LTC3609EWKG#PBF Linear Technology, LTC3609EWKG#PBF Datasheet - Page 16

• Manufacturer Part Number: LTC3609EWKG#PBF
• Description: IC DC/DC CONV STP-DWN 6A 52-QFN
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC3609EWKG#PBF

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 2
• Voltage - Output: 0.6 ~ 36 V
• Current - Output: 6A
• Voltage - Input: 4 ~ 32 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 52-QFN
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Frequency - Switching: -

LTC3609
applicaTions inForMaTion
The EXTV
and control power from the output or another external
source during normal operation. Whenever the EXTV
pin is above 4.7V the internal 5V regulator is shut off and
an internal 50mA P-channel switch connects the EXTV
pin to INTV
until this pin drops below 4.5V. Do not apply more than
7V to the EXTV
following list summarizes the possible connections for
EXTV
1. EXTV
internal 5V regulator.
2. EXTV
supply compatible with the MOSFET gate drive require-
ments (typically 5V) can improve overall efficiency.
3. EXTV
The low voltage output can be boosted using a charge
pump or flyback winding to greater than 4.7V. The system
will start-up using the internal linear regulator until the
boosted output supply is available.
Soft-Start and Latchoff with the RUN/SS Pin
The RUN/SS pin provides a means to shut down the LTC3609
as well as a timer for soft-start and overcurrent latchoff.
Pulling the RUN/SS pin below 0.8V puts the LTC3609 into
a low quiescent current shutdown (I
the pin allows an internal 1.2µA current source to charge
up the external timing capacitor, C
pulled all the way to ground, there is a delay before start-
ing of about:
When the voltage on RUN/SS reaches 1.5V, the LTC3609
begins operating with a clamp on I
0.9V. As the RUN/SS voltage rises to 3V, the clamp on I
is raised until its full 2.4V range is available. This takes an

t
DELAY
CC
:
CC
CC
CC
CC
connected to an external supply. A high efficiency
=
grounded. INTV
connected to an output derived boost network.
CC
pin can be used to provide MOSFET gate drive
1 2
1 5
. INTV
.
.
CC
µ
V
A
pin and ensure that EXTV
C
CC
SS
power is supplied from EXTV
=
(
CC
1 3
. /
is always powered from the
s F C
µ
SS
)
Q
. If RUN/SS has been
TH
SS
< 30µA). Releasing
of approximately
CC
≤ V
IN
. The
CC
CC
CC
TH
additional 1.3s/µF , during which the load current is folded
back until the output reaches 75% of its final value.
After the controller has been started and given adequate
time to charge up the output capacitor, C
short-circuit timer. After the RUN/SS pin charges above 4V,
if the output voltage falls below 75% of its regulated value,
then a short-circuit fault is assumed. A 1.8µA current then
begins discharging C
the RUN/SS pin drops to 3.5V, then the controller turns
off both power MOSFETs, shutting down the converter
permanently. The RUN/SS pin must be actively pulled
down to ground in order to restart operation.
The overcurrent protection timer requires that the soft-start
timing capacitor, C
that the output is in regulation by the time C
the 4V threshold. In general, this will depend upon the
size of the output capacitance, output voltage and load
current characteristic. A minimum soft-start capacitor
can be estimated from:
Generally 0.1µF is more than sufficient.
Overcurrent latchoff operation is not always needed or
desired. Load current is already limited during a short
circuit by the current foldback circuitry and latchoff op-
eration can prove annoying during troubleshooting. The
feature can be overridden by adding a pull-up current
greater than 5µA to the RUN/SS pin. The additional cur-
rent prevents the discharge of C
shortens the soft-start period. Using a resistor to V
shown in Figure 5a is simple, but slightly increases shut-
down current. Connecting a resistor to INTV
in Figure 5b eliminates the additional shutdown current,
but requires a diode to isolate C
must be able to pull RUN/SS above the 4.2V maximum
threshold of the latchoff circuit and overcome the 4µA
maximum discharge current.
C
SS
> C
OUT
V
OUT
SS
R
, be made large enough to guarantee
SS
SENSE
. If the fault condition persists until
(10
–4
SS
SS
[F/V s])
during a fault and also
. Any pull-up network
SS
SS
CC
is used as a
has reached
as shown
IN
3609fb
as