PCA9551 Philips Semiconductors, PCA9551 Datasheet - Page 6

• Manufacturer Part Number: PCA9551
• Description: 8-bit I2C LED driver with programmable blink rates
• Manufacturer: Philips Semiconductors

1. Prescaler calculation is different between the PCA9551 and
Philips Semiconductors
PSC1 — FREQUENCY PRESCALER 1
PSC1 is used to program the period of PWM output.
The period of BLINK1
NOTE:
PWM1 — PWM REGISTER 1
The PWM1 register determines the duty cycle of BLINK1. The
outputs are LOW (LED off) when the count is less than the value in
PWM1 and HIGH when it is greater. If PWM1 is programmed with
00h, then the PWM1 output is always LOW (LED off).
The duty cycle of BLINK1 is: 256 – PWM1
LS0 — LED0–3 SELECTOR
LS1 — LED4–7 SELECTOR
The LSx LED select registers determine the source of the LED data.
2004 Oct 01
default
default
default
default
8-bit I
other PCA955x LED Blinkers. A divider ratio of 38 instead of 44
is used. This different divider ratio causes the blinking frequency
to be 13% (1 – 38/44) lower when the same 8-bit word is used.
The programmed value of the FREQUENCY PRESCALER must
be adjusted to compensate for this difference in applications
where the PCA9551 is used in conjunction with other PCA955x
LED Blinkers and the observed blinking frequencies need to be
the same.
00 = Output is set LOW (LED on)
01 = Output is set Hi-Z (LED off – default)
10 = Output blinks at PWM0 rate
11 = Output blinks at PWM1 rate
bit
bit
bit
bit
2
7
1
7
1
7
0
7
0
LED 3
LED 7
C LED driver with programmable blink rates
6
1
6
0
6
1
6
1
(PSC1
5
1
5
0
5
0
5
0
LED 2
LED 6
38
4
1
4
0
4
1
4
1
256
1)
1
3
1
3
0
3
0
3
0
LED 1
LED 5
2
1
2
0
2
1
2
1
1
1
1
0
1
0
1
0
LED 0
LED 4
0
1
0
0
0
1
0
1
6
PINS USED AS GENERAL PURPOSE I/Os
LED pins not used to control LEDs can be used as general purpose
I/Os.
For use as input: Set LEDx to high-impedance (01) and then read
the pin state via the input register.
For use as output: Connect external pull-up resistor to the pin and
size it according to the DC recommended operating characteristics.
LED output pin is HIGH when the output is programmed as
high-impedance, and LOW when the output is programmed LOW
through the “LED selector” register. The output can be pulse-width
controlled when PWM0 or PWM1 are used.
POWER-ON RESET
When power is applied to V
the PCA9551 in a reset condition until V
this point, the reset condition is released and the PCA9551 registers
are initialized to their default states, all the outputs in the off state.
Thereafter, V
EXTERNAL RESET
A reset can be accomplished by holding the RESET pin LOW for a
minimum of t
be held in their default state until the RESET input is once again
HIGH.
This input requires a pull-up resistor to V
used.
W
DD
. The PCA9551 registers and I
must be lowered below 0.2 V to reset the device.
DD
, an internal Power-On Reset holds
DD
DD
has reached V
if no active connection is
2
C state machine will
PCA9551
Product data sheet
POR
. At