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TC43EOR Datasheet(PDF) 4 Page - TelCom Semiconductor, Inc |
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TC43EOR Datasheet(HTML) 4 Page - TelCom Semiconductor, Inc |
4 / 6 page TC43 LINEAR BUILDING BLOCK – VOLTAGE REFERENCE, DUAL OP AMP, DUAL COMPARATOR WITH SHUTDOWN MODE 4 PRELIMINARY INFORMATION Voltage Reference A 4% tolerance, internally biased, 1.20V bandgap volt- age reference is included in the TC43. It has a push-pull output capable of sourcing 5mA or sinking 200 µA. The voltage reference remains fully enabled during shutdown. Shutdown Input SHDN at VIL disables both op amps and one compara- tor. The SHDN input cannot be allowed to float; when not used, connect to VDD. TYPICAL APPLICATIONS The TC43 lends itself to a wide variety of applications, particularly in battery-powered systems. It typically finds application in power management, processor supervisory, and interface circuitry. Wake-up Timer Many microcontrollers have a low power “sleep” mode that significantly reduces their supply current. Typically, the microcontroller is placed in this mode via a software instruc- tion, and returns to a fully enabled state upon reception of an external signal (“wake-up”). The wake-up signal is usu- ally supplied by a hardware timer. Most system applications demand that this timer have a long duration (typically seconds or minutes), and consume as little supply current as possible. The circuit shown in Figure 1 is a wake-up timer made from comparator CMPTR2. (CMPTR2 is used because the wake-up timer must operate when SHDN is active.) Capaci- tor C1 charges through R1 until a voltage equal to VDD/2 is reached, at which point the WAKE is driven active. Upon wake-up, the microcontroller resets the timer by forcing a logic low on a dedicated, open drain I/O port pin. This discharges C1 through R4 (the value of R4 is chosen to limit maximum current sunk by the I/O port pin). With a 3V supply, the circuit as shown consumes typically 8 µA and furnishes a nominal timer duration of 25 seconds. Precision Battery Monitor Figure 2 is a precision battery low/battery dead monitor- ing circuit. Typically, the battery low output warns the user that a battery dead condition is eminent. Battery dead typically initiates a forced shutdown to prevent operation at low internal supply voltages (which can cause unstable system operation). The circuit of Figure 2 uses a single TC43 (one Op Amp unused) and only 7 external resistors. AMP 1 is a simple buffer while CMPTR1 and CMPTR2 provide precision volt- age detection using Vr as a reference. Resistors R2 and R4 set the detection threshold for BATT LOW while resistors R1 and R7 set the detection threshold for BATT FAIL. The component values shown assert BATT LOW at 2.2V (typi- cal) and BATT FAIL at 2.0V (typical). Total current con- sumed by this circuit is typically 22 µA at 3V. DUAL LDO with Shutdown Figure 3 shows a portion of a TC43 configured as a dual low drop regulator with shutdown. AMP1 and AMP2 are independent error amplifiers that use Vr as a reference. Resistors RA and RB set the feedback around the amplifier and therefore determine the output voltage setting (please see equation in the figure). RA and RB can have large ohmic values (i.e. 100’s of K Ω) to minimize supply current. Using the 2N2222 output transistors as shown, these regulators exhibit low dropout operation. For example, with VOUT = 3.0V, the typical drop out voltage is only 50mV at an output current of 50mA. The unused comparators can be used in conjunction with this circuit as power-on reset or low voltage detectors for a complete LDO solution at a very low installed cost. EVALUATION KIT The TC43EV consists of a four inch by six inch pre-wired application circuit board. Pre-configured circuits include a pulse width modulator, wake-up timer, function generator, and others. On-board current meter terminals, voltage regu- lator and a user-prototyping area speed circuit develop- ment. Please contact your local TelCom Semiconductor representative for more information. Figure 1. Wake-Up Timer WAKE-UP R1 5M R4 R2, 1M R3, 1M C1 10 µF VDD + – I/O* *OPEN DRAIN PORT PIN MICROCONTROLLER CMPTR2 |
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