lt3845ife-trpbf Linear Technology Corporation, lt3845ife-trpbf Datasheet - Page 6

• Manufacturer Part Number: lt3845ife-trpbf
• Description: High Voltage Synchronous Current Mode Step-down Controller With Adjustable Operating Frequency
• Manufacturer: Linear Technology Corporation

LT3845
TYPICAL PERFORMANCE CHARACTERISTICS
TYPICAL APPLICATION
V
be decoupled to SGND with a low ESR capacitor (at least
0.1μF) located close to the pin.
SHDN (Pin 2): The SHDN pin has a precision IC enable
threshold of 1.35V (rising) with 120mV of hysteresis. It is
used to implement an undervoltage lockout (UVLO) circuit.
See Application Information section for implementing a
UVLO function. When the SHDN pin is pulled below a
transistor V
entered, all internal circuitry is disabled and the V
current is reduced to approximately 9μA. Typical pin input
bias current is <10nA and the pin is internally clamped to
6V. If the function is not used, this pin may be tied to V
through a high value resistor.
C
supply soft-start function. Use the following formula to
calculate C
The pin should be left unconnected when not using the
soft-start function.
BURST_EN (Pin 4): Burst Mode Operation Enable Pin. This
pin also controls reverse-current inhibit mode of operation.
When the pin voltage is below 0.5V, Burst Mode operation
and reverse-current inhibit functions are enabled. When
6
IN
SS
C
106
104
102
100
98
94
96
(Pin 1): The V
SS
(Pin 3): The soft-start pin is used to program the
–50
Maximum Current Sense
Threshold vs Temperature
= 2μA(t
–25
SS
BE
for a given output voltage slew rate:
0
TEMPERATURE (°C)
SS
(0.7V), a low current shutdown mode is
/1.231V)
IN
25
pin is the main supply pin and should
50
75
100
3845 G13
125
4.54
4.52
4.50
4.48
4.46
4.44
4.42
4.40
–50
V
vs Temperature
IN
IN
–25
UVLO Threshold (Rising)
supply
0
TEMPERATURE (°C)
IN
25
the pin voltage is above 0.5V, Burst Mode operation is dis-
abled, but reverse-current inhibit operation is maintained.
In this mode of operation (BURST_EN = V
1mA minimum load requirement. Reverse-current inhibit
is disabled when the pin voltage is above 2.5V. This pin is
typically shorted to ground to enable Burst Mode operation
and reverse-current inhibit, shorted to V
Mode operation while enabling reverse-current inhibit,
and connected to V
Applications Information section.
V
externally connected to the supply output voltage via a
resistive divider. The V
the inverting input of the error amplifi er. In regulation,
V
V
fi er whose voltage corresponds to the maximum (peak)
switch current per oscillator cycle. The error amplifi er is
typically confi gured as an integrator by connecting an RC
network from the V
dominant pole for the converter regulation control loop.
Specifi c integrator characteristics can be confi gured to
optimize transient response. When Burst Mode operation
is enabled (see Pin 4 description), an internal low imped-
ance clamp on the V
50
FB
FB
C
(Pin 6): The V
is 1.231V.
(Pin 5): The output voltage feedback pin, V
75
100
3845 G14
125
C
C
CC
pin is the output of the error ampli-
C
pin to SGND. This circuit creates the
pin is set at 100mV below the burst
3.86
3.84
3.82
3.80
3.78
3.76
pin to disable both functions. See
FB
–50
V
vs Temperature
pin is internally connected to
IN
–25
UVLO Threshold (Falling)
0
TEMPERATURE (°C)
25
FB
to disable Burst
50
FB
) there is a
75
100
FB
3845 G15
3845fc
, is
125