MIC74BQS Micrel Inc, MIC74BQS Datasheet - Page 17

• Manufacturer Part Number: MIC74BQS
• Description: IC I/O EXPANDER I2C 8B 16QSOP
• Manufacturer: Micrel Inc
• Series: -r

Specifications of MIC74BQS

• Interface: I²C, SMBus
• Number Of I /o: 8
• Interrupt Output: Yes
• Frequency - Clock: -
• Voltage - Supply: 2.7 V ~ 3.6 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-SSOP (0.154", 3.90mm Width)
• Includes: -
• Lead Free Status / Rohs Status: Contains lead / RoHS non-compliant

the fan will be shutdown by the assertion of the /SHDN
output if FAN_SPEED is zero. If FAN_SPEED is
programmed with any nonzero value, the fan will be
driven to its maximum speed for the duration of t
(about 1 second) and then assume the programmed
speed. Note that the circuit in Figure 14 contains an
additional transistor, Q1, as an inverter because the
regulator in this example has an active-high shutdown
input rather than an enable input. Otherwise the circuits
function identically.
Table 3 lists the output voltages corresponding to all the
fan speeds and system states possible with these
circuits. The following equations are used to calculate
the resistor values used in MIC74 fan speed control
circuits. It is assumed here that the regulator’s internal
reference voltage is 1.24V. If the regulator uses a
different reference voltage, that value should be used
instead.
Micrel, Inc.
October 2006
FAN_SPEED
0000 0000b
0000 0000b
0000 0001b
0000 0010b
0000 0011b
0000 0100b
0000 0101b
0000 0110b
0000 0111b
Value
Fan Speed
2
3
2
power-up
3
Selected
nd
medium
rd
nd
rd
highest
fan off
lowest
highest
highest
lowest
lowest
Table 3. Fan Speed Selection
R
3k
3k
3k
3k
3k
3k
3k
3k
3k
FB
START
R
1k
1k
1k
1k
1k
1k
1k
1k
1k
MIN
17
open
open
open
open
open
R
The following equations show how to calculate the
resistor values for the fan controllers. For example, when
the fan speed register contains 011
lowest speed, R
equivalence resistor (R
The output voltage is calculated by using:
1k
1k
1k
1k
F2
open
open
open
open
open
1.8k
1.8k
1.8k
1.8k
R
R
R
R
V
V
V
F1
EQ
EQ
EQ
OUT
OUT
OUT
= R
= 1.8k || 3.6k || 1k
= 545Ω
=
=
=
open
open
open
open
open
3.6k
3.6k
3.6k
3.6k
R
F1
F1
1.24V
1.24V
8.06V
F0
|| R
and R
F0
⎛
⎜
⎜
⎝
⎛
⎜
⎝
EQ
1
1
R
783
643
545
500
439
391
353
|| R
F0
1k
1k
+
+
) value of 545Ω.
EQ
R
R
545Ω
are parallel to R
MIN
3k
EQ
FB
10.75V
11.78V
⎞
⎟
⎟
⎠
4.96V
5.99V
7.03V
8.06V
8.68V
9.71V
V
⎞
⎟
⎠
0V
OUT
b
, which is the 3rd
M9999-101006
MIN
to give the
MIC74