MAX6967 MAXIM [Maxim Integrated Products], MAX6967 Datasheet - Page 8

• Manufacturer Part Number: MAX6967
• Description: 10-Port Constant-Current LED Drivers and I/O Expanders with PWM Intensity Control
• Manufacturer: MAXIM [Maxim Integrated Products]

Figure 1 shows the I/O port structure of the MAX6966/
MAX6967. I/O ports P0 to P9 default to high impedance
on power-up, so LED or other port loads connected
draw no current, and ports used as inputs do not load
their source signals.
When all the ports are configured as logic inputs or out-
puts (all output registers set to value 0x00 or 0x01) or
LED off (output register set to value 0xFF), the
MAX6966/MAX6967 operate at their lowest supply cur-
rent, called standby mode.
When PWM intensity control is used (one or more out-
put registers set to a value between 0x03 and 0xFE),
the operating current increases because the internal
PWM circuitry is running.
The operating current also increases whenever a port
that is set is active low as a constant-current output
(output register set to a value between 0x02 and 0xFE),
even if a load is not applied to the port. This current
increase is due to an internal current mirror being
enabled for that port output to provide the accurate
constant-current sink. There is a gated mirror for each
output, and each mirror is only enabled when required.
When PWM is used, a current mirror is only turned on
for the output’s on-time. This means that operating cur-
rent varies as constant-current outputs are turned on
10-Port Constant-Current LED Drivers and I/O
Expanders with PWM Intensity Control
Figure 1. Simplified Schematic of I/O Ports
8
_______________________________________________________________________________________
Standby Mode and Operating Current
INTERFACE
TO/FROM
SERIAL
OUTPUT CURRENT
GLOBAL CURRENT
OUTPUT PORT
8-BIT LATCH
1-BIT LATCH
3-BIT LATCH
REGISTER
REGISTER
REGISTER
PORT COMMAND
READ I/O
MSB
CLOSE SWITCH: 0x02-0xFE
POSITION A: 0x00 - 0x01
POSITION B: 0x02 - 0xFF
4-BIT DAC
GENERATOR
PWM
and off through the serial interface, as well as by the
PWM intensity control.
In shutdown mode, all ports configured as constant-cur-
rent outputs (output register set to a value between 0x02
and 0xFE) are switched off, and these outputs go high
impedance as if their registers were set to value 0xFF.
Ports configured as logic inputs or outputs (output regis-
ters set to value 0x00 or 0x01) are unaffected (Table 1).
This means that any ports used for GPIOs are still fully
operational in shutdown mode, and port inputs can be
read and output ports can be toggled at any time using
the serial interface. The MAX6966/MAX6967 can there-
fore be used for a mix of logic inputs, logic outputs, and
PWM LED drivers, and only the LED drivers are turned
off automatically in shutdown.
The MAX6966/MAX6967 are put into shutdown mode
by clearing the run bit (bit D0) in the configuration reg-
ister (Table 4). Shutdown is exited by setting the run bit
through the serial interface, or by using the CS run
option discussed below. The MAX6966/MAX6967 can
be configured and controlled in the normal way through
the serial interface in shutdown mode. All registers are
accessible in shutdown mode, and no register is
changed by shutdown mode. When shutdown mode is
exited, ports configured as constant-current outputs at
that time start instantly with their current PWM values.
CURRENT
ENABLE
SET
A
N
B
I/O PORT
Shutdown Mode