LT3686 LINER [Linear Technology], LT3686 Datasheet - Page 10

• Manufacturer Part Number: LT3686
• Manufacturer: LINER [Linear Technology]

ApplicAtions inForMAtion
LT3686
FB Resistor Network
The output voltage is programmed with a resistor divider
between the output and the FB pin. Choose the 1% resis-
tors according to:
R2 should be 20k or less to avoid bias current errors.
Reference designators refer to the Block Diagram.
Programmable Undervoltage Lockout
The EN/UVLO pin can be programmed by an external re-
sistor divider between V
the resistors according to:
R4 also sets the hysteresis voltage for the programmable
UVLO:
Once V
will enter a low quiescent current state (I
shutdown the LT3686 completely (I
UVLO pin voltage to below 0.4V.
0
Hysteresis = R4 • 2.4µA
R1= R2
R4 =R5
IN
drops below the programmed voltage, the LT3686
10000
1000
⎛
⎝ ⎜



100
0.1
1.27V
10
V
0.8V
1
OUT
V
0
Figure 1. I
IN
– 1
1
– 1
⎞
⎠ ⎟
2



Q
IN
vs V
EN/UVLO (V)
3
and the EN/UVLO pin. Choose
EN/UVLO
4
5
(V
Q
6
IN
< 2µA), reduce EN/
= 10V)
7
3686 F01
Q
8
≈ 15µA). To
Input Voltage Range
The input voltage range for the LT3686 applications depends
on the output voltage and on the absolute maximum ratings
of the V
is determined by either the LT3686’s minimum operating
voltage of 3.6V, or by its maximum duty cycle.
The duty cycle is the fraction of time that the internal
switch is on and is determined by the input and output
voltages:
Where V
(~0.4V) and V
(~0.67V at maximum load). This leads to a minimum input
voltage of:
DC
The boost capacitor is charged with the energy stored in
the inductor, the circuit will rely on some minimum load
current to sustain the charge across the boost capacitor.
DC =
MAX
V
IN(MIN)
can be adjusted with frequency.
IN
V
D
IN
and BOOST pins. The minimum input voltage
is the forward voltage drop of the catch diode
V
=
– V
OUT
V
45
40
35
30
25
20
15
10
SW
5
0
DC
OUT
Figure 2. EN/UVLO Pin Current
SW
0
+ V
is the voltage drop of the internal switch
MAX
+ V
+ V
D
10
D
D
– V
20
EN/UVLO (V)
D
+ V
30
SW
40
50
3686 F02
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