Datasheet

LT3593
9
3593f
APPLICATIONS INFORMATION
Figure 5. Output Open-Circuit Waveform
Figure 6. Two AA Cells to Three White LEDs
Overvoltage Protection
The LT3593 has an internal open-circuit protection circuit.
In the case of an output open circuit, when the LEDs are
disconnected from the circuit or the LEDs fail open, V
CAP
is clamped at 38V. The LT3593 will then switch at a very
low frequency to minimize input current. V
CAP
and input
current during output open circuit are shown in the Typical
Performance Characteristics. Figure 5 shows the transient
response when the LEDs are disconnected.
Low Input Voltage Applications
The LT3593 can be used in low input voltage applications.
The input supply voltage to the LT3593 must be 2.7V or
higher, but the inductor can be run off a lower battery
voltage. This technique allows the LEDs to be powered off
two alkaline cells. Most portable devices have a 3.3V logic
supply voltage which can be used to power the LT3593.
The LEDs can be driven straight from the battery, resulting
in higher effi ciency.
Figure 6 shows three LEDs powered by two AA cells.
The battery is connected to the inductors and the chip is
powered off a 3.3V logic supply voltage.
CTRL
C1: TAIYO YUDEN EMK107B5105MA
C2: MURATA GRM31MR71H105KA88
L1: MURATA LQH43CN100
D1: CENTRAL CMDSH05-4
V
IN
L1
10
µH
2 AA CELLS
2V TO 3.2V
3.3V
3593 F06
LT3593
SHUTDOWN AND
CURRENT CONTROL
SW
CAP
LED
GND
C1
1
µF
C2
1
µF
C3
1
µF
D1
V
CAP
20V/DIV
400µs/DIVV
IN
= 3.6V
FRONT PAGE
APPLICATION CIRCUIT
3593 F05
I
L
200mA/DIV
V
SW
20V/DIV
LEDs DISCONNECTED
AT THIS INSTANT