MAX1865TEEP+T Maxim Integrated Products, MAX1865TEEP+T Datasheet - Page 15

• Manufacturer Part Number: MAX1865TEEP+T
• Description: IC PWR SUPPLY CONTROLLER 20QSOP
• Manufacturer: Maxim Integrated Products

Specifications of MAX1865TEEP+T

• Applications: Power Supply Controller
• Voltage - Input: 4.5 ~ 28 V
• Current - Supply: 1.4mA
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 20-QSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Supply: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

where f
MAX186_U. The exact inductor value is not critical and
can be adjusted to make trade-offs among size, cost,
and efficiency. Lower inductor values minimize size
and cost, but they also increase the output ripple and
reduce the efficiency due to higher peak currents. On
the other hand, higher inductor values increase effi-
ciency, but at some point resistive losses due to extra
turns of wire will exceed the benefit gained from lower
AC current levels.
Find a low-loss inductor having the lowest possible DC
resistance that fits in the allotted dimensions. Ferrite
cores are often the best choice, though powdered iron
is inexpensive and can work well at 200kHz. The cho-
sen inductor’s saturation rating must exceed the peak
inductor current:
The minimum current-limit threshold must be high
enough to support the maximum load current at the
minimum tolerance level of the current-limit circuit. The
Figure 4. Adjustable Output Voltage
I
SW
PEAK
xDSL/Cable Modem Triple/Quintuple Output
is 200kHz for MAX186_T and 100kHz for
=
I
LOAD MAX
______________________________________________________________________________________
* FOR OUTPUT VOLTAGES > 5V, SEE "OUTPUT VOLTAGE SELECTION."
(
)
+
Setting the Current Limit
⎛
⎜
⎝
LIR
2
C2
C1
C
COMP
⎞
⎟
⎠
R
R
COMP
I
POK
LOAD MAX
(
IN
VL
ILIM
POK
COMP
)
MAX1864
MAX1865
D1
GND
OUT
BST
DH
LX
DL
FB
valley of the inductor current occurs at I
minus half of the ripple current:
where R
MOSFET (N
mum current-limit threshold is 190mV (for the typical
250mV default setting). Use the worst-case maximum
value for R
add some margin for the rise in R
ture. A good general rule is to allow 0.5% additional
resistance for each °C of the MOSFET junction temper-
ature rise.
Connect ILIM to VL for the default 250mV (typ) current-
limit threshold. For an adjustable threshold, connect a
resistive-divider from VL to ILIM to GND. The 500mV to
2.5V external adjustment range corresponds to a
106mV to 530mV current-limit threshold. When adjust-
ing the current limit, use 1% tolerance resistors and a
10µA divider current to prevent a significant increase in
the current-limit tolerance.
V
VALLEY LOW
C
BST
R
DS ON
DS(ON)
(
DS(ON
(
L
N
N
). For the MAX1864/MAX1865, the mini-
H
L
)
)
) from the MOSFET N
is the on-resistance of the low-side
L
Power Supplies
C
>
IN
INPUT
4.5V TO 28V
I
LOAD MAX
R1
R2
(
C
OUT
)
-
OUTPUT
1.25V TO 5V*
DS(ON)
⎛
⎜
⎝
LIR
2
L
⎞
⎟
⎠
data sheet, and
I
LOAD MAX
over tempera-
LOAD(MAX)
(
)
15