Datasheet

The tradeoff for LED intensity control is between
depth of current-control resolution, noise constraints,
and software complexity:
• For high LED resolution where each LED needs
individual intensity settings, use the 8-bit PWM
control plus the 1-bit analog control to get 9 bits
of individual LED intensity control.
• For absolute maximum LED resolution where the
LED uses the same intensity settings, use the 8-
bit PWM control plus the 1-bit analog control,
plus the global 3-bit analog control to get 12 bits
of LED intensity control.
• For lowest noise applications where PWM cannot
be used, 1 bit of individual analog control is
available. If all LEDs use the same intensity set-
tings, the 1-bit analog control plus the global 3-
bit analog control provide 4 bits of static LED
intensity control.
• If the standard half/full constant-current settings
of 10mA/20mA are not acceptable, then the
global 3-bit analog control can be used to
reduce the currents for all the constant-current
outputs.
6) Take care with PC board layout. The MAX6966/
MAX6967 are switching moderate currents in PWM
applications, so the MAX6966/MAX6967 and the
load supplies need careful decoupling to minimize
conducted noise. Also, the serial interface is fast, so
simple overshoot-damping terminations may be
required if the tracks are long.
Detailed Description
The MAX6966/MAX6967 are general-purpose input/out-
put (GPIO) peripherals that provide 10 I/O ports, P0 to
P9, controlled through a high-speed SPI-compatible
serial interface. The 10 I/O ports can be used as logic
inputs, open-drain logic outputs, or constant-current
sinks in any combination. Ports withstand 7V indepen-
dent of the MAX6966’s or MAX6967’s supply voltage
whether used as logic inputs, logic outputs, or con-
stant-current sinks.
Ports configured as constant-current outputs can be set
to sink either a constant current of either 10mA or 20mA.
The static port current may be PWM with a duty cycle
ranging from 3/256 to 254/256 to reduce the average
current, or remain static.
Ports configured as open-drain logic outputs have a
relatively weak sink capability, which should still be
adequate for normal logic-level outputs. Open-drain
logic outputs typically require external pullup resistors
to the appropriate positive supply to provide the logic-
high reference. The weak drive means that the short-
circuit current is low enough that inadvertently driving
an LED from a port configured as a logic output is
unlikely to damage the LED.
The MAX6966/MAX6967 are rated for all 10 outputs to
carry their maximum 20mA loads at the same time. The
port configuration options are shown in Table 1.
10-Port Constant-Current LED Drivers and I/O
Expanders with PWM Intensity Control
PORT TYPE
OUTPUT
REGISTER
CODE
BEHAVIOR OUT OF
SHUTDOWN (CONFIGURATION
REGISTER BIT D0 = 1)
BEHAVIOR IN SHUTDOWN
(CONFIGURATION REGISTER
BIT D0 = 0)
APPLICATION NOTES
Low-logic
output
0x00 Logic-low output, not constant current
High-logic
output
Logic-high output with external pullup resistor; otherwise, high
impedance
Logic input
0x01
CMOS logic input
Lowest supply current
unaffected by shutdown
Constant-
current static
sink output
0x02
Static constant-current sink
output
Full constant-current drive
with no PWM noise
Constant-
current PWM
output
0x03–0xFE PWM constant-current sink output
High impedance
Adjustable constant current
LED off 0xFF
Logic-high output with external pullup resistor; otherwise, high
impedance
LED off
Table 1. Port Configuration Options
MAX6966/MAX6967
Maxim Integrated
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