Panasonic AN8022L Ac-dc switching power supply control ic Datasheet

Voltage Regulators
AN8022L, AN8022SB
AC-DC switching power supply control IC
9
5
1.2±0.25
21.7±0.3
6
0.5±0.1
8
7
Unit: mm
0.4±0.25
AN8022L
The AN8022L and AN8022SB are ICs which are
suitable for controlling a switching power supply using
primary side control method.
Those are most suited for a switching power supply
of relatively small capacity. Less frequently used functions are removed, and only the necessary minimum functions are incorporated, so that they are compact and very
easy to use.
Moreover, the internal settings are incorporated as
much as possible, thus cost down can be realized by decreasing the peripheral parts.
4
3
2
2.54
■ Overview
1
1.0±0.25
2.7±0.25
4.3±0.3
+0.1
0.3 –0.05
1.4±0.25
1.35±0.25
SIP009-P-0000D
■ Features
AN8022SB
Unit: mm
6.50±0.30
+0.10
0.15 -0.05
4.30±0.30
1.00±0.20
0.50±0.05
8
0.35±0.10
Seating plane
0.65
1.50±0.20
1
(0.45) 0.80
6.30±0.30
9
16
0.10±0.10
• It operates at a control frequency up to 700 kHz, realizing the output rise time of 35 ns and the output fall time
of 25 ns.
• Pre-start operating current is as small as 70 µA (typical)
so that it is possible to miniaturize the start resistor.
• Output block employs totem pole method.
The absolute maximum rating of ±1.0 A (peak) allows
the direct drive of power MOSFET.
• Built-in pulse-by-pulse overcurrent protection circuit
• Built-in protection circuit against malfunction at low
voltage (on/off: 14.2 V/9.2 V)
• Maximum Duty is 44% (typical)
• Equipped with timer latch function and overvoltage protection circuit.
• Two kinds of packages: 9-pin SIP, 16-pin SOP
Seatng plane
SSOP016-P-0225B
■ Applications
• Various power supply equipment
1
AN8022L, AN8022SB
Voltage Regulators
(4)SVCC
■ Block Diagram
TIM/OVP
(5)
8
Start/Stop
OVP
7
VREF
VCC
(3)PVCC
6
VOUT
(2)
Drive
5
GND
(1)PGND
(16)SGND
4.1 V
3
FB
CT
(13)
2
RT
(12)
OSC
PWM
OCL
4
CLM(−)
(15)
1
CLM
SS
(11)
IFB
(6)
9
Reset
Note) The number in ( ) shows the pin number for the AN8022SB.
■ Pin Descriptions
• AN8022L
Pin No.
Symbol
Description
1
SS
Soft start pin
2
RT
Resistor connection pin that determines charge and discharge current of triangular wave
3
CT
Triangular wave generating capacitor connection pin
4
CLM(−)
5
GND
Grounding pin
6
VOUT
Power MOSFET direct drive pin
7
VCC
Power supply voltage pin
8
TIM/OVP
9
IFB
Pulse-by-pulse overcurrent protection input pin
Pin for overvoltage protection and timer latch (joint use)
Current feedback signal input pin from power-supply-output photocoupler
• AN8022SB
Pin No. Symbol
Description
Description
1
PGND
Grounding pin
10
N.C.
2
VOUT
Power MOSFET direct drive pin
11
SS
Soft start pin
3
PVCC
Power supply voltage pin
12
RT
Charge and discharge current of
4
SVCC
Power supply voltage pin
triangular wave determining resistance
5
TIM/OVP
Pin for overvoltage protection and
connection pin
timer latch combined use
6
2
Pin No. Symbol
IFB
13
CT
current feedback signal input pin
14
N.C.
15
CLM(−)
N.C.
N.C.
8
N.C.
N.C.
9
N.C.
N.C.
Triangular wave generating capacitance
connection pin
Power supply output photocoupler
7
N.C.
N.C.
Pulse-by-pulse overcurrent protection
input pin
16
SGND
Grounding pin
Voltage Regulators
AN8022L, AN8022SB
■ Absolute Maximum Ratings
Parameter
Symbol
Rating
Unit
Supply voltage
VCC
35
V
OVP terminal allowable application voltage
VOVP
VCC
V
CLM terminal allowable application voltage
VCLM
− 0.3 to +7.0
V
VSS
− 0.3 to +7.0
V
Constant output current
IO
±150
mA
Peak output current
IOP
±1 000
mA
IFB terminal allowable application voltage
IFB
−5
mA
Power dissipation
AN8022L
PD
658
mW
Operating ambient temperature
*
SS terminal allowable application voltage
AN8022SB
Storage temperature
*
340
Topr
−30 to +85
°C
Tstg
−55 to +150
°C
Note) *: Expect for the operating ambient temperature and storage temperature, all ratings are for Ta = 25°C.
■ Recommended Operating Range
Parameter
Timing resistor RT
Symbol
Range
Unit
R7
15 to 20
kΩ
■ Electrical Characteristics at Ta = 25°C
Parameter
Symbol
Conditions
Min
Typ
Max
Unit
Start voltage
VCC-START
13.0
14.2
15.4
V
Stop voltage
VCC-STOP
8.5
9.2
9.9
V
Standby bias current
ICC-STB
VCC = 12 V
50
70
105
µA
Operating bias current
ICC-OPR
VCC = 34 V
6.4
8.0
9.6
mA
OVP operating bias current 1
ICC-OVP1
VCC = 20 V
2.4
3.0
3.6
mA
OVP operating bias current 2
ICC-OVP2
VCC = 10 V
0.44
0.55
0.66
mA
OVP operating threshold voltage
VTH-OVP
VCC = 18 V
5.4
6.0
6.6
V
OVP release supply voltage
VCC-OVPC
7.6
8.4
9.2
V
Timer latch charge current
ICH-TIM
VCC = 18 V, RT = 19 kΩ
−20
−30
−40
µA
Timer latch start feedback current
IFB-TIM
VCC = 18 V
Soft-start charge current
ICH-SS
VCC = 18 V, RT = 19 kΩ
−20
−30
−40
µA
−180
−200
−220
mV
− 0.32 − 0.44 − 0.56
mA
Overcurrent protection threshold voltage 1
VTH-CLM1
VCC = 18 V
Pre-start low-level output voltage
VOL-STB
VCC = 12 V, IO = 10 mA

