MAX8741EAI+T Maxim Integrated, MAX8741EAI+T Datasheet - Page 26

• Manufacturer Part Number: MAX8741EAI+T
• Description: Current & Power Monitors & Regulators 500kHz Multi-Out Pwr Supply Controller
• Manufacturer: Maxim Integrated

Specifications of MAX8741EAI+T

• Rohs: yes
• Product: Power Monitors
• Supply Voltage - Max: 30 V
• Supply Voltage - Min: 4.2 V
• Input Voltage Range: 4.2 V to 30 V

500kHz Multi-Output Power-Supply Controllers
with High Impedance in Shutdown
scale down the voltage. Use the maximum inductance
and minimum DCR to get the maximum possible induc-
tor time constant. Select R
mum sense-network time constant is equal to or greater
than the maximum inductor time constant.
In applications where higher output ripple is accept-
able, lower output capacitance or higher ESR output
capacitors can be used. In such cases, cycle-by-cycle
stability is maintained by adding feed-forward compen-
sation to offset for the increased output ESR. Figure 8
shows the addition of the feed-forward compensation
circuit. C
ward resistor, and C
100pF for C
equation below:
Set the value for R
make R
forward, possibly causing an overvoltage to be seen at
the feedback pin, and changing the mode of operation
to a voltage mode.
Good PC board layout is required in order to achieve
specified noise, efficiency, and stability performance.
Figure 7. Lossless Inductor Current Sensing
26
Reduced Output-Capacitance Application
______________________________________________________________________________________
MAX8741
MAX8742
FF
FB
too small as that introduces too much feed-
provides noise filtering, R
FB
PC Board Layout Considerations
CSH_
CSL_
DH_
and C
LX_
DL_
R
FF
FF
≤
LX
LX
close to the calculation. Do not
4
. Select R
×
V
provides DC blocking. Use
IN
R
S
ESR
3
R
and C
× ×
S
L
L
C
INDUCTOR
IN
FF
f
S
FF
so that the maxi-
according to the
R
is the feed-for-
L
C
S
V
OUT
C
OUT
The PC board layout artist must be given explicit
instructions, preferably a pencil sketch showing the
placement of power-switching components and high-
current routing. A ground plane is essential for optimum
performance. In most applications, the circuit is located
on a multilayer board, and full use of the four or more
copper layers is recommended. Use the top layer for
high-current connections, the bottom layer for quiet
connections (REF, SS, GND), and the inner layers for
an uninterrupted ground plane. Use the following step-
by-step guide:
1) Place the high-power components (Figure 1, C1, C3,
Figure 8. Adding Feed-Forward Compensation
C4, Q1, Q2, L1, and R1) first, with their grounds
adjacent:
• Priority 1: Minimize current-sense resistor trace
• Priority 2: Minimize ground trace lengths in the
• Priority 3: Minimize other trace lengths in the
MAX8741
MAX8742
lengths and ensure accurate current sensing with
Kelvin connections (Figure 9).
high-current paths (discussed below).
high-current paths.
a) Use >5mm-wide traces
b) CIN to high-side MOSFET drain: 10mm max
c) Rectifier diode cathode to low-side MOSFET:
length
5mm max length
CSH_
CSL_
DH_
FB_
DL_
LX_
V
IN
C
LX
L
C
R
IN
FF
R
SENSE
C
FB
C
V
R3
R4
OUT
OUT