PRODUCT DATASHEET
AAT3176
TM
ChargePump
500mA LED Flash Driver IC
Application Information
VIN
(5V/div)
IIN
(1A/div)
VF
Flash and Movie Mode
LED Current Setting
(2V/div)
ILED
The AAT3176 has two independent LED current setting
pins for LED current in flash and movie mode: RSETF and
(1A/div)
VC1
(5V/div)
R
SETM. The MODE pin is designed to select which current
set flows through the LED. When MODE is high, the cur-
rent set by RSETF is the maximum LED current; when
MODE is low, the maximum current is set by RSETM. The
calculation method of the LED current set resistor value
RSET is the same for either mode and can be calculated
using the following formula:
VRSETF
(2V/div)
Time (100ms/div)
Figure 2: AAT3176 Operating Waveform
at 500mA LED Current with
500ms Flash Time (RSETF = 21kΩ).
1.22
ILED
RSETF = RSETM
=
· 8652
Thermal Considerations
Table 2 shows some examples of 1% standard metal film
resistor values for different maximum LED currents
(DATA = 1) in movie and flash mode.
The AAT3176 is designed to deliver continuous LED cur-
rent in movie mode. The limiting characteristic for max-
imum safe operating output LED current is package
power dissipation. In order to obtain high operating cur-
rents, careful device layout and circuit operating condi-
tions must be taken into account. The following discus-
sions assume that the AAT3176 is mounted on a printed
circuit board utilizing the minimum recommended foot-
print as stated in the “Printed Circuit Board Layout
Recommendations” section of this datasheet.
RSETM
(kΩ)
Maximum LED
Current (mA)
RSETF
(kΩ)
Maximum LED
Current (mA)
210.0
174.0
150.0
130.0
118.0
105.0
50
60
70
80
90
105.0
69.8
52.3
42.2
35.7
30.1
26.1
23.7
21.0
100
150
200
250
300
350
400
450
500
100
At any given ambient temperature (TA), the maximum
package power dissipation can be determined by the fol-
lowing equation:
Table 2: Maximum LED Current
RSETM and RSETF Example.
(TJ(MAX) - TA)
PD(MAX)
=
θJA
LED current can be set to levels lower than maximum via
S2C DATA transferred through the EN/SET pin, corre-
sponding to percentage of the maximum setting value.
In movie mode, continuous high level of EN/SET lights
the LED light continuously at the programmed current.
In flash mode, EN/SET high level duration controls flash
time; the maximum flash time is 1 second for 500mA
LED current limited by the thermal characteristics of the
package. Figure 2 shows the operating waveform of the
AAT3176 driving an LED for 500ms flash time in flash
mode with 500mA LED current at 3.6V VIN (2x mode).
The AAT3176 is available in the TDFN2.2x2.2-10 pack-
age, which has 71.4°C/W of thermal resistance (θJA).
With 125°C TJ(MAX), its PD(MAX) is 1.4W. The maximum
power dissipation occurs when the mode transfers from
1x to 2x. If the die temperature rises above the thermal
limit of 140°C, the internal thermal protection circuit
activates to shut down the charge pump and recovers
when the die temperature drops below 125°C.
To avoid entering thermal protection in flash mode at the
500mA high flash LED current setting, the flash time
should not exceed 1 second at 25°C ambient tempera-
ture. Longer flash time causes the junction temperature
to increase quickly, causing thermal shutdown. The LED
current recovers automatically when the junction tem-
perature decreases.
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