ZSCT1555N8TA - Diodes Incorporated

Issue 3 - July 2006

DEVICE DESCRIPTION

These devices are precision timing circuits for

generation of accurate time delays or

oscillation. Advanced circuit design means that

these devices can operate from a single battery

cell with the minimum of quiescent current.

In monostable mode time delays are

controlled by a single resistor and capacitor

network. In astable mode the frequency and

duty cycle can be accurately and

independently controlled with two external

resistors and one capacitor.

The threshold and trigger levels are normally

set as a proportion of VCC by internal resistors.

These levels can be programmed by the use

of the control input pin.

When the trigger input reduces to a value

below the trigger level, the flip-flop is set and

the output goes high. With the trigger input

above the trigger level and the threshold input

above the threshold level, the flip-flop is reset

and the output goes low. The reset pin has

priority over all the other inputs and is used

to start new timing cycles. A low on the reset

input causes the flip-flop to reset forcing the

output low. Whenever the output is forced

low then the internal discharge transistor is

turned on.

FEATURES

•0.9V supply operating voltage guaranteed

•Pin connections comparable with 555

series timers

•Very low quiescent current 74 µA

•SO8 and DIL8 packages

•Operating temperature range

compatible with battery technologies

APPLICATIONS

•Portable and battery powered

equipment

•Low voltage and low power systems

PRECISION SINGLE CELL TIMER

ISSUE 3 - JULY 2006

ZSCT1555

DISCHARGE

THRESH

TRIGGER

CONTROL

VCC

RESET

OUTPUT

GND

SCHEMATIC DIAGRAM

Issue 3 - July 2006 www.zetex.com

ABSOLUTE MAXIMUM RATINGS

Supply Voltage 9V

Input Voltages 9V

(Cont, Reset, Thres, Trig)

Output Current 100mA

Operating Temperature -20 to 100°C

Storage Temperature -55 to 150°C

Power Dissipation (Tamb=25°C)

DIL8 625mW

SO8 625mW

Recommended Operating Conditions

Supply Voltage 0.9V(min) 6V(max)

Input Voltages 6V(max)

(Cont, Reset, Thres, Trig)

Output Current Sink 100mA(max)

Source 150µA(max)

ELECTRICAL CHARACTERISTICS

TEST CONDITIONS (Unless otherwise stated):Tamb= 25°C,VCC= 1.5V

SYMBOL PARAMETER CONDITIONS LIMITS UNITS

MIN. TYP. MAX.

VCC Supply Voltage 0.9 6 V

ICC Supply Current no load

VCC= 5V, no load

150

120

200

µA

VTH Threshold Voltage

VCC= 5V

1.195

3.9

1.22

1.245

4.1

ITH Threshold Current (Note 1) 0 20 100 nA

VTR Trigger Voltage

VCC= 5V

0.2

0.57

0.25

0.62

0.3

0.67

ITR Trigger Current 0 -35 -100 nA

tPD Trigger Propagation delay Delay from trigger

to output

2µs

VRS Reset Voltage 0.1 0.2 0.4 V

IRS Reset Current Reset @ 0V 0 -5 -10 µA

IDS Discharge switch Off-state

current

0 10 100 nA

VDS Discharge switch On-state

voltage

IDS= 0.2mA

VCC= 5V, IDS= 0.3mA

180

240

225

350

VCT Control Voltage (Open Circuit)

VCC= 5V

1.195

3.9

1.22

1.245

4.1

VOL Output Voltage (Low) IOL=10mA

IOL=50mA

VCC=5V, IOL=10mA

VCC=5V, IOL=100mA

0.15

0.45

0.13

0.65

0.3

0.65

0.3

VOH Output Voltage (High) IOH= 100µA

VCC= 5V, IOH= 150µA

4.5

1.1

4.6

1.5

ZSCT1555

Issue 3 - July 2006 www.zetex.com

SYMBOL PARAMETER CONDITIONS LIMITS UNITS

MIN. TYP. MAX.

tROutput pulse rise time CL= 10pF

VCC=5V, CL=10pF

1.6

1.2 µs

tFOutput pulse fall time CL= 10pF

VCC=5V, CL=10pF

240

∆tIA(m)

∆tV(m)

∆tT(m)

Timing error, Monostable

Initial accuracy (Note 2)

