A4401
Automotive Quasi-Resonant Flyback Control IC
Features and Benefits
▪
Multiple output regulator
▪
7 to 40 V input supply
▪
Low EMI conducted and radiated emissions
▪
Adaptive quasi-resonant turn on/off control
▪
Minimal number of external components
▪
Enable input which can be driven with respect to the
battery voltage
Description
This device provides all the necessary control functions to
provide the power rails for driving a vacuum fluorescent
display (VFD) using minimal external components. The power
supply is based on a quasi-resonant, discontinuous flyback
converter, operating near the critical conduction boundary. A
novel adaptive turn-on control scheme is used to optimize the
turn-on and turn-off phase of the MOSFET, to reduce EMI
emissions while minimizing switching losses.
The converter is self-oscillating, operating at switching
frequencies depending on the input voltage, load, and external
components. An onboard linear regulator that is powered
directly from the battery provides the housekeeping supply,
avoiding the need for complex bias supplies.
Package: 8-pin narrow SOIC (suffix L)
Internal diagnostics provide comprehensive protection
against overloads, input undervoltage, and overtemperature
conditions.
The A4401 is supplied in an 8-pin narrow SOIC package
(suffix L), which is lead (Pb) free, with 100% matte-tin
leadframe plating.
Approximate Scale 1:1
Typical Application
+V
BAT
VIN
LX
VFD
A4401
GD
ECU
EN
ISS
0V
0V
VA
GND
COMP
A4401-DS, Rev. 2
A4401
Automotive Quasi-Resonant Flyback Control IC
Selection Guide
Part Number
A4401KLTR-T
Packing
Tape and reel, 3000 pieces/reel
Absolute Maximum Ratings*
Characteristic
VIN Pin Voltage
LX Pin Voltage
ISS Pin Voltage
EN Pin Voltage
VA Pin Voltage
ESD Rating – Human Body Model
ESD Rating – Charged Device Model
Operating Ambient Temperature
Junction Temperature
Storage Temperature
* With respect to ground
T
A
T
J
T
stg
Symbol
V
IN
V
LX
V
ISS
V
EN
V
VA
AEC-Q100-002; all pins
AEC-Q100-011; all pins; inside
AEC-Q100-011; all pins; corner
Range K
Notes
Rating
–0.3 to 40
–0.6 to 60
–1 to 1
–0.3 to 40
–0.3 to 5
2000
500
750
–40 to 125
–40 to 150
–55 to 150
Units
V
V
V
V
V
V
V
V
ºC
ºC
ºC
Characteristic
Package Thermal Resistance
Symbol
R
θJA
Test Conditions*
4-layer PCB based on JEDEC standard
Value
80
Units
ºC/W
*Additional thermal information available on Allegro website.
Allegro MicroSystems, LLC
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
2
A4401
Automotive Quasi-Resonant Flyback Control IC
Functional Block Diagram
D2
US1J
LS1
C4
22 F
D3
US1J
C6
22 F
D4
STPS160U
LP
C3
100 nF
R2
VIN
LX
GD
C5
100 nF
Anode
84 V
50mA
Grid
58 V
50 mA
V
BAT
7 to 40V
Optional
EMI Filter
L1
LS2
C2
C7
100 nF
C1
LS3
C8
22 F
C9
100 nF
Filament
8V
200 mA
10 kΩ
C11
2.2 nF
Linear
ZD1
4.7 V
C10
100 nF
Q1
Adaptive
turn-on
control
ISS
R
+
-
R3
0.100
Ω
Enable
R1
10 kΩ
EN
Control
Logic
S
Shutdown
Optional feedback
resistor
R4
27 kΩ
R5
330 kΩ
Gm
Amp
-
VA
Fault
UVLO
TSD
GND
COMP
Soft
Start
+
Ref.
R6
4.7 kΩ
C12
220 pF
R7
220 kΩ
C13
6.8 nF
R8
1 MΩ
Pin-out Diagram
Number
1
2
3
4
5
6
7
8
Name
EN
COMP
VA
GND
ISS
GD
LX
VIN
Description
Enable input; active high
Compensation node for Gm amplifier stage
Output voltage feedback input
Ground reference connection; connect to negative terminal of battery supply
MOSFET, Q1, current sense input
MOSFET gate drive output
Regulator switching node: MOSFET drive output
Supply input to power control circuit, MOSFET driver, and reference voltages
EN
COMP
VA
GND
1
2
3
4
8 VIN
7 LX
6 GD
5 ISS
Allegro MicroSystems, LLC
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
3
A4401
Automotive Quasi-Resonant Flyback Control IC
ELECTRICAL CHARACTERISTICS
1,2
valid at T
J
= –40°C to +150°C, V
IN
= 7 to 40 V (unless noted otherwise)
Characteristics
General
VIN Quiescent Current
LX Leakage Current
LX Input Bias Current
Minimum Frequency
Soft Start
Gate Drive
Drive High Voltage, V
IN
> 10 V
Drive High Voltage, 10 V > V
IN
> 7 V
Rise Time, V
IN
> 10 V
Rise Time, 10 V > V
IN
> 7 V
Fall Time, V
IN
> 10 V
Fall Time, 10 V > V
IN
> 7 V
Current Sense Input
Maximum Sense Voltage (Current Limit)
Sense Input Bias Current
Current Sense Blanking
Reference Supply
Reference Voltage Tolerance
Operational Transconductance Amplifier
Output Impedance
Gm Constant
3
Output Source Current
Output Sink Current
Input Bias Current
Enable Input
EN Input Low Voltage
EN Input High Voltage
EN Input Hysteresis
EN Input Current
V
IL
V
IH
V
Ihys
I
INL
I
INH
V
IN
= 0 V
V
IN
= 14 V
V
IN
= 40 V
Voltage rising
Voltage falling
Temperature increasing
–
2.4
200
–10
–
–
5.4
4.9
–
–
–
–
–
500
–
–
–
–
–
0.5
165
15
0.8
–
–
10
50
200
7
6.5
–
–
–
V
V
mV
μA
μA
μA
V
V
V
ºC
ºC
Z
OP
K
Gm
I
SRC
I
SIN
I
BIAS
V
COMP
= 1.4 V, V
A
= 1.06 V, T
A
= 25ºC
V
COMP
= 1.4 V, V
A
