MAX256ASA+ Maxim Integrated Products, MAX256ASA+ Datasheet - Page 7

• Manufacturer Part Number: MAX256ASA+
• Description: IC DVR H-BRIDGE 3W 8-SOIC
• Manufacturer: Maxim Integrated Products
• Type: H Bridger

Specifications of MAX256ASA+

• Input Type: Non-Inverting
• Number Of Outputs: 2
• On-state Resistance: 500 mOhm
• Current - Output / Channel: 600mA
• Current - Peak Output: 1A
• Voltage - Supply: 3 V ~ 5.5 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width) Exposed Pad, 8-eSOIC. 8-HSOIC
• Supply Voltage (max): 5.5 V
• Supply Voltage (min): 3 V
• Maximum Operating Temperature: + 125 C
• Mounting Style: SMD/SMT
• Maximum Power Dissipation: 1509 mW
• Minimum Operating Temperature: - 40 C
• Supply Current: 1.06 mA
• Supply Voltage: 5V
• Digital Ic Case Style: SOIC
• No. Of Pins: 8
• No. Of Regulated Outputs: 2
• Operating Temperature Range: -40°C To +125°C
• Device Type: Half Bridge
• Filter Terminals: SMD
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Table 1. Oscillator Modes
With a supply voltage of +5V over the extended -40°C to
+85°C temperature range, the MAX256 is specified to
provide up to 3W of power to the primary side of a trans-
former in an isolated power supply. The device provides
up to 2.5W of power to the primary winding over the
+85°C to +125°C temperature range. The output power
is specified at ST1 and ST2 since losses in the trans-
former and rectification network are dependent upon
component selection and topology. The power dissipa-
tion of the MAX256 is approximated by:
where R
tance of the internal FET drivers, and I
current flowing through the transformer primary between
ST1 and ST2. For low output load currents, include the
contribution to P
I
As with all power-supply circuits, careful PC board lay-
out is important to achieve low switching losses and sta-
ble operation. For thermal performance, connect the
exposed paddle to a solid copper ground plane.
The traces from ST1 and ST2 to the transformer must be
low-resistance and inductance paths. Place the trans-
former as close as possible to the MAX256 using short,
wide traces.
When the device is operating with the internal oscillator,
it is possible for high-frequency switching components
on ST1 and ST2 to couple into the CK_RS circuitry
through PC board parasitic capacitance. This capacitive
CC
OSCILLATOR
Programmable
External Clock
x V
Frequency
Internal
Disable
3W Primary-Side Transformer H-Bridge Driver
MODE
CC
OHL
.
is the total high-side and low-side on-resis-
Applications Information
D
_______________________________________________________________________________________
P
from the quiescent supply current:
PC Board Layout Guidelines
Unconnected or pulled to ground by R
be greater than 10kΩ.
Digital input. Drive CK_RS with an external clock
signal.
Connected to V
(external clock mode)
Unconnected or pulled to ground with R
(internal clock mode)
D
=
R
Available Output Power
OHL
×
CC
I
PRI
or GND
2
CK_RS
PRI
is the load
S
. R
S
S
must
coupling can induce duty-cycle errors in the oscillator,
resulting in a DC current through the transformer. To
ensure proper operation, shield the CK_RS circuitry
from ST1 and ST2 by placing a grounded trace between
Figure 1. Secondary-Side Rectification Topologies
for Isolated Supplies
Ground
Ground
MODE
V
CC
V
V
V
+
-
+
-
+
-
IN
IN
IN
1:N CT
1:N
1:N
100kHz to 1MHz (typ).
Leave CK_RS unconnected for minimum
switching frequency.
CK_RS is pulled to ground by an internal
165kΩ resistor. The device switches at one
half the external clock frequency.
The device is disabled after a maximum of
55µs following the last rising edge on
CK_RS.
FIGURE 1A. PUSH-PULL RECTIFICATION
FIGURE 1B. VOLTAGE DOUBLER
FIGURE 1C. FULL-WAVE RECTIFIER
V
D =
OPERATION
DIODE FORWARD VOLTAGE
V
+
-
OUT =
N / 2 * V
IN -
V
+
+
V
-
-
OUT =
V
OUT =
D
2(NV
NV
IN -
IN -
2V
V
D
D
)
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