(RTHEVENIN
參數(shù)資料
型號: MAX44268EWL+T
廠商: Maxim Integrated Products
文件頁數(shù): 4/15頁
文件大?。?/td> 0K
描述: IC COMPARATOR W/REF DUAL 9WLP
產(chǎn)品培訓(xùn)模塊: Obsolescence Mitigation Program
標(biāo)準(zhǔn)包裝: 2,500
類型: 通用
元件數(shù): 2
輸出類型: 開路漏極
電壓 - 電源,單路/雙路(±): 1.8 V ~ 5.5 V
電壓 - 輸入偏移(最小值): 5mV @ 5V
電流 - 輸入偏壓(最小值): 0.15nA
電流 - 輸出(標(biāo)準(zhǔn)): 50mA
電流 - 靜態(tài)(最大值): 1.15µA
CMRR, PSRR(標(biāo)準(zhǔn)): 80dB PSRR
傳輸延遲(最大): 39µs
磁滯: 6mV
工作溫度: -40°C ~ 85°C
封裝/外殼: 9-WFBGA,WLBGA
安裝類型: 表面貼裝
包裝: 帶卷 (TR)
Maxim Integrated Products 12
MAX44268
1.3mm x 1.3mm, Low-Power
Dual Comparator with Reference
(RTHEVENIN) in series with the capacitor C1. tHIGH can
then be computed using the basic time domain equa-
tions for the charging RC circuit as:
T_RISE
THEVENIN
HIGH
THEVENIN
T_FALL
THEVENIN
V- V
R
C1 ln
t
V- V
=
[
]
[
]
THEVENIN
CC
THEVENIN
R
(R2 R4) R3 R1 R5
V
(R2 R4) R3
V
x R4
V
(R2 R4) R3 R1
R2 R4
R1
x
(R2 R4) R3 R1
=
++
+
=
+
++
+
++
The tHIGH calculation can be simplified by selecting the
component values in such a way that R3 >> R1 and R5
>> R1. This ensures that the output of the comparator
goes close to VCC when at logic-high (that is, VTHEVENIN
~ VCC and RTHEVENIN ~ R5). With this selection, tHIGH
can be approximated as:
T_RISE
CC
HIGH
T_FALL
CC
V
- V
R5C1 ln
t
V
- V
=
The frequency of the relaxation oscillator is:
(
)
(
)
HIGH
LOW
CC
T_RISE
T_FALL
T_RISE
T_FALL
CC
11
f
V
-V
tt
V
R5C11n
V
-
V
=
+
Window Detector Circuit
The IC is ideal for window detectors (undervoltage/over-
voltage detectors). Typical Application Circuit shows a
simple window detector circuit. By changing the values
of R1, R2, and R3 different voltage threshold values can
be chosen. For this example, assume a single-cell Li+
battery with a 2.9V end-of-life charge, a peak charge of
4.2V, and a nominal value of 3.6V. OUTA provides an
active-low undervoltage indication, and OUTB provides
an active-low overvoltage indication. The open-drain out-
puts of both the comparators are wired ORed to give an
active-high power-good signal.
The design procedure is as follows:
1) Select R1. The input bias current into INB- is less than
15nA, so the current through R1 should exceed 1.5A
for the thresholds to be accurate. In this example,
choose R1 = 825kI (1.236V/1.5A).
2) Calculate R2 + R3. The overvoltage threshold should
be 4.2V when VIN is rising. The design equation is as
follows:
OTH
REF
V
R2 R3 R1 x
- 1
V
4.2
825 x
- 1
1.236
= 1969k
+
=
=
3) Calculate R2. The undervoltage threshold should be
2.9V when VIN is falling. The design equation is as
follows:
(
) (
)
(
)
REF
UTH
V
R2 (R1 R2 R3)x
- R1
V
825
1969 x 1.236/2.9 - 825
370k
=
++
=
+
=
For this example, choose a 374kI standard value 1%
resistor.
4) Calculate R3:
R3 (R2 R3) - R2
1969k - 374k
=1.595M
=
+
=
For this example, choose a 1.58MI standard value 1%
resistor.
Figure 7. Relaxation Oscillator Waveforms
VT_RISE
C1 WAVEFORM
OUT
WAVEFORM
VT_FALL
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