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LTC6991

6991fb

TYPICAL APPLICATION

FEATURES DESCRIPTION

TimerBlox: Resettable, Low

Frequency Oscillator

The LTC

6991 is a silicon oscillator with a programmable

period range of 1.024ms to 9.54 hours (29.1µHz to 977Hz),

specifically intended for long duration timing events. The

LTC6991 is part of the TimerBlox

family of versatile silicon

timing devices.

A single resistor, R

SET

, programs the LTC6991’s internal

master oscillator frequency. The output clock period

is determined by this master oscillator and an internal

frequency divider, N

DIV

, programmable to eight settings

from 1 to 2

OUT

DIV

•R

SET

50kΩ

•1.024ms, N

DIV

= 1,8,64,...,2

In normal operation, the LTC6991 oscillates with a 50%

duty cycle. A reset function is provided to truncate the

pulse (reducing the duty cycle). The reset pin can also be

used to prevent the output from oscillating.

The RST and OUT pins can be configured for active-low

or active-high operation using a polarity function.

POL BIT RST PIN OUTPUT STATE

0 0 Oscillating

0 1 0 (reset)

1 0 1 (reset)

1 1 Oscillating

For easy configuration of the LTC6991, download the

TimerBlox Designer tool at

www.linear.com/timerblox.

APPLICATIONS

Period Range: 1ms to 9.5 Hours

Configured with 1 to 3 Resistors

<1.5% Maximum Frequency Error

Output Reset Function

2.25V to 5.5V Single Supply Operation

55µA to 80µA Supply Current

(2ms to 9.5hr Clock Period)

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 Packages

“Heartbeat” Timers

Watchdog Timers

Intervalometers

Periodic “Wake-Up” Call

High Vibration, High Acceleration Environments

Portable and Battery-Powered Equipment

L, LT, LTC, LTM, Linear Technology, TimerBlox and the Linear logo are registered trademarks

and ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the

property of their respective owners.

Low Frequency Pulse Generator

Clock Period Range over Eight Divider Settings

DIV PIN VOLTAGE, V

DIV

(V)

CLOCK PERIOD (LOG SCALE)

10Sec

10Min

2.5

6991 TA01b

100ms

1ms

0.625

1.25

1.875

10Hr

1Sec

1Min

10ms

1Hr

LTC6991

0.1µF

OUT

392k

SET

715k

RST

GND

SET

OUT

DIV

470pF

2.26k

6991 TA01a

60 SECONDS

1µs PULSE WIDTH

PULSE

≈ R

t$

≈ 1µs

Summary of content (24 pages)

