Datasheet
The EV kit input power is typically a +5V DC source that
provides at least 450mA of current to the MAX256 inte-
grated primary-side controller and H-bridge driver cir-
cuit. The MAX256 contains an on-board oscillator, pro-
tection circuitry, and internal H-bridge FETs to provide
power to the primary of the transformer T1. The MAX256
prevents cross conduction of the H-bridge MOSFETs by
implementing break-before-make switching. The
MAX256 programmable oscillator is programmed to
420kHz by resistor R1. The switching-frequency duty
cycle is fixed at 50% to control energy transfer to trans-
former T1 isolated output.
The MAX256 IC includes UVLO for controlled startup
and provides controlled turn-on during power-up and
during brownouts. If the input voltage at VIN falls below
1.9V (typ), the MAX256 IC will shut down.
Surface-mount transformer T1 provides galvanic isola-
tion and the VOUT output is powered from a center-
tapped full-wave rectifier circuit (D1 or D2) to reduce
output-voltage ripple. It feeds a MAX1659 LDO regula-
tor configured for +5V output. The LDO output is
current limited and features thermal shutdown to pro-
vide for a robust isolated supply at VOUT, which can
provide up to 300mA of current.
The two-layer PCB is designed for 2500V
RMS
isolation,
with 300 mils spacing between the PGND and GND
planes. The bottom PCB PGND plane under U2 is uti-
lized as a thermal heat sink for power dissipation of the
MAX256 thermally enhanced SO package. Test points
TP1 (PGND) and TP2 (GND) are provided on the PCB
for probing the respective ground plane or to connect
the PGND to GND planes for nonisolated evaluation of
the circuit.
Jumper Selection
The MAX13487E EV kit features several jumpers to
reconfigure the receiver/driver enable circuits, and shut-
down for the MAX256 and MAX13487E ICs. Additionally,
PCB pads are provided for connecting an external load
to the isolated +5V output at VOUT and GND.
Shutdown Control
The MAX13487E EV kit features two jumpers that con-
figure the shutdown mode of the circuit. Jumper JU1
configures the MAX256 DC-DC converter and JU2 con-
figures the MAX13487E IC for shutdown mode. See
Table 1 for placing the EV kit circuit or the desired IC in
shutdown mode.
AutoDirection and Receiver Enable Selection
The MAX13487E EV kit features a 2-pin jumper (JU3) to
set the MAX13487E receiver mode of operation,
AutoDirection, or receiver output enabled. Refer to the
AutoDirection Circuitry
section in the MAX13487E/
MAX13488E IC data sheet for more information on the
MAX13487E RE pin modes of operation. See Table 2
for configuring the receiver mode of operation using
jumper JU3.
Evaluates: MAX13487E/MAX13488E
MAX13487E Evaluation Kit
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Table 1. JU1 and JU2 Shutdown Mode Control
*
To avoid bus contention, ensure that only one driver has control of the bus at a time.
JU1 SHUNT
POSITION
MAX256 MODE PIN
JU2 SHUNT
POSITION
MAX13487E SHDN PIN EV KIT OPERATION MODE
Not installed Connected to VIN through R2 1-2 Connected to VOUT All ICs operational
Installed Connected to PGND 2-3 Connected to GND Shutdown
Not installed Connected to VIN through R2 2-3 Connected to GND
MAX13487E shutdown, all other
ICs operational
Table 2. Driver and Receiver JU3 Functions
SHUNT POSITION RE PIN MAX13487E AUTODIRECTION OR RECEIVER MODE
Installed Connected to VOUT AutoDirection enabled*
Not installed Connected to GND through R9 Receiver RO output enabled