
threshold. The power-on states can also be reset with
the SPOR command through the SMBus.
The MAX1608’s outputs reset to a low state, while the
MAX1609’s outputs reset to a high-impedance state.
Below V+ = 0.8V (typical), the POR states can’t be
enforced, and the I/O pins of both devices exhibit
increasingly weak pull-down current capability, eventu-
ally becoming high impedance.
The MAX1608 is designed for applications that control
N-channel MOSFETs, while the MAX1609 is designed
to control P-channel MOSFETs. The power-on state
keeps the external MOSFETs off at power-up. Both
devices are suited for applications that use the parallel
input for serial functionality, although IO_s serving as
inputs must first be programmed to high impedance
when using the MAX1608.
Thermal Shutdown
These devices have internal thermal-shutdown circuitry
that sets all outputs to a high-impedance state (IO_
pins) when the junction temperature exceeds +140°C
typical. Thermal shutdown only occurs during an over-
load condition on the IO_ pins. The device cycles
between thermal shutdown and the overcurrent condi-
tion (with 10°C hysteresis) until the overload condition
is removed. The device asserts
ALERT
low while it is in
thermal shutdown, indicating this fault status.
ALERT
will be reasserted immediately after it is cleared if the
device is still hot.
ALERT
can only be completely
cleared once the fault condition is removed and the
device has cooled. Alternatively, forcing the IO_ to high
impedance will allow the junction to cool down.
M
Octal SMBus-to-Parallel I/O Expanders
12
______________________________________________________________________________________
POR STATE
7
MASKL7
1
6
MASKL6
1
5
MASKL5
1
4
MASKL4
1
1
MASKL1
1
NAME
BIT
2
MASKL2
1
3
MASKL3
1
MASKL0
1
0
Masks IO1 high-to-low interrupt. 0 = interrupts, 1 = masked.
Masks IO7 high-to-low interrupt. 0 = interrupts, 1 = masked.
Masks IO6 high-to-low interrupt. 0 = interrupts, 1 = masked.
Masks IO5 high-to-low interrupt. 0 = interrupts, 1 = masked.
Masks IO4 high-to-low interrupt. 0 = interrupts, 1 = masked.
Masks IO2 high-to-low interrupt. 0 = interrupts, 1 = masked.
Masks IO3 high-to-low interrupt. 0 = interrupts, 1 = masked.
FUNCTION
Masks IO0 high-to-low interrupt. 0 = interrupts, 1 = masked.
Table 5. IO_ Status Data Register (RSB) Bit Assignments (read only)
Table 6. Data Register 3 (NDR3 and SDR3) Bit Assignments (read or write)
7
DATA7
6
DATA6
5
DATA5
4
DATA4
1
DATA1
NAME
BIT
2
DATA2
3
DATA3
DATA0
0
Indicates the current state of IO1. 1 = high, 0 = low.
Indicates the current state of IO7. 1 = high, 0 = low.
Indicates the current state of IO6. 1 = high, 0 = low.
Indicates the current state of IO5. 1 = high, 0 = low.
Indicates the current state of IO4. 1 = high, 0 = low.
Indicates the current state of IO2. 1 = high, 0 = low.
Indicates the current state of IO3. 1 = high, 0 = low.
FUNCTION
Indicates the current state of IO0. 1 = high, 0 = low.