6
Rev A
DEMO MANUAL DC2685B
I/O LED Indicators
The DC2684A-B features two LEDs to indicate the states
of the LTC4291-1/LTC4292 general purpose input/output
pins GP0 and GP1. These pins are configured as inputs
or outputs via I
2
C. GP1 and GP0 are referenced to DGND
and driven by the LTC4291-1 when set as outputs (Figure
5). J2 provides test points for these pins.
DEMONSTRATION CIRCUIT 2684A-B DAUGHTER CARD
V
DD
GP1
GP0
DGND
J2, PIN 5
J2, PIN 6
U2
LTC4291-1
DC2685B F05
R28
560Ω
R29
560Ω
D3
GRN
GP0
D2
GRN
GP1
Figure 5. DC2684A-B, LTC4291-1 General Purpose I/O LED
Indicators
Figure 6. DC2684A-B, LTC4291-1 I
2
C and Address Connections
I
2
C Communication and Addressing
The LTC4292/LTC4291 internal registers are accessed via
I
2
C to read and/or write configuration, status, events and
interrupt registers. The I
2
C lines SDAOUT, SDAIN and SCL
connect to the 30-pin connector (Figure 6). Subsequently,
the I
2
C bus is accessed on the motherboard. SDAOUT and
SDAIN are tied together through shunt resistor R11 on
the DC2684A-B for a common SDA line.
The LTC4291-1 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 con-
figuration on the motherboard. See Figure 6 and Table 4.
4PV# Jumpers
The
4PVALID
pin of the LTC4291-1 is set by the 4PV#
jumper JP2 on the DC2684A-B. See Table 1 for jumper
settings. This jumper configuration along with Auto mode
reset state is used to automatically determine the number
DGND
SDAOUT
SDAIN
SCL
INT
SDAOUT
SDAIN
SCL
INT
AD3
AD2
AD1
AD0
AD3
AD2
TO 30-PIN
CONNECTOR
U2
LTC4291-1
R11
0Ω
DC2685B F06
R9
0Ω
R10
0Ω
of powered pairs. Refer to Table 1 for the configuration
description.
Power Mode and Power Path Components
The DC2684A-B power mode jumpers PM1 and PM0
either tie the respective LTC4291-1/LTC4292 PWRMD1
and PWRMD0 pins to V
EE
or CAP2 through a 100Ω resis-
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-B have been selected to handle
all four power levels.
Surge Protection
The DC2684A-B has basic surge protection components
across the V
EE
supply, V
EE
and AGNDP supply pins, and
OUTnM pins. Refer to the LTC4291-1/LTC4292 hardware
data sheet for further details on surge protection. D5 and
C27 on the DC2684A-B provide example bulk TVS and
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