MAX7315 Maxim, MAX7315 Datasheet - Page 17

• Manufacturer Part Number: MAX7315
• Description: The MAX7315 I²C-/SMBus™-compatible serial interfaced peripheral provides microprocessors with 8 I/O ports
• Manufacturer: Maxim

When blink is enabled (Table 7), the blink phase 0 regis-
ter and blink phase 1 register specify each output’s logic
level during the PWM on-time during the respective blink
phases (Tables 8 and 9). The effect of setting an output’s
blink phase X register bit to 0 or 1 is shown in Table 12.
LEDs can be flipped between either directly on and off,
or between a variety of high/low PWM intensities.
The 4 bits used for output O8’s PWM individual intensity
setting also double as the global intensity control (Table
13). Global intensity simplifies the PWM settings when
the application requires them all to be the same, such
as for backlight applications, by replacing the 9 individ-
ual settings with 1 setting. Global intensity is enabled
with the global intensity flag G in the configuration reg-
ister (Table 4). When global PWM control is used, the 4
bits of master intensity and 4 bits of O8 intensity effec-
tively combine to provide an 8 bit, 240-step intensity
control applying to all outputs.
It is not possible to apply global PWM control to a sub-
set of the ports, and use the others as logic outputs. To
mix static logic outputs and PWM outputs, individual
PWM control must be selected (Table 10).
I/O ports PO-P7, interrupt output INT/08, and serial
interface SDA, SCL, AD0-2 remain high impedance with
up to 6V asserted on them when the MAX7315 is pow-
ered down (V+ = 0V). The MAX7315 can therefore be
used in hot-swap applications.
Table 8. Blink Phase 0 Register
Table 9. Blink Phase 1 Register
Control, Interrupt, and Hot-Insertion Protection
Using PWM Intensity Controls with Blink Enabled
Read-back outputs phase 0
Read-back outputs phase 1
Write outputs phase 0
Write outputs phase 1
REGISTER
REGISTER
Applications Information
______________________________________________________________________________________
8-Port I/O Expander with LED Intensity
Global/O8 Intensity Control
Hot Insertion
R/W
R/W
0
1
0
1
ADDRESS
ADDRESS
CODE
CODE
(HEX)
(HEX)
0x01
0x09
OP7
OP7
D7
D7
The open-drain output architecture allows the ports to
level translate the outputs to higher or lower voltages
than the MAX7315 supply. An external pullup resistor
can be used on any output to convert the high-imped-
ance logic-high condition to a positive voltage level.
The resistor can be connected to any voltage up to
5.5V. For interfacing CMOS inputs, a pullup resistor
value of 220kΩ is a good starting point. Use a lower
resistance to improve noise immunity, in applications
where power consumption is less critical, or where a
faster rise time is needed for a given capacitive load.
The MAX7315 is pin compatible and software compatible
with PCA9534, and its variants PCA9554 and PCA9554A.
However, some PCA9534 and PCA9554(A) functions are
not implemented in the MAX7315, and the MAX7315's
PWM and blink functionality is not supported in the
PCA9534 and PCA9554(A). Software compatibility is
clearly not 100%, but the MAX7315 was designed so the
subset (omitted) features default to the same power-up
behavior as the PCA9534 and PCA9554(A), and the
superset features do not use existing registers in a differ-
ent way. In practice, many applications can use the
MAX7315 as a drop-in replacement for the PCA9534 or
PCA9554(A) with no software change.
When driving LEDs, a resistor in series with the LED
must be used to limit the LED current to no more than
50mA. Choose the resistor value according to the fol-
lowing formula:
OP6
OP6
D6
D6
R
LED
OP5
OP5
D5
D5
Compatibility with PCA9534 and
= (V
REGISTER DATA
REGISTER DATA
SUPPLY
OP4
OP4
D4
D4
Output Level Translation
- V
OP3
OP3
D3
D3
LED
Driving LED Loads
- V
OP2
OP2
D2
D2
OL
) / I
PCA9554(A)
OP1
OP1
LED
D1
D1
OP0
OP0
D0
D0
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