MAX1576 Datasheet, PDF (7/22 Pages) Maxim Integrated Products – 480mA White LED 1x/1.5x/2x Charge Pump for Backlighting and Camera Flash

a through h (Pins 1, 2, 4 – 7, 19, 20)
Anode–Driver Current Sources. These outputs are close-
ly–matched current sources which directly tie to the anodes
of external discrete LEDs (lamps) or display segment LEDs.
Each output is capable of sourcing up to 35 mA.
When used with lamps, outputs a, b, c, and d are used to
independently control up to 20 lamps. Output h is used to con-
trol up to 5 lamps dependently. (See Figure 17.) For lamps,
the No Decode mode is selected via the configuration regis-
ter, forcing e, f, and g inactive (low).
When used with segmented displays, outputs a through g
drive segments a through g, respectively. Output h is used to
drive the decimals. Refer to Figure 9. If unused, h must be left
open.
Bank 1 through Bank 5 (Pins 9, 13, 15, 16, 17)
Diode–Bank FET Switches. These outputs are low–resis-
tance switches to ground (VSS) capable of handling currents
of up to 320 mA each. These pins directly tie to the common
cathodes of segmented displays or the cathodes of lamps
(wired with cathodes common).
The display is refreshed at a nominal 1 kHz rate to achieve
optimum brightness from the LEDs. A 20% duty cycle is uti-
lized.
Special design techniques are used on–chip to accommo-
date the high currents with low EMI (electromagnetic interfer-
ence) and minimal spiking on the power lines.
POWER SUPPLY
VSS (Pin 14)
Most–negative supply potential. This pin is usually ground.
Resistor Rx is externally tied to ground (VSS). Therefore,
the chip’s VSS pin does not contain the Rx current compo-
nent.
VDD (Pin 13)
Most–positive supply potential.
To guarantee data integrity in the registers and to ensure
the serial interface is functional, this voltage may range from
3 to 6 volts with respect to VSS. For example, within this volt-
age range, the chip could be placed in and out of the low–
power mode.
To adequately drive the LEDs, this voltage must be 4.5 to
6 volts with respect to VSS.
The VDD pin contains the Rx current component plus the
chip’s current drain. In the low–power mode, the current mir-
ror and clock oscillator are turned off, thus significantly reduc-
ing the VDD current, IDD.
35
5 V SUPPLY
30
BIT D23 = HIGH (BRIGHTEN LEDs)
WITH D23 = LOW, iOH IS CUT BY ∼50%.
25
20
15
10
5
400 800
1.2 k 1.6 k 2.0 k 2.4 k 2.8 k 3.2 k
Rx, EXTERNAL RESISTOR (Ω)
3.6 k 4.0 k
NOTE: Drive current tolerance is approximately ± 15%.
Figure 7. a through h Nominal Current per Output versus Rx
MOTOROLA
MC14489B
7