MIC1555/1557
Micrel
MIC1555/1557
IttyBitty™ RC Timer / Oscillator
General Description
The MIC1555 IttyBitty™ CMOS RC timer/oscillator and
MIC1557 IttyBitty CMOS RC oscillator are designed to pro-
vide rail-to-rail pulses for precise time delay or frequency
generation.
The devices are similar in function to the industry standard
“555”, without a frequency control (F
C
) pin or an open-
collector discharge (D) pin. The threshold pin (TH) has
precedence over the trigger (TR) input, ensuring that the
BiCMOS output is off when TR is high.
The MIC1555 may be used as an astable (oscillator) or
monostable (one-shot) with separate threshold and trigger
inputs. In the one-shot mode, the output pulse width is
precisely controlled by an external resistor and a capacitor.
Time delays may be accurately controlled from microsec-
onds to hours. In the oscillator mode, the output is used to
provide precise feedback, with a minimum of one resistor and
one capacitor producing a 50% duty cycle square wave.
The MIC1557 is designed for astable (oscillator) operation
only, with a chip select/reset (CS) input for low power shut-
down. One resistor and one capacitor provide a 50% duty
cycle square wave. Other duty-cycle ratios may be produced
using two diodes and two resistors.
The MIC1555/7 is powered from a +2.7V to +18V supply
voltage.
The MIC1555/7 is available in the SOT-23-5 5-lead package,
and is rated for –40°C to +85°C ambient temperature range.
Features
• +2.7V to +18V operation
• Low current
<1µA typical shutdown mode (MIC1557)
200µA typical (TRG and THR low) at 3V supply
• Timing from microseconds to hours
• “Zero” leakage trigger and threshold inputs
• 50% square wave with one Resistor, one Capacitor
• Threshold input precedence over trigger input
• <15Ω output on resistance
• No output cross-conduction current spikes
• <0.005%/°C temperature stability
• <0.055%/V supply stability
• Small SOT-23-5 surface mount package
Applications
•
•
•
•
•
•
•
•
•
•
•
•
Precision timer
Pulse generation
Sequential timing
Time-delay generation
Missing pulse detector
Micropower oscillator to 5MHz
Charge-pump driver
LED blinker
Voltage converter
Linear sweep generator
Variable frequency and duty cycle oscillator
Isolated feedback for power supplies
Ordering Information
Part Number
MIC1555BM5
MIC1557BM5
Temp. Range
–40°C to +85°C
–40°C to +85°C
Package
SOT-23-5
SOT-23-5
Marking
T10
T11
Typical Applications
+5V
MIC1555
1
Standby
Trigger
4
2
3
100µs
VS
TRG
GND
THR
5
+5V
8kHz
MIC1557
Output
4
Enabled
Disabled
3
2
5
OUT
VS
CS
GND
OUT
Output
1k
1k
0.1µF
T/T
1
0.1µF
Monostable (One-Shot)
Astable (Oscillator)
October 1998
1
MIC1555/1557
MIC1555/1557
Micrel
Pin Configuration
OUT GND VS
3
2
1
CS GND T/T
3
2
1
T10
Part Number
MIC1555BM5
MIC1557BM5
Identification
T10
T11
4
5
4
T11
5
Part
Identification
TRG
THR
VS
OUT
SOT-23-5 (M5)
Pin Description
Pin Number
MIC1555
1
2
Pin Number
MIC1557
4
2
3
3
4
5
1
5
Pin Name
VS
GND
CS
OUT
TRG
THR
T/T
Pin Function
Supply (Input): +2.7 to +18V supply.
Ground: Supply return.
Chip Select/Reset (Input): Active high at
>2
⁄
3
V
S
. Output off when low at
<
1
⁄
3
V
S
.
Output: CMOS totem-pole output.
Trigger (Input): Sets output high. Active low (at
≤
2
⁄
3
V
S
nominal)
.
Threshold (Dominant Input): Sets output low. Active high (at
≥
2
⁄
3
V
S
nominal).
Trigger/Threshold (Input): Internally connected to both threshold and trigger
functions. See TRG and THR.
