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參數(shù)資料
| 型號： | SML2120 |
| 廠商： | Summit Microelectronics, Inc. |
| 英文描述： | Programmable Adaptive Laser Power Controller with Dual Lookup Tables |
| 中文描述： | 可編程控制器自適應(yīng)激光功率雙查找表 |
| 文件頁數(shù)： | 10/32頁 |
| 文件大?。?/td> | 1196K |
| 代理商： | SML2120 |
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Applications Information
SML2120
10
2066 6.3 1/22/04
Summit Microelectronics
–
APPLICATIONS INFORMATION
Power-Up Sequence
When power is first applied to the SML2120, the device
reads configuration register information from the array and
loads it to volatile latches. This procedure begins once the
supply voltage exceeds the power-on reset voltage (VPOR)
and requires about 3 ms to complete. During this
initialization period, all current outputs (BIAS, ILU0, ILU1)
are placed into a high impedance state.
At the conclusion of the initialization period, the ENA# pin
determines the state of the current output. However, the
autonomous monitoring (auto-monitor) function is not yet
allowed to activate, regardless of the state of the AM# pin.
A holdoff timer period (t
HOLDOFF
) is counted off at the
conclusion of the initialization period to allow the laser
control loop to stabilize. After t
HOLDOFF
, the AM# pin
determines whether the device begins its auto-monitor
sequence or not. If AM# is asserted, the device enters auto-
monitor mode.
Automatic Power Control (APC) Loop
The SML2120 provides an efficient feedback mechanism
for controlling the light output of the laser. Once the power-
on initialization period has expired, current to the laser is
driven by the BIAS pin, which can sink up to 100 mA of
current to Vss. An on-board amplifier controls the bias
output circuitry. The Monitor Photo Diode (MPD) pin is
driven from the anode of a photo-diode that monitors the
light power being given off by the laser. Adding an
integration capacitor between C1 and C2, and a
corresponding resistor between MPD and C1, completes
and stabilizes the loop, as is shown in Figure 5.
The APC loop attempts to drive the C1 node to the internal
VAPC voltage reference of 0.75V. If the voltage on the MPD
pin exceeds VAPC, the SML2120 reduces the amount of
current on the BIAS pin accordingly, thereby reducing the
amount of current to the laser. Conversely, if the voltage on
MPD falls below VAPC, the amount of current supplied to
the laser is increased. Note that the VAPC pin may be over-
driven using an external reference if a different steady state
value is desired.
The integration time constant of the APC loop is typically set
to a relatively long period (such as 1ms) in order to reduce
pattern dependent jitter. Unfortunately, a long time constant
also leads to a long start-up time. The SML2120 provides an
internal 'Quick Start' transistor, shown in Figure 5, that can
be used to accelerate the turn-on time of the laser. When
this feature is enabled, the Quick Start transistor effectively
shorts out the external resistor for a brief time period after
the outputs are first enabled.
Figure 5. Bias Control Circuit
Bias Output
The user may limit the maximum BIAS current in increments
of 12.5mA (up to a maximum of 100mA), using register 14
bits 2:0. This feature is useful in preventing damage to the
laser even during start-up or open-loop conditions.
Additionally, the BIAS output may be configured to provide
a fixed current. The value of current is based on the ILU1
output and scales proportionally. This fixed bias current may
be configured so that it is available at power-up only, or
whenever ENA# is disabled. This feature is useful in
systems without a monitor diode, or in systems where feed-
forward current is desired. A fixed current is also useful for
providing reasonable BIAS when no data is yet flowing, and
for diagnostics and board debugging.
Autonomous Monitoring Function (Auto-
Monitor)
The Autonomous Monitoring (Auto-Monitor) Function
provides a control loop for setting two independent output
currents (ILU0 and ILU1) based on various programmable
input stimuli within the system. For each channel, the user
selects: 1) an input stimulus for the Analog/Digital Converter
(ADC), 2) scale and offset values for the conversion to
maximize the usable input range, 3) lookup table values that
translate the resulting ADC conversion to an output current,
and 4) minimum and maximum limits for the output current
driver. Refer to Figure 6.
-
+
GND
Laser
C2
C1
MPD
Photodiode
Quick
Start
0.75
Internal
Reference
Voltage
VAPC
BIAS
SML2120
20K
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| SML2120N | 制造商:SUMMIT 制造商全稱:SUMMIT 功能描述:Programmable Adaptive Laser Power Controller with Dual Lookup Tables |
| SML-212DT | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:LEDs, Surface Mount |
| SML-212DTT86 | 功能描述:標(biāo)準(zhǔn)LED-SMD 611NM ORN WTR CLR RoHS:否 制造商:Vishay Semiconductors 封裝 / 箱體:0402 LED 大小:1 mm x 0.5 mm x 0.35 mm 照明顏色:Red 波長/色溫:631 nm 透鏡顏色/類型:Water Clear 正向電流:30 mA 正向電壓:2 V 光強(qiáng)度:54 mcd 顯示角:130 deg 系列:VLMx1500 封裝:Reel |
| SML-212DTT86Q | 制造商:ROHM Semiconductor 功能描述:LED Orange 611nm 17deg Clear 0805 |
| SML-212DTT86S2 | 制造商:ROHM Semiconductor 功能描述:LED SMD 0805 HB ORG 制造商:ROHM Semiconductor 功能描述:LED, SMD, 0805, HB ORG 制造商:ROHM Semiconductor 功能描述:LED, ORANGE, 1.25MM X 1.4MM, 63MCD, 608NM; Bulb Size:1.25mm x 1.4mm; LED Color:Orange; Luminous Intensity:63mcd; Forward Current If:20mA; Forward Voltage:2.05V; LED Mounting:SMD; Lens Shape:Rectangular; Wavelength Typ:608nm ;RoHS Compliant: Yes |
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