LT1683
6
1683fd
TYPICAL PERFORMANCE CHARACTERISTICS
Soft-Start Current vs Temperature V5 Voltage vs Load Current
Gate Drive Undervoltage Lockout
Voltage vs Temperature
TEMPERATURE (°C)
–50 –25 0 25 50 75 100 125 150
V
IN
PIN VOLTAGE (V)
1683 G15
7.3
7.2
7.1
7.0
6.9
6.8
6.7
6.6
6.5
6.4
6.3
GCL = 6V
TEMPERATURE (°C)
–50 –25 0 25 50 75 100 125 150
SS PIN CURRENT (µA)
1683 G16
9.5
9.3
9.1
8.9
8.7
8.5
8.3
8.1
7.9
7.7
7.5
SS VOLTAGE = 0.9V
LOAD CURRENT (mA)
–15
–10 –5 0 5 10 15
V5 PIN VOLTAGE (V)
1683 G17
5.08
5.06
5.04
5.02
5.00
4.98
4.96
T = 125°C
T = 25°C
T = –40°C
PIN FUNCTIONS
Part Supply
V5 (Pin 5): This pin provides a 5V output that can sink or
source 10mA for use by external components. V5 source
current comes from V
IN
. Sink current goes to GND. V
IN
must be greater than 6.5V in order for this voltage to be
in regulation. If this pin is used, a small capacitor (<1µF)
may be placed on this pin to reduce noise. This pin can
be left open if not used.
GND (Pin 11): Signal Ground. The internal error ampli-
fier, negative feedback amplifier, oscillator, slew control
circuitry, V5 regulator, current sense and the bandgap
reference are referred to this ground. Keep the connec-
tion to this pin, the feedback divider and V
C
compensation
network free of large ground currents.
SHDN (Pin 14): The shutdown pin can disable the switcher.
Grounding this pin will disable all internal circuitry.
Increasing SHDN voltage will initially turn on the internal
bandgap regulator. This provides a precision threshold for
the turn on of the rest of the IC. As SHDN increases past
1.39V the internal LDO regulator turns on, enabling the
control and logic circuitry.
24µA of current is sourced out of the pin above the turn on
threshold. This can be used to provide hysteresis for the
shutdown function. The hysteresis voltage will be set by the
Thevenin resistance of the resistor divider driving this pin
times the current sourced out. Above approximately 2.1V
the hysteresis current is removed. There is approximately
0.1V of voltage hysteresis on this pin as well.
The pin can be tied high (to V
IN
for instance).
V
IN
(Pin 17): Input Supply. All supply current for the part
comes from this pin including gate drives and V5 regula-
tor. Charge current for gate drives can produce current
pulses of hundreds of milliamperes. Bypass this pin with
a low ESR capacitor.
When V
IN
is below 2.55V the part will go into supply
undervoltage lockout where the gate drivers are driven low.
This, along with gate drive undervoltage lockout, prevents
unpredictable behavior during power up.
PGND (Pin 20): Power Driver Ground. This ground comes
from the MOSFET gate drivers. This pin can have several
hundred milliamperes of current on it when the external
MOSFETs are being turned off.
Oscillator
SYNC (Pin 6): The SYNC pin can be used to synchronize
the part to an external clock. The oscillator frequency