Drift with supply voltage

Drift with temperature

RA= 10 to 50 kΩ

RB= 10 to 50 kΩ

CT = 68nF

1.6

0.262

100

%/V

ppm/°C

∆tIA(a)

∆tV(a)

∆tT(a)

Timing error, Astable

Initial accuracy (Note 2)

Drift with supply voltage

Drift with temperature

RA= 10 to 50 kΩ

RB= 10 to 50 kΩ

CT = 68nF

4.8

0.662

150

%/V

ppm/°C

fAAstable maximum frequency RA=20 kΩ

RB= 10 kΩ

CT =47pF

330 kHz

Note 1: This will influence the maximum values of RA and RB (RAMAX=10MΩ,RBMAX=1.5MΩ)

Note 2: Is defined as the difference between the measured value and the average value of a

random sample taken on a batch basis

ZSCT1555

ELECTRICAL CHARACTERISTICS (Continued)

TEST CONDITIONS (Unless otherwise stated):Tamb=25°C,VCC=1.5V

Issue 3 - July 2006 www.zetex.com

ZSCT1555

01234 5

0.80

0.85

0.90

0.95

1.00

1.05

Pulse Duration

relative to Vcc=5v

Supply Voltage (V)

Normalized Output Pulse Duration

v Supply Voltage

-20°C

+25°C

+100°C

200

160

120

01.0 2.0 3.0 4.0 5.00.0

Supply Current (µA)

Supply Voltage (V)

Supply Current v Supply Voltage

000.2

Propagation Delay (µs)

Lowest Voltage Level of Trigger Pulse (xVcc)

Output Propagation Delay

Vcc=5v

0.1

+100°C

+25°C

-20°C

Rout/Vcc=1K

000.10.2

Propagation Delay (µs)

Lowest Voltage Level of Trigger Pulse (xVcc)

Output Propagation Delay

Vcc=1.5v

+25°C

-20°C

Rout/Vcc=1K

000.1

+100°C

+25°C

-20°C

Minimum Pulse Width (µs)

Lowest Voltage Level of Trigger Pulse (xVcc)

Minimum Pulse Width Required for

Triggering

Vcc=1.5v

Rout/Vcc = 1K

000.2

+100°C

+25°C

-20°C

Minimum Pulse Width (µs)

Lowest Voltage Level of Trigger Pulse (xVcc)

Minimum Pulse Width Required for

Triggering

Vcc=5v

0.1

Rout/Vcc = 1K

+100°C

TYPICAL CHARACTERISTICS

Issue 3 - July 2006 www.zetex.com

ZSCT1555

Vcc=5v

-20°C

+25°C

+100°C

0.10.010.001

Sink Current (mA)

Discharge Transistor Voltage

v Sink Current

0.1

0.01

Discharge Transistor Voltage (V)

Vcc=1.5v

-20°C

+25°C

+100°C

0.10.010.001

Sink Current (mA)

Discharge Transistor Voltage

v Sink Current

0.1

0.001

Discharge Transistor Voltage (V)

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0.0

0.01 0.1 1 10 100

Low Level Output Current (mA)

Output Low Voltage Drop v

Output Current

Low Level Output Voltage (V)

Vcc=1.5v

-20°C

+25°C

+100°C

1.0

0.8

0.6

0.4

0.2

0.0

0.01 0.1 1 10 100

Low Level Output Current (mA)

Output Low Voltage Drop v

Output Current

Low Level Output Voltage (V)

-20°C

+25°C

+100°C

Vcc=5v

0.5

0.4

0.3

0.2

0.1

0.0

-20°C

+25°C

+100°C

Vcc=5v

Vcc - Vout (V)

0.001 0.01 0.1 1.0

High Level Output Current (mA)

Output High Voltage Drop v

Output Current

1.0

0.8

0.6

0.4

0.2

0.0 1.0

0.10.01

0.001

-20°C

+25°C

+100°C

Vcc=1.5v

High-Level Output Current (mA)

Output High Voltage Drop v

Output Current

Vcc - Vout (V)