0.8
1.8
V
Low-level output voltage
VOL
VCC = 18 V, IO = 100 mA

1.3
1.8
V
High-level output voltage
VOH
VCC = 18 V, IO = −100 mA
15.0
16.5

V
Oscillation frequency 1
fOSC1
VCC = 18 V
175
200
225
kHz
Maximum duty 1
Dumax1
VCC = 18 V
40
44
48
%
Feedback current at 0% duty
IFB-Dumin
VCC = 18 V
− 0.9
−1.2
−1.5
mA
Feedback current at maximum duty
IFB-Dumax
VCC = 18 V
− 0.45 − 0.6 − 0.75
mA
3
AN8022L, AN8022SB
Voltage Regulators
■ Electrical Characteristics at Ta = 25°C (continued)
• Design reference data
Note) The characteristics listed below are theoretical values based on the IC design and are not guaranteed.
Parameter
Symbol
Conditions
Min
Typ
Max
Unit
Ta = −30°C to +85°C
160

240
kHz
tDry-CLM
VCC = 18 V under no load

200

ns
Output voltage rise time
tr
VCC = 18 V under no load

35

ns
Output voltage fall time
tf
VCC = 18 V under no load

25

ns
Oscillation frequency 2
fOSC2
Overcurrent protection delay time
■ Terminal Equivalent Circuits
Pin No.
Equivalent circuit
1
(11)
Description
SS:
Soft start terminal.
PWM
comp.
I/O

When VCC is applied, the capacitor connected to
this pin is charged, and the output duty is decreased by inputting the capacitor voltage to the
500 Ω
PWM.
1 (11)
2
(12)
RT:
The terminal for connecting a resistor to deter-
VREF

mine the charge and discharge current of the
triangular wave.
500 Ω
(12) 2
3
(13)
CT:
The terminal for connecting a capacitor to gener-
VREF
(13)
3
IO

ate the triangular wave.
2IO
PWM
comp.
4
(15)
VREF
CLM(−):
The input terminal for pulse-by-pulse overcurrent
Reset
I
protection. It is usually required to attach an external filter.
4 (15)
5
(1)(16)

Note) The number in ( ) is the pin number for the AN8022SB.
4
GND, (PGND), (SGND):
Grounding terminal.

