GMT1555/1557
TIMER/OSCILLATOR
GMT
G
re
a
t
Mixed
Signal Technologies
Page 1 of 9
Rev. 1.4. 1999-07-01
GMT Microelectronics
22-001-700
DESCRIPTION
The GMT1555/1557 Timer/Oscillator devices
are designed to offer the one-shot or oscillator
user the specific function needed, in the
smallest possible package
.
The classic 555
timer, now in a SOT 23-5 package, has been
split into two simple parts: the 1555
monostable and the 1557 astable device.
This design has been executed in a BCDMOS
process, allowing for significant power reduc-
tion when compared to the bipolar 555 device.
One-shot pulse widths are available over the
wide range of 0.1 mSec to several hours, and
oscillation frequencies of up to 5.0 MHz are
easily obtainable. Duty cycles other than 50%
are easily commanded with only a few exter-
nal components (refer to the applications
section). Both devices operate over the broad
supply voltage range of +2.7 V to +18 V, and
feature a unique built-in logic lockout to
provide a controlled, well behaved turn-on
characteristic.
Figure 1:
GMT1555 - ONE-SHOT
FEATURES
•
Built in logic lock-out to ensure stable
turn-on.
•
Broad range Vcc; +2.7 V to +18 V
operation.
•
Low Current Consumption = 110 uA
typical with a 5.0 V supply.
•
TTL compatible I/O.
•
Compact SOT 23-5 package.
•
Resistant to supply and temperature
variations.
•
1.0 uA sleep mode (1557 only, CS forced
low).
Figure 2:
GMT1557 - OSCILLATOR/TIMER
+5.0 V
1
4
2
5
3
Output
R
C
GND
TRG
VS
OUT
THR
+5.0 V
4
3
2
1
5
R
C
GND
CS
VS
OUT
T/T
GMT1555/1557
TIMER/OSCILLATOR
Rev. 1.4. 1999-07-01
Page 2 of 9
22-001-700
GMT Microelectronics
ABSOLUTE MAXIMUM RATINGS
OPERATING RATINGS
Supply Voltage(V
S
).............................+20 V
Supply Voltage (V
S
).................+2.7 V to +18 V
Threshold Voltage (V
THR
, V
T/T
)............+20 V
Package Thermal Resistance
Trigger Voltage (V
TRG
, V
T/T
)................+20 V
SOT-23-5
θ
JA
........................220
°
C/W
Ambient Temperature Range..-40°C to +85°C
Lead Temperature, Soldering..260
°
C for 10 seconds
Table 1: PIN DESCRIPTION
PIN NO.
GMT1555
PIN NO.
GMT1557
FUNCTION
DESCRIPTION
1
4
VS
Supply (Input) = 2.7 V to +18 V supply.
2
2
GND
Ground: supply return.
3
CS
Chip Select/Reset (Input): Active high at 2/3 V
S
.
Output off (Sleep Mode) when CS is low (<1/3 V
S
)
.
3
5
OUT
Output: CMOS totem-pole output.
4
TRG
Trigger (Input): Sets output high.
Active low at < 1/3 V
S
nominal.
5
THR
Threshold (Dominant Input): Sets output low.
Active high at < 2/3 V
S
nominal.
1
T/T
Trigger/Threshold (Input): Internally connected to
both threshold and trigger functions. See TRG and
THR.
