Datasheet MAX987, MAX988, MAX991, MAX992, MAX995, MAX996 (Maxim) - 9
| Manufacturer | Maxim |
| Description | High-Speed, Micropower, Low-Voltage, Rail-to-Rail I/O Comparators |
| Pages / Page | 13 / 9 — MAX988/MAX992/MAX996. Circuit Layout and Bypassing. MAX988. MAX992. MAX996 |
| File Format / Size | PDF / 1.7 Mb |
| Document Language | English |
MAX988/MAX992/MAX996. Circuit Layout and Bypassing. MAX988. MAX992. MAX996
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Text Version of Document
MAX987/MAX988/MAX991/ High-Speed, Micropower, Low-Voltage, MAX992/MAX995/MAX996 Rail-to-Rail I/O Comparators 5) Calculate R2 as shown. For this example, choose an Use the following procedure to calculate resistor 8.2kΩ standard value: values: 1 1) Select R3 according to the formulas R3 = V R2 = REF / 1µA V or R3 = (V THR 1 1 REF - VCC) / 1µA - R4. Use the smaller of − − the two resulting resistor values. RE V F x R1 R1 R3 2) Choose the hysteresis band required (V 1 HB). For this R2 = 8. = 03kΩ example, choose 50mV. 3.0V 1 1 − − 3) Calculate R1 according to the following equation: 1.2 x 12kΩ 12kΩ 2.2MΩ R1 = (R3 + R4) x (VHB / VCC) 6) Verify trip voltages and hysteresis as follows: 4) Choose the trip point for VIN rising (VTHR; VTHF is the trip point for V 1 1 1 IN falling). This is the threshold voltage I V N rising: VTHR = RE V F x R1 x + + at which the comparator switches its output from low R1 R2 R3 to high as VIN rises above the trip point. R1 x VCC 5) Calculate R2 as follows: I V N falling: VTHF V = THR − R3 1 Hysteresis V = THR V − THF R2 = VTHR 1 1 − −
MAX988/MAX992/MAX996
RE V F x R1 R1 R3 R + 4 The MAX988/MAX992/MAX996 have ±2.5mV internal 6) Verify trip voltages and hysteresis as follows: hysteresis. They have open-drain outputs and require an external pullup resistor (Figure 2). Additional hysteresis can be generated using positive feedback, but the formulas I V N rising: VTHR = RE V F x R1 x differ slightly from those of the MAX987/MAX991/MAX995. 1 1 1 + + R1 R2 R3 R4 + R1 x VCC I V N falling: VTHF V = THR − VCC R3 R4 + Hysteresis V = R3 THR V − THF 0.1µF R1 R4
Circuit Layout and Bypassing
VIN These comparators’ high-gain bandwidth requires design VCC OUT precautions to maximize their high-speed capability. The R2 recommended precautions are: VEE 1) Use a PCB with an unbroken, low-inductance ground
MAX988
plane. V
MAX992
REF
MAX996
2) Place a decoupling capacitor (a 0.1µF ceramic capacitor is a good choice) as close to VCC as possible. 3) On the inputs and outputs, keep lead lengths short Figure 2. Additional Hysteresis (MAX988/MAX992/MAX996) to avoid unwanted parasitic feedback around the comparators. 4) Solder the devices directly to the PCB instead of using a socket. www.maximintegrated.com Maxim Integrated │ 9
MAX988/MAX992/MAX996
RE V F x R1 R1 R3 R + 4 The MAX988/MAX992/MAX996 have ±2.5mV internal 6) Verify trip voltages and hysteresis as follows: hysteresis. They have open-drain outputs and require an external pullup resistor (Figure 2). Additional hysteresis can be generated using positive feedback, but the formulas I V N rising: VTHR = RE V F x R1 x differ slightly from those of the MAX987/MAX991/MAX995. 1 1 1 + + R1 R2 R3 R4 + R1 x VCC I V N falling: VTHF V = THR − VCC R3 R4 + Hysteresis V = R3 THR V − THF 0.1µF R1 R4
Circuit Layout and Bypassing
VIN These comparators’ high-gain bandwidth requires design VCC OUT precautions to maximize their high-speed capability. The R2 recommended precautions are: VEE 1) Use a PCB with an unbroken, low-inductance ground
MAX988
plane. V
MAX992
REF
MAX996
2) Place a decoupling capacitor (a 0.1µF ceramic capacitor is a good choice) as close to VCC as possible. 3) On the inputs and outputs, keep lead lengths short Figure 2. Additional Hysteresis (MAX988/MAX992/MAX996) to avoid unwanted parasitic feedback around the comparators. 4) Solder the devices directly to the PCB instead of using a socket. www.maximintegrated.com Maxim Integrated │ 9
