Additional Information - Linear Technology DC1880A Demo Manual

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
DC590 DC1880A
METHOD JP6 JP12
1a 5V* ON*
1b 3.3V ON*
1c OPEN (2.7V) ON*
2 EXT ON*
3 EXT OPEN
4 5V* or 3.3V OPEN
* (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 TXEN
SETTING TURRET
GND X
VL X
X X
EXT L/H
Control the output CQ states using the TXD turrets and/
or jumpers JP2/4/8/10. See Table 3.
4
DC1880A SOURCE FOR
JP11 VL POWER
5V* LDO or DC590
3.3V LDO or DC590
OPEN (2.9V) LDO or DC590
X** LDO
X** DC1880A VL TURRET
X** DC590
DRVEN CQ DRIVER
BIT MODE
0 OFF
X ON
1 ON
0 OFF/ON
Table 3. CQ Driver Output Level Configuration
JP2/4/8/10 TXD
SETTING TURRET
GND X
GND/VL X
EXT L/H
DB9 X
* 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.
DRVEN CQ DRIVER CQ
BIT MODE* LEVEL
X OFF L
X ON H/L
X ON H/L
H/L** ON H/L
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