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參數(shù)資料
| 型號： | SSM2018PZ |
| 廠商： | Analog Devices Inc |
| 文件頁數(shù)： | 2/16頁 |
| 文件大?。?/td> | 0K |
| 描述： | IC AMP AUDIO MONO CLASS AB 16DIP |
| 標(biāo)準(zhǔn)包裝： | 25 |
| 放大器類型： | 音頻 |
| 電路數(shù)： | 1 |
| 轉(zhuǎn)換速率： | 5 V/µs |
| 增益帶寬積： | 14MHz |
| 電流 - 輸入偏壓： | 250nA |
| 電壓 - 輸入偏移： | 1000µV |
| 電流 - 電源： | 11mA |
| 電壓 - 電源，單路/雙路(±)： | 10 V ~ 36 V，±5 V ~ 18 V |
| 工作溫度： | -40°C ~ 85°C |
| 安裝類型： | 通孔 |
| 封裝/外殼： | 16-DIP（0.300"，7.62mm） |
| 供應(yīng)商設(shè)備封裝： | 16-PDIP |
| 包裝： | 管件 |
| 產(chǎn)品目錄頁面： | 775 (CN2011-ZH PDF) |
REV. B
–10–
SSM2018T
Proper Operating Mode for the SSM2018T
The SSM2018T has the flexibility of operating in either Class A
or Class AB. This is accomplished by adjusting the amount of
current flowing in the gain core (IM in Figure 2). The traditional
trade-off between the two classes is that Class A tends to have
lower THD but higher noise than Class AB. However, by using
well matched gain core transistors, distortion compensation
circuitry and laser trimming, the SSM2018T has excellent THD
performance in Class AB. Thus, it offers the best of both worlds
in having the low noise of Class AB with low THD.
Because the SSM2018T operates optimally in Class AB, the
distortion trim is performed for this class. To guarantee conform-
ance to the data sheet THD specifications, the SSM2018T must be
operated in class AB. This does not mean that it can not be oper-
ated in Class A, but the optimal THD trim point is different for
the two classes. Using Class A operation results to 0.05% with-
out trim. An external potentiometer could be added to change
the trim back to its optimal point as shown in the OVCE appli-
cation circuit, but this adds the expense and time in adjusting a
potentiometer.
The class of operation is set by selecting the proper value for RB
shown in Figure 1. RB determines the current flowing into the
MODE input (Pin 12). For class AB operation with
± 15 V
supplies, RB should be 150 k
W. This results in a current of
95
mA. For other supply voltages, adjust the value of R
B such
that current remains at 95
mA. This current follows the formula:
I
MODE =
(V
CC –0. 7 V )
R
B
(3)
The factor of 0.7 V arises from the fact that the dc bias on Pin
12 is a diode drop above ground.
Output Drive
The SSM2018T is buffered by an internal op amp to provide a low
impedance output. This output is capable of driving to within
1.2 V of either rail at 1% distortion for a 100 k
W load. Note: This
100 k
W load is in parallel with the feedback resistor of 18 kW, so
the effective load is 15.3 k
W. For better than 0.01% distortion,
the output should remain about 3.5 V away from either rail as
shown in TPC 2. As the graph of output swing versus load resis-
tance shows (TPC 9), to maintain less than 1% distortion the
output current should be limited to approximately
±1.3 mA. If
higher current drive is required, the output should be buffered with
a high quality op amp such as the OP176 or AD797.
The internal amplifiers are compensated for unity gain stability
and are capable of driving a capacitive load up to 4700 pF.
Larger capacitive loads should be isolated from the output of the
SSM2018T by the use of a 50
W series resistor.
18k
50pF
V+
VOUT
47pF
NC
1 F
1k
3k
V–
V+
1 F
18k
1 F 18k
RB: 150k
FOR CLASS AB
NC = NO CONNECT
RB
VCONTROL
VIN+
VIN–
SSM2018T
470k
500k
100k
10M
OFFSET
TRIM
V+
V–
SYMMETRY
TRIM
REMOVE FOR SSM2018T
Figure 3. Upgrading SSM2018 Sockets
Upgrading SSM2018 Sockets
The SSM2018T easily replaces the SSM2018 in the basic VCA
configuration. The parts are pin for pin compatible allowing
direct replacement. At the same time, the trimming potentiom-
eters for symmetry and offset should be removed, as shown in
Figure 3. Upgrading immediately to the SSM2018T saves the
expense of the potentiometers and the time in production of
trimming for minimum distortion and control feedthrough.
If the SSM2018 is used in the OVCE or VCP configuration, the
SSM2018T can still directly replace it; however, the potentiom-
eters cannot necessarily be removed, as explained in the OVCE
and VCP sections.
Temperature Compensation of the Gain Constant
As explained above, the gain constant has a –3500 ppm/
∞C
temperature drift due to the inherent nature of the control port.
Over the full temperature range of –40
∞C to +85∞C, the drift
causes the gain to change by 7 dB if the part is in a gain of
±20 dB. If the application requires the gain constant to be the
same over a wide temperature range, external temperature com-
pensation should be employed. The simplest form of compensa-
tion is a temperature compensating resistor (TCR) such as the
PT146 from Precision Resistor Co. These elements are different
than a standard thermistor in that they are linear over tempera-
ture to better match the linear drift of the gain constant.
*PT146 AVAILABLE FROM
PRECISION RESISTOR CO.
10601 75TH ST. NORTH
LARGO, FL 34647
(813) 541-5771
+15V
–15V
1k *
2k
OP27
PIN 11
SSM2018T
CONTROL
VOLTAGE
Figure 4. Two TCRs Compensate for Temperature Drift of
Gain Constant
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