4
dc1880af
DEMO MANUAL DC1880A
aDDitional information
VL Logic Supply
Table 1 lists several ways to supply power to the VL pin.
Methods 1a/b/c are recommended for most purposes.
Table 1. Recommended Options for Powering the VL Supply
METHOD
DC590
JP6
DC1880A
JP12
DC1880A
JP11
SOURCE FOR
VL POWER
1a
1b
1c
5V*
3.3V
OPEN (2.7V)
ON*
ON*
ON*
5V*
3.3V
OPEN (2.9V)
LDO or DC590
LDO or DC590
LDO or DC590
2
EXT
ON*
X**
LDO
3
EXT
OPEN
X**
DC1880A VL TURRET
4
5V* or 3.3V
OPEN
X**
DC590
* (Default)
** Including OPEN (2.9V)
L+ Power Supply Outputs
Enable the L+ power supply outputs by setting their
respective EN_L+ register bits high.
CQ Line Driver Outputs
Enable the CQ line drivers either by input pin (using the
TXEN turrets and/or jumpers JP1/3/7/9) or via the SPI
interface (by setting DRVEN register bits high). See Table 2.
Table 2. CQ Driver Mode Configuration
JP1/3/7/9
SETTING
TXEN
TURRET
DRVEN
BIT
CQ DRIVER
MODE
GND
VL
X
EXT
X
X
X
L/H
0
X
1
0
OFF
ON
ON
OFF/ON
Control the output CQ states using the TXD turrets and/
or jumpers JP2/4/8/10. See Table 3.
Table 3. CQ Driver Output Level Configuration
JP2/4/8/10
SETTING
TXD
TURRET
DRVEN
BIT
CQ DRIVER
MODE*
CQ
LEVEL
GND
GND/VL
EXT
DB9
X
X
L/H
X
X
X
X
H/L**
OFF
ON
ON
ON
L
H/L
H/L
H/L
* From Table 2
** RS232 transceiver U2 inverts
Alternatively, operate the CQ drivers solely via the SPI
interface by tying TXD low and controlling the DRVEN
register bits. This method is suitable for SIO mode and
switching at or below COM2 data rates (38.4kb/s).
TVS Protection
The CQ and L+ pins are protected by 36V TVS diodes for
cable-driving applications.
Serial Port
A DB9 connector enables CQ data to be sent (for one or
more ports) and received (for one port) using PC software
such as a serial terminal program. Jumper JP5 enables
the required RS-232 transceiver.
Select the desired combination of drivers by setting one
or more of JP2/4/8/10 to the DB9 position. Select one CQ
receiver using JP6.
L+ Isolation
If L+ isolation is not needed, Schottky diodes D1-D4 may
be replaced with 0Ω resistors.
Interrupts
The LTC2874 includes an open-drain interrupt line for
signaling the host controller when it needs service. This
signal is accessible on the DC1880A board at the
IRQ
test
point. An LED is also included for convenience.