FEATURES

Delay Range: 1µs to 33.6 Seconds

Configured with 1 to 3 Resistors

Delay Max Error:

– <2.3% for Delay > 512µs

– <3.4% for Delay of 8µs to 512µs

– <5.1% for Delay of 1µs to 8µs

Delay One or Both Rising/Falling Edges

2.25V to 5.5V Single Supply Operation

70µA Supply Current at 10µs Delay

500µs Start-Up Time

CMOS Output Driver Sources/Sinks 20mA

–55°C to 125°C Operating Temperature Range

Available in Low Profile (1mm) SOT-23 (ThinSOT™) and 2mm × 3mm DFN

AEC-Q100 Qualified for Automotive Applications

 

ANWENDUNGEN

Noise Discriminators/Pulse Qualifiers

Delay Matching

Switch Debouncing

High Vibration, High Acceleration Environments

Portable and Battery-Powered Equipment

 

OPERATION

Edge-Controlled Delay

The LTC6994 is a programmable delay or pulse qualifier. It can perform noise filtering, which distinguishes it from a delay line (which simply delays all input transitions).

When the voltage on the LTC6994 input pin (IN) transitions low or high, the LTC6994 can delay the corresponding output transition by any time from 1µs to 33.6 seconds.

LTC6994-1 Functionality

Figures 3 details the basic operation of the LTC6994-1 when configured to delay rising edge transitions (POL = 0). A rising edge on the IN pin initiates the timing. OUT remains low for the duration of tDELAY . If IN stays high then OUT will transition high after this time. If the input doesn’t remain high long enough for OUT to transition high then the timing will restart on each successive rising edge. In this way, the LTC6994-1 can serve as a pulse qualifier, filtering out noisy or short signals.

On a falling edge at the input, the output will follow immediately (after a short propagation delay tPD).Note that the output pulse width may be extremely short if IN falls immediately after OUT rises.

 

PIN-FUNKTIONEN

V+ (Pin 1/Pin 5): Supply Voltage (2.25V to 5.5V). This supply should be kept free from noise and ripple. It should be bypassed directly to the GND pin with a 0.1µF capacitor.

DIV (Pin 2/Pin 4): Programmable Divider and Polarity Input. The DIV pin voltage (VDIV) is internally converted into a 4-bit result (DIVCODE). VDIV may be generated by a resistor divider between V+ and GND. Use 1% resistors to ensure an accurate result. The DIV pin and resistors should be shielded from the OUT pin or any other traces that have fast edges. Limit the capacitance on the DIV pin to less than 100pF so that VDIV settles quickly. The MSB of DIVCODE (POL) selects the delay functionality. For the LTC6994-1, POL = 0 will delay the rising transition and POL = 1 will delay the falling transition. For the LTC6994 2, both transitions are delayed so POL = 1 can be used to invert the output.

SET (Pin 3/Pin 3): Delay Setting Input. The voltage on the SET pin (VSET) is regulated to 1V above GND. The amount of current sourced from the SET pin (ISET) programs the master oscillator frequency. The ISET current range is 1.25µA to 20µA. The delayed output transition will be not occur if ISET drops below approximately 500nA. Once ISET increases above 500nA the delayed edge will transition.

A resistor connected between SET and GND is the most accurate way to set the delay. For best performance, use a precision metal or thin film resistor of 0.5% or better tolerance and 50ppm/°C or better temperature coefficient. For lower accuracy applications an inexpensive 1% thick film resistor may be used.

Limit the capacitance on the SET pin to less than 10pF to minimize jitter and ensure stability. Capacitance less than 100pF maintains the stability of the feedback circuit regulating the VSET voltage.

IN (Pin 4/Pin 1): Logic Input. Depending on the version and POL bit setting, rising or falling edges on IN will propagate to OUT after a programmable delay. The LTC6994-1 will delay only the rising or falling edge. The LTC6994-2 will delay both edges.

GND (Pin 5/Pin 2): Ground. Tie to a low inductance ground plane for best performance.

OUT (Pin 6/Pin 6): Output. The OUT pin swings from GND to V+ with an output resistance of approximately 30Ω. When driving an LED or other low impedance load a series output resistor should be used to limit source/ sink current to 20mA.