3
1
4
5
3
2
1
5
4
GMT1555
GMT1557
G1
G2
THR
VS
OUT
TRG
2
OUT
GND
VS
CS
GND
T/T
GMT1555/1557
TIMER/OSCILLATOR
Page 3 of 9
Rev. 1.4. 1999-07-01
GMT Microelectronics
22-001-700
Table 2: DEVICE SELECTION GUIDE
Table 3: ELECTRICAL SPECIFICATIONS
PART NUMBER
TEMPERATURE
RANGE
PACKAGE TYPE
IDENTIFICATION
GMT1555S
-40°C to +85°C
SOT-23-5
G1
GMT1557S
-40°C to +85°C
SOT-23-5
G2
PARAMETER
CONDITION (Note 1)
GMT1555/1557
UNITS
MIN
TYP
MAX
Supply Current
V
S
= 5.0 V
110
130
µ
A
V
S
= 15 V
300
400
µ
A
Monostable Timing
Accuracy
R
A
= 10 k, C = 0.1 uF, V
S
= 5.0 V
2.0
%
R
A
= 10 k, C = 0.1 uF, V
S
= 5.0 V
858
1161
µ
s
Monostable Drift
Over Temperature
V
S
= 5.0 V, -55< T
A
< +125
o
C, Note 2
100
ppm/
o
C
V
S
=10.0 V, -55 < T
A
< +125
o
C, Note 2
150
ppm/
o
C
V
S
= 15 V, -55< T
A
< +125
o
C, Note 2
200
ppm/
o
C
Monostable Drift
Over Supply
V
S
= 5.0 V to 1 5V, Note 2
0.5
%/V
Astable Timing
Accuracy
R
A
= R
B
= 10 k, C = 0.1 uF, V
S
= 5.0 V
2.0
%
R
A
= R
B
= 10 k, C = 0.1 uF, V
S
= 5.0 V
1717
2323
µ
S
Maximum Astable
Frequency
R
T
= 1.0 k, Ct = 47pF, V
S
= 8.0 V
5.0
MHz
General Note: Devices are ESD protected; however, standard ESD handling precautions should be observed.
Note 1: Typical Values at T
A
=25
o
C, Minimum and Maximum values at T
A
= -40
o
C to 85
o
C for GMT1555/1557.
Note 2: Not tested. Guaranteed by design.
GMT1555/1557
TIMER/OSCILLATOR
Rev. 1.4. 1999-07-01
Page 4 of 9
22-001-700
GMT Microelectronics
Astable Drift over
Temperature
V
S
= 5.0 V, -55 < T
A
< +125
o
C, Note 2
100
ppm/
o
C
V
S
=10.0 V, -55 < T
A
< +125
o
C, Note 2
150
ppm/
o
C
V
S
= 15 V, -55 < T
A
< +125
o
C, Note 2
200
ppm/
o
C
Astable Drift over
Supply
V
S
= 5.0 V to 15 V, Note 2
0.5
%/V
Threshold Voltage
V
S
= 15 V
61
67
72
%V
S
Trigger Voltage
V
S
= 15 V
27
32
37
%V
S
Trigger Current
V
S
= 15 V
50
nA
Threshold Current
V
S
= 15 V
50
nA
Chip Select
V
S
= 15 V
CS High (active)
CS Low (asleep)
61
28
67
33
72
39
%V
S
%V
S
Sleep Mode Supply
Current (1557 only)
CS = low (<33% Vs)
1.0
uA
Output Voltage Drop
V
S
= 15 V, I
SINK
= 20 mA
0.4
1.25
V
V
S
= 5.0 V, I
SINK
=3.2 mA
0.2
0.5
V
Output Voltage Drop
V
S
= 15 V, I
SOURCE
= 20 mA
14.1
14.7
V
V
S
= 5.0 V, I
SOURCE
=3.2 mA
3.8
4.82
V
Supply Voltage
Functional Oper., Note 2
2.7
18
V
Output Rise Time
R
L
= 10 M, C
L
= 10 pF, V
S
= 5.0 V,
Note 2
15
ns
Output Fall Time
R
L
= 10 M, C
L
= 10 pF, V
S
= 5.0 V,
Note 2
-
15
-
ns
PARAMETER
CONDITION (Note 1)
GMT1555/1557
UNITS
MIN
TYP
MAX
General Note: Devices are ESD protected; however, standard ESD handling precautions should be observed.
Note 1: Typical Values at T
A
=25
o
C, Minimum and Maximum values at T
A
= -40
o
C to 85
o
C for GMT1555/1557.
Note 2: Not tested. Guaranteed by design.
