MAX13253 Datasheet, PDF (9/14 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
1CT: nCT
T1
V_IN
+
V_OUT = nV_IN - V_D
-
T2
V_D = DIODE FORWARD VOLTAGE
(A) PUSH-PULL RECTIFICATION
1CT: nCT
T1
+
VIN
V_OUT = 2(nV_IN - V_D)
-
T2
V_D = DIODE FORWARD VOLTAGE
(B) VOLTAGE DOUBLER
T1
1CT: nCT
V_IN
+
VOUT = nVIN - 2VD
T2
-
V_D = DIODE FORWARD VOLTAGE
(C) FULL-WAVE RECTIFIER
Figure 3. Secondary-Side Rectification Topologies
SPRD input low or leave unconnected to disable spread
spectrum on the internal oscillator. SPRD has an internal
10µA pulldown to ground.
External Clock Mode
The MAX13253 provides an external clock mode for syn-
chronizing multiple MAX13253 devices. Apply an external
clock source to the CLK input to enable external clock
mode. An internal flip-flop divides the external clock by
two in order to generate a switching signal with a guaran-
teed 50% duty cycle. As a result, the MAX13253 outputs
switch at one-half of the external clock frequency. T1 and
T2 switch on the rising edge of the external clock signal.
SPRD has no effect when an external signal is applied
to CLK.
Watchdog
When the MAX13253 is operating in external clock
mode, a stalled clock can cause excessive DC current
to flow through the primary winding of the transformer.
The MAX13253 integrates internal watchdog circuitry to
prevent damage from this condition. The internal oscilla-
tor provides the switching signal to the driver whenever
the period between edges on CLK exceeds the watchdog
timeout period of 20µs (min).
Slew-Rate Control
The T1 and T2 drivers feature a controlled slew rate to
limit EMI.
Disable Mode
The MAX13253 includes a pin-selectable disable mode to
reduce current consumption. In disable mode the device
consumes less than 5µA (max) of supply current. The T1
and T2 outputs are high impedance in disable mode.
Power-Up and Undervoltage Lockout
The MAX13253 provides an undervoltage lockout feature
to ensure controlled power-up state and prevent opera-
tion before the oscillator has stabilized. On power-up and
during normal operation, if the supply voltage drops below
the V_UVLO, the undervoltage-lockout circuit forces the
device into disable mode. The T1 and T2 outputs are high
impedance in disable mode.
Overcurrent Limiting
The MAX13253 features overcurrent limiting to protect the
IC from excessive currents when charging large capaci-
tive loads or driving into short circuits. Current limiting is
achieved in two stages: internal circuity monitors the out-
put current and detects when the peak current rises above
2A. When the 2A limit is exceeded, internal protection cir-
cuitry is immediately enabled, reducing the output current
and regulating it to the 1.4A (typ) current-limit threshold.
The MAX13253 monitors the driver current on a cycle-by-
cycle basis, and the driver output current is regulated to
the current-limit threshold until the short is removed.
The MAX13253 can dissipate large amounts of power
during overcurrent limiting, causing the IC to enter ther-
mal shutdown.
FAULT Output
The FAULT output is asserted low during an overcurrent
or overtemperature fault. FAULT is an open-drain output.
Thermal Shutdown
The MAX13253 is protected from overtemperature dam-
age by integrated thermal-shutdown circuitry. When the
junction temperature (T_J) exceeds +160ºC (typ), the
device is disabled and FAULT is asserted. FAULT is
asserted for the duration of either an overcurrent or over-
temperature event. The device resumes normal operation
when T_J falls below +130°C (typ).
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