MAX6957AAX+T Maxim Integrated Products, MAX6957AAX+T Datasheet - Page 10

• Manufacturer Part Number: MAX6957AAX+T
• Description: IC DRVR DSPL LED 36-SSOP
• Manufacturer: Maxim Integrated Products

Specifications of MAX6957AAX+T

• Display Type: LED
• Configuration: 7, 16, 20 Segment
• Interface: 4-Wire Serial
• Current - Supply: 180µA
• Voltage - Supply: 2.5 V ~ 5.5 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 36-SSOP
• Number Of Segments: 28
• Low Level Output Current: 18 mA
• Operating Supply Voltage: 2.5 V to 5.5 V
• Maximum Supply Current: 230 uA
• Maximum Power Dissipation: 941 mW
• Maximum Operating Temperature: + 125 C
• Mounting Style: SMD/SMT
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Digits Or Characters: -
• Lead Free Status / Rohs Status: Details

4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
It is acceptable to clock more than 16 bits into the
MAX6957 between taking CS low and taking CS high
again. In this case, only the last 16 bits clocked into the
MAX6957 are retained.
Any register data within the MAX6957 may be read by
sending a logic high to bit D15. The sequence is:
1) Take SCLK low.
2) Take CS low (this enables the internal 16-bit shift
3) Clock 16 bits of data into DIN—D15 first to D0 last.
4) Take CS high (either while SCLK is still high after
5) Take SCLK low (if not already low).
6) Issue another read or write command (which can
On initial power-up, all control registers are reset, cur-
rent registers are set to minimum value, and the
MAX6957 enters shutdown mode
LED segment drive current can be set either globally or
individually. Global control simplifies the operation
when all LEDs are set to the same current level,
because writing one register, the Global Current regis-
ter, sets the current for all ports configured as LED seg-
ment drivers. It is also possible to individually control
the current drive of each LED segment driver.
Individual/global brightness control is selected by set-
ting the configuration register I bit (Table7). The global
current register (0x02) data are then ignored, and seg-
ment currents are set using register addresses 0x12
through 0x1F (Tables 10, 11, and 12). Each segment is
controlled by a nibble of one of the 16 current registers.
Port transition detection allows any combination of the
seven ports P24–P30 to be continuously monitored for
changes in their logic status (Figure 6). A detected
change is flagged on port P31, which is used as an
10
register).
D15 is high, indicating a read command and bits
D14 through D8 containing the address of the regis-
ter to be read. Bits D7–D0 contain dummy data,
which is discarded.
clocking in the last data bit, or after taking SCLK
low), positions D7 through D0 in the Shift register
are now loaded with the register data addressed by
bits D1 through D8.
be a No-Op), and examine the bit stream at DOUT;
the second 8 bits are the contents of the register
addressed by bits D1 through D8 in step 3.
Transition (Port Data Change) Detection
______________________________________________________________________________________
Reading Device Registers
LED Current Control
Initial Power-Up
(Table 4).
active-high interrupt output (INT). Note that the
MAX6957 does not identify which specific port(s)
caused the interrupt, but provides an alert that one or
more port levels have changed.
The mask register contains 7 mask bits that select
which of the seven ports P24–P30 are to be monitored
(Table 13). Set the appropriate mask bit to enable that
port for transition detect. Clear the mask bit if transitions
on that port are to be ignored. Transition detection
works regardless of whether the port being monitored is
set to input or output, but generally it is not particularly
useful to enable transition detection for outputs.
Port P31 must be configured as an output in order to
work as the interrupt output INT when transition detec-
tion is used. Port P31 is set as output by writing bit D7
= 0 and bit D6 = 1 to the port configuration register
(Table 1).
To use transition detection, first set up the mask regis-
ter and configure port P31 as an output, as described
above. Then enable transition detection by setting the
M bit in the configuration register (Table 8). Whenever
the configuration register is written with the M bit set,
the MAX6957 updates an internal 7-bit snapshot regis-
ter, which holds the comparison copy of the logic states
of ports P24 through P30. The update action occurs
regardless of the previous state of the M bit, so that it is
not necessary to clear the M bit and then set it again to
update the snapshot register.
When the configuration register is written with the M bit
set, transition detection is enabled and remains
enabled until either the configuration register is written
with the M bit clear, or a transition is detected. The INT
output port P31 goes low, if it was not already low.
Once transition detection is enabled, the MAX6957
continuously compares the snapshot register against
the changing states of P24 through P31. If a change on
any of the monitored ports is detected, even for a short
time (like a pulse), INT output port P31 is latched high.
The INT output is not cleared if more changes occur or
if the data pattern returns to its original snapshot condi-
tion. The only way to clear INT is to access (read or
write) the transition detection mask register (Table 13).
Transition detection is a one-shot event. When INT has
been cleared after responding to a transition event,
transition detection is automatically disabled, even
though the M bit in the configuration register remains
set (unless cleared by the user). Reenable transition
detection by writing the configuration register with the
M bit set to take a new snapshot of the seven ports,
P24 to P30.