GMT1555/1557
TIMER/OSCILLATOR
Page 5 of 9
Rev. 1.4. 1999-07-01
GMT Microelectronics
22-001-700
Figure 3:
Figure 4:
GMT1555
GMT1557
Monostable
Astable
Bias
and
UVLO
+
-
+
-
R
S
Q
Output
Stage
GND
THR
TRG
C
R
D
OUT
Vs
Vsupply
C Bypass
+
Trigger
Input
+
Bias
and
UVLO
+
-
+
-
R
S
Q
Output
Stage
GND
C
R
OUT
Vs
Vsupply
C Bypass
+
1M
CS
T/T
Vs
+
Pulse Width
0.00001
0.0001
0.001
0.01
0.1
1
10
100
1000
1.00E-01
1.00E+00
1.00E+01
1.00E+02
1.00E+03
1.00E+04
1.00E+05
1.00E+06
1.00E+07
1.00E+08
Period (
µµ
s)
Capacitance (
F)
RT= 1k
10k
100k
1M
Astable Frequency
0.00001
0.0001
0.001
0.01
0.1
1
10
100
1.00E-03
1.00E-02
1.00E-01
1.00E+00
1.00E+01
1.00E+02
1.00E+03
1.00E+04
1.00E+05
1.00E+06
1.00E+07
Frequency (Hz)
Capacitance (uF)
RT= 1K
10K
100K
1M
GMT1555/1557
TIMER/OSCILLATOR
Rev. 1.4. 1999-07-01
Page 6 of 9
22-001-700
GMT Microelectronics
Rds on Vs. Supply
0
50
100
150
200
250
0
5
10
15
20
Vsupply (Volts)
R (ohms)
Rds on Vs. Temperature
0
5
10
15
20
25
30
-40
10
60
Temperature (Celcius)
Rds on (Ohms)
1555/1557 PERFORMANCE GRAPHS
Supply Current Vs. Supply Voltage
0
50
100
150
200
250
300
350
0
5
10
15
20
Supply Voltage (V)
Current (uA)
GMT1555/1557
TIMER/OSCILLATOR
Page 7 of 9
Rev. 1.4. 1999-07-01
GMT Microelectronics
22-001-700
MONOSTABLE (ONE-SHOT) OPERATION
The basic Monostable configuration is indicated in Figure 3. A momentary LOW signal applied to
the TRIGGER input sets the output voltage HIGH, for a duration set by the external RC timing
components. The actual cycle width is determined by when the THRESHOLD voltage level
reaches approximately 2/3 of the supply voltage. Pulse durations from
u
S to seconds are possi-
ble. Refer to the RC COMPONENT section for a discussion of allowable ranges.
ASTABLE OPERATION
The basic Astable configuration is indicated in Figure 4. The THRESHOLD / TRIGGER input ini-
tially begins in a LOW state, which resets the OUTPUT to a HIGH state. The external timing
capacitor C is then charged through the external resistor R until the 2/3 Vs level is achieved at
the THRESHOLD/ TRIGGER input. The output is then set LOW, and C is discharged. When V
THRESHOLD / TRIGGER crosses 1/3 Vs, the output againis switched HIGH, and the cycle
repeats itself. Frequencies of up to 5.0 MHz are achievable, with stable duty cycle performance
of approximately 50%. Please refer to the ASTABLE HIGH FREQUENCY section for further dis-
cussion.
SELECTING THE EXTERNAL RC TIMING COMPONENTS
Referring to Graph 3, there are two lines drawn (K
1
, K
2
) which provide the needed constants for
selecting the RC timing components for either One-Shot or the Astable modes of operation. RC
component selection may be cross-checked by referring to the Pulse Width and Astable Fre-
quency Graphs (graphs 1 and 2) in the specifications section.
MONOSTABLE MODE (1555)
The timing relationship is defined by:
T = K1 R C
T = Pulse width in mS
K1 = Constant from graph
R = External timing resistor (Ohms)
C = External timing capacitor (uF)
ASTABLE MODE (1557)
The timing relationship is defined by:
F = 1/ K2 R C
F = Frequency (Hz)
K2 = Constant from graph
R = External timing resistor (Ohms)
C = External timing capacitor (uF)
k Factors Times RC
1.00E+00
1.10E+00
1.20E+00
1.30E+00
1.40E+00
1.50E+00
1.60E+00
1.70E+00
1.80E+00
1.90E+00
2.00E+00
1.00E-06
1.00E-05
1.00E-04
1.00E-03
RC (seconds)
k Factor
F + 1/k2R C
T = k 1 R C
GMT1555/1557
TIMER/OSCILLATOR
Rev. 1.4. 1999-07-01
Page 8 of 9
22-001-700
GMT Microelectronics
RC COMPONENT SELECTION; MONOSTABLE
The external RC component values selected for the GMT1555 monostable device are dictated
by the desired timing pulse duration. At the minimum end, which is approximately in the 100
nanosecond range, RC limitations are fundamentally due to the total effective capacitance on the
timing pin. Printed circuit board, layout, and device parasitics all play a role at these small pulse
widths. Although theoretically possible, operation at such small pulse widths is not preferred.
