INTEGRATED CIRCUITS
DATA SHEET
PCF1252-X family
Threshold detector and reset
generator
Product specification
Supersedes data of 1996 Jan 23
File under Integrated Circuits, IC11
1998 Apr 16
Philips Semiconductors
Product specification
Threshold detector and reset generator
FEATURES
•
Very low current consumption, typically 10
µA
•
10 factory programmed threshold voltages available
covering trip voltages from 4.75 to 2.55 V
• ±50
mV trip point accuracy over full temperature range
•
Variable RESET delay
•
RESET pulse polarity selection
•
Defined outputs at 0.6 V (typ.)
•
Comparator for second level detection
(e.g. overvoltage detection)
•
Advance warning of power fail
•
Operating temperature range
−40
to +85
°C.
ORDERING INFORMATION
PACKAGE
TYPE NUMBER
NAME
PCF1252-XP
(1)
PCF1252-XT
(1)
Note
1. X = 0 to 9; depending on threshold voltage.
BLOCK DIAGRAM
DIP8
SO8
DESCRIPTION
plastic dual in-line package; 8 leads (300 mil)
PCF1252-X family
GENERAL DESCRIPTION
The PCF1252-Xs are low-power CMOS voltage threshold
detectors designed especially for supervision of
microcontroller/microprocessor systems for detection of
power-on/off conditions and generation of a system reset
pulse. The PCF1252-X also provides a POWF (power fail)
output which is activated at a precise factory-programmed
trip point. A system RESET output has a built-in delay with
duration determined by an external capacitor (C
CT
).
A second comparator (comparator 2) has been included to
enable the possibility of a second monitoring point in the
system.
VERSION
SOT97-1
SOT96-1
plastic small outline package; 8 leads; body width 3.9 mm
handbook, full pagewidth
VDD
8
COMIN
3
comparator 2
+
−
comparator 1
+
−
5
COMOUT
PCF1252-X
7
POWF
1.30 V
DELAY
6
RESET
4
VSS
1
CT
2
MGC915
SELECT
Fig.1 Block diagram.
1998 Apr 16
2
Philips Semiconductors
Product specification
Threshold detector and reset generator
PINNING
SYMBOL
CT
SELECT
COMIN
V
SS
COMOUT
RESET
POWF
V
DD
PIN
1
2
3
4
5
6
7
8
DESCRIPTION
connection for the external capacitor
select polarity or external reset input
comparator input
ground (0 V)
comparator output
reset output
power failure signal output
supply voltage
handbook, halfpage
PCF1252-X family
CT
SELECT
COMIN
VSS
1
2
8 VDD
7
POWF
RESET
COMOUT
PCF1252-X
3
4
MGC916
6
5
Fig.2 Pinning diagram.
FUNCTIONAL DESCRIPTION
(see Fig.1)
The PCF1252-X contains:
•
A precise factory-programmed voltage reference
•
Two comparators
•
A delay circuit.
The PCF1252-X family is comprised of 10 versions with
different factory-programmed voltage trip-points (V
TRIP
),
see Chapter “Characteristics”.
Supply
The supply voltage (V
DD
) is internally divided before being
compared, via comparator 1, with the internal reference
voltage.
POWF
(see Fig.3)
The POWF output is:
•
LOW, if V
DD
is below V
TRIP
•
HIGH, if V
DD
is above V
TRIP
.
Power-on reset (SELECT = LOW)
As V
DD
rises past V
TRIP
, a positive reset pulse is generated
at RESET. The duration of the reset pulse (t
R
) is
determined by the value of the external capacitor (C
CT
;
maximum 1
µF,
see Fig.8) connected to CT. With no
external capacitor connected, C
CT
assumes a minimum
value of 100 pF. If SELECT is HIGH, the reset pulse is
inverted.
Power failure
During a power-off condition (V
DD
< V
TRIP
), POWF goes
LOW. After a time delay (t
S
), also determined by C
CT
,
RESET goes HIGH. Any POWF assertion (V
DD
< V
TRIP
)
will result in a subsequent RESET pulse.
Voltage trip-point
By selecting the voltage trip-point slightly higher than the
minimum operating voltage of the
microcontroller/microprocessor, there is sufficient time for
data storage before the power actually fails.
In order to prevent oscillations around the voltage
trip-point, a small hysteresis has been included, resulting
in a power-on switching point that is higher than the
voltage trip-point (minimum of 15 mV). The voltage
trip-point refers to the value at which power-off is signalled.
COMIN
Input to the second comparator (comparator 2).
When used in conjunction with an external voltage divider,
this allows a second point in the system to be monitored.
