LTM4606IV-PBF View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTM4606IV-PBF' PDF : 24 Pages View PDF
LTM4606
APPLICATIONS INFORMATION
1.00
0.95
1-PHASE
0.90
2-PHASE
3-PHASE
0.85
4-PHASE
6-PHASE
0.80
0.75
0.70
0.65
0.60
0.55
0.50
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0
0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9
DUTY CYCLE (VO/VIN)
4612 F05
Figure 3. Normalized Output Ripple Current vs Duty Cycle, Dlr = VOT/LI
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 1.5ÎĽA 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 •
0.6V – VOUT(MARGIN)
• CSS
1.5µA
When the RUN pin falls below 2.5V, 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 Tracking
Output voltage tracking can be programmed externally
using the TRACK/SS pin. The output can be tracked up and
12
down with another regulator. The master regulator’s output
is divided down with an external resistor divider that is the
same as the slave regulator’s feedback divider. Figure 4
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 5 shows the coincident output
tracking characteristics.
VIN
CIN
MASTER
OUTPUT
TRACK
CONTROL
R2
60.4k
R1
19.1k
100k
VD
VIN PLLIN
PGOOD
VOUT
RUN LTM4606 VFB
COMP
FCB
INTVCC
DRVCC
fSET
TRACK/SS
SGND
MARG0
MARG1
MPGM
PGND
SLAVE
OUTPUT
COUT 2.5V
19.1k
4606 F04
Figure 4. Output Voltage Coincident Tracking
4606f
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