CS+ and CS- pins
to decouple the high-frequency noise pickup. Place
C10 (same value as C9) across R5 to aid in short-
circuit recovery.
Figure 7. Inductor R
Figure 8. Using a Current-Sense Resistor
MAX8543/
MAX8544
DC
MAX8543/
MAX8544
× R4). Add a resistor (R5) equal in value to
CS+
CS-
LX
DC
CS+
CS-
LX
Current Sensing
C11
C11
L1
DC
R4
).
L1
C9
R4
R3
C9
R5
V
OUT
R5
V
OUT
C10
C10
DC
)