The maximum time-out duration is effectively limited by capacitive leakage currents, which are
virtually always present in the large value electrolytic capacitors. If the current flowing through the
selected timing resistor value approaches the leakage current of the timing capacitor, inaccura-
cies will result. Digital counter techniques may be used for long timing delays.
MODIFYING THE ASTABLE DUTY CYCLE
Replacing the resistor R (Figure 4) with two series Resistor/ Diode networks placed in parallel
(diodes opposite each other) allows control of the duty cycle. The following timing equation hold:
T
charge
= 0.7 Ra x C
T
discharge
= 0.7 Rb x C
From the above, we can easily derive the frequency of operation to be:
F
osc
= 1/ [0.7C x (Ra + Rb)]
Keeping the diodes in close physical proximity, or at the same temperature, will provide improved
temperature tracking of duty cycle changes.
ASTABLE OPERATION AT HIGH FREQUENCIES
The GMT1557 device has been specially designed with equalized internal comparators to pro-
vide improved high frequency performance, and tracking over temperature. The duty cycle at 5
MHz will typically be 50%, plus or minus 5%. This simplifies usage for those designers who need
consistant 50% duty cycle performance at high frequencies.
LOCK OUT AND CHIP SELECT FEATURES
The GMT1555 and 1557 both have been designed with a logic lock-out feature. This feature pro-
hibits any outputs from the devices until Vcc rises above 1.2 volts nominal. This eliminates any
undesired or false trigger pulses, which can seriously upset the operation of timing and sensing
circuits.
An additional feature which has been incorporated into the GMT1557 Astable device is the CS,
or CHIP SELECT pin. This pin allows ON/OFF control of the device, and for normal operation is
tied to Vcc through a 1 meg ohm resistor. Pulling the CS pin LOW, pulls the output LOW, and
results in a SLEEP mode, which draws less than 1.0 uA of supply current. The CS pin should
not be left floating.
GMT1555/1557
TIMER/OSCILLATOR
Page 9 of 9
Rev. 1.4. 1999-07-01
GMT Microelectronics
22-001-700
CURRENT SENSE ENHANCEMENT
Various techniques have been independently developed by users whereby the 555 timer is used in con-
junction with a PWM, to provide enhanced current limiting capability. These techniques enhance the cur-
rent sense response speed, which is important for high frequency applications. Please be advised that
these techniques may be protected under various United States patents.
This information is believed to be correct and reliable at the time of publication, however, GMT reserves
the right to change the circuitry and specifications at any time and without notice. GMT assumes no
responsibility for use of any circuitry except that contained entirely within a GMT product. No patent
licenses are granted or implied.
LIFE SUPPORT USAGE POLICY:
GMT’s products are not authorized for use as critical components in life support devices or systems with-
out the express written approval of the CEO of GMT. As used herein:
(a) Life support devices or systems are devices or systems which (1) are intended for surgical implant into
the body, or (2) support or sustain life, and whose failure to perform when properly used in accordance with
instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to
the user.
(b) A critical component in any component of a life support device or system whose failure to perform can
be reasonably expected to cause the failure of the life support device or system.
GMT Microelectronics Corporation
950 Rittenhouse Road
Norristown, PA 19403
Toll Free: (888) GMT-4771
Ph: (610) 728-9300
Fax: (610) 676-7066
E-Mail: marketing @ gmtme.com
Website: www.gmtme.com
GMT Microelectronics
6 Journey
Suite 230
AlisoViejo, CA 92656
(949) 425-3756
Fax (949) 425-3767
GMT Microelectronics
17218 Preston Road
Suite 400
Dallas, TX 75287
(972) 735-3155
Fax (972) 735-3156
GMT Microelectronics
14502 North Dale Mabry
Suite 400
Tampa, FL 33618
(813) 908-9544
Fax (813) 908-7683
Sales Offices
GMT Microelectronics Singapore
No. 25, #05-02
Woodlands Industrial Park E1
Singapore 757743
(65) 368-6266
Fax (65) 368-6166
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