HEF4541B データシートの表示（PDF） - Philips Electronics
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HEF4541B Datasheet PDF : 8 Pages
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Philips Semiconductors
Programmable timer
Product specification
HEF4541B
MSI
PINNING
A0, A1
MODE
AR
MR
PH
RTC
CTC
RS
address inputs
mode select input
auto reset input
master reset input
phase input
external resistor connection (Rt)
external capacitor connection (Ct)
external resistor connection (RS) or
external clock input
FREQUENCY SELECTION TABLE
A0
A1
NUMBER OF
COUNTER STAGES n
f-f-o-o--s-u--c-t = 2n
L
L
13
L
H
10
H
L
8
H
H
16
8 192
1 024
256
65 536
FUNCTION TABLE
INPUTS
MODE
AR MR PH MODE
HL X
LLX
X auto reset disabled
X auto reset enabled (1)
XHX
X master reset active
XLX
H normal operation selected
XLX
division to output
L single-cycle mode (2)
XL L
X output initially LOW,
after reset
XLH
X output initially HIGH,
after reset
Notes
1. For correct power-on reset, the supply voltage should
be above 8.5 V. For VDD < 8.5 V, disable the autoreset
and connect AR to VDD.
2. The timer is initialized on a reset pulse and the output
changes state after 2n-1 counts and remains in that
state (latched). Reset of this latch is obtained by
master reset or by a LOW to HIGH transition on the
MODE input.
RC oscillator
H = HIGH state (the more positive voltage)
L = LOW state (the less positive voltage)
X = state is immaterial
Typical formula for oscillator
frequency:
fosc = -2---,---3-----×----1R-----t---×-----C----t
Fig.4 External component connection for RC
oscillator; RS ≈ 2 Rt.
Timing component limitations
The oscillator frequency is mainly determined by
RtCt, provided Rt << RS and RSC2 << RtCt. The function of
RS is to minimize the influence of the forward voltage
across the input protection diodes on the frequency. The
stray capacitance C2 should be kept as small as possible.
In consideration of accuracy, Ct must be larger than the
inherent stray capacitance. Rt must be larger than the
LOCMOS ‘ON’ resistance in series with it, which typically
is 500 Ω at VDD = 5 V, 300 Ω at VDD = 10 V and 200 Ω at
VDD = 15 V.
The recommended values for these components to
maintain agreement with the typical oscillation formula are:
Ct ≥ 100 pF, up to any typical value,
10 kΩ ≤ Rt ≤ 1 MΩ.
January 1995
4
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