LTC3719EG Linear Technology, LTC3719EG Datasheet - Page 12

• Manufacturer Part Number: LTC3719EG
• Description: IC SW REG SYNC STEP-DOWN 36-SSOP
• Manufacturer: Linear Technology

Specifications of LTC3719EG

• Applications: Controller, AMD Opteron™
• Voltage - Input: 4 ~ 36 V
• Number Of Outputs: 1
• Voltage - Output: 0.8 ~ 1.55 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 36-SSOP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

LTC3719
OPERATIO
Frequency Synchronization
The phase-locked loop allows the internal oscillator to be
synchronized to an external source via the PLLIN pin. The
output of the phase detector at the PLLFLTR pin is also the
DC frequency control input of the oscillator that operates
over a 140kHz to 310kHz range corresponding to a DC
voltage input from 0V to 2.4V. When locked, the PLL aligns
the turn on of the top MOSFET to the rising edge of the
synchronizing signal. When PLLIN is left open, the PLLFLTR
pin goes low, forcing the oscillator to minimum frequency.
Input capacitance ESR requirements and efficiency losses
are substantially reduced because the peak current drawn
from the input capacitor is effectively divided by two and
power loss is proportional to the RMS current squared. A
two stage, single output voltage implementation can
reduce input path power loss by 75% and radically reduce
the required RMS current rating of the input capacitor(s).
INTV
Power for the top and bottom MOSFET drivers and most
of the IC circuitry is derived from INTV
EXTV
regulator supplies INTV
taken above 4.8V, the 5V regulator is turned off and an
internal switch is turned on connecting EXTV
This allows the INTV
efficiency external source such as the output of the regu-
lator itself or a secondary winding, as described in the
Applications Information section. An external Schottky
diode can be used to minimize the voltage drop from
EXTV
the specified INTV
applied to EXTV
Differential Amplifier
This controller includes a true unity-gain differential am-
plifier. Sensing both V
lation in high current applications and/or applications
having electrical interconnection losses. The amplifier is
a unity-gain stable, 2MHz gain-bandwidth, >120dB open-
loop gain design. The amplifier has an output slew rate of
5V/ s and is capable of driving capacitive loads with an
12
CC
CC
CC
/EXTV
to INTV
pin is left open, an internal 5V low dropout
CC
CC
CC
Power
U
CC
for additional gate drive capability.
in applications requiring greater than
CC
current. Voltages up to 7V can be
(Refer to Functional Diagram)
power to be derived from a high
OUT
CC
power. If the EXTV
+
and V
OUT
–
benefits regu-
CC
CC
. When the
to INTV
CC
pin is
CC
.
output RMS current typically up to 25mA. The amplifier
is not capable of sinking current and therefore must be
resistively loaded to do so.
Output Overvoltage Protection
An overvoltage comparator, 0V, guards against transient
overshoots (>10%) as well as other more serious condi-
tions that may overvoltage the output. In this case, the top
MOSFET is turned off and the bottom MOSFET is turned on
until the overvoltage condition is cleared.
Power Good (PGOOD)
The PGOOD pin is connected to the drain of an internal
MOSFET. The MOSFET turns on when the output voltage
is not within 10% of its nominal output level as deter-
mined by the feedback divider. When the output is within
10 s and the PGOOD pin should be pulled up by an
external resistor to a source of up to 7V.
Short-Circuit Detection
The RUN/SS capacitor is used initially to limit the inrush
current from the input power source. Once the control-
lers have been given time, as determined by the capacitor
on the RUN/SS pin, to charge up the output capacitors
and provide full-load current, the RUN/SS capacitor is
then used as a short-circuit timeout circuit. If the output
voltage falls to less than 70% of its nominal output
voltage the RUN/SS capacitor begins discharging as-
suming that the output is in a severe overcurrent and/or
short-circuit condition. If the condition lasts for a long
enough period as determined by the size of the RUN/SS
capacitor, the controller will be shut down until the
RUN/SS pin voltage is recycled. This built-in latchoff can
be overidden by providing a current >5 A at a compli-
ance of 5V to the RUN/SS pin. This current shortens the
soft-start period but also prevents net discharge of the
RUN/SS capacitor during a severe overcurrent and/or
short-circuit condition. Foldback current limiting is acti-
vated when the output voltage falls below 70% of its
nominal level whether or not the short-circuit latchoff
circuit is enabled.
10% of its nominal value, the MOSFET is turned off within
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