Datasheet

LTC2978A
77
2978afa
For more information www.linear.com/LTC2978A
Figure 31. DC1613 Controller Connections When LTC2978A Powered Directly from 3.3V
V
PWR
V
DD33
V
DD33
V
DD25
SCL
SDA
SHARE_CLK
LTC2978A_3.3V
IDEAL
DIODE
0R’d 3.3V
0.1µF0.1µF
WP GND
2978a F31
5.49k
LTC2978A
PIN CONNECTIONS
OMITTED FOR
CLARITY
TO DC1613
I
2
C/SMBUS/PMBUS
CONTROLLER
NOTE: DC1613 CONTROLLER I
2
C CONNECTIONS ARE OPTO-ISOLATED
ISOLATED 3.3V FROM CONTROLLER CAN BE BACK DRIVEN AND WILL ONLY DRAW < 10µA
ISOLATED 3.3V CURRENT LIMIT = 100mA
TO/FROM OTHER
LTC2978As
10k10k
SYSTEM
3.3V
TP0101K-SSOT23
V
IN
GND
CTL
SENSE
GATE
STAT
LTC4412
ISOLATED 3.3V
SCL
SDA
GND
APPLICATIONS INFORMATION
Figure 31 shows the recommended schematic to use when
the LTC2978A is powered by the system 3.3V through its
V
DD33
and V
PWR
pins. The LTC4412 ideal ORing circuit al-
lows either the
controller or system to power the LTC2978A.
Because of the controller’s limited current sourcing capabil-
ity, only
the LTC2978As, their associated pull up resistors
and
the I
2
C/SMBus pull-up resistors should be powered
from the ORed 3.3V supply. In addition, any device sharing
I
2
C/SMBus bus connections with the LTC2978A should not
have body diodes between the SDA/SCL pins and its V
DD
node because this will interfere with bus communication
in the absence of system power.
The DC1613 controller’s I
2
C/SMBus connections are
opto-isolated from the PC’s USB port. The 3.3V supply
from the controller and the LTC2978A’s V
DD33
pin can be
paralleled because the LTC LDOs that generate these volt-
ages can
be backdriven and draw <10μA. The controller’s
3.3V current limit is 100mA.