MIC1555/1557
2
October 1998
MIC1555/1557
Micrel
Absolute Maximum Ratings
Supply Voltage (V
S
) .................................................... +22V
Threshold Voltage (V
THR
, V
T/T
) .................................. +22V
Trigger Voltage (V
TRG
, V
T/T
) ....................................... +22V
Lead Temperature (soldering 10sec.) ....................... 300°C
Operating Ratings
Supply Voltage (V
S
) ..................................... +2.7V to +18V
Ambient Temperature Range (T
A
) ............. –40°C to +85°C
Package Thermal Resistance
(θ
JA
) ................................................................... 220°C/W
(θ
JC
) .................................................................. 130°C/W
Electrical Characteristics
T
A
= 25°C,
bold
values indicate –40°C
≤
T
A
≤
+85°C; unless noted.
Parameter
Supply current
Condition
V
S
= 5V
V
S
= 15V
Monostable Timing Accuracy
R
A
= 10k, C =0.1µF, V
S
= 5V
R
A
= 10k, C =0.1µF, V
S
= 5V
Monostable Drift over Temp
V
S
= 5V, –55
≤
T
A
≤
+125°C, Note 1
V
S
=10V, –55
≤
T
A
≤
+125°C, Note 1
V
S
= 15V, –55
≤
T
A
≤
+125°C, Note 1
Monostable Drift over Supply
Astable Timing Accuracy
V
S
= 5V to 15V, Note 1
R
A
= R
B
= 10k, C = 0.1µF, V
S
= 5V
R
A
= R
B
= 10k, C = 0.1µF, V
S
= 5V
Maximum Astable Frequency
Astable Drift over Temp
R
T
= 1k, C
T
= 47pF, V
s
= 8V
V
S
= 5V, –55
≤
T
A
≤
+125°C, Note 1
V
S
=10V, –55
≤
T
A
≤
+125°C, Note 1
V
S
= 15V, –55
≤
T
A
≤
+125°C, Note 1
Astable Drift over Supply
Threshold Voltage
Trigger Voltage
Trigger Current
Threshold Current
Chip Select
V
S
= 5V to 15V, Note 1
V
S
= 15V
V
S
= 15V
V
S
= 15V
V
S
= 15V
on >
2
/
3
V
S
off <
1
/
3
V
S
Output Voltage Drop
V
S
= 15V, I
SINK
= 20mA
V
S
= 5V, I
SINK
= 3.2mA
Output Voltage Drop
V
S
= 15V, I
SOURCE
= 20mA
V
S
= 5V, I
SOURCE
= 3.2mA
Supply Voltage
Output Rise Time
Output Fall Time
functional operation, Note 1
R
L
= 10M, C
L
= 10pF, V
S
= 5V, Note 1
R
L
= 10M, C
L
= 10pF, V
S
= 5V, Note 1
14.1
3.8
2.7
15
15
50
28
67
33
0.3
0.08
14.7
4.7
18
61
27
1717
5
100
150
200
0.5
67
32
72
37
50
50
72
50
1.25
0.5
858
100
150
200
0.5
2
2323
Min
Typ
240
350
2
1161
Max
300
400
Units
µA
µA
%
µs
ppm/°C
ppm/°C
ppm/°C
%/V
%
µs
MHz
ppm/°C
ppm/°C
ppm/°C
%/V
%V
S
%V
S
nA
nA
%V
S
%V
S
V
V
V
V
V
ns
ns
General Note:
Devices are ESD protected, however handling precautions are recommended.
Note 1:
Not tested.
