LTC3601EUD#PBF Linear Technology, LTC3601EUD#PBF Datasheet - Page 9

• Manufacturer Part Number: LTC3601EUD#PBF
• Description: IC REG BUCK 1.5A ADJ 16QFN
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC3601EUD#PBF

• Internal Switch(s): Yes
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 0.5 ~ 14.52 V
• Current - Output: 1.5A
• Frequency - Switching: 800kHz ~ 4MHz
• Voltage - Input: 4 ~ 15 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-WQFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

OPERATION
The LTC3601 is a current mode, monolithic, step-down
regulator capable of providing up to 1.5A of output current.
Its unique controlled on-time architecture allows extremely
low step-down ratios while maintaining a constant switch-
ing frequency. Part operation is enabled by raising the
voltage on the RUN pin above 1.25V nominally.
Main Control Loop
In normal operation the internal top power MOSFET is
turned on for a fi xed interval determined by an internal
one-shot timer (“ON” signal in the Block Diagram). When
the top power MOSFET turns off, the bottom power
MOSFET turns on until the current comparator, I
trips, thus restarting the one-shot timer and initiating the
next cycle. The inductor current is monitored by sensing
the voltage drop across the SW and PGND nodes of the
bottom power MOSFET. The voltage at the ITH pin sets the
I
tor valley current. The error amplifi er EA adjusts this ITH
voltage by comparing an internal 0.6V reference to the
feedback signal, V
example, the load current increases, the feedback voltage
will decrease relative to the internal 0.6V reference. The
ITH voltage then rises until the average inductor current
matches that of the load current.
The operating frequency is determined by the value of the
RT resistor, which programs the current for the internal
oscillator. An internal phase-locked loop servos the switch-
ing regulator on-time to track the internal oscillator edge
and force a constant switching frequency. A clock signal
can be applied to the SYNC/MODE pin to synchronize the
switching frequency to an external source. The regulator
defaults to forced continuous operation once the clock
signal is applied.
At low load currents the inductor current can drop to
zero or become negative. If the LTC3601 is confi gured for
Burst Mode operation, this inductor current condition is
detected by the current reversal comparator, I
in turn shuts off the bottom power MOSFET and places
CMP
comparator threshold corresponding to the induc-
FB
, derived from the output voltage. If, for
REV
, which
CMP
,
the part into a low quiescent current sleep state resulting
in discontinuous operation and increased effi ciency at low
load currents. Both power MOSFETs will remain off with
the part in sleep and the output capacitor supplying the
load current until the ITH voltage rises suffi ciently to initi-
ate another cycle. Discontinuous operation is disabled by
tying the MODE/SYNC pin to ground placing the LTC3601
into forced continuous mode. During forced continuous
mode, continuous synchronous operation occurs regard-
less of the output load current.
“Power Good” Status Output
The PGOOD open-drain output will be pulled low if the
regulator output exits a ±8% window around the regulation
point. This condition is released once regulation within
a 5% window is achieved. To prevent unwanted PGOOD
glitches during transients or dynamic V
LTC3601 PGOOD falling edge includes a fi lter time of ap-
proximately 40μs.
V
In order to protect the internal power MOSFET devices
against transient voltage spikes, the LTC3601 constantly
monitors the V
V
by shutting off both power MOSFETs. Once V
below 16.5V, the regulator immediately resumes normal
operation. The regulator does not execute its soft-start
function when exiting an overvoltage condition.
Short-Circuit Protection
Foldback current limiting is provided in the event the
output is inadvertently shorted to ground. During this
condition the internal current limit (I
to approximately one-third its normal value. This feature
reduces the heat dissipation in the LTC3601 during short-
circuit conditions and protects both the IC and the input
supply from any potential damage.
IN
IN
Overvoltage Protection
rises above 17.5V, the regulator suspends operation
IN
pin for an overvoltage condition. When
LIM
LTC3601
OUT
) will be lowered
changes, the
IN
drops
3601fa
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