MAX256ASA-T Maxim Integrated Products, MAX256ASA-T Datasheet - Page 8

• Manufacturer Part Number: MAX256ASA-T
• Description: MOSFET & Power Driver ICs
• Manufacturer: Maxim Integrated Products

Specifications of MAX256ASA-T

• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

these circuits. Place R
CK_RS pin. An additional capacitance of 100nF from
CK_RS to GND may be required in some applications.
For many applications, the unregulated output of the
MAX256 meets the supply voltage tolerances. This con-
figuration represents the highest efficiency possible
with the MAX256.
For applications requiring a regulated output voltage,
Maxim provides several solutions. In the following
examples, assume a tolerance of ±10% variation for the
input voltage.
When a full-bridge power supply is operated under
maximum input voltage and low output load current, the
voltage at the output of the rectifier network can exceed
the absolute maximum input voltage of the low dropout
regulator (LDO). If the minimum output load current is
less than approximately 5mA, connect a zener diode
from the output voltage to ground (as shown in Figure
2) to limit the output to a safe value.
In the circuit of Figure 2, the MAX1659 LDO regulates
the output of the MAX256 to +5V. The Halo TGM-
H281NF provides a center-tapped 1:2.6 turns ratio, and
the secondary circuit implements a 4-diode bridge rec-
tifier (Figure 1C).
For a minimum input voltage of +3.0V, the output volt-
age of the bridge rectifier is approximately +5.5V at a
current of 200mA. A 15V zener diode protects the LDO
from high input voltages, but adds a few microamps to
the no-load input current of the MAX256.
In Figure 3, the MAX1658 LDO is used with the TGM-
H281NF transformer and a 2-diode push-pull rectifier
(Figure 1A). This topology produces approximately
+4.5V at a current of 350mA. The MAX1658 produces a
regulated +3.3V output voltage.
In Figure 4, the 7812 LDO is used with the TGM-
H281NF transformer and the voltage doubler network
(Figure 1B). This circuit produces approximately
+12.5V at a load current of 150mA. The 7812 produces
a regulated +12V output.
In Figure 5, the MAX256 is used with two TGM-280NS
transformers and voltage doubler networks (Figure 1B)
to supply 20V to a pair of 7815 regulators. The circuit
produces a regulated ±15V at 50mA.
8
_______________________________________________________________________________________
3W Primary-Side Transformer H-Bridge Driver
+3.3V to Isolated, Regulated +5.0V
+5V to Isolated, Regulated +3.3V
Output Voltage Regulation
+5V to Isolated, Regulated +12V
+5V to Isolated, Regulated ±15V
S
as close as possible to the
The MAX256 provides isolated power for data convert-
ers in industrial process control applications (Figure 6).
The 3W isolated power output capability allows for data
converters operating across multiple isolation barriers.
The power output capability also supports circuitry for
signal conditioning and multiplexing.
The MAX256 provides power for multiple transceivers in
isolated RS-485/RS-232 data interface applications. The
3W isolated power output capability of the MAX256
allows more than ten RS-485 transceivers simultaneously.
The MAX256 allows a versatile range of secondary-side
rectification circuits (see Figure 1). The secondary
transformer winding can be wound to provide a wide
range of isolated voltages. The MAX256 delivers 3W of
power to the transformer with a +5V supply (-40°C to
+85°C). The MAX256 produces up to 2.5W over the
+85°C to +125°C temperature range. For a supply volt-
age of +3.3V, the MAX256 delivers 2W of power to the
transformer over the -40°C to +85°C temperature
range, and 1.4W between +85°C and +125°C. Figure
8A shows a +5V to isolated +5V application that deliv-
ers up to 500mA. In Figure 8B, the MAX256 is config-
ured to provide +5V from a +3.3V supply at 350mA,
and in Figure 8C, the MAX256 provides isolated +15V
and -15V at a total current up to 75mA.
The MAX256 provides the advantages of the full-bridge
converter topology, including multiple isolated outputs,
step-up/step-down or inverted output, relaxed filtering
requirements, and low output ripple.
Bypass V
as close to the device as possible. Additionally, place a
4.7µF capacitor from V
Ensure that the exposed paddle is soldered to the bot-
tom layer ground for best thermal performance. Failure
to provide a low thermal impedance path to the ground
plane will result in excessive junction temperatures
when delivering maximum output power.
Isolated DAC/ADC Interface for Industrial
Isolated RS-485/RS-232 Data Interfaces
for Isolated Supplies
CC
to ground with a 0.47µF ceramic capacitor
CC
Power-Supply Decoupling
to ground.
Isolated Power Supply
Process Control
Exposed Paddle