= 1.36 V, T
A
= 25ºC
10
–
–30
20
–
–
470
–25
25
–100
–
–
–20
30
–
MΩ
μS
μA
μA
nA
V
REF
1.180
1.205
1.230
V
V
CL
I
ISS
t
BLANK
V
ISS
= –300 mV to 1 V
600
–
100
800
–
145
1000
10
190
mV
μA
ns
V
GDH
t
r
t
f
C
LOAD
= 1 nF, 10% to 90% of V
GS
= 9 V
C
LOAD
= 1 nF, 10% to 90% of V
GS
, V
IN
= 7 V
C
LOAD
= 1 nF, 90% to 10% of V
GS
= 0 V
C
LOAD
= 1 nF, 90% to 10% of V
GS
, V
IN
= 7 V
–
–
–
–
–
–
8.4
V
IN
– 0.5
60
90
30
40
9.5
V
IN
– 0.25
–
–
–
–
V
V
ns
ns
ns
ns
I
INOFF
I
INON
I
LXLEAK
I
LX
f
SW
t
SS
EN = Low
EN = High, no MOSFET switching
EN = Low, V
LX
= 40 V
EN = High, V
LX
= 60 V
–
–
–
–
25
5
–
2.3
–
–
35
10
10
3.3
1
145
45
15
μA
mA
μA
μA
kHz
ms
Symbol
Test Conditions
Min.
Typ.
Max.
Units
Protection
VIN Turn-On Threshold
VIN Turn-Off Threshold
Undervoltage Hysteresis
Overtemperature Shutdown
Overtemperature Hysteresis
1
For
2
Specifications
V
UVON
V
UVOFF
V
UVhys
T
JSD
T
JSDhys
input and output current specifications, negative current is defined as coming out of (sourcing) the specified device pin.
over operating temperature range are assured by design and characterization.
3
Guaranteed by design.
Allegro MicroSystems, LLC
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
4
A4401
Automotive Quasi-Resonant Flyback Control IC
Functional Description
Basic Operation
A peak current-mode control scheme is used to regu-
late one of the converter outputs, which will typically
be the highest output voltage. The regulated output
voltage is potentially divided down and fed into a
Gm stage, where the resulting error signal acts as the
control reference. This reference signal is compared
against the signal that is produced by the inductor
magnetization current flowing through the sense resis-
tor.
As shown in figure 1, at the beginning of a switching
cycle, the external MOSFET, Q1, is turned on. After
the sense resistor signal reaches the control reference
amplitude, the PWM comparator resets the synchronous
rectification (SR) latch and turns off the MOSFET.
When the MOSFET is turned off, the voltage on the
LX node rises until the voltage clamps at the bat-
tery voltage, V
BAT
, plus the reflected output voltage,
V
OUT(RFL)
. The secondary rectification diodes are
forward biased and the energy stored in the coupled
inductor is released to the output circuits. During this
period, the current through the inductor decreases lin-
+V
Coupled inductor goes discontinuous;
resonant ring occurs
V
OUT(RFL)
early. As the current falls to 0 A, a resonance is set up
between the primary magnetizing inductance and any
capacitance appearing between the drain and ground.
A damped voltage ringing occurs, which resonates
around the battery voltage, V
BAT
. As the resonant ring
swings negative, the adaptive turn-on circuit moni-
tors to detect the point at which the voltage reaches a
minimum. At this point the MOSFET is commanded
on, thereby minimizing the turn-on losses. Also, the
relatively slow resonant dV/dt helps to reduce EMI.
In most applications, the converter will be operated
with a battery input voltage of 13.5 V. To optimize
the performance of the regulator at this voltage, the
magnetics can be designed to force 0 V across the
MOSFET at turn-on. This minimizes switching losses
and perhaps more importantly reduces EMI caused by
voltage ringing due to the drain to ground capacitor
resonating with the primary inductance. The voltage
resonance at the MOSFET turn-off can be reduced by
a simple low-loss R-C snubber, as described in the
Electromagnetic Interference section.
If a small enough load is applied to the outputs, and
the output of the Gm stage falls below a certain level,
the converter will enter a burst mode of operation.
Burst mode reduces switching losses while maintain-
ing regulation of the outputs.
During startup, assuming the battery voltage is above
the turn-on threshold and the EN input is enabled, the
controller turns on. A soft start circuit controls the ref-
erence voltage, limiting the amount of current drawn
on the input and the amount of charge transferred to
the output, preventing voltage overshoot. During the
initial phase of the soft start, very little or no voltage is
present on the output. This means that there will be no
resonant phase and the converter will operate in con-
tinuous-conduction mode. The converter effectively
operates in constant-current mode until regulation is
achieved.
V
MOSFET
( V
LX
)
V
OUT(RFL)
V
BAT
0
+I
MOSFET
turns off
MOSFET
turns on
I
MOSFET
Current released from
coupled inductor into
output circuit
½ resonant
period
Current builds up in
primary winding of
coupled inductor
Figure 1. External MOSFET voltage and current
Allegro MicroSystems, LLC
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
www.allegromicro.com
5
京公网安备 11010802033920号
EEWORLD
