MAX1533AETJ+ Maxim Integrated Products, MAX1533AETJ+ Datasheet - Page 27

• Manufacturer Part Number: MAX1533AETJ+
• Description: IC POWER SUPPLY CONTROLER 32TQFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX1533AETJ+

• Applications: Power Supply Controller
• Voltage - Input: 4.5 ~ 26 V
• Current - Supply: 15µA
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 32-TQFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Supply: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

The MAX1533A/MAX1537A feature a thermal fault-pro-
tection circuit. When the junction temperature rises
above +160°C, a thermal sensor activates the fault
latch, pulls PGOOD low, and shuts down both SMPS
controllers using discharge mode (see the Output
Discharge (Soft-Shutdown) section). When an SMPS
output voltage drops to 0.3V, its synchronous rectifier
turns on, clamping the discharged output to GND.
Cycle V
SHDN to clear the fault latch and restart the controllers
after the junction temperature cools by 15°C.
The MAX1537A includes an auxiliary linear regulator
that delivers up to 150mA of load current. The output
(LDOA) can be preset to 12V, ideal for PCMCIA power
requirements, and for biasing the gates of load switch-
es in a portable device. In adjustable mode, LDOA can
be set to anywhere from 5V to 23V. The auxiliary regu-
lator has an independent ON/OFF control, allowing it to
be shut down when not needed, reducing power con-
sumption when the system is in a low-power state.
A flyback-winding control loop regulates a secondary
winding output, improving cross-regulation when the pri-
mary output is lightly loaded or when there is a low
input-output differential voltage. If V
below 0.8V, the low-side switch is turned on for a time
equal to 33% of the switching period. This reverses the
inductor (primary) current, pulling current from the out-
put filter capacitor and causing the flyback transformer
to operate in forward mode. The low impedance pre-
sented 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 fly-
back mode, where the main (primary) output is heavily
loaded. In this condition, secondary output accuracy is
determined by the secondary rectifier drop, transformer
turns ratio, and accuracy of the main output voltage.
Connect ADJA to GND to enable the fixed, preset 12V
auxiliary output. Connect a resistive voltage-divider at
ADJA between LDOA and GND to adjust the respective
output voltage between 5V and 23V (Figure 8). Choose
R2 (resistance from ADJA to GND) to be approximately
High-Efficiency, 5x Output, Main Power-Supply
CC
Description (MAX1537A Only)
below 1V or toggle either ON3, ON5, or
______________________________________________________________________________________
Auxiliary LDO Detailed
Adjustable LDOA Voltage
(Dual-Mode Feedback)
Controllers for Notebook Computers
Thermal Fault Protection
INA
- V
INA
LDOA
- V
LDOA
falls
100kΩ and solve for R1 (resistance from LDOA to
ADJA) using the following equation:
where V
Firmly establish the input voltage range and maximum
load current before choosing a switching frequency
and inductor operating point (ripple-current ratio). The
primary design trade-off lies in choosing a good switch-
ing frequency and inductor operating point, and the fol-
lowing four factors dictate the rest of the design:
• Input Voltage Range. The maximum value
Figure 8. Linear-Regulator Functional Diagram
REF (2.0V)
(V
AC-adapter voltage. The minimum value (V
must account for the lowest battery voltage after
drops due to connectors, fuses, and battery-selector
switches. If there is a choice at all, lower input volt-
ages result in better efficiency.
ADJA
ONA
IN(MAX)
INA
ADJA
) must accommodate the worst-case, high
= 2V nominal.
R
1
=
0.15V
R
2
⎛
⎜
⎝
Design Procedure
V
V
LDOA
ADJA
-
1
⎞
⎟
⎠
SECONDARY
FEEDBACK
FIXED 12V
R
5R
LDOA
IN(MIN)
27
)