LT1932ES6 Linear Technology, LT1932ES6 Datasheet - Page 8

• Manufacturer Part Number: LT1932ES6
• Manufacturer: Linear Technology

Specifications of LT1932ES6

• Operating Supply Voltage (typ): 1.8/2.5/3.3/5/9V
• Number Of Segments: 8
• Operating Temperature (min): -40C
• Operating Temperature (max): 85C
• Operating Temperature Classification: Industrial
• Package Type: TSOT-23
• Pin Count: 6
• Mounting: Surface Mount
• Operating Supply Voltage (min): 1V
• Operating Supply Voltage (max): 10V
• Lead Free Status / Rohs Status: Not Compliant

APPLICATIO S I FOR ATIO
LT1932
Dimming Using a Filtered PWM Signal
While the direct PWM method provides the widest dim-
ming range and the purest white light output, it causes the
LT1932 to enter into Burst Mode
tion may be undesirable for some systems, as it may
reflect some noise to the input source at the PWM fre-
quency. The solution is to filter the control signal by adding
a 10k resistor and a 0.1 F capacitor as shown in Figure 6,
converting the PWM to a DC level before it reaches the
R
by the R
Dimming Using a Logic Signal
For applications that need to adjust the LED brightness in
discrete steps, a logic signal can be used as shown in
Figure 6. R
the NMOS is off):
R
the NMOS is turned on:
Dimming Using a DC Voltage
For some applications, the preferred method of brightness
control uses a variable DC voltage to adjust the LED
current. As the DC voltage is increased, current flows
through R
8
SET
INCR
LT1932
PWM
R
R
SHDN
INCR
MIN
pin. The 10k resistor minimizes the capacitance seen
5
sets how much the LED current is increased when
SET
ADJ
MIN
225
225
pin.
PWM
into R
sets the minimum LED current value (when
•
•
I
LED MIN
I
U
LED INCREASE
SET
0 1
.
(
(
, reducing the current flowing out
V
0 1
PWM
LT1932
R
.
U
SET
)
4
V
R
SET
R
PWM
)
®
operation. This opera-
W
PWM
Figure 6. Five Methods of LED Dimming
FILTERED PWM
U
LT1932
R
SET
4
R
SET
10k
R
0.1 F
PWM
of the R
R
DC control voltage, I
by R
the DC control voltage is at V
Regulating LED Current when V
The LT1932 contains special circuitry that enables it to
regulate the LED current even when the input voltage is
higher than the output voltage. When V
the internal NPN LED switch (transistor Q2 in Figure 1) is
saturated to provide a lower power loss. When V
greater than V
saturation to keep the LED current in regulation.
Soft-Start/Controlling Inrush Current
For many applications, it is necessary to minimize the
inrush current at start-up. When first turned on and the
LED current is zero, the LT1932 will initially command the
maximum switch current of 500mA to 600mA, which may
give an inrush current too high for some applications. A
soft-start circuit (Figure 7) can be added to significantly
reduce the start-up current spike. Figure 8 shows that
without soft-start the input current reaches almost 600mA.
Figure 9 shows that when the soft-start circuit is added,
the input current has only a brief 300mA spike, and on
average does not exceed 100mA.
Burst Mode is a registered trademark of Linear Technology Corporation.
ADJ
R
SET
PWM
ADJ
value as shown below where V
SET
, and I
DC VOLTAGE
225
pin, thus reducing the LED current. Choose the
LED(MIN)
LT1932
R
OUT
•
SET
4
R
I
SET
, the NPN LED switch comes out of
LED MAX
LED(MAX)
R
ADJ
is the minimum value of I
(
V
MAX
)
V
DC
–
– .
MAX
is the current programmed
I
0 1
LED MIN
IN
).
V
(
LOGIC
> V
LT1932
MAX
R
SET
IN
)
4
OUT
R
MIN
is less than V
is the maximum
R
INCR
LED
1932 F06
(when
LOGIC
SIGNAL
IN
OUT
1932f
is
,