Analog Devices DC2685A Demo Manual page 6

DEMO MANUAL DC2685A
DEMONSTRATION CIRCUIT 2684A DAUGHTER CARD
I/O LED Indicators
The DC2684A features two LEDs to indicate the states
of the LTC4292/LTC4291 general purpose input/output
pins GP0 and GP1. These pins are configured as inputs
2
or outputs via I C. GP1 and GP0 are referenced to DGND
and driven by the LTC4291 when set as outputs (Figure
5). J2 provides test points for these pins.
V
DD
U2
LTC4291
GP1
GP0
DGND
DC2685A F05
Figure 5. DC2684A, LTC4291 General Purpose I/O LED Indicators
2
I C Communication and Addressing
The LTC4292/LTC4291 internal registers are accessed via
2
I C to read and/or write configuration, status, events and
2
interrupt registers. The I
connect to the 30-pin connector (Figure 6). Subsequently,
2
the I C bus is accessed on the motherboard. SDAOUT and
SDAIN are tied together through shunt resistor R11 on
the DC2684A for a common SDA line.
The LTC4291 address pins AD0 and AD1 are tied to DGND
through shunt resistors R9 and R10 respectively. This
sets these two address bits low. Address pins AD2 and
AD3 are brought out to the 30-pin connector for configu-
ration on the motherboard. See Figure 6 and Table 4.
4PV# Jumpers
The 4PVALID pin of the LTC4291 is set by the 4PV# jumper
JP2 on the DC2684A. See Table 1 for jumper settings. This
jumper configuration along with Auto mode reset state is
used to automatically determine the number of powered
pairs. Refer to Table 1 for the configuration description.
6
R28 R29
560 560
D2 D3
GRN GRN
GP1 GP0
J2, PIN 5
J2, PIN 6
C lines SDAOUT, SDAIN and SCL
SDAOUT
SDAIN
SCL
INT
U2
LTC4291
AD3
AD2
AD1
AD0
DGND
DC2685A F06
Figure 6. DC2684A, LTC4291 I
Power Mode and Power Path Components
The DC2684A power mode jumpers PM1 and PM0 either
tie the respective LTC4292/LTC4291 PWRMD1 and
PWRMD0 pins to V or CAP2 through a 100Ω resis-
EE
tor. This configures the maximum port output power in
the Auto mode reset state (see Table 2). The power path
components (Hot Swap MOSFETs and resistors) for each
channel on the DC2684A have been selected to handle all
four power levels.
Surge Protection
The DC2684A has basic surge protection components
across the V supply, V
EE EE
OUTnM pins. Refer to the LTC4292/LTC4291 hardware
data sheet for further details on surge protection. D5
and C27 on the DC2684A provide example bulk TVS and
capacitance components; these components must be
sized to the final system requirements.
R11
0
SDAOUT
SDAIN
SCL
TO 30-PIN
INT
CONNECTOR
AD3
AD2
R9 R10
0 0
2
C and Address Connections
and AGNDP supply pins, and
UG-1339 Rev 0