Datasheet

LTM4614
9
4614fb
applicaTions inForMaTion
Figure 2. Dual Outputs (1.5V and 1.2V) with Tracking
4614 F02
PGOOD1
V
OUT1
FB1
COMP1
TRACK1
RUN/SS1
PGOOD2
V
OUT2
FB2
COMP2
TRACK2
RUN/SS2
LTM4614
V
IN1
V
IN2
GND1 GND2
R3
10k
R
TB
4.99k
R
FB2
5.76k
V
IN
OR
CONTROL
RAMP
C4
22µF
6.3V
C7
100µF
6.3V
C3
100µF
6.3V
1.2V
4A
1.5V
4A
PGOOD1
R4
10k
PGOOD2
C9
22µF
6.3V
C2
22µF
6.3V
C1
22µF
6.3V
V
IN
3V TO 5.5V
R
FB1
10k
R
TA
10k
1.5V
C
SSEXT1
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 0.6V, the LTM4614 will be in a low quiescent
current state. At least a 0.9V level applied to the enable
pins will turn on the LTM4614 regulators. The voltage on
the RUN/SS pins clamp the control loop’s current com-
parator threshold. A RUN/SS pin voltage of 2.375V upon
completion of soft-start guarantees the regulator can deliver
full output current. These pins can be used to sequence
the regulator channels. Soft-start control is provided by
a 1M pull-up resistor (R
SS
) and a 1000pF capacitor (C
SS
)
as shown in the Block Diagram for each channel. Option-
ally, an
external capacitor (C
SSEXT
) can be applied to the
RUN/SS pin to increase soft-start time. A typical value is
0.01µF. Soft-start time is approximately given by:
t
SOFTSTART
=In
V
IN
V
IN
–1.8V






•R
SS
• C
SS
+C
SSEXT
( )
where R
SS
and C
SS
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. To turn off the module while V
IN
remains active, the
RUN/SS pin should be pulled low with a falling edge ≤ 1µs
to ensure the device does not transition slowly through
the internal undervoltage lockout threshold.
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=
R
FB1
4.99k +R
FB1






• Master
Slave = 1+
4.99k
R
FB1






• TRACK1