Current Limits; Regulating Iout(Slave); Out(Slave) : Circuit Description - Linear Technology Analog Devices LT8708-1 Datasheet

LT8708-1
APPLICATIONS INFORMATION
more chips' VINHIMON or VOUTLOMON comparator is
triggered, the RVSOFF pin is pulled low to prevent the
entire multiphase system from delivering reverse current
and power. The multiphase system will exit the RVSOFF
operation when all the VINHIMON and VOUTLOMON com-
parators are de-asserted.
CONFIGURING THE I
IN(SLAVE)
As discussed in the Monitoring and Limiting: I
section, the LT8708-1 can monitor and limit the input
current independently of the master. The current limiting
discussed in this section is intended to be secondary, or
redundant, since the master is primarily in control of the
amount of current commanded from the slave.
As shown in Figure 9, the LT8708-1 measures I
with the CSPIN and CSNIN pins and can independently
monitor and limit the current in both positive and nega-
tive directions. The operation of the input current moni-
tor circuits is identical to the LT8708. More information
about configuring these circuits can be found in the I
and I Current Monitoring and Limiting section of the
OUT
LT8708 data sheet.
When setting the I
IN(SLAVE)
mended to set them equal to or higher than the magni-
tudes of the I limits. Consider that if the slave
IN(MASTER)
R
SENSE1
FROM
SYSTEM
V
IN I
IN(SLAVE)
CSPIN CSNIN
LT8708-1
+
–
g = 1m
m
– +
A3
1.21V
20 A
1.209V
20 A
IMON_INN IMON_INP
R C R
IMON_INN IMON_INN IMON_INP
Figure 9. I
IN(SLAVE)
26

CURRENT LIMITS

IN(SLAVE)
IN(SLAVE)
current limits, it is recom-
TO
CONTROLLER
V
IN
+
TO INDUCTOR
CURRENT
EA1
CONTROL
–
+
EA5
–
V
C
C
IMON_INP
Current Monitor and Limit
For more information
reaches input current limiting before the master, the slave
can no longer deliver additional current as requested by
the master. With equal I
slight output current mismatch, and hence slight thermal
imbalance can still happen due to device tolerance. Bench
evaluation should be carried out to ensure the selected
I limits meet the application's thermal and stabil-
IN(SLAVE)
ity requirements.
REGULATING I
OUT(SLAVE)
I : Circuit Description
OUT(SLAVE)
This section describes the control circuitry in the
LT8708-1 that regulates the output current I
The master LT8708 sends the ICP and ICN control signals
to the slave LT8708-1 to set I
Function: I
OUT(SLAVE)
information.
Figure 10 shows the primary LT8708-1 circuits involved in
the regulation of I
IN
in Figure 1. I
OUT(SLAVE)
with ICP and ICN setting the desired current. The feedback
loop involves the following sections:
• The V pin controls the inductor current, thus indi-
C
rectly controlling I
FROM
CONTROLLER
V
OUT
LT8708-1
87081 F08
R
17.4k
Figure 10. I
OUT(SLAVE)
www.analog.com
and I
IN(SLAVE) IN(MASTER)
. See the Transfer
OUT(SLAVE)
vs I section for related
OUT(MASTER)
. Additional circuitry is shown
OUT(SLAVE)
is regulated by a feedback loop
. Higher V
OUT(SLAVE)
R
SENSE2
TO SYSTEM
V
OUT
I
OUT(SLAVE)
ICP ICN
FROM FROM
MASTER MASTER
CSPOUT CSNOUT ICP ICN
+ – + –
A1
+
1.209V
EA6
–
IMON_OP
70 A
IMON_OP
C
IMON_OP
Current Regulation and Monitor
limits,
.
OUT(SLAVE)
voltage
C
TO INDUCTOR
CURRENT
CONTROL
V
C
87081 F09
Rev 0