Rainbow Electronics MAX7315 - Manual (Page 20)

MAX7315
V OL is the output low voltage of the MAX7313 when
sinking I
LED
(V).
I LED is the desired operating current of the LED (A).
For example, to operate a 2.2V red LED at 14mA from a
5V supply, R
LED = (5 - 2.2 - 0.25) / 0.014 = 182
Ω.
Driving Load Currents Higher than 50mA
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
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.
Power-Supply Considerations
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.
Chip Information
TRANSISTOR COUNT: 17,611
PROCESS: BiCMOS
8-Port I/O Expander with LED Intensity
Control and Interrupt
20 ______________________________________________________________________________________
Table 12. PWM Intensity Settings (Blink Enabled)
EXAMPLES OF LED BLINK BEHAVIOR
(LED IS ON WHEN OUTPUT IS LOW)
PWM DUTY CYCLE
OUTPUT BLINK
PHASE X
REGISTER BIT = 0
PWM DUTY CYCLE
OUTPUT BLINK
PHASE X
REGISTER BIT = 1
OUTPUT
(OR
GLOBAL)
INTENSITY
SETTING
LOW
TIME HIGH
TIME
LOW
TIME HIGH
TIME
BLINK PHASE 0
REGISTER BIT = 0
BLINK PHASE 1
REGISTER BIT = 1
BLINK PHASE 0
REGISTER BIT = 1
BLINK PHASE 1
REGISTER BIT = 0
0x0 1/16 15/16 15/16 1/16
0x1 2/16 14/16 14/16 2/16
0x2 3/16 13/16 13/16 3/16
0x3 4/16 12/16 12/16 4/16
0x4 5/16 11/16 11/16 5/16
0x5 6/16 10/16 10/16 6/16
0x6 7/16 9/16 9/16 7/16
P hase 0: LE D on at l ow i ntensi ty
P hase 1: LE D on at hi g h i ntensi ty
P hase 0: LE D on at hi g h i ntensi ty
P hase 1: LE D on at l ow i ntensi ty
0x7 8/16 8/16 8/16 8/16 Output is half intensity during both blink phases
0x8 9/16 7/16 7/16 9/16
0x9 10/16 6/16 6/16 10/16
0xA 11/16 5/16 5/16 11/16
0xB 12/16 4/16 4/16 12/16
0xC 13/16 3/16 3/16 13/16
0xD 14/16 2/16 2/16 14/16
0xE 15/16 1/16 1/16 15/16
P hase 0: LE D on at hi g h i ntensi ty
P hase 1: LE D on at l ow i ntensi ty
P hase 0: LE D on at l ow i ntensi ty
P hase 1: LE D on at hi g h i ntensi ty
0xF Static low Static low
Static high
impedance
Static high
impedance
Phase 0: LED on continuously
Phase 1: LED off continuously Phase 0: LED off continuously
Phase 1: LED on continuously