This input has no built-in hysteresis. When not in use
connect to V
DD
. COMOUT will be LOW or HIGH
depending on the voltage at COMIN:
•
COMOUT = HIGH, if voltage at COMIN is above the
switch point V
SP
(typically 1.30 V).
•
COMOUT = LOW, if voltage at COMIN is below the
switch point V
SP
(typically 1.30 V).
1998 Apr 16
3
Philips Semiconductors
Product specification
Threshold detector and reset generator
LIMITING VALUES
In accordance with the Absolute Maximum Rating System (IEC 134).
SYMBOL
V
DD
V
I
I
I
I
O
P
tot
T
stg
T
amb
HANDLING
PARAMETER
supply voltage
input voltage
DC clamp-diode current
output current
total power dissipation
storage temperature
operating ambient temperature
all pins: V
I
<
−0.5
V
or V
I
> V
DD
+ 0.5 V
CONDITIONS
−0.5
−0.5
−
−
−
−65
−40
MIN.
PCF1252-X family
MAX.
+7.0
V
DD
+ 0.5
20
20
150
+100
+85
V
V
UNIT
mA
mA
mW
°C
°C
Inputs and outputs are protected against electrostatic discharge in normal handling. However, to be totally safe, it is
desirable to take normal handling precautions appropriate to handling MOS devices (see
“Handling MOS Devices”).
CHARACTERISTICS
V
DD
= 2.4 to 6.0 V; V
SS
= 0 V; T
amb
=
−40
to +85
°C;
(see Fig.3); unless otherwise specified.
SYMBOL
V
DD
V
TRIP
PARAMETER
supply voltage
Voltage trip-point:
PCF1252-0
PCF1252-1
PCF1252-2
PCF1252-3
PCF1252-4
PCF1252-5
PCF1252-6
PCF1252-7
PCF1252-8
PCF1252-9
I
DD
supply current
T
amb
= 25
°C;
V
DD
= V
TRIP
+ 0.5 V;
COMIN = V
DD
;
see Figs. 4 and 5
note 2
T
amb
= 25
°C;
note 1
4.70
4.50
4.20
4.00
3.70
3.50
3.20
3.00
2.70
2.50
−
4.75
4.55
4.25
4.05
3.75
3.55
3.25
3.05
2.75
2.55
10
4.80
4.60
4.30
4.10
3.80
3.60
3.30
3.10
2.80
2.60
15
V
V
V
V
V
V
V
V
V
V
µA
CONDITIONS
MIN.
2.4
−
TYP.
6.0
MAX.
UNIT
V
∆V
TRIP
V
hys
voltage trip-point temperature
coefficient
voltage trip-point hysteresis
−
15
±100 ×
10
−6
±400 ×
10
−6
mV/K
30
50
mV
1998 Apr 16
4
Philips Semiconductors
Product specification
Threshold detector and reset generator
PCF1252-X family
SYMBOL
COMIN
V
SP
∆V
SP
SELECT
V
IL
V
IH
I
LI
I
LI
I
O
PARAMETER
CONDITIONS
T
amb
= 25
°C;
note 1
note 2
MIN.
TYP.
MAX.
UNIT
COMIN switch point
COMIN switch point temperature
coefficient
1.28
−
1.30
±0.1
1.32
±0.5
V
mV/K
LOW level input voltage
HIGH level input voltage
−
0.7V
DD
−
−
−
−
−
−
0.3V
DD
−
−1.0
1.0
−
V
V
µA
µA
SELECT and COMIN
LOW level leakage input current
HIGH level leakage input current
POWF, RESET and COMOUT
output sink current
V
O
= 0.4 V;
V
DD
= 2.4 V;
see Fig.6
V
O
= 2.0 V;
V
DD
= 2.4 V;
see Fig.7
C
CT
= 1 nF; note 3
C
CT
= 1 nF; note 3
1
3
mA
I
O
output source current
−0.75
−2
−
mA
t
R
t
S
t
R
/t
S
C
int
Notes
reset time
save time
reset to save time ratio
CT internal capacitance
400
40
−
−
1000
100
10
100
2000
200
−
−
µs
µs
pF
1. Long time stability of COMIN switch point V
SP
and voltage trip point V
TRIP
: within 10 years of continuous operation
at V
DD(max)
and an average operating temperature of 55
°C
the drift of V
SP
will not exceed
±10
mV. The maximum
drift for V
TRIP
will not exceed (±V
TRIP(typ)
/V
SP(typ)
) 10 mV.
2. Values given per degree Kelvin; tested on a sample basis.
3. Conformance to these specifications is only guaranteed if the slew rate of V
DD
is less than 25 V/ms.
1998 Apr 16
5
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