LTC1435
W
U
TYPICAL PERFORMANCE CHARACTERISTICS
Soft Start: Load Current vs Time
Burst Mode Operation
VOUT
20mV/DIV
RUN/SS
5V/DIV
INDUCTOR
CURRENT
1A/DIV
VITH
200mV/DIV
1435 G17
ILOAD = 50mA
1435 G16
U
U
U
PIN FUNCTIONS
ever EXTVCC is higher than 4.7V. See EXTVCC connection
in Applications Information section. Do notexceed10V on
this pin. Connect to VOUT if VOUT ≥ 5V.
COSC (Pin 1): External capacitor COSC from this pin to
ground sets the operating frequency.
RUN/SS (Pin 2): Combination of Soft Start and Run
Control Inputs. A capacitor to ground at this pin sets the
ramp timeto fullcurrentoutput. The timeis approximately
0.5s/µF. Forcing this pin below 1.3V causes the device to
be shut down. In shutdown all functions are disabled.
PGND (Pin 10): Driver Power Ground. Connects to source
of bottom N-channel MOSFET and the (–) terminal of CIN.
BG (Pin 11): High Current Gate Drive for Bottom
N-Channel MOSFET. Voltage swing at this pin is from
ground to INTVCC.
ITH (Pin 3): Error Amplifier Compensation Point. The
current comparator threshold increases with this control
voltage. Nominal voltage range for this pin is 0V to 2.5V.
INTVCC (Pin 12): Output of the Internal 5V Regulator and
EXTVCC Switch. The driver and control circuits are pow-
ered from this voltage. Must be closely decoupled to power
ground with a minimum of 2.2µF tantalum or electrolytic
capacitor.
SFB (Pin 4): Secondary Winding Feedback Input. Nor-
mally connected to a feedback resistive divider from the
secondary winding. This pin should be tied to: ground to
force continuous operation; INTVCC in applications that
don’tuseasecondarywinding;andaresistivedividerfrom
the output in applications using a secondary winding.
VIN (Pin 13): Main Supply Pin. Must be closely decoupled
to the IC’s signal ground pin.
SW (Pin 14): Switch Node Connection to Inductor. Volt-
age swing at this pin is from a Schottky diode (external)
voltage drop below ground to VIN.
SGND (Pin 5): Small-Signal Ground. Must be routed
separately from other grounds to the (–) terminal of COUT
.
VOSENSE (Pin 6): Receives the feedback voltage from an
BOOST (Pin 15): Supply to Topside Floating Driver. The
bootstrap capacitor is returned to this pin. Voltage swing
at this pin is from INTVCC to VIN + INTVCC.
external resistive divider across the output.
SENSE– (Pin 7): The (–) Input to the Current Comparator.
SENSE+ (Pin 8): The (+) Input to the Current Comparator.
Built-in offsets between SENSE– and SENSE+ pins in
conjunction with RSENSE set the current trip thresholds.
TG (Pin 16): High Current Gate Drive for Top N-Channel
MOSFET. This is the output of a floating driver with a
voltage swing equal to INTVCC superimposed on the
switch node voltage SW.
EXTVCC (Pin 9): Input to the Internal Switch Connected to
INTVCC. This switch closes and supplies VCC power when-
5
Linear [ Linear ]