PAGE 1
LTC6991 TimerBlox: Resettable, Low Frequency Oscillator DESCRIPTION FEATURES n n n n n n n n n n Period Range: 1ms to 9.5 Hours Configured with 1 to 3 Resistors <1.5% Maximum Frequency Error Output Reset Function 2.25V to 5.5V Single Supply Operation 55μA to 80μA Supply Current (2ms to 9.
PAGE 2
LTC6991 ABSOLUTE MAXIMUM RATINGS (Note 1) Supply Voltage (V+) to GND ........................................6V Maximum Voltage on Any Pin ................ (GND – 0.3V) ≤ VPIN ≤ (V+ + 0.3V) Operating Temperature Range (Note 2) LTC6991C ............................................–40°C to 85°C LTC6991I .............................................–40°C to 85°C LTC6991H .......................................... –40°C to 125°C LTC6991MP .......................................
PAGE 3
LTC6991 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. Test conditions are V+ = 2.25V to 5.5V, RST = 0V, DIVCODE = 0 to 15 (NDIV = 1 to 221), RSET = 50k to 800k, RLOAD = 5k, CLOAD = 5pF unless otherwise noted.
PAGE 4
LTC6991 ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. Test conditions are V+ = 2.25V to 5.5V, RST = 0V, DIVCODE = 0 to 15 (NDIV = 1 to 221), RSET = 50k to 800k, RLOAD = ∞, CLOAD = 5pF unless otherwise noted.
PAGE 5
LTC6991 TYPICAL PERFORMANCE CHARACTERISTICS V+ = 3.3V, RSET = 200k, TA = 25°C unless otherwise noted. Frequency Error vs Temperature Frequency Error vs Temperature 3 GUARANTEED MAX OVER TEMPERATURE RSET = 50k 3 PARTS 2 RSET = 200k 3 PARTS 0 –1 0 GUARANTEED MIN OVER TEMPERATURE –3 –50 –25 50 25 75 0 TEMPERATURE (°C) 100 GUARANTEED MIN OVER TEMPERATURE –2 –3 –50 –25 125 50 25 75 0 TEMPERATURE (°C) 100 6991 G01 Frequency Error vs RSET 200 0.3 3 PARTS DRIFT (%) –1 NUMBER OF UNITS 0.
PAGE 6
LTC6991 TYPICAL PERFORMANCE CHARACTERISTICS + V = 3.3V, RSET = 200k, TA = 25°C unless otherwise noted. Supply Current vs Supply Voltage 250 150 125 100 RSET = 100k RSET = 200k 75 RSET = 800k 50 25 0 2 3 4 5 SUPPLY VOLTAGE (V) 125 5V, RSET = 100k 100 2.5V, RSET = 100k 75 5V, RSET = 800k 50 2.5V, RSET = 800k 25 50 25 75 0 TEMPERATURE (°C) 6991 G10 100 5V RST FALLING 5V RST RISING 150 3.3V RST FALLING 3.3V RST RISING 100 50 125 0 0.2 0.6 0.4 VRST/V+ (V/V) 1.
PAGE 7
LTC6991 TYPICAL PERFORMANCE CHARACTERISTICS + V = 3.3V, RSET = 200k, TA = 25°C unless otherwise noted. Output Resistance vs Supply Current Typical Start-Up with POL = 1 50 OUTPUT RESISTANCE (Ω) 45 40 V+ 1V/DIV 35 OUTPUT SOURCING CURRENT 30 1μs (tMASTER) WIDE INITIAL PULSE 25 500μs 20 OUT 1V/DIV OUTPUT SINKING CURRENT 15 10 5 0 2 3 4 5 SUPPLY VOLTAGE (V) 6 6991 G22 PIN FUNCTIONS V+ = 2.5V DIVCODE = 15 RSET = 50k 250μs/DIV 6991 G19 (DCB/S6) V+ (Pin 1/Pin 5): Supply Voltage (2.25V to 5.
PAGE 8
LTC6991 PIN FUNCTIONS (DCB/S6) GND (Pin 5/Pin 2): Ground. Tie to a low inductance ground plane for best performance. 30Ω. When driving an LED or other low impedance load a series output resistor should be used to limit source/ sink current to 20mA. OUT (Pin 6/Pin 6): Oscillator Output.
PAGE 9
LTC6991 OPERATION The LTC6991 is built around a master oscillator with a 1MHz maximum frequency. The oscillator is controlled by the SET pin current (ISET) and voltage (VSET), with a 1MHz • 50k conversion factor that is accurate to ±0.8% under typical conditions. fMASTER = 1 tMASTER I = 1MHz • 50kΩ • SET VSET A feedback loop maintains VSET at 1V ±30mV, leaving ISET as the primary means of controlling the output frequency.
PAGE 10
