MAX1904ETJ+T Maxim Integrated Products, MAX1904ETJ+T Datasheet - Page 26

• Manufacturer Part Number: MAX1904ETJ+T
• Description: IC CNTRLR PWR SPLY LN 32-TQFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX1904ETJ+T

• Applications: Controller, Notebook Computers
• Voltage - Input: 4.2 ~ 30 V
• Number Of Outputs: 4
• Voltage - Output: 2.5 ~ 5 V
• Operating Temperature: 0°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 32-TQFN Exposed Pad
• Output Voltage: 3.3 V, 5 V, 2.5 V to 5.5 V
• Output Current: 5 A
• Input Voltage: 4.2 V to 30 V
• Mounting Style: SMD/SMT
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The DC resistance (DCR) of the inductor can be used
to sense inductor current to improve the efficiency and
to reduce the cost by eliminating the sense resistor.
Figure 7 shows the sense circuit, where L is the induc-
tance, R
low-pass sense network. If the time constant of the
inductor is equal to that of the sense network, i.e.:
then the voltage across C
where I
Determine the required sense-resistor value using the
equation given in the Current-Sense Resistor Value
section. Choose an inductor with DCR equal or greater
than the sense resistor value. If the DCR is greater than
the sense-resistor value, use a divider to scale down
the voltage. Use the maximum inductance and mini-
mum DCR to get the maximum possible inductor time
constant. Select R
network time constant is equal or greater than the maxi-
mum inductor time constant.
500kHz Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
Figure 7. Lossless Inductor Current Sensing
26
______________________________________________________________________________________
MAX1901
MAX1902
MAX1904
L
L
is the inductor current.
is the inductor DCR, R
Lossless-Inductor Current-Sensing
CSH_
CSL_
DH_
LX_
DL_
S
V
R
L
S
and C
L
=
=
R
R C
L
S
S S
S
×
V
becomes
IN
I
so that the maximum sense
L
R
S
L
C
INDUCTOR
S
IN
, and C
R
L
S
C
S
form an RC
V
OUT
C
OUT
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 feedforward compen-
sation to offset for the increased output ESR. Figure 8
shows the addition of the feedforward compensation
circuit. C
ward resistor and C
100pF for C
equation below:
Set the value for R
make R
feedforward, 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.
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
Figure 8. Adding Feedforward Compensation
Reduced Output Capacitance Application
MAX1901
MAX1902
MAX1904
FF
FB
CSH_
too small as that will introduce too much
CSL_
DH_
provides noise filtering, R
FB_
DL_
LX_
FB
PC Board Layout Considerations
and C
R
FF
FF
≤
V
LX
LX
4
IN
close to the calculation. Do not
C
×
. Select R
LX
provides DC blocking. Use
R
L
ESR
3
× ×
C
R
IN
FF
L
f
FF
R
SENSE
FF
according to the
C
FB
is the feedfor-
C
V
R3
R4
OUT
OUT