MAX13253 Datasheet, PDF (10/14 Pages) Maxim Integrated Products – 1A, Spread-Spectrum, Push-Pull, Transformer Driver for Isolated Power Supplies

MAX13253
1A, Spread-Spectrum, Push-Pull, Transformer
Driver for Isolated Power Supplies
Applications Information
Power Dissipation
The power dissipation of the device is approximated by:
P_D = (R_O x I_PRI²) + (I_DD x V_DD)
where R_O is the resistance of the internal FET drivers and
I_PRI is the load current flowing into T1 and T2. Ensure that
the power dissipation of the MAX13253 is kept below the
Absolute Maximum Ratings for proper operation.
High-Temperature Operation
When the MAX13253 is operated under high ambient
temperatures, the power dissipated in the package can
raise the junction temperature close to the thermal shut-
down threshold. Under such temperature conditions, the
power dissipation should be held low enough that the
junction temperature observes a factor of safety margin.
The maximum junction temperature should be held below
+140°C. Use the package’s thermal resistance to calcu-
late the junction temperature.
Power-Supply Decoupling
Bypass V_DD to ground with a 1µF ceramic capacitor as
close as possible to the device.
Connect at least 10µF between V_DD and ground as close
as possible to the primary-side center tap of the trans-
former. This capacitor helps to stabilize the voltage on
the supply line and protects the IC against large voltage
spikes on V_DD.
Output Voltage Regulation
For many applications, the unregulated output of the
MAX13253 circuit meets output voltage tolerances. This
configuration represents the highest efficiency possible.
When the load currents on the transformer’s second-
ary side are low, the output voltage of the rectifier can
strongly increase. To protect downstream circuitry, limit
the output voltage when operating the circuit under low
load conditions. If the minimum output load current is less
than approximately 5mA, connect a zener diode from the
output node of the rectifier to ground to limit the output
voltage to a safe value.
For applications requiring a regulated output voltage,
Maxim provides several solutions. In the following exam-
ples, assume a tolerance of ±10% for the input voltage.
Example 1: 5V to Isolated, Unregulated 6V
In the circuit of Figure 4, the MAX13253 is used to gener-
ate an isolated 6V output. For a minimum input voltage of
5V, the output voltage of the rectifier is approximately 6V.
Example 2: 3.3V to Isolated, Regulated 5V
In the circuit of Figure 5, the MAX8881 low-dropout lin-
ear regulator regulates the isolated output voltage to 5V.
A 1:2 center-tapped transformer is used to step-up the
secondary side voltage from a 3.3V input. For a minimum
input voltage of 3.3V, the output voltage of the rectifier is
approximately 5V.
5V
HICLK
SPRD
FAULT
1µF
VDD
T2
MAX13253
EN
CLK
GND
T1
PGND
1CT:1.3CT
10µF
1µF
5V
ISO OUTPUT
Figure 4. 5V to Isolated, Unregulated 6V Application Circuit
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