Voltage Regulators
AN8022L, AN8022SB
■ Terminal Equivalent Circuits (continued)
Pin No.
6
(2)
Equivalent circuit
PVCC
Description
I/O
VOUT:
The terminal for directly driving a power
O
MOSFET.
6
(2)

7
(3)(4)
VCC , (PVCC), (SVCC):
Supply voltage terminal.

It monitors the supply voltage and has operating
threshold value for start/stop/OVP reset.
8
(5)
TIM/OVP:
The terminal with double functions such as OVP
I
(overcurrent protection) and timer latch terminal.
[OVP]
When it receives the overvoltage signal of the
SVCC
power supply output and high is input to the
terminal, internal circuit is turned off. At the same
time, this condition (latch) is held. To reset the
6V
Comp.
OVP latch, it is necessary to reduce VCC under the
release voltage.
5 µA
500 Ω
[Timer latch]
The output voltage drop due to the overcurrent
8 (5)
condition of power supply output is detected
through the current level of IFB-input. When IFB
becomes less than a current of a certain value,
charge current flows into the capacitor connected
to this terminal. When the capacitor is charged to
the threshold voltage of OVP, OVP
starts to operate and the IC stays stop.
9
(6)
IFB:
The terminal into which the current feedback sig-
VREF
I
nal is input from the photocoupler of the power
PWM
comp.
supply output.
500 Ω
I/V
conversion
9 (6)
Note) The number in ( ) shows the pin number for the AN8022SB.
5
AN8022L, AN8022SB
Voltage Regulators
■ Application Notes
[1] Main characteristics [Load: CL = 3 300 pF, RL = 20 Ω]
Start/stop voltage characteristics
OVP operation threshold voltage characteristics
VCC = 18 V
VCC = 18 V
7.0
Threshold voltage (V)
Start/stop voltage (V)
16
14
12
10
6.0
5.5
5.0
8
−50
6.5
−25
0
25
50
75
−50
100
−25
0
25
50
Ambient temperature (°C)
Standby bias current characteristics
Operating bias current characteristics
VCC = 34 V
8.5
Bias current (mA)
Bias current (µA)
75
70
65
60
55
8.0
7.5
7.0
6.5
−25
0
25
50
75
−50
100
−25
0
25
50
75
Ambient temperature (°C)
Ambient temperature (°C)
Overcurrent protection threshold voltage characteristics
OVP release voltage characteristics
VCC = 18 V
OVP release voltage (V)
Threshold voltage (mV)
9.5
−210
−200
−190
−180
9.0
8.5
8.0
7.5
−25
0
25
50
Ambient temperature (°C)
6
100
VCC = 18 V
−220
−50
100
Ambient temperature (°C)
VCC = 12 V
−50
75
75
100
−50
−25
0
25
50
Ambient temperature (°C)
75
100
Voltage Regulators
AN8022L, AN8022SB
■ Application Notes (continued)
[1] Main characteristics [Load: CL = 3 300 pF, RL = 20 Ω] (continued)
OVP operating bias current characteristics 1
OVP operating bias current characteristics 2
VCC = 20 V
VCC = 10 V
2.5
Bias current (mA)
Bias current (mA)
4.5
4.0
3.5
3.0
2.5
-50
2.0
1.5
1.0
0.5
-25
0
25
50
75
100
-50
Ambient temperature (°C)
0
-25
25
50
75
100
Ambient temperature (°C)
[2] Operation descriptions
1. Start/stop circuit block
• Start mechanism
When AC voltage is applied and the supply
voltage reaches the start voltage through the current from the start resistor, the IC starts operation. Then the power MOSFET driving starts.
Thereby, bias is generated in the transformer
and the supply voltage is given from the bias
coil to the IC. (This is point a in figure 1.)
During the period from the time when the
start voltage is reached and the voltage is generated in the bias coil to the time when the IC is
provided with a sufficient supply voltage, the
supply voltage of the IC is supplied by the capacitor (C1) connected to VCC.
Since the supply voltage continuously decreases during the above period (area b in figure
1), the power supply is not able to start (state c
in figure 1), if the stop voltage of the IC is
reached before the sufficient supply voltage is
supplied from the bias coil.
After AC rectification
Start resistance
R1
VCC
VOUT
C1
GND
Before start
Start voltage
Start
Voltage supplied
from bias coil
a
Start condition
Stop voltage
b
c Start failure
Figure 1
• Function
The start/stop circuit block is provided with the function to monitor the VCC voltage, and to start the operation
of IC when VCC voltage reaches the start voltage (14.2 V typical), and to stop when it decreases under the stop
voltage (9.2 V typical). A large voltage difference is set between start and stop (5.0 V typical), so that it is easier
to select the start resistor and the capacitor to be connected to VCC .
Note) To start up the IC operation, the startup current which is a pre-start current plus a circuit drive current is necessary.
Set the resistance value so as to supply a startup current of 450 µA.
7
AN8022L, AN8022SB
Voltage Regulators
■ Application Notes (continued)
[2] Operation descriptions (continued)
2. Oscillation circuit
