HA7210IB Intersil, HA7210IB Datasheet - Page 5

• Manufacturer Part Number: HA7210IB
• Manufacturer: Intersil

Specifications of HA7210IB

• Output Level: CMOS
• Symmetry Max: 60%
• Operating Supply Voltage (typ): 5
• Pin Count: 8
• Mounting Style: Surface Mount
• Screening Level: Industrial
• Product Height (mm): 1.5mm
• Product Depth (mm): 4mm
• Product Length (mm): 5mm
• Rad Hardened: No
• Package / Case: SOIC N
• Lead Free Status / RoHS Status: Not Compliant

Crystal Selection
For general purpose applications, a Parallel Mode Crystal is
a good choice for use with the HA7210. However for
applications where a precision frequency is required, the
designer needs to consider other factors.
Crystals are available in two types or modes of oscillation,
Series and Parallel. Series Mode crystals are manufactured
to operate at a specified frequency with zero load
capacitance and appear as a near resistive impedance when
oscillating. Parallel Mode crystals are manufactured to
operate with a specific capacitive load in series, causing the
crystal to operate at a more inductive impedance to cancel
the load capacitor. Loading a crystal with a different
capacitance will “pull” the frequency off its value.
The HA7210 has 4 operating frequency ranges. The higher
three ranges do not add any loading capacitance to the
oscillator circuit. The lowest range, 10kHz to 100kHz,
automatically switches in two 15pF capacitors onto OSC IN
and OSC OUT to eliminate potential start-up problems.
These capacitors create an effective crystal loading
capacitor equal to the series combination of these two
capacitors. For the HA7210 in the lowest range, the effective
loading capacitance is 7.5pF. Therefore the choice for a
crystal, in this range, should be a Parallel Mode crystal that
requires a 7.5pF load.
In the higher 3 frequency ranges, the capacitance on OSC
IN and OSC OUT will be determined by package and layout
parasitics, typically 4 to 5pF. Ideally the choice for crystal
should be a Parallel Mode set for 2.5pF load. A crystal
manufactured for a different load will be “pulled” from its
nominal frequency (see Crystal Pullability).
Frequency Fine Tuning
Two Methods will be discussed for fine adjustment of the
crystal frequency. The first and preferred method (Figure 2),
provides better frequency accuracy and oscillator stability
than method two (Figure 3). Method one also eliminates
start-up problems sometimes encountered with 32kHz
tuning fork crystals.
For best oscillator performance, two conditions must be met:
the capacitive load must be matched to both the inverter and
crystal to provide ideal conditions for oscillation, and the
frequency of the oscillator must be adjustable to the desired
C
1
2
OSC IN
XTAL
C
3
FIGURE 2.
HA7210
3
OSC OUT
5
C
2
+
-
1
V
+5V
DD
V
REG
HA7210
frequency. In Method two these two goals can be at odds
with each other; either the oscillator is trimmed to frequency
by de-tuning the load circuit, or stability is increased at the
expense of absolute frequency accuracy.
Method one allows these two conditions to be met
independently. The two fixed capacitors, C
the optimum load to the oscillator and crystal. C
frequency at which the circuit oscillates without appreciably
changing the load (and thus the stability) of the system.
Once a value for C
type of crystal being used, it could be replaced with a fixed
capacitor. For the most precise control over oscillator
frequency, C
This three capacitor tuning method will be more accurate
and stable than method two and is recommended for 32kHz
tuning fork crystals; without it they may leap into an overtone
mode when power is initially applied.
Method two has been used for many years and may be
preferred in applications where cost or space is critical. Note
that in both cases the crystal loading capacitors are
connected between the oscillator and V
as an AC ground. The Simplified Block Diagram shows that
the oscillating inverter does not directly connect to V
referenced to V
ground available.
Typical values of the capacitors in Figure 2 are shown below.
Some trial and error may be required before the best
combination is determined. The values listed are total
capacitance including parasitic or other sources. Remember
that in the 10kHz to 100kHz frequency range setting the
HA7210 switches in two internal 15pF capacitors.
FREQUENCY
CRYSTAL
32kHz
1MHz
2MHz
4MHz
C
1
3
2
OSC IN
should remain adjustable.
DD
XTAL
3
and V
has been determined for the particular
LOAD CAPS
C
RN
FIGURE 3.
2
C
33pF
33pF
25pF
22pF
1
. Therefore V
HA7210
3
OSC OUT
, C
2
+
-
DD
1
V
+5V
DD
DD
1
V
; do not use V
TRIMMER CAP
REG
and C
5pF to 100pF
5pF to 50pF
5pF to 50pF
5pF to 50pF
is the best AC
3
C
adjusts the
2
3
, provide
SS
but is
SS