参数资料
型号: LMH6643MAX/NOPB
厂商: National Semiconductor
文件页数: 11/33页
文件大小: 0K
描述: IC OP AMP R-R LP 3V 75MA 8-SOIC
标准包装: 2,500
系列: PowerWise®
放大器类型: 电压反馈
电路数: 2
输出类型: 满摆幅
转换速率: 135 V/µs
-3db带宽: 130MHz
电流 - 输入偏压: 1.6µA
电压 - 输入偏移: 1000µV
电流 - 电源: 2.7mA
电流 - 输出 / 通道: 75mA
电压 - 电源,单路/双路(±): 2.7 V ~ 12.8 V,±1.35 V ~ 6.4 V
工作温度: -40°C ~ 85°C
安装类型: 表面贴装
封装/外壳: 8-SOIC(0.154",3.90mm 宽)
供应商设备封装: 8-SOIC
包装: 带卷 (TR)
其它名称: LMH6643MAX
LMH6643MAX-ND
LMH6643MAX/NOPBTR
200 mV/DIV
20 ns/DIV
+
-
Vbias
Cd
10
-
200pF
Photodiode
Rd
C1
100nF
Q1
2N3904
R5
510:
R2
1.8k:
D1
1N4148
R3
1k:
R11
910
:
R10
1k:
-1mAPP
Cf
5pF
Rf
1k:
VCC =
+5V
Rbias
Photodiode
Equivalent
Circuit
Id
×100k:
Vout
+5V
x
SQRT
GBWP/(2SRF CIN)
fP =
CF =
SQRT
(CIN)/(2S GBWP RF)
SNOS966P – MAY 2001 – REVISED MARCH 2013
No matter how low an Rf is selected, there is a need for Cf in order to stabilize the circuit. The reason for this is
that the Op Amp input capacitance and Q1 equivalent collector capacitance together (CIN) will cause additional
phase shift to the signal fed back to the inverting node. Cf will function as a zero in the feedback path counter-
acting the effect of the CIN and acting to stabilized the circuit. By proper selection of Cf such that the Op Amp
open loop gain is equal to the inverse of the feedback factor at that frequency, the response is optimized with a
theoretical 45° phase margin.
(1)
where GBWP is the Gain Bandwidth Product of the Op Amp
Optimized as such, the I-V converter will have a theoretical pole, fp, at:
(2)
With Op Amp input capacitance of 3pF and an estimate for Q1 output capacitance of about 3pF as well, CIN =
6pF. From the typical performance plots, LMH6642/6643 family GBWP is approximately 57MHz. Therefore, with
Rf = 1k, from Equation 1 and Equation 2 above.
Cf = 4.1pF and fp = 39MHz
Figure 63. Single Supply Photodiode I-V Converter
For this example, optimum Cf was empirically determined to be around 5pF. This time domain response is shown
in Figure 64 below showing about 9ns rise/fall times, corresponding to about 39MHz for fp. The overall supply
current from the +5V supply is around 5mA with no load.
Figure 64. Converter Step Response (1VPP, 20 ns/DIV)
Copyright 2001–2013, Texas Instruments Incorporated
19
Product Folder Links: LMH6642 LMH6643 LMH6644
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