LTM4614(RevA) Ver la hoja de datos (PDF) - Linear Technology
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LTM4614 Datasheet PDF : 20 Pages
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LTM4614
APPLICATIONS INFORMATION
Fault Conditions: Current Limit and Overcurrent
Foldback
The LTM4614 has current mode control, which inher-
ently limits the cycle-by-cycle inductor current not only
in steady-state operation, but also in transient.
Along with foldback current limiting in the event of an
overload condition, the LTM4614 has overtemperature
shutdown protection that inhibits switching operation
around 150°C for each channel.
Run Enable and Soft-Start
The RUN/SS pins provide a dual function of enable and
soft-start control for each channel. The RUN/SS pins are
used to control turn on of the LTM4614. While each enable
pin is below 0.5V, the LTM4614 will be in a low quiescent
current state. At least a 0.8V level applied to the enable
pins will turn on the LTM4614 regulators. This pin can be
used to sequence the regulator channels. The soft-start
control is provided by a 1M pull-up resistor (RSS) and a
1000pF capacitor (CSS) as drawn in the Block Diagram for
each channel. An external capacitor can be applied to the
RUN/SS pin to increase the soft-start time. A typical value
is 0.01μF. The approximate equation for soft-start:
tSOFTSTART
=
In
⎛
âŽâŽœ
VIN
VIN ⎞
– 1.8V ⎠⎟
• RSS
• CSS
where RSS and CSS are shown in the Block Diagram of
Figure 1, and 1.8V is the soft-start upper range. 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 pins. Either output can be tracked up
or 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 to
implement coincident tracking. The LTM4614 uses a very
accurate 4.99k resistor for the internal top feedback resistor.
Figure 2 shows an example of coincident tracking.
Equations:
TRACK1=
⎛
âŽâŽœ
RFB1
4.99k + RFB1
⎞
⎠⎟
•
Master
Slave
=
⎛
âŽâŽœ
1+
4.99k
RFB1
⎞
⎠⎟
•
TRACK1
VIN 3V TO 5.5V
C1
C2
22μF
22μF
6.3V
6.3V
PGOOD1
R3
10k
VIN1
PGOOD1
VIN2
PGOOD2
1.2V
4A
VOUT1
VOUT2
C3
100μF
6.3V
C4
RTB
22μF
4.99k
6.3V 1.5V
RFB1
10k
RTA
10k
FB1
COMP1
LTM4614
FB2
COMP2
TRACK1
TRACK2
RUN/SS1
RUN/SS2
GND1 GND2
PGOOD2
R4
10k
VIN OR
CONTROL
RAMP
CSSEXT1
RFB2
5.76k
C7
100μF
6.3V
1.5V
4A
C9
22μF
6.3V
4614 F02
Figure 2. Dual Outputs (1.5V and 1.2V) with Tracking
4614fa
10
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