MAX1901EAI+ Maxim Integrated Products, MAX1901EAI+ Datasheet - Page 20

• Manufacturer Part Number: MAX1901EAI+
• Description: IC CNTRLR PWR SPLY LN 28-SSOP
• Manufacturer: Maxim Integrated Products

Specifications of MAX1901EAI+

• 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: 28-SSOP
• 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

tor (primary) current, pulling current from the output fil-
ter capacitor and causing the flyback transformer to
operate in forward mode. The low impedance present-
ed by the transformer secondary in forward mode
dumps current into the secondary output, charging up
the secondary capacitor and bringing V
back into regulation. The secondary feedback loop
does not improve secondary output accuracy in normal
flyback mode, where the main (primary) output is heavi-
ly loaded. In this condition, secondary output accuracy
is determined by the secondary rectifier drop, trans-
former turns ratio, and accuracy of the main output volt-
age. A linear post-regulator may still be needed to meet
strict output-accuracy specifications.
MAX1902 has a V
set by an internal resistor-divider. The MAX1901/
MAX1904 have an adjustable secondary-output voltage
set by an external resistor-divider on SECFB (Figure 5).
Ordinarily, the secondary regulation point is set 5% to
10% below the voltage normally produced by the flyback
effect. For example, if the output voltage as determined
by turns ratio is 15V, set the feedback resistor ratio to pro-
duce 13.5V. Otherwise, the SECFB one-shot might be
triggered unintentionally, unnecessarily increasing supply
current and output noise.
500kHz Multi-Output, Low-Noise Power-Supply
Controllers for Notebook Computers
Figure 5. Adjusting the Secondary Output Voltage with SECFB
20
1-SHOT
______________________________________________________________________________________
TRIG
MAX1901
MAX1904
+V
TRIP
2.5V REF
= V
SECFB
DH_
DL_
REF
DD
(
1 + –––
R1
R2
pin that regulates at a fixed 13.5V,
V+
)
WHERE V
REF
(NOMINAL) = 2.5V
R2
R1
DD
or SECFB
POSITIVE
SECONDARY
OUTPUT
MAIN
OUTPUT
The MAX1902 includes a 12V linear regulator output
capable of delivering 120mA of output current.
Typically, greater current is available at the expense of
output accuracy. If an accurate output of more than
120mA is needed, an external pass transistor can be
added. The circuit in Figure 6 delivers more than
200mA. Total output current is constrained by the V+
input voltage and the transformer primary load (see
Maximum V
in the Typical Operating Characteristics).
The three predesigned 3V/5V standard application cir-
cuits (Figure 1 and Table 1) contain ready-to-use solu-
tions for common application needs. Also, one
standard flyback transformer circuit supports the
12OUT linear regulator in the Applications Information
section. Use the following design procedure to optimize
these basic schematics for different voltage or current
requirements. But before beginning a design, firmly
establish the following:
Maximum Input (Battery) Voltage, V
should include the worst-case conditions, such as no-
load operation when a battery charger or AC adapter is
Figure 6. Increased 12V Linear Regulator Output Current
12V Linear Regulator Output (MAX1902)
MAX1902
DD
12OUT
DH_
V
DL_
Output Current vs. Input Voltage graphs
DD
V+
0.1µF
0.1µF
Design Procedure
0.1µF
10Ω
2N3906
IN(MAX)
10µF
. This value
2.2µF
12V OUTPUT
200mA
MAIN
OUTPUT
V
DD
OUTPUT