TYPICAL CHARACTERISTICS

Issue 3 - July 2006 www.zetex.com

FUNCTIONAL DIAGRAM

FUNCTIONAL TABLE

RESET TRIGGER VALUE THRESHOLD

VOLTAGE

OUTPUT DISCHARGE

SWITCH

Low N/A N/A Low On

High <VCC/5 N/A High Off

High >VCC/5 >4VCC/5 Low On

High >VCC/5 <4VCC/5 As Previously established

POWER DERATING TABLE

Package TA≤25°C

Power Rating

Derating Factor

Above TA=25°C

TA=70°C Power

Rating

TA=85°C Power

Rating

N8 625mW 6.25mW/°C 330mW 250mW

D8 625mW 6.25mW/°C 330mW 250mW

ZSCT1555

Issue 3 - July 2006 www.zetex.com

APPLICATIONS INFORMATION

Many configurations of the ZSCT1555 are

possible. The following gives a selection of a

few of these using the most basic monostable

and astable connections. The final application

example in astable mode shows the device

optimum use for low voltage and power

economy in a single cell boost converter.

Monostable Operation

Figure 1 shows connection of the timer as a

one-shot whose pulse period is independent

of supply voltage. Initially the capacitor is held

discharged. The application of a negative

going trigger pulse sets an internal flip flop

which allows the capacitor to start to charge

up via RA and forces the output high. The

voltage on the capacitor increases for time t,

where t = 1.63RACT, at the end of this period

the voltage on the capacitor is 0.8 VCC. At this

point the flip flop resets, the capacitor is

discharged and the output is driven low.

Figure 2 shows the timing diagram for this

function. During the output high period

further trigger pulses are locked out however

the circuit can be reset by application of a

negative going pulse on the reset pin. Once

the output is driven low it remains in this state

until the application of the next trigger pulse.

If the reset function is not used then it is

recommended to connect to VCC to eliminate

any possibility of false triggering.

Figure 3 gives an easy selection of RA and CT

values for various time delays.

This configuration of circuit can be used as a

frequency divider by adjusting the timing

period. Figure 4 indicates a divide by three.

Figure 1

Figure 2

Figure 3

100

0.1

0.01

0.001

10us 100us 1ms 10ms 100ms 1s 10s

C - Capacitance (uF)

Time Delay

100k

10M

Figure 4

ZSCT1555

Issue 3 - July 2006 www.zetex.com

Figure 5 shows the monostable mode used as

a pulse width modulator. Here the trigger pin

is supplied with a continuous pulse train, the

resulting output pulse width is modulated by

a signal applied to the control pin.

Figure 6 shows typical waveform examples.

Astable operation

The configuration of Figure 7 produces a free

running multivibrator circuit whose frequency

is independent of supply voltage. The ratio of

resistors RA and RB precisely sets the circuit

duty cycle. The capacitor is charged and

discharged between thresholds at 0.2VCC and

0.8VCC. Oscillation frequency (f) and duty cycle

(d) can be calculated using the following

equations:-

f = 0.62/(RA + 2RB)CT

d = RB /(RA + 2RB)

Figure 8 shows the waveforms generated in

this mode of operation.

Figure 5

Figure 6

Figure 8

ZSCT1555

Figure 7

Issue 3 - July 2006 www.zetex.com

ZSCT1555

Figure 9 gives an easy selection for RA, RB and

CT values.

Similar to the PWM circuit of Figure 5 the astable

circuit can be configured with modulation of the

control input as shown in Figure 10. The result is a

pulse position modulated, PPM, circuit where the

pulse position is altered by the control input voltage.

Figure 11 shows the result of modulation with

a triangle wave input to the control pin.

Figure 11

(RA+2RB)

100

0.1

0.01

0.001

0.1 1 10 100 1k 10k 100k

C - Capacitance (uF)

Free Running Frequency (Hz)

10M

100k

Figure 10

Figure 9

Issue 3 - July 2006 www.zetex.com

Figure 12

ZSCT1555

The circuit of Figure 12 shows the device in

astable mode operating as part of a single

cell boost converter. This circuit generates

a 5 volt supply from a single battery cell. The

circuit output voltage is maintained down

to 0.9 volts input and power economy is

optimised for extended battery life.

ORDERING INFORMATION

Part Number Package Part Mark

ZSCT1555D8 DIL8 ZSCT1555

ZSCT1555N8 SO8 ZSCT1555

CONNECTION DIAGRAM

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Issue 3 - July 2006 www.zetex.com