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参数资料
| 型号： | LTC5100EUF#TR |
| 厂商： | Linear Technology |
| 文件页数： | 23/52页 |
| 文件大小： | 0K |
| 描述： | IC DRIVER VCSEL 3.2GBPS 16QFN |
| 标准包装： | 2,500 |
| 类型： | 激光二极管驱动器 |
| 数据速率： | 3.2Gbps |
| 通道数： | 1 |
| 电源电压： | 3.135 V ~ 3.465 V |
| 电流 - 电源： | 54mA |
| 电流 - 调制： | 12mA |
| 工作温度： | -40°C ~ 85°C |
| 封装/外壳： | 16-WQFN 裸露焊盘 |
| 供应商设备封装： | 16-QFN（4x4） |
| 包装： | 带卷 (TR) |
| 安装类型： | 表面贴装 |
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LTC5100
OPERATIO
Im_ set = Im_ nom ? ? ? (18)
Reducing Im_gain slows the settling time and increasing
Im_gain speeds the settling time. For example, with Im_gain
= 1, the residual loop error is cut by 1/8 with each servo
iteration. In this case it would take 35 servo iterations
(about 140ms) to settle to 1%. With Im_gain = 7, the
residual servo loop error is cut by 7/8 with each servo
iteration. In this case it would take only three servo
iterations (about 12ms) to settle to 1%, but the servo loop
will tend to “hunt” or oscillate at a low level with such a
high loop gain.
Temperature Compensation
The set point value for the modulation current, Im_set in
Figure 3 and Figure 4, changes with temperature to com-
pensate the temperature dependence of the laser diode’s
slope efficiency. Temperature measurements are supplied
either by an on-chip temperature sensor or by an external
microprocessor, according to the setting of Ext_temp_en.
The temperature compensated expression for Im_set is
given by:
? Im_ tc 2 ? 2 – 18 ? ? T 2 ?
? + Im_ tc 1 ? 2 – 13 ? ? T + 1 ?
Im_tc1 and Im_tc2 are the first and second order tempera-
ture coefficients for the modulation current.
LASER BIAS CURRENT CONTROL IN APC MODE
Figure 3 is a functional diagram of the LTC5100 operating
in automatic power control (APC) mode. In APC mode, the
LTC5100 servo controls the average optical power with
feedback from a monitor photodiode. Setting Apc_en = 1
selects this mode. In APC mode the monitor diode current
can be temperature compensated with first and second
order temperature coefficients.
Figure 9 shows an equivalent circuit for the MD pin and
Figure 23 shows details of the monitor diode circuit. The
Md_polarity bit selects whether the monitor diode sources
or sinks current from the MD pin. A programmable attenu-
ator and logarithmic amplifier permit a very wide range of
monitor diode currents spanning 4.25 μ A to 2176 μ A (typi-
cal) with constant 0.2% set point resolution. The attenu-
ator divides the monitor diode current by 1, 4, 16 or 64
depending on the value of Imd_rng. Two bits called Imd_rng
control the attenuator setting, selecting a full scale current
range of 34, 136, 544 or 2176 μ A typical. A 5kHz lowpass
filter provides antialiasing and limits noise. The logarithmic
amplifier compresses the dynamic range of the monitor
diode current and plays a role in maintaining constant and
predictable settling times regardless of the photodiode
characteristics.
Range Selection
Figure 24 depicts the current ranges for the monitor diode
current. The full-scale range of the monitor diode current
is 34 μ A ? 4 Imd_rng typical where Imd_rng = 0, 1, 2 or 3. The
minimum operating level should be limited to 20% of full
scale to ensure adequate settling time of the optical power
output of the laser. The range should be selected so that
the monitor diode current stays within the guaranteed
current limits over temperature.
LTC5100
Imd_rng
Md_polarity
V DD
Md_polarity = 1
5kHz
LOWPASS
FILTER
ATTENUATOR
÷ 1, ÷ 4, ÷ 16, ÷ 64
POLARITY
CONTROL
MD
13
Md_polarity = 0
LOG AMP
10-BIT ADC
Imd_adc
5100 F32
Figure 23. Detail of the Monitor Photodiode Circuit
sn5100 5100fs
23
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