pca9952 NXP Semiconductors, pca9952 Datasheet - Page 32

• Manufacturer Part Number: pca9952
• Description: 16-channel Fm+ I 2c-bus 57 Ma Constant Current Led Driver
• Manufacturer: NXP Semiconductors

NXP Semiconductors
PCA9952_PCA9955
Product data sheet
string. Reducing this to a minimum (e.g., 0.8 V) helps to keep the power dissipation down.
Therefore LEDs binning is recommended to minimize LED voltage forward variation and
reduce power dissipation in the device.
In order to ensure that the device will not go into thermal shutdown when operating under
certain application conditions, its junction temperature (T
that is below the overtemperature threshold limit (125 C). The T
on the ambient temperature (T
resistance.
The device junction temperature can be calculated by using the following equation:
where:
An example of this calculation is show below:
Conditions:
P
T
tot
j
T
T
R
P
T
R
I
I
V
LEDs per channel = 10 LEDs / channel
LED V
LED V
V
voltage.)
V
P
IC_power = (I
IC_power = (0.012 A  5 V) + [(0.4 V  0.03 A) + (0.4 V  0.03 A)] = 0.084 W
LED drivers_power = [(16  1)  (I
(I
LED drivers_power = [15  0.05 A  (2 V + 0.8 V)] + (0.05 A  0.8 V) = 2.14 W
P
LED
DD(max)
=
j
amb
amb
LED
tot
DD
reg(drv)
sup
tot
tot
th(j-a)
th(j-a)
calculation:
= junction temperature
T
= (device) total power dissipation
= IC_power + LED drivers_power;
= 0.084 W + 2.14 W = 2.224 W
= 50 mA / channel
= 5 V
amb
= LED V
= ambient temperature
= 50 C
 V
F(typ)
F
= junction to ambient thermal resistance
= 31 C/W (per JEDEC 51 standard for multilayer PCB)
= 12 mA
= 0.8 V (This will be present only in the LED string with the highest LED forward
mismatch = 0.2 V per LED (2 V total for 10 LEDs in series)
+
reg(drv)
R
= 3 V per LED (30 V total for 10 LEDs in series)
th j-a
F(typ)

All information provided in this document is subject to legal disclaimers.
DD
)

 V

+ LED V
P
Rev. 1 — 2 December 2011
DD
tot
) + [(SCL_V
16-channel Fm+ I
F
amb
mismatch + V
), device’s total power dissipation (P
LED
OL
 I
)  (LED V
OL
2
) + (SDA_V
reg(drv)
C-bus 57 mA constant current LED driver
PCA9952; PCA9955
F
= 30 V + 2 V + 0.8 V = 32.8 V
mismatch + V
OL
j
) should be calculated to ensure
 I
OL
)]
j
of the device depends
reg(drv)
tot
© NXP B.V. 2011. All rights reserved.
)] +
), and thermal
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