Part Number: STM6315SDW13F

Manufacturer: STMicroelectronics

Description: Supervisory Circuits Supervisor reset

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Technical Specifications of STM6315SDW13F

Datasheet  STM6315SDW13F datasheet
Category Integrated Circuits (ICs)
Family PMIC – Supervisors
Manufacturer STMicroelectronics
Packaging Digi-Reel?
Part Status Active
Type Simple Reset/Power-On Reset
Number of Voltages Monitored 1
Output Open Drain or Open Collector
Reset Active Low
Reset Timeout 112 ms Minimum
Voltage – Threshold 2.93V
Operating Temperature -40°C ~ 125°C (TA)
Mounting Type Surface Mount
Package / Case TO-253-4, TO-253AA
Supplier Device Package SOT-143-4

If your central processor ever fails, this STMicroelectronics STM6315SDW13F microprocessor supervisory circuit will take over and keep everything running smoothly. Power consumption is limited to 320 mW with this gadget. It can withstand a maximum power consumption of 320 mW. To facilitate assembly, this item will be sent on tape and reel. This gadget requires a power supply between 1 V and 5.5 V to function. Reset threshold voltages range from a low of 2.87 V to a high of 2.98 V, with 2.93 V being the norm. The temperature range for this component is between -40 and 125 degrees Celsius.

STM6315SDW13F Features and Specifications

Attribute Value
Number of Supervisors 1
Manual Reset Yes
Output Driver Active Low, Open Drain
Maximum Reset Active Time 210ms
Mounting Type Surface Mount
Package Type SOT-143
Pin Count 4
Dimensions 3.04 x 1.4 x 1.02mm
Maximum Monitored Voltage 3V
Maximum Operating Supply Voltage 5.5 V
Maximum Operating Temperature +125 °C
Minimum Operating Supply Voltage 1 V
Minimum Monitored Voltage 2.93V
Minimum Operating Temperature -40 °C

Regulatory Circuits Keep Control of Your Microprocessor

These days, we probably take microprocessor-supervising circuits for granted because they’ve been there for so long. Today’s integrated circuits, however, come in various forms, from the simplest three-terminal reset chips to very sophisticated multipurpose gadgets. Even just Maxim’s almost 100 part numbers cover hundreds of products’ worth of customizations. Board-level designers can take on any project, no matter how simple or complex if they have a firm grasp on these items and their fundamental uses.

When it comes to microprocessor (P) supervisors, “power-on-reset” is the most fundamental function (POR). Power-on or brief drops in supply voltage might cause behavior changes in otherwise well-behaved P-based systems (brownout). Adding a resistor, capacitor, and diode to the P’s Active-low RESET line has been a common workaround for this issue for quite some time (Figure 1).

The extra RC maintains active-low RESET at a low level, even after the supply voltage has begun to rise. Active-low RESET will keep the P reset if the voltage increases rapidly enough, giving the internal circuitry time to stabilize before a regular operation is restored. As the voltage from the power source decreases to zero, the diode quickly changes from high to low, guaranteeing a successful Active-low RESET.

Assuming a rapid increase in the power supply relative to the RC time constant, this technique is used for powering up. The circuit is meant to safeguard the P from less-than-ideal power-ups, but it depends on a rapid increase in supply voltage to do its job. When there’s a brownout, it’s also iffy about resetting the P. Assuming that circumstance, resetting the supply voltage to VIL minus one diode drop is required. The supply voltage, however, is significantly lower than its minimum spec well before it reaches this level.

Microprocessor manufacturers typically advise a circuit like that shown in Figure 2 when faced with this problem. When the power goes out, it automatically resets, but the voltage is only as accurate as the Zener diode, plus any mistakes caused by the transistor’s characteristics.

Adding a capacitor and a diode to this circuit will allow us to implement a timeout feature. The final circuit includes seven parts and suffers inaccuracy and slowly increasing supply voltages.

How Accurate is Accurate Enough?

Here’s a typical scenario: the processor requires a 5V supply, but it’s also acceptable to run at 4.5V. The lowest threshold of the reset circuit must be 4.5V since it must maintain reset at all voltages below that value. Consequently, what should be the maximum allowable variation in reset thresholds over temperature and between individual units? If you want to get in trouble with the power supply designers, you can define the supply voltage as 5V 0%, but more realistically, it will be in the range of 4.75V to 5.25V. For this reason, you must ensure a voltage of 4.63V 2.7%, or between 4.5V and 4.75V.

To control the threshold voltage, a Zener diode can be used; however, its typical accuracy is only 5–10%. Higher premiums allow for more precise tolerance (to 1%), limited to room temperature and a fixed current. The normal temperature coefficient (TC) for Zener is several mV/°C, and all of them exhibit noticeable voltage-current changes.  Over the temperature range of 0 to 70 degrees Celsius, TC alone can produce a shift of several hundred millivolts. Reset circuits based on Zener diodes cannot reliably reset devices at startup or during a brownout. Another issue is that even low-current Zener need 100A to achieve regulation, which is a significant burden in battery-powered systems.

If there were a perfect reset circuit, how would it work?

We have determined that a voltage tolerance of 2.7% over temperature is required for the reset circuit. A slow-rising supply voltage, as discussed above, or a supply voltage that displays noise or no monotonic behavior during startup or recovery from brownout conditions can cause the circuit to malfunction if the reset pulse is not terminated with an appropriate delay. Oscillation of the P’s Active-low RESET input can be caused by noise if the monitoring supply voltage is placed near the reset circuit’s threshold.

Many voltage-detector product lines on the market employ hysteresis to remedy this situation. The voltage tolerance at the threshold is unfortunately reduced due to hysteresis. The above example shows a voltage range of 250mV (4.75V 5.0V). Putting in an extra 100mV of hysteresis makes the threshold for a rising voltage 100mV higher, from 4.5V to 4.6V. This adjustment is required to ensure that the voltage drop threshold (during brownouts) will never be less than 4.5V. Therefore, the highest limit must be 4.67V 1.6% to guarantee both thresholds are within 4.5 and 4.75V.

Most voltage detectors, including the Ricoh Rx5VL/Rx5VT and the Seiko S-807, have a threshold accuracy of 2.5% and 2.4%, respectively, at 25°C. Products only specify typical temperature coefficients of 100ppm/°C and 120ppm/°C, even though real-world devices operate at temperatures over 25°C. Based on these TCs, the temperature dependence of the threshold tolerances is 2.85% and 2.82% from room temperature to 70 degrees Celsius, respectively.

The most up-to-date examples of such precision components are the Seiko S-808 series. At 25 degrees Celsius, they call for an accuracy of 2% and a maximum temperature coefficient of 350 ppm/°C. This leading temperature coefficient equals a range-wide change of 350e-6 x 70 = 0.0245 or 2.45% between 0 and 70 degrees Celsius. Therefore, our absolute minimum precision is 3.225%. For this example, we may get by with a maximum variation of 2.6125 percent if we assume that even the worst-case component will not display the leading temperature coefficient over temperature but rather (on average) around half the maximum.

Hysteresis isn’t anything we’ve thought of yet. The results of the preceding study confirm that the rising-edge threshold meets our requirements. However, the threshold for the falling edge will be reduced. Each of these detectors has a hysteresis of no more than 7% or 8%, with 5% being the norm. Our example’s rising-edge threshold falls within the acceptable range (4.5V to 4.75V); however, the falling-edge point can be as low as 4.13V. That is until the supply voltage deviates from the norm by nearly 0.4V, we cannot promise that a brownout will be detected.


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