LTM4601AV-1 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTM4601AV-1' PDF : 28 Pages View PDF
LTM4601A/LTM4601A-1
APPLICATIONS INFORMATION
is frequency and m is the number of parallel phases. This
calculation process can be easily fulļ¬lled using our Linear
Technology Ī¼Module Design Tool.
Fault Conditions: Current Limit and Overcurrent
Foldback
LTM4601A has a current mode controller, which inher-
ently limits the cycle-by-cycle inductor current not only
in steady-state operation, but also in transient.
To further limit current in the event of an overload condition,
the LTM4601A provides foldback current limiting. If the
output voltage falls by more than 50%, then the maximum
output current is progressively lowered to about one sixth
of its full current limit value.
Soft-Start and Tracking
The TRACK/SS pin provides a means to either soft-start
the regulator or track it to a different power supply. A
capacitor on this pin will program the ramp rate of the
output voltage. A 1.5Ī¼A current source will charge up the
external soft-start capacitor to 80% of the 0.6V internal
voltage reference minus any margin delta. This will control
the ramp of the internal reference and the output voltage.
The total soft-start time can be calculated as:
tSOFTSTART 0.8 ā¢
0.6V ā VOUT(MARGIN)
ā¢ CSS
1.5Ī¼A
down with another regulator. The master regulatorās output
is divided down with an external resistor divider that is the
same as the slave regulatorās feedback divider. Figure 5
shows an example of coincident tracking. Ratiometric
modes of tracking can be achieved by selecting different
resistor values to change the output tracking ratio. The
master output must be greater than the slave output for
the tracking to work. Figure 6 shows the coincident output
tracking characteristics.
MASTER
OUTPUT
R2
TRACK CONTROL
60.4k
VIN
R1
40.2k
100k
VIN PLLIN TRACK/SS
PGOOD
VOUT
SLAVE OUTPUT
MPGM
RUN
VFB
MARG0
COUT
CIN
COMP
INTVCC
LTM4601A MARG1
VOUT_LCL
DRVCC
DIFFVOUT
VOSNS+
VOSNSā
SGND PGND fSET
RSET
40.2k
4601A F05
Figure 5. Coincident Tracking
When the RUN pin falls below 1.5V, then the SS pin is reset
to allow for proper soft-start control when the regulator
is enabled again. Current foldback and force continuous
mode are disabled during the soft-start process. The
soft-start function can also be used to control the output
ramp up time, so that another regulator can be easily
tracked to it.
OUTPUT
VOLTAGE
MASTER OUTPUT
SLAVE OUTPUT
Output Voltage Tracking
Output voltage tracking can be programmed externally
using the TRACK/SS pin. The output can be tracked up and
TIME
4601A F06
Figure 6. Coincident Output Tracking Characteristics
4601afb
13
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