Fault detection, Applications information – Rainbow Electronics MAX6963 User Manual

Page 26

MAX6960–MAX6963

Global Clear Planes Command

Writing the global clear planes counter (Table 31) allows
any or all display memory planes to be cleared with one
command. The selected plane(s) are cleared on the ris-
ing edge of

CS at the end of the 16-bit transmission.

Fault Detection

LED Fault Detection

The MAX6960 detects open-circuit and short-circuit
LEDs. It can only detect an LED fault when attempting
to light that LED, so a good strategy to check a panel is
to program the panel with all LEDs on power-up to
check the displays.

The fault and device ID register (Table 32) uses 3 bits
to flag and distinguish open-circuit (open flag), short-
circuit (short flag), and overtemperature (OT flag)
faults, and a fourth flag (fault flag), which is an OR of
the open flag, short flag, and OT flag.

The fault and device ID register is cleared on power-
up, and can also be cleared by writing to it. The fault
flags are NOT cleared by a read. When writing the fault
register, the data written is ignored; all fault flags are
cleared, including the OT flag. It is possible to clear all
MAX6960s on a bus by performing a global write to the
fault and device ID register.

Overtemperature Fault Detection

The MAX6960 contains an overtemperature (OT) detec-
tion circuit, which trips at a die temperature of typically
+150°C. The OT event is latched, and is readable in the
fault and device ID register (Table 32). When the OT
trips, the MAX6960 shutdown bit in the configuration

register (Table 31) is cleared, and the driver goes into
shutdown. Data is not lost; the effect is the same as the
user setting the shutdown bit. The user can attempt to
set the shutdown bit at any time. However, if the driver
is still over temperature, then the attempt to set the
shutdown bit is ignored. The OT fault flag is NOT auto-
matically cleared when the device cools, or when the
device is taken out of shutdown.

The fault and device ID register is cleared on power-
up, and can also be cleared by writing to it. The fault
flags are NOT cleared by a read. When writing the fault
register, the data written is ignored; all fault flags are
cleared, including the LED flags. It is possible to clear
all MAX6960s on a bus by performing a global write to
the fault and device ID register.

Applications Information

Setting LED Drive Current

The MAX6960 can be configured for pretrimmed 20mA
or 40mA LED current, or a 20mA to 40mA adjustable
current, on a digit-by-digit basis by the RISET0 and
RISET1 pin connections (Figures 13 and 14). The digit
intensity registers can be used to digitally adjust the
segment current, again on a digit-by-digit basis, by
controlling the PWM. Some applications best use one
or the other technique; some applications may require
the flexibility of both.

Power Supplies

The MAX6960 operates from a single 2.7V to 3.6V
power supply. Accuracy of the LED drive current of
20mA is guaranteed over this supply range. Accuracy

4-Wire Serially Interfaced
8 x 8 Matrix Graphic LED Drivers

______________________________________________________________________________________

REGISTER DATA

REGISTER

PLANES/INTENSITY BIT

(SEE TABLE 22):

0 FOR 1 BIT/PIXEL;

4 PLANES

1 FOR 1 BIT/PIXEL;

4 PLANES

ADDRESS

CODE

(HEX)

PLANE COUNTER

0x0B

Fast

slow

Auto

manual

Counter setting

Auto fast plane counter—2 frames per
second

0x0B

—

Auto fast plane counter— 62 frames
per second

0x0B

Auto fast plane counter— 63 frames
per second

0x0B

Table 30. Global Plane Counter Register Format (continued)