LTC6991 OPERATION Table 1. DIVCODE Programming DIVCODE POL NDIV RECOMMENDED tOUT R1 (kΩ) R2 (kΩ) VDIV/V+ 0 0 1 1.024ms to 16.384ms Open Short ≤0.03125 ±0.015 1 0 8 8.192ms to 131ms 976 102 0.09375 ±0.015 2 0 64 65.5ms to 1.05sec 976 182 0.15625 ±0.015 3 0 512 524ms to 8.39sec 1000 280 0.21875 ±0.015 4 0 4,096 4.19sec to 67.1sec 1000 392 0.28125 ±0.015 5 0 32,768 33.6sec to 537sec 1000 523 0.34375 ±0.015 6 0 262,144 268sec to 4,295sec 1000 681 0.
PAGE 11
LTC6991 OPERATION RST Pin and Polarity (POL) Bit The RST pin controls the state of the LTC6991’s output as seen on the OUT pin. The active/inactive voltage levels depend on the POL bit setting. If POL = 0, the reset pin is active high and the output latch is not inverted. Therefore, pulling the RST pin high will reset the output latch and force the OUT pin low. Pulling RST low will allow the output to oscillate, with the next rising edge dependent on the internal oscillator. Table 2.
PAGE 12
LTC6991 OPERATION Changing DIVCODE After Start-Up Following start-up, the A/D converter will continue monitoring VDIV for changes. The LTC6991 will respond to DIVCODE changes in less than one cycle. tDIVCODE < 500 • tMASTER < tOUT The start-up time may increase if the supply or DIV pin voltages are not stable. For this reason, it is recommended to minimize the capacitance on the DIV pin so it will properly track V+. Less than 100pF will not affect performance.
PAGE 13
LTC6991 OPERATION RST OUT tSTART tOUT 6991 F07 Figure 7. Start-Up Timing Diagram (RST = 0, POL = 0) RST OUT tSTART OUTPUT DISABLED FOR INTEGER MULTIPLE OF tOUT 6991 F08 Figure 8. Start-Up Timing Diagram (RST = 1, POL = 0) RST 6991 F09 OUT tSTART tMASTER OUTPUT DISABLED FOR INTEGER MULTIPLE OF tOUT Figure 9. Start-Up Timing Diagram (RST = 0, POL = 1) RST 6991 F10 OUT tSTART tOUT tMASTER Figure 10.
PAGE 14
LTC6991 APPLICATIONS INFORMATION Basic Operation The simplest and most accurate method to program the LTC6991 is to use a single resistor, RSET , between the SET and GND pins. The design procedure is a 3-step process. First select the POL bit setting and NDIV value, then calculate the value for the RSET resistor. Alternatively, Linear Technology offers the easy to use TimerBlox Designer tool to quickly design any LTC6991 based circuit. Download the free TimerBlox Designer software at www.linear.
PAGE 15
LTC6991 APPLICATIONS INFORMATION LTC6991 as “Wake-Up Timer” input to filter start-up glitches from the system as it is powered on. The output latch reset function provided by the RST pin allows the LTC6991 to enable a larger system at regular intervals. The on-time can be controlled by the system. This allows the system to shut itself down immediately after performing its tasks, reducing power consumption. If the LTC6991 is enabling a switching regulator that can operate on supplies greater than 5.
PAGE 16
LTC6991 APPLICATIONS INFORMATION Self-Resetting Circuits OUT RPW 2.26k The RST pin has hysteresis to accommodate slow-changing input voltages. Furthermore, the trip points are proportional to the supply voltage (see Note 6 and the RST Threshold Voltage vs Supply Voltage curve in Typical Performance Characteristics). This allows an RC time constant at the RST input to generate a delay that is nearly independent of the supply voltage. RST CPW 470pF OUT LTC6991 2.25V TO 5.
PAGE 17
