A4401KLTR-T Allegro Microsystems Inc, A4401KLTR-T Datasheet - Page 15

• Manufacturer Part Number: A4401KLTR-T
• Description: IC,Vacuum Fluorescent Display Driver,SOP,8PIN,PLASTIC
• Manufacturer: Allegro Microsystems Inc

Specifications of A4401KLTR-T

• Display Type: Vacuum Fluorescent (VF)
• Current - Supply: 2.3mA
• Voltage - Supply: 7 V ~ 40 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Interface: -
• Configuration: -
• Digits Or Characters: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 620-1217-2

A simple low-loss R-C snubber can be deployed to
dampen these oscillations. To do so, follow these sim-
ple steps to determine the component values required:
1. Measure the voltage resonant frequency, f
2. Add an additional capacitance (C11) between LX
3. Now to calculate component values that will result
4. With C
5. Finally, solve for the characteristic impedance of the
R
shown in functional block diagram). Typically a
resistor is adequate.
A4401
O
the LX node.
and ground until the resonant frequency is halved,
f
where:
Note that the value of the additional capacitance
should be in the region of a few hundredths of pico-
farads.
in f
parasitic components:
RES
can be selected as the damping resistor value (not
C
C
L
RES
LEAK
ADD
LEAK
/2:
/2, first calculate C
LEAK
is the additional capacitance added,
is the parasitic capacitance, and
is the parasitic inductance.
f
f
RES
RES
C
solved, solve for L
R
LEAK
O
=
=
C
=
NEW
⎛
⎜ ⎜
⎝
× × (L
+ C
× × (L
C
L
C
LEAK
LEAK
=
LEAK
ADD
C
LEAK
LEAK
LEAK
⎞
⎟ ⎟
⎠
LEAK
=
=
½
1
1
4 × C
C
Automotive Quasi-Resonant Flyback Control IC
+ C
.
× C
ADD
3
, given:
× C
LEAK
ADD
LEAK
LEAK
NEW
,
)
.
)
½
½
,
,
RES
,
, on
1
/
8
(35)
(36)
(37)
(38)
(39)
(40)
W
Figure 6 illustrates a converter running at full power
with V
across LX and the lower trace is the voltage across the
sense resistor, R3. It can be seen that at turn-on, the
noise is very low, as the resonant action introduces a
very slow voltage slew which reaches 0 V before the
MOSFET is turned on. This action ensures minimal
noise is produced. However, at turn-off there is a high
frequency ringing of 25 MHz which could cause issues
in terms of complying with radiated emissions.
Figure 7 illustrates the effects of adding an R-C snub-
ber (R = 30 Ω and C = 330 pF in series between the
LX pin and GND). It can be seen that, through the
addition of the snubber, the turn-off ringing has been
considerably damped. This was achieved with almost
negligible additional power loss.
Conducted Emissions
emissions, an EMI filter may be necessary as shown in
the Functional Block diagram.
Figure 7. Voltages with 0 V switching of Q1 with an R-C snubber
BAT
MOSFET
Turn-On
V
RSENSE
V
LX
= 13.5 V. The upper trace is the voltage
MOSFET
Turn-Off
115 Northeast Cutoff, Box 15036
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 [phone]
www.allegromicro.com
To help reduce the conducted
15