October 1998
3
MIC1555/1557
MIC1555/1557
Micrel
Typical Characteristics
(T
A
= 25°C, V
IN
= +5)
On Resistance
vs. Supply Voltage
70
ON RESISTANCE (Ω)
60
50
40
30
20
10
0
0
5
10
15
SUPPLY VOLTAGE (V)
20
Astable Frequency
100
CAPACITANCE (µF)
100
Pulse Width
R
T
=1k
R
T
=1k
1
0.1
0.01
0.001
1x10
0
1x10
-2
1x10
-1
CAPACITANCE (µF)
10
10
1
10k
0.1
0.01
0.001
1M
100k
100k
10k
1M
1x10
1
1x10
2
1x10
3
1x10
4
1x10
5
1x10
6
1x10
7
0.0001
1x10
0
1x10
1
1x10
2
1x10
3
1x10
4
1x10
5
1x10
6
FREQUENCY (Hz)
1x10
-1
PERIOD (µs)
On Resistance
vs. Temperature
70
SUPPLY CURRENT (µA)
ON RESISTANCE (Ω)
60
50
40
30
20
10
0
-40 -20 0 20 40 60 80 100
TEMPERATURE (°C)
300
280
260
240
220
Supply Current
vs. Temperature
500
SUPPLY CURRENT (µA)
400
300
200
100
0
1x10
7
0.0001
Supply Current
vs. Supply Voltage
200
-40 -20 0 20 40 60 80 100
TEMPERATURE (°C)
0
5
10
15
SUPPLY VOLTAGE (V)
20
2.0
1.9
1.8
k FACTOR
1.7
1.6
1.5
1.4
1.3
1.2
1.1
1.0
10
k Factors
Times RC
f=1⁄k
1
RC
t=k
2
RC
100
RC (µs)
1000
14
CHIP SELECT VOLTAGE (V)
12
10
8
6
4
2
0
3
MIC1557 Chip Select
vs. Supply Voltage
ON
OFF
6
9
12
15
SUPPLY VOLTAGE (V)
18
MIC1555/1557
4
October 1998
MIC1555/1557
Micrel
Functional Diagrams
V
SUPPLY
VS
MIC1555
1M
MIC1557
V
SUPPLY
VS
Bias
THR
S
Q
R
Standby
Trigger
CS
Bias
100µs
S
8kHz
Q
OUT
Output
OUT
Output
R
<100µs
TRG
T/T
GND
1k
GND
1k
0.1µF
0.1µF
MIC1555 Block Diagram with External Components
(Monostable Configuration)
MIC1557 Block Diagram with External Components
(Astable Configuration)
Functional Description
Refer to the block diagrams.
The MIC1555/7 provides the logic for creating simple RC
timer or oscillator circuits.
The MIC1555 has separate THR (threshold) and TRG
(trigger) connections for monostable (one-shot) or astable
(oscillator) operation.
The MIC1557 has a single T/T (threshold and trigger) con-
nection for astable (oscillator) operation only. The MIC1557
includes a CS (chip select/reset) control.
Supply
VS (supply) is rated for +2.7V to +18V. An external capacitor
is recommended to decouple noise.
Resistive Divider
The resistive voltage divider is constructed of three equal
value resistors to produce
1
⁄
3
V
S
and
2
⁄
3
V
S
voltage for trigger
and threshold reference voltages.
Chip Select/Reset (MIC1557 only)
CS (chip select/reset) controls the bias supply to the oscillator’s
internal circuitry. CS must be connected to CMOS logic-high
or logic-low levels. Floating CS will result in unpredictable
operation. When the chip is deselected, the supply current is
less than 1µA. Forcing CS low resets the MIC1557 by setting
the flip flop, forcing the output low.
Threshold Comparator
The threshold comparator is connected to S (set) on the RS
flip-flop. When the threshold voltage (
2
⁄
3
V
S
) is reached, the
flip-flop is set, making the output low. THR is dominant over
TRG.
October 1998
5
Trigger Comparator
The trigger comparator is connected to R (reset) on the RS
flip-flop. When TRG (trigger) goes below the trigger voltage
(
1
⁄
3
V
S
), the flip-flop resets, making the output high.
Flip-Flop and Output
A reset signal causes Q to go low, turning on the P-channel
MOSFET and turning off the N-channel MOSFET. This
makes the output rise to nearly V
S
.
A set signal causes Q to go high, turning off the P-channel
MOSFET, and turning on the N-channel MOSFET, grounding
OUT.
Basic Monostable Operation
Refer to the MIC1555 functional diagram.
A momentary low signal applied to TRG causes the output to
go high. The external capacitor charges slowly through the
external resistor. When V
THR
(threshold voltage) reaches
2
⁄
3
V
S
, the output is switched off, discharging the capacitor.
During power-on, a single pulse may be generated.
Basic Astable Operation
Refer to the MIC1557 functional diagram.
The MIC1557 starts with T/T low, causing the output to go
high. The external capacitor charges slowly through the
external resistor. When V
T/T
reaches
2
⁄
3
V
S
(threshold volt-
age), the output is switched off, slowly discharging the
capacitor. When V
T/T
decreases to
1
⁄
3
V
S
(trigger voltage), the
output is switched on, causing V
T/T
to rise again, repeating
the cycle.
MIC1555/1557
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