AS1121 datasheet(13/22 Pages) AMSCO

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AS1121

Datasheet - Detailed Descr i pti on

OUTn Enable

All OUTn channels can be collectively switched off with one signal. When OEN is set to 1, all OUTn channels are disabled, regardless of the

device logic operations. The greyscale counter is also reset when OEN is set to 1.

When OEN is set to 0, all OUTn channels are in normal operation.

Setting Maximum Channel Current

The maximum output current per channel is programmed by a single resistor, RIREF, which is placed between pin IREF and GND. The voltage

on pin IREF is set by an internal band gap VIREF (1.27V typ). The maximum channel current is equivalent to the current flowing through RIREF

multiplied by a factor of 31.5. The maximum output current is calculated as:

Where:

VIREF = 1.27V;

RIREF = User-selected external resistor.

Power Dissipation

To ensure proper operation of the device, the total power dissipation of the AS1121 must be below the power dissipation rating of the device

package. Total power dissipation is calculated as:

Where:

VCC is the device supply voltage;

ICC is the device supply current;

VOUT is the device OUTn voltage when driving LED current;

IMAX is the LED current adjusted by RIREF;

DCn is the maximum dot correction value for OUTn;

n is the number of OUTn driving LED at the same time;

dPWM is the duty cycle defined by pin OEN or the greyscale PWM value.

Operating Modes

The AS1121 operates in two modes (see Table 8). Greyscale operating mode (see Figure 22 on page 14) and the shift registers are in reset state

at power-up.

Table 7. Pin OEN Truth Table

OEN

OUT0:OUT15

Normal Operation

1Disabled

Table 8. Operating Modes

Mode

Input Shift Register

Operating Mode

192-bit

Greyscale PWM Mode

96-bit

Dot Correction Data Input Mode

IMAX =

VIREF

RIREF

x 31.5

(EQ 1)

PD = (VCC x ICC) + (VOUT x IMAX x n x

DCn

(EQ 2)

dPWM)

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