The PWM is an abbreviation of Pulse Width Modulation. In this IC, a smaller voltage between the voltage level
which is converted from the current input to IFB terminal and dead-time control level which is fixed internally is
compared with the internal triangular oscillation level through PWM comparator, and optimal duty is determined,
and then it is output via output driving stage.
• Triangular wave oscillation
The triangular waveform oscillation is performed through constant current charge/constant current
discharge to/from the external capacitor connected to the CT. The ratio of the charge current to the discharge
current is set inside, and the current value is determined by the external resistor connected to the RT terminal.
The RT terminal voltage is determined by the level which is a resistor-divided voltage of the internal
reference voltage (which is determined by Zener diode and VBE of NPN transistor, and temperaturecompensated). For this reason, the effect of fluctuation with temperature and dispersion is small. By the use
of a temperature-compensated external resistor, the effect of the fluctuation with temperature and dispersion
on the charge and discharge current value will be reduced further.
Moreover, since the upper/lower voltage level of the triangular wave oscillation is given by the resistordivider internal reference voltage, the effect of fluctuation with temperature and dispersion has been
suppressed.
Moreover, since the upper/lower voltage level of the triangular wave oscillation is given by the resistordivision of internal reference voltage, the effect of fluctuation with temperature and dispersion has been
suppressed.
As described above, the sufficient consideration has been given to the effect of fluctuation with
temperature and dispersion in the design of the triangular wave oscillation frequency.
(Reference calculation of oscillation frequency)
5
fOSC =
[Hz]
6 × CT × RT
3. Overvoltage protection circuit (OVP)
OVP is an abbreviation of Over Voltage Protection. It refers to a self-diagnosis function, which stops the power
supply to protect the load when the power supply output generates abnormal voltage higher than the normal
output voltage due to failure of the control system or an abnormal voltage applied from the outside (figure 2 and
figure 3).
Basically, it is set to monitor the voltage of supply voltage VCC terminal of the IC. Normally, the VCC voltage
is supplied from the transformer drive coil. Since this voltage is proportional to the secondary side output voltage,
it still operates even when the secondary side output has over voltage.
1) When the voltage input to the OVP terminal exceeds the threshold voltage (6.0 V typical) as the result of power
supply output abnormality, the protective circuit shuts down the internal reference voltage of the IC to stop all
of the controls and keeps this stop condition.
2) The OVP is released (reset) under the following conditions:
• Decreasing the supply voltage (VCC < 8.4 V typical: OVP release supply voltage)
The discharge circuit is incorporated so that the electric charge which is charged in the capacitor
connected to the OVP terminal can be discharged with the constant current of 5 µA (typical) for the next re-start.
Secondary side output voltage under normal operation VOUT
× V7
VCC terminal voltage under normal operation
V7 = Vth(OVP) + VZ
Vth(OUT) : Secondary side output overvoltage threshold
Vth(OVP) : OVP operation threshold
VZ
: Zener voltage (external parts of OVP terminal)
Vth(OUT) =
8
Voltage Regulators
AN8022L, AN8022SB
■ Application Notes (continued)
[2] Operation descriptions (continued)
3. Overvoltage protection circuit (OVP) (continued)
OVP
VTH
(to 6 V)
TIM/OVP terminal voltage
0V
Internal reference voltage
Time
(to 7.1 V)
(IC stop state)
0V
Time
(to 5 V)
Triangular wave oscillation
(to 2 V)
(IC stop state)
0V
Time
(to VCC)
IC output
(IC stop state)
0V
Time
Figure 2. Explanation of OVP operation
After AC rectification
Start resistor
R1
VCC
FRD
Load
OVP
VOUT
GND
Power supply output
Abnormal voltage applied from outside
It detects abnormal voltage applied from the outside to the
power supply output (the voltage which is higher than voltage
of the power supply output and may damage the load) by the
primary side of the bias coil and operates the OVP.
Figure 3
• Operating supply current characteristics
While the OVP is operating, the decrease of the supply current causes the rise of the supply voltage VCC , and
in the worst case, the guaranteed breakdown voltage of the IC (35 V) can be exceeded. In order to prevent the rise
of supply voltage, the IC is provided with such characteristics as the supply current rises in the constant resistance
