Rainbow Electronics MAX13256 - Manual (Page 8)

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MAX13256
36V H-Bridge Transformer
Driver for Isolated Supplies
Detailed Description
The MAX13256 is an integrated primary-side controller
and H-bridge driver for isolated power-supply circuits.
The device contains an on-board oscillator, protec-
tion circuitry, and internal MOSFETs to provide up to
300mA of current to the primary winding of a trans-
former. The device can be operated using the internal
oscillator or driven by an external clock to synchronize
multiple MAX13256 devices and control EMI behavior.
Regardless of the clock source being used, an internal
flip-flop stage guarantees a fixed 50% duty cycle to
prevent DC current flow in the transformer as long as the
period of the clock is constant.
The device operates from a wide single-supply voltage
of 8V to 36V, and includes undervoltage lockout for con-
trolled startup. The device features break-before-make
switching to prevent cross conduction of the H-bridge
MOSFETs. An external resistor sets an overcurrent limit,
allowing primary-side limiting of load currents on the
transformer’s secondary side. Thermal-shutdown cir-
cuitry provides additional protection against excessive
power dissipation.
Isolated Power Supply
The MAX13256 allows a versatile range of secondary-
side rectification circuits (see
Figure 3 ). The primary-to-
secondary transformer winding ratio can be chosen to
adjust the isolated output voltage. The device delivers
up to 300mA of current to the transformer with a supply
up to +36V.
The MAX13256 provides the advantages of the H-bridge
converter topology, including multiple isolated outputs,
step-up/step-down or inverted output, relaxed filtering
requirements, and low output ripple.
Functional Diagram
CLK
ST1
V DD
ST2
EN
ITH
MOSFET
H-BRIDGE
DRIVER
UVLO
MUX
FLIP-
FLOP
V UVLO
V DD
P
N
CURRENT
LIMIT
OSC
WATCHDOG
V DD
P
N
FAULT
GND
MAX13256