Datasheet

REFIN/MODE Operation Modes
The EV kit jumper JU1 configures the MAX4208 for direct
reference, buffered reference, or shutdown mode. The
reference voltage at REF sets the output voltage DC sig-
nal, OUT, when the differential input signal V
IN+
- V
IN-
equals zero. In direct-reference-mode operation, con-
nect a user reference voltage directly to the REF PCB
pad. In buffered-reference-mode operation, connect a
user reference voltage to the REFIN/MODE input PCB
pad or use the resistor-divider network R3 and R4 to
provide a reference voltage for REFIN/MODE, scaled
from VDD. The network is configured to scale the volt-
age at REFIN/MODE to one-half of VDD. Replace resis-
tors R3 and R4 to modify the voltage applied to
REFIN/MODE using the following equation:
where VDD is the input supply voltage to the EV kit.
In buffered-reference mode, the MAX4208 internally
buffers the REFIN/MODE voltage onto REF.
Note: Do not connect an external source to the REF PCB
pad in buffered-reference mode. See Table 2 for jumper
JU1 configurations.
REF Input
The EV kit’s jumper JU3 must be configured properly
for appropriate reference-voltage operation. In direct
reference mode, install a shunt on jumper JU3 to con-
nect REF to the on-board ground (GND), or remove the
shunt to connect a user reference voltage to the REF
input PCB pad. For either buffered-reference mode,
REF must not be connected to a reference voltage;
thus, the shunt on jumper JU3 must not be installed.
See Table 2 for jumper JU3 configurations.
Optional capacitor C6 can be used for reference-volt-
age stability/filtering. Choose an appropriate value as
needed.
On-Board Current Sensing
The MAX4208 EV kit can be configured for on-board
current sensing by installing a surface-mount 1206
sense resistor at R7, located between the IN+ and IN-
PCB pads. Use the following equation to select the
value for resistor R7:
where I
IN
is the maximum current flowing across resis-
tor R7 and 30mV is a suggested sense voltage. 30mV x
148V/V gives a 4.4V output swing. Refer to the
R7
30mV
I
IN
=
V VDD x
R4
R3 R4
REFIN/MODE
=
+
⎛
⎝
⎜
⎞
⎠
⎟
Evaluates: MAX4208/MAX4209
MAX4208 Evaluation Kit
_______________________________________________________________________________________ 3
Table 2. Jumpers JU1 and JU3 Configurations
MODE
JU1 SHUNT
POSITION
REFIN/MODE
PIN
JU3 SHUNT
POSITION
REF PIN EV KIT FUNCTION
Installed
Connected to
GND
JU1 disables the internal REF buffer.
JU3 sets the REF voltage to GND.
Direct-reference-mode
operation
1-2
Connected to
VSS
Not installed
Connected to
user reference
voltage
JU1 disables the internal REF buffer.
JU3 allows the user to set the REF
voltage directly. Apply a user reference
voltage to the REF PCB pad in the 0V
and VDD - 1.6V range.
Shutdown mode 1-3
Connected to
VDD
— — Entire IC is in shutdown. I
CC
< 5µA.
Buffered-reference-
mode operation
(on-board reference)
1-4
Connected to
VDD / 2
Not installed Not connected
The IC buffers the on-board VDD / 2
onto REF. Do not install JU3 or connect
an external source to the REF PCB pad.
Buffered-reference-
mode operation (user
reference)
Not installed
Connected to
user reference
voltage
Not installed Not connected
The IC buffers a user reference voltage
onto REF. Apply a user reference
voltage to the REFIN/MODE PCB pad in
the range of VSS + 200mV and VDD -
1.6V. Do not install JU3 or connect an
external source to the REF PCB pad.