参数资料
型号: USB-I2C-SS
厂商: Flexipanel
文件页数: 5/9页
文件大小: 0K
描述: IC USB SYNC SRL I2C 20-SSOP
标准包装: 25
应用: USB
接口: I²C
电源电压: 1.8 V ~ 5 V
封装/外壳: 20-SSOP
供应商设备封装: 20-SSOP
包装: 散装
安装类型: 表面贴装
产品目录页面: 659 (CN2011-ZH PDF)
其它名称: 658-1037-5
p5 of 9
26-Aug-10
USB-SPI
HW144-8
www.hexwax.com
Table 4. Suggested component values
Label
Component
R6
1k resistor
R2x
470Ω resistor
R40
100k resistor
T1, T2
P-channel Mosfet, e.g. NDS352P
D1, D2
Low Vf switching diode
LED1x
Light emitting diode
C1
1μF capacitor
C2, C3
22pF capacitor
C4, C6-C7
100nF capacitor
C8
470nF capacitor
PB1x
Pushbutton or switch
X1
12MHz parallel cut crystal
Bus Powered Device
Figure 2 is the suggested circuit when initially evaluating
USB-I2C.
R
es
et
#
P
G
D
V
dd
V
ss
TEAclipper
connector 1
5
OSC1
OSC2
D+
Vusb
Figure 2
USB-I2C
USB
C2
C3
X1
2
3
4
Vdd
Vss
Vdd
P
G
C
1
2
3
4
Vss
D-
Vss
C1
C6
C7
V
ss
C8
Reset#
Send
AllSysGo#
Vdd
Vss
R1x
PB1x
One pushbutton
circuit for each input
(Active low shown)
Tx Ind
Rx Ind
Vdd
R2x
One LED circuit
for each output
(Active low shown)
S
us
pe
nd
#
Host
Microcontroller
S
C
L
S
D
A
S
ht
D
n#
Vss
Vdd
B
uf
fN
ot
F
ul
l
B
uf
fE
m
pt
y
B
uf
fN
ot
F
ul
l
B
uf
fE
m
pt
y
S
C
L
S
D
A
R4
Vdd
R5
The microcontroller sends and receives data via its I2C
pins SCL and SDA. These bus lines require 4k7 pull-
ups. The Rx Buff Not Full and Tx Buffer Full can be
monitored if required for flow control. When Rx Buffer
Not Full is low, no data should be sent to the USB-SPI.
If Tx Buff Empty is high and the microcontroller reads
data from USB-SPI, then Null Tx Char will be read.
When it ShtDn# low, the microcontroller and the rest of
the circuit should go into a sleep state.
The pushbutton circuits allow you to apply logic 1 or
logic 0 to input pins. The LED circuits allow you to view
the state of output pins. As shown they are active low.
For commercial applications these circuits need only be
provided if required.
Oscillator X1/C2/C3 may be replaced by a low-cost
resonator, provided its frequency tolerance is greater
than 0.25%. C1 and C6 should be placed close to the
USB connector. C7 should be placed near the Vss and
Vdd pins of the USB-I2C and is required only if it would
be some distance from C6. C8 is a filter capacitor for an
internal regulator and is required.
The TEAclipper connector is for in-circuit programming
of devices where the firmware has been purchased from
HexWax. It is recommended to allow firmware updates,
even if the firmware is initially supplied pre-programmed.
Self Powered Device
A self-powered device does not need to draw power
from the USB bus. In this case, the USB-I2C can be put
into sleep mode when USB power is not available. The
sub-circuit required to do this is shown in figure 3. If the
device is self-powered, it is not necessary to enter the
sleep state if the Suspend indicate is active.
D+
Figure 3
USB-I2C
USB
1
2
3
4
Vss
D-
USB Pwr Sns
R3
Vdd
Vss
Self Power Source
R4
Vss
Both-powered Powered Device
If both self-powered and bus powered configurations are
possible, a circuit must be provided to switch over power
to USB power. An example sub-circuit is given in figure
4, where it is assumed that USB power is used when it
is available. To give self-power priority, place T2 so that
it switches the USB power line instead. D1 and D2
ensure that the two power lines are not in contention. If
the self-power source is 3.3V, the diodes will be
sufficient and T2 will not be required at all.
Figure 4
USB-I2C
Vdd
Self-Power Vdd
3.3V - 5V
R40
USB-Power Vdd
Vss
T2
R50
Self Pwr
Sns
USB Pwr
Sns
R30
D1
D2
Power Take-Off
A device should only draw current from the USB line
once USB configuration is complete and the host PC is
not is sleep mode. The AllSysGo# output (active low)
can provide such a switch using the sub-circuit shown in
figure 5. C4 / R6 provide a slow switch-on to prevent
inrush current exceeding USB power limitations. 1μF
and 100nF smoothing capacitors are recommended on
both self and USB power lines. The Low Pwr output
should be monitored if the device can draw more than
100mA.
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