Datasheet MAX9140, MAX9141, MAX9142, MAX9144 (Maxim) - 7

link to page 7 link to page 7 link to page 8 link to page 8 MAX9140/MAX9141/ 40ns, Low-Power, 3V/5V, Rail-to-Rail MAX9142/MAX9144 Single-Supply Comparators
Detailed Description
The MAX9140/MAX9141/MAX9142/MAX9144 single- supply comparators feature internal hysteresis, high speed, and low power. Their outputs are pulled to within VTRIP+ 300mV of either supply rail without external pullup or VIN+ pulldown circuitry. Rail-to-rail input voltage range and low- VHYST VTRIP+ + VTRIP- V voltage single-supply operation make these devices ideal OS = 2 for portable equipment. The devices interface directly to VIN- = 0 V CMOS and TTL logic. TRIP- Most high-speed comparators oscillate in the linear region because of noise or undesired parasitic feedback. This tends to occur when the voltage on one input is at or VOH equal to the voltage on the other input. To counter the COMPARATOR parasitic effects and noise, the devices have an internal OUTPUT hysteresis of 1.5mV. VOL The hysteresis in a comparator creates two trip points: one for the rising input voltage and one for the falling input voltage (Figure 1). The difference between the trip points is the hysteresis. The average of the trip points is the of set Figure 1. Input and Output Waveform, Noninverting Input voltage. When the comparator’s input voltages are equal, Varied the hysteresis effectively causes one comparator input voltage to move quickly past the other, thus taking the input out of the region where oscillation occurs. Standard
Input Stage Circuitry
comparators require hysteresis to be added with external The devices include internal protection circuitry that prevents resistors. The devices’ fixed internal hysteresis eliminates damage to the precision input stage from large differential these resistors. To increase hysteresis and noise margin input voltages. This protection circuitry consists of two even more, add positive feedback with two resistors as a back-toback diodes between IN+ and IN- as well as two voltage divider from the output to the noninverting input. series 4.1kΩ resistors (Figure 3). The diodes limit the Figure 1 illustrates the case where IN- is fixed and IN+ is differential voltage applied to the internal circuitry of the varied. If the inputs were reversed, the figure would look comparators to be no more than 2VF, where VF is the the same, except the output would be inverted. forward voltage drop of the diode (about 0.7V at +25°C). The MAX9141 includes an internal latch that allows For a large differential input voltage (exceeding 2VF), this storage of comparison results. The LE pin has a high input protection circuitry increases the input bias current at IN+ impedance. If LE is high, the latch is transparent (i.e., the (source) and IN- (sink). comparator operates as though the latch is not present). The comparator’s output state is latched when LEis pulled (IN+ - IN-) - 2V low (Figure 2). F Input Current = 2 × 4.1kΩ
Shutdown Mode (MAX9141 Only)
The MAX9141 shuts down when the SHDN pin is low. When Input current with large differential input voltages should shut down, the supply current drops to less than 12μA, and not be confused with input bias current (IB). As long as the the three-state output becomes high impedance. The SHDN differential input voltage is less than 2VF, this input current pin has a high-input impedance. Connect SHDN to V is equal to I CC for B. The output is in the correct logic state if one normal operation. Exit shutdown with LE high (transparent or both inputs are within the common-mode range. state); otherwise, the output will be indeterminate. www.maximintegrated.com Maxim Integrated │ 7