lt3592emse-trpbf Linear Technology Corporation, lt3592emse-trpbf Datasheet - Page 11

• Manufacturer Part Number: lt3592emse-trpbf
• Description: 500ma Wide Input Voltage Range Step-down Led Driver With 10 1 Dimming
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
(~0.4V at maximum load). This leads to a minimum input
voltage of:
with DCmax = 0.90.
The maximum input voltage is determined by the absolute
maximum ratings of the V
tinuous mode operation, the maximum input voltage is
determined by the minimum duty cycle, which is dependent
upon the oscillator frequency:
Note that this is a restriction on the operating input voltage
for continuous mode operation. The circuit will tolerate
transient inputs up to the absolute maximum of the V
and BOOST pins. The input voltage should be limited to
DC
V
V
IN(MIN)
IN(MAX)
500mA/DIV
MIN
500mA/DIV
50mV/DIV
50mV/DIV
20V/DIV
20V/DIV
V
= F
V
V
V
OUT
OUT
SW
SW
=
I
I
=
L
L
OSC
V
V
OUT
DC
OUT
DC
• 70nsec
MAX
MIN
+ V
+ V
D
D
Figure 1.
Figure 2.
– V
– V
1μs/DIV
1μs/DIV
IN
D
D
and BOOST pins. The con-
+ V
+ V
SW
SW
3592 F02
3592 F01
IN
the V
conditions (short circuit or startup).
Minimum On Time
The LT3592 will still regulate the output properly at input
voltages that exceed V
output voltage ripple increases as the input voltage is
increased.
Figure 1 illustrates switching waveforms in a 2.2mHz single
red LED application near V
As the input voltage is increased, the part is required to
switch for shorter periods of time. Delays associated with
turning off the power switch dictate the minimum on time
of the part. The minimum on time for the LT3592 is ~70ns.
Figure 2 illustrates the switching waveforms when the
input voltage is increased to V
Now the required on time has decreased below the mini-
mum on time of 70ns. Instead of the switch pulse width
becoming narrower to accommodate the lower duty
cycle requirement, the switch pulse width remains fi xed
at 70ns. In Figure 2, the inductor current ramps up to a
value exceeding the load current and the output ripple
increases to about 70mV. The part then remains off until
the output voltage dips below the programmed value
before it switches again.
Provided that the load can tolerate the increases output
voltage ripple and the the components have been properly
selected, operation about V
age the part. Figure 3 illustrates the switching waveforms
when the input voltage is increased to 36V.
IN
500mA/DIV
50mV/DIV
absolute maximum range (36V) during overload
20V/DIV
V
V
OUT
SW
I
L
IN(MAX)
Figure 3.
1μs/DIV
IN(MAX)
IN(MAX)
IN
(up to 36V); however, the
= 26V.
is safe and will not dam-
= 24V.
3592 F03
LT3592
11
3592f