MAX7315 Maxim, MAX7315 Datasheet - Page 20

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

8-Port I/O Expander with LED Intensity
Control, Interrupt, and Hot-Insertion Protection
where:
R
LED (Ω).
V
V
V
sinking I
I
For example, to operate a 2.2V red LED at 14mA from a
5V supply, R
The MAX7315 can be used to drive loads drawing more
than 50mA, like relays and high-current white LEDs, by
paralleling outputs. Use at least one output per 50mA of
load current; for example, a 5V 330mW relay draws
66mA and needs two paralleled outputs to drive it.
Ensure that the paralleled outputs chosen are controlled
by the same blink phase register, i.e., select outputs
from the P0 through P7 range. This way, the paralleled
Table 12. PWM Intensity Settings (Blink Enabled)
20
LED
INTENSITY
SUPPLY
LED
OL
LED
GLOBAL)
SETTING
OUTPUT
Driving Load Currents Higher than 50mA
(OR
0x0
0x1
0x2
0x3
0x4
0x5
0x6
0x7
0x8
0x9
0xA
0xB
0xC
0xD
0xE
0xF
______________________________________________________________________________________
is the output low voltage of the MAX7315 when
is the desired operating current of the LED (A).
is the forward voltage of the LED (V).
is the resistance of the resistor in series with the
LED
is the supply voltage used to drive the LED (V).
(V).
LED
Static low
PWM DUTY CYCLE
REGISTER BIT = 0
10/16
11/16
12/16
13/16
14/16
15/16
LOW
TIME
1/16
2/16
3/16
4/16
5/16
6/16
7/16
8/16
9/16
OUTPUT BLINK
= (5 - 2.2 - 0.25) / 0.014 = 182Ω.
PHASE X
Static low
HIGH
15/16
14/16
13/16
12/16
11/16
10/16
TIME
9/16
8/16
7/16
6/16
5/16
4/16
3/16
2/16
1/16
impedance
Static high
PWM DUTY CYCLE
REGISTER BIT = 1
15/16
14/16
13/16
12/16
11/16
10/16
LOW
TIME
9/16
8/16
7/16
6/16
5/16
4/16
3/16
2/16
1/16
OUTPUT BLINK
PHASE X
impedance
Static high
HIGH
10/16
11/16
12/16
13/16
14/16
15/16
TIME
1/16
2/16
3/16
4/16
5/16
6/16
7/16
8/16
9/16
Phase 0: LE D on at hi gh intensi ty
Phase 1: LE D on at hi gh intensi ty
Phase 1: LE D on at l ow intensi ty
Phase 0: LED on continuously
Phase 1: LED off continuously
Phase 0: LE D on at l ow intensi ty
outputs are turned on and off together. Do not use out-
put O8 as part of a load-sharing design. O8 cannot be
switched at the same time as any of the other outputs
because it is controlled by a different register.
The MAX7315 must be protected from the negative
voltage transient generated when switching off induc-
tive loads, such as relays, by connecting a reverse-
biased diode across the inductive load (Figure 18). The
peak current through the diode is the inductive load’s
operating current.
The MAX7315 operates with a power-supply voltage of
2V to 3.6V. Bypass the power supply to GND with at
least 0.047µF as close to the device as possible. For
the QFN version, connect the underside exposed pad
to GND.
TRANSISTOR COUNT: 17,611
PROCESS: BiCMOS
REGISTER BIT = 0
REGISTER BIT = 1
BLINK PHASE 0
BLINK PHASE 1
Output is half intensity during both blink phases
EXAMPLES OF LED BLINK BEHAVIOR
(LED IS ON WHEN OUTPUT IS LOW)
Power-Supply Considerations
Phase 0: LE D on at hi gh intensi ty
Phase 1: LE D on at l ow intensi ty
Phase 1: LE D on at hi gh intensi ty
Phase 0: LED off continuously
Phase 1: LED on continuously
Chip Information
Phase 0: LE D on at l ow intensi ty
REGISTER BIT = 1
REGISTER BIT = 0
BLINK PHASE 0
BLINK PHASE 1