LTC6991 APPLICATIONS INFORMATION RST OUT V+ LTC6991 V+ GND 0.1μF + SET V+ C1 0.1μF R1 DIV 1/2 LTC6078 R2 – V+ 6991 F15 0.1μF R D 1MHz • 50kΩ • 1 + VCO – IN RSET 4096 1024 • NDIV • RVCO DIN = 0 TO 4095 fOUT = VCC REF DIN μP CLK LTC1659 VOUT RVCO CS/LD RSET GND Figure 15. Digitally-Controlled Oscillator The oscillator can still function with reduced accuracy for ISET < 1.25μA. At approximately 500nA, the oscillator output will be frozen in its current state.
PAGE 18
LTC6991 APPLICATIONS INFORMATION RST OUT LTC6991 GND SET V+ V+ C1 0.1μF R1 DIV RSET R2 V+ R1 R2 V+ C1 C1 V+ OUT RST OUT DIV GND GND V+ SET RST SET DIV R1 RSET RSET R2 6991 F18 DFN PACKAGE TSOT-23 PACKAGE Figure 18. Supply Bypassing and PCB Layout 1. Connect the bypass capacitor, C1, directly to the V+ and GND pins using a low inductance path. The connection from C1 to the V+ pin is easily done directly on the top layer.
PAGE 19
LTC6991 TYPICAL APPLICATIONS 5 Second On/Off Timed Relay Driver 12V 0.1μF L C D1 1N4148 RESET NO 1 R4 15k RUN RELAY ENABLE RST Q1 2N2219A OUT LTC6991 COTO 1022 RELAY 9001-12-01 5V V+ GND C2 0.1μF R1 1M DIV SET R2 392k R3 118k 6991 TA02 1.5ms Radio Control Servo Reference Pulse Generator 5V 20ms FRAME RATE GENERATOR R7 10k RESET = OPEN RUN = GND RST 1.5ms REFERENCE PULSE 20ms PERIOD OUT LTC6991 TRIG 5V V+ GND SET GND C1 0.01μF R4 976k 5V V+ R1 1M SET DIV R6 121k 1.
PAGE 20
LTC6991 TYPICAL APPLICATIONS Isolated AC Load Flasher 5V R3 10k OPEN = OFF GND = ON 0.1μF 5 1 RST V+ OUT LTC6991 3 SET DIV 4 GND RSET 237k R4 215Ω 6 1 R1 1M R5 5.94k 6 40W LAMP HOT 117V AC R7 100Ω 2 5V ZERO CROSSING R2 392k 2 U2 MOC3041M U3 NTE5642 4 C2 0.022μF R6 10k 10 SECONDS ON/OFF 6991 TA05 NEUTRAL AC ISOLATION BARRIER = 7500V Interval (Wiper) Timer 2s 5V 5s 15s 30s V+ 1m 2m 4m OFF RST 66.5k 280k 182k 18.2k OUT TRIG LTC6991 2s 5s 15s 30s GND V+ V+ 0.
PAGE 21
LTC6991 PACKAGE DESCRIPTION Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. DCB Package 6-Lead Plastic DFN (2mm × 3mm) (Reference LTC DWG # 05-08-1715 Rev A) 0.70 p0.05 3.55 p0.05 1.65 p0.05 (2 SIDES) 2.15 p0.05 PACKAGE OUTLINE 0.25 p 0.05 0.50 BSC 1.35 p0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS R = 0.115 TYP R = 0.05 TYP 2.00 p0.10 (2 SIDES) 3.00 p0.10 (2 SIDES) 0.40 p 0.10 4 6 1.65 p 0.10 (2 SIDES) PIN 1 NOTCH R0.20 OR 0.
PAGE 22
LTC6991 PACKAGE DESCRIPTION Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. S6 Package 6-Lead Plastic TSOT-23 (Reference LTC DWG # 05-08-1636) 0.62 MAX 2.90 BSC (NOTE 4) 0.95 REF 1.22 REF 3.85 MAX 2.62 REF 1.4 MIN 2.80 BSC 1.50 – 1.75 (NOTE 4) PIN ONE ID RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR 0.30 – 0.45 6 PLCS (NOTE 3) 0.95 BSC 0.80 – 0.90 0.20 BSC 0.01 – 0.10 1.00 MAX DATUM ‘A’ 0.30 – 0.50 REF 0.09 – 0.20 (NOTE 3) 1.
PAGE 23
LTC6991 REVISION HISTORY REV DATE DESCRIPTION A 7/11 Updated Description, Typical Application, and Order Information sections 1, 2 Added additional information to ΔfOUT/ΔV+ and included Note 11 in Electrical Characteristics section 3, 4 B 1/12 PAGE NUMBER Added Typical Frequency Error vs Time curve to Typical Performance Characteristics section 6 Added text to Basic Operation paragraph in Applications Information section 14 Added MP grade 1, 2, 4 6991fb Information furnished by Linear Tec
PAGE 24
LTC6991 TYPICAL APPLICATION Intervalometer for Time-Lapse Photography ACTIVATES SHUTTER AT 8SEC TO 8.5MIN INTERVALS RPW 100k RST CPW 33μF OUT GND V+ R1A 332k RS3 95.3k SET 8SEC TO 64SEC RS1 1M SHUTTER LTC6991 DIV R1B 1M 1μF “SLOW RANGE” 1.1MIN TO 8.