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参数资料
| 型号： | MAX1932ETC+T |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 8/16页 |
| 文件大小： | 0K |
| 描述： | IC SUPPLY BIAS APD 12-TQFN |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 2,500 |
| 应用： | 控制器，光纤网络 |
| 输入电压： | 2.7 V ~ 5.5 V |
| 输出数： | 1 |
| 输出电压： | 4.5 V ~ 90 V |
| 工作温度： | 0°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 12-WQFN 裸露焊盘 |
| 供应商设备封装： | 12-TQFN-EP（4x4） |
| 包装： | 带卷 (TR) |
Digitally Controlled, 0.5% Accurate,
Safest APD Bias Supply
(<10pF) are recommended to minimize losses. A small-
signal silicon switching diode is suitable if efficiency is
not critical.
Output Filter Capacitor Selection
where R EA = 310M Ω ,
g M = 110μS,
R LD is the parallel combination of feedback network
and the load resistance.
The output capacitors of the MAX1932 must have high
enough voltage rating to operate with the V OUT
required. Output capacitor effective series resistance
(ESR) determines the amplitude of the high-frequency
ripple seen on the output voltage. In the typical applica-
K 1 =
2 × V OUT - V IN
V OUT - V IN
K 2 = ×
tion circuit, a second RC formed by R1 and C3 further
reduces ripple.
V FB ( Volts ) 2 × V IN
0 . 75 ( Volts ) 2 × V OUT - V IN
×
? ? V OUT - V IN ? ? 2 × L ( Henries ) ?
Input Bypass Capacitor Selection
The input bypass capacitor reduces the peak currents
drawn from the voltage source and reduces noise
caused by the MAX1932’s switching action. The input
source impedance determines the size of the capacitor
required at the input (VIN). A low ESR capacitor is rec-
ommended. A 1μF ceramic capacitor is adequate for
most applications. Place the bypass capacitor as close
as possible to the VIN and GND pins.
Current-Sense Resistor Selection
Current limit is used to set the maximum delivered out-
put current. In the typical application circuit, MAX1932
is designed to current limit at:
? ? V OUT ? R LD × T ( sec ond ) ?
? ? ?
? ?
A properly compensated MAX1932 results in a gain vs.
frequency plot that crosses 0dB with a single pole
slope (20dB per decade). See Figure 6.
Table 1 lists suggested component values for several
typical applications.
Further Noise Reduction
The current-limit sense resistor is typically used as part
of an output lowpass filter to reduce noise and ripple.
For further reduction of noise, an LC filter can be added
R 1 =
2 V
I LIMIT
as shown in Figure 7. Output ripple and noise with and
without the LC filter are shown in the Typical Operating
Characteristics . If a post LC filter is used, it is best to
Note that I LIMIT must include current drawn by the feed-
back divider (if sensing feedback after R1) and the
input current of CS-.
Stability and Compensation
Component Selection
Compensation components, R7 and C4, introduce a
pole and a zero necessary to stabilize the MAX1932
(see Figure 6). The dominant pole, POLE1, is formed by
the output impedance of the error amplifier (R EA ) and
C4. The R7/C4 zero, ZERO1, is selected to cancel the
pole formed by the output filter cap C3 and output load
R LD , POLE2. The additional pole of R1/C3, POLE3,
should be at least a decade past the crossover fre-
quency to not affect stability:
POLE1 (dominant pole) = 1 / (2 π ? R EA ? C4)
ZERO1 (integrator zero) = 1 / (2 π ? R7 ? C4)
POLE2 (output load pole) = K1 / (2 π ? R LD ? (C2 + C3))
POLE3 (output filter pole) = 1 / (2 π ? R1 ? C3)
The DC open-loop gain is given by:
A OL = K2 ? Gm ? R EA
use a coil with fairly large resistance (or a series resis-
tor) so that ringing at the response peak of the LC filter
is damped. For a 330μH and 1μF filter, 22 Ω accom-
plishes this, but a resistor is not needed if the coil resis-
tance is greater than 15 Ω .
Output Accuracy and Feedback
Resistor Selection
The MAX1932 features 0.5% feedback accuracy. The
total voltage accuracy of a complete APD bias circuit is
the sum of the FB set-point accuracy, plus resistor ratio
error and temperature coefficient. If absolute accuracy
is critical, the best resistor choice is an integrated net-
work with specified ratio tolerance and temperature
coefficient. If using discrete resistors in high-accuracy
applications, pay close attention to resistor tolerance
and temperature coefficients.
Temperature Compensation
APDs exhibit a change in gain as a function of tempera-
ture. This gain change can be compensated with an
appropriate adjustment in bias voltage. For this reason
it may be desirable to vary the MAX1932 output voltage
as a function of temperature. This can be done in soft-
8
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