ZHCSCB4A March 2014 – April 2014 TPS3700-Q1
The TPS3700-Q1 device combines two comparators for overvoltage and undervoltage detection. The TPS3700-Q1 device is a wide-supply voltage range (1.8 to 18 V) device with a high-accuracy rising input threshold of 400 mV (1% over temperature) and built-in hysteresis. The outputs are also rated to 18 V and can sink up to 40 mA.
The TPS3700-Q1 device is designed to assert the output signals, as shown in Table 1. Each input terminal can be set to monitor any voltage above 0.4 V using an external resistor divider network. With the use of two input terminals of different polarities, the TPS3700-Q1 device forms a window comparator. Broad voltage thresholds can be supported that allow the device to be used in a wide array of applications.
|INA+ > VIT+||OUTA high||Output A not asserted|
|INA+ < VIT–||OUTA low||Output A asserted|
|INB– > VIT+||OUTB low||Output B asserted|
|INB– < VIT–||OUTB high||Output B not asserted|
The TPS3700-Q1 device combines two comparators. Each comparator has one external input (inverting and noninverting); the other input is connected to the internal reference. The comparator rising threshold is designed and trimmed to be equal to the reference voltage (400 mV). Both comparators also have a built-in falling hysteresis that makes the device less sensitive to supply rail noise and ensures stable operation.
The comparator inputs can swing from ground to 6.5 V, regardless of the device supply voltage used. Although not required in most cases, it is good analog design practice to place a 1-nF to 10-nF bypass capacitor at the comparator input for extremely noisy applications in order to reduce sensitivity to transients and layout parasitics.
For comparator A, the corresponding output (OUTA) is driven to logic low when the input INA+ voltage drops below (VIT+ – Vhys). When the voltage exceeds VIT+, the output (OUTA) goes to a high-impedance state; see Figure 1.
For comparator B, the corresponding output (OUTB) is driven to logic low when the voltage at input INB– exceeds VIT+. When the voltage drops below VIT+ – Vhys the output (OUTB) goes to a high-impedance state; see Figure 1. Together, these comparators form a window-detection function as discussed in the Window Comparator section.
In a typical TPS3700-Q1 application, the outputs are connected to a reset or enable input of the processor (such as a digital signal processor [DSP], central processing unit [CPU], field-programmable gate array [FPGA], or application-specific integrated circuit [ASIC]) or the outputs are connected to the enable input of a voltage regulator (such as a DC-DC or low-dropout regulator [LDO]).
The TPS3700-Q1 device provides two open-drain outputs (OUTA and OUTB). Pullup resistors must be used to hold these lines high when the output goes to high impedance (not asserted). By connecting pullup resistors to the proper voltage rails, the outputs can be connected to other devices at the correct interface-voltage levels. The TPS3700-Q1 outputs can be pulled up to 18 V, independent of the device supply voltage. To ensure proper voltage levels, some thought should be given while choosing the pullup resistor values. The pullup resistor value is determined by VOL, sink-current capability, and output-leakage current (Ilkg(OD)). These values are specified in the Electrical Characteristics table. By using wired-AND logic, OUTA and OUTB can merge into one logic signal.
Table 1 and the Inputs (INA+, INB–) section describe how the outputs are asserted or de-asserted. See Figure 1 for a timing diagram that describes the relationship between threshold voltages and the respective output.
The inverting and noninverting configuration of the comparators forms a window-comparator detection circuit using a resistor divider network, as shown in Figure 14 and Figure 15. The input terminals can monitor any system voltage above 400 mV with the use of a resistor divider network. The INA+ and INB– terminals monitor for undervoltage and overvoltage conditions, respectively.
The TPS3700-Q1 device is relatively immune to short voltage transient spikes on the input terminals. Sensitivity to transients is dependent on both transient duration and amplitude; see the Minimum Pulse Width vs Threshold Overdrive Voltage curve (Figure 7) in the Typical Characteristics section.
The TPS3700-Q1 has a single functional mode, which is on when VDD is greater than 1.8 V.