Datasheet

PCAL6408A All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
Product data sheet Rev. 3 — 18 September 2013 19 of 49
NXP Semiconductors
PCAL6408A
Low-voltage translating, 8-bit I
2
C-bus/SMBus I/O expander
9.2 Output drive strength control
The Output drive strength registers allow the user to control the output drive level of the
GPIO. Each GPIO can be configured independently to one of the four possible output
current levels. By programming these bits the user is changing the number of transistor
pairs or ‘fingers’ that drive the I/O pad.
Figure 18
shows a simplified output stage. The behavior of the pad is affected by the
Configuration register, the output port data, and the current control register. When the
Current Control register bits are programmed to 10b, then only two of the fingers are
active, reducing the current drive capability by 50 %.
Fig 16. High-value resistor in parallel
with the LED
Fig 17. Device supplied by a lower voltage
002aah278
LED
V
DD(P)
Pn
100 kΩ
V
DD
002aah279
LED
V
DD(P)
Pn
3.3 V 5 V
Fig 18. Simplified output stage
V
DD(P)
P0 to P7
Configuration
register
002aah093
DECODER
PMOS_EN0
PMOS_EN1
PMOS_EN2
PMOS_EN3
NMOS_EN3
NMOS_EN2
NMOS_EN1
NMOS_EN0
Output port
register
Current Control
register
PMOS_EN[3:0]
NMOS_EN[3:0]