LTM4604AV Ver la hoja de datos (PDF) - Analog Devices
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LTM4604AV Datasheet PDF : 22 Pages
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LTM4604A
APPLICATIONS INFORMATION
Run Enable and Soft-Start
The RUN/SS pin provides dual functions of enable and soft-
start control. The RUN/SS pin is used to control turn on of
the LTM4604A. While this pin is below 0.5V, the LTM4604A
will be in a 7µA low quiescent current state. A 0.8V thresh-
old will enable the LTM4604A. This pin can be used to
sequence LTM4604A devices. The voltage on the RUN/SS
pin clamps the control loop’s current comparator thresh-
old. A RUN/SS pin voltage of 2.375V upon completion of
soft-start guarantees the regulator can deliver full output
current. The soft-start control is provided by a 1M pull-up
resistor (RSS) and a 1000pF capacitor (CSS) as shown in
the Block Diagram. An external capacitor can be applied to
the RUN/SS pin to increase the soft-start time. A typical
value is 0.01µF. Soft-start time is approximately given by:
( ) tSOFTSTART
=
⎛
lnâŽâŽœ
VIN
VIN
– 1.8V
⎞
⎠⎟
• RSS
CSS + CSSEXT
where RSS and CSS are shown in the Block Diagram of
Figure 1, 1.8V is the soft-start upper range, and CSSEXT
is the additional capacitance for further soft-start con-
trol. The soft-start function can also be used to control
the output ramp-up time, so that another regulator can
be easily tracked. An independent ramp control signal
can be applied to the master ramp, otherwise, connect
the TRACK pin to VIN to disable tracking. To turn off the
module while VIN 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 undervolt-
age lockout threshold.
VTRACK is the track ramp applied to the slave’s TRACK pin.
VTRACK applies the track reference for the slave output up
to the point of the programmed value at which VTRACK
proceeds beyond the 0.8V reference value. The VTRACK
VIN
5V
CIN1
10µF
6.3V
X5R OR X7R
CSSEXT
VIN
PGOOD VOUT
LTM4604A
COMP
FB
RUN/SS TRACK
GND
RAMP
CONTROL
OR VIN
RFB3
1.62k
COUT1
22µF
6.3V ×3
X5R OR
X7R
VMASTER
3.3V
4A
VIN
5V
CIN2
10µF
6.3V
X5R OR X7R
VIN
PGOOD VOUT
LTM4604A
COMP
FB
RUN/SS TRACK
GND
RFB2
5.76k
RFB
5.76k
COUT2
22µF
6.3V ×3
X5R OR
X7R
VSLAVE
1.5V
4A
RFB1
4.99k
4604A F02
Figure 2. Dual Outputs (3.3V and 1.5V) with Tracking
Output Voltage Tracking
MASTER OUTPUT
Output voltage tracking can be programmed externally
using the TRACK pin. The output can be tracked up and
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 LTM4604A uses a very accurate
4.99k resistor for the top feedback resistor. Figure 2 and
Figure 3 show an example of coincident tracking.
SLAVE OUTPUT
TIME
4604A F03
VTRACK
=
RFB2
4.99k + RFB2
•
VMASTER
Figure 3. Output Voltage Coincident Tracking
Rev. D
For more information www.analog.com
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