mode. This characteristics ensure that the OVP can not be released unless the AC input is cut, if the supply voltage
VCC under OVP operation is stabilized over the OVP release supply voltage (which depends on start resistor
selection). (Refer to figure 4.)
9
AN8022L, AN8022SB
Voltage Regulators
■ Application Notes (continued)
[2] Operation descriptions (continued)
3. Over voltage protection circuit (OVP) (continued)
The current supply from the start resistor continues
as long as the voltage of the power supply input (AC)
is given.
After AC rectification
Start resistor
R1
After OVP starts operation, since the output is
stopped, this bias coil does not supply current.
VCC
* Select the resistance value so that the following
relationship can be kept by current supply from
the start resistor: VCC > VCC−OVP
VOUT
GND
ICC
At VCC-OVP (voltage under which OVP is released),
the operating current is temporarily increased.
This prevents VCC from exceeding its breakdown
voltage through the current from above mentioned.
VCC− OVP
VCC
Figure 4
4. Overcurrent protection circuit (OVP)
The overcurrent of the power supply output is proportional to the value of current flowing in the main switch
in the primary side (power MOSFET). Taking advantage of the above fact, by regulating the upper limit of the pulse
current flowing in the main switch, the circuit protects the parts which are easily damaged by the overcurrent.
For the current flowing in the main switch, the current detection is achieved by monitoring the voltage in both
ends of the low resistance, which is connected between the source of power MOSFET and the power supply GND.
When the power MOSFET is turned on and the threshold voltage of CLM (Current Limit) is detected, the
overcurrent protection circuit controls so that current can not flow further by turning off the output to turn off the
power MOSFET. The threshold voltage of CLM is approximately −200 mV (typical) under Ta = 25°C with respect
to GND of the IC. This control is repeated for each cycle. Once the overcurrent is detected, the off condition is
kept during that cycle, and it can not be turned on until the next cycle. The overcurrent detection method described
in the above is called pulse-by-pulse overcurrent detection. (Refer to figure 6.)
The R4, R5 and C3 in figure 5 construct the filter circuit, which
functions to remove the noise generated by the parasitic capacitance which is equivalently formed at turning-on of the power
MOSFET.
GND
R4
R5
C3
R3
CLM
Figure 5
• Notes on the detection level precision
This overcurrent detection level is reflected on the operating current level of the power supply overcurrent
protection. Therefore, if this detection level fluctuates with temperature or dispersion, the operating current level
of the power supply overcurrent protection also fluctuates. Since such level fluctuation increases the necessity of
withstand capability for the parts to be used and in the worst case it means the cause of destruction, the accuracy
of detection level is raised as much as possible for these ICs, the AN8022L and AN8022SB.
10
Voltage Regulators
AN8022L, AN8022SB
■ Application Notes (continued)
[2] Operation descriptions (continued)
4. Overcurrent protection circuit (OVP) (continued)
0
CLM (−)
Terminal
voltage
Time
VTH (−200 mV typ.)
Overshoot
due to
delay
Pulse width can not be made
shorter than this width due to delay
VOUT
Terminal
voltage
0
Time
Power
MOSFET
current
0
Time
Figure 6. Pulse-by-pulse overcurrent detector operation waveform
5. Soft start
At start of the power supply, the capacitor connected to the power supply output causes the power supply to
rise under overload condition. Under this condition, the power supply output is low. For the normal PWM control,
attempt is made to limit the current by the pulse-by-pulse over current protection so that the power supply output
could rise at maximum duty. However, pulses can not be made down to zero due to circuit delay. As a result, large
current flows in the mains switch (the power MOSFET) or in the diode in the secondary side, and in the worst case
these parts are damaged.
For this reason, soft start function in which the power supply output does not rise with maximum duty but rise
with gradually widening duty from the minimum one (0%) at the power supply start is adopted.
The use of this function requires more rise time of power supply output. However, it can extend the service
life of parts and raise the reliability of the power supply.
The soft start (SS) terminal is connected to the PWM input (hereinafter its voltage is referred to as VSS). In the
