lm27965sqx-m National Semiconductor Corporation, lm27965sqx-m Datasheet - Page 10

• Manufacturer Part Number: lm27965sqx-m
• Description: Dual Display White Led Driver With I2c Compatible Brightness Control
• Manufacturer: National Semiconductor Corporation

www.national.com
Brightness Level Control Table (BankA and BankB)
BankC Brightness Levels (%of Full-Scale) = 20%, 40%, 70%,
100%
Application Information
SETTING LED CURRENT
The current through the LEDs connected to DxA and DxB can
be set to a desired level simply by connecting an appropriately
sized resistor (R
GND. The DxA and DxB LED currents are proportional to the
current that flows out of the I
times greater than the I
internal amplifiers set the voltage of the I
(typ.). The statements above are simplified in the equations
below:
Brightness Code (hex)
R
I
DxA/B/C
SET
SET
(Ω)= 200 × (1.25V / I
) between the I
(A)= 200 × (V
SET
0C
0D
1C
1D
00
01
02
03
04
05
06
07
08
09
0A
0B
0E
0F
10
11
12
13
14
15
16
17
18
19
1A
1B
1E
1F
current. The feedback loops of the
SET
pin and are a factor of 200
SET
ISET
pin of the LM27965 and
/ R
DxA/B/C
Analog Current (% of
SET
SET
)
Full-Scale)
)
pin to 1.25V
100
100
100
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
40
40
40
40
40
40
40
70
70
70
70
70
70
10
Duty Cycle (%)
Once the desired R
has the ability to internally dim the LEDs using a mix of Pulse
Width Modulation (PWM) and analog current scaling. The
PWM duty cycle is set through the I
LEDs connected to BankA and BankB current sinks (DxA and
DxB) can be dimmed to 32 different levels/duty-cycles. The
internal PWM frequency for BankA and BankB is fixed at
20kHz. BankC(D1C) has 4 analog current levels.
Please refer to the I
datasheet for detailed instructions on how to adjust the bright-
ness control registers.
MAXIMUM OUTPUT CURRENT, MAXIMUM LED
VOLTAGE, MINIMUM INPUT VOLTAGE
The LM27965 can drive 8 LEDs at 22.5mA each (BankA and
BankB) from an input voltage as low as 3.2V, so long as the
LEDs have a forward voltage of 3.6V or less (room tempera-
ture).
10/16
11/16
12/16
13/16
14/16
15/16
16/16
10/16
11/16
12/16
13/16
14/16
15/16
16/16
11/16
12/16
13/16
14/16
15/16
16/16
13/16
15/16
16/16
1/16
2/16
3/16
4/16
5/16
6/16
7/16
8/16
9/16
SET
2
C Compatible Interface section of this
value has been chosen, the LM27965
Perceived Brightness
Level (%)
48.125
56.875
65.625
11.25
13.75
16.25
18.75
61.25
81.25
93.75
1.25
3.75
6.25
8.75
12.5
17.5
27.5
32.5
37.5
52.5
100
2.5
7.5
10
15
20
25
30
35
40
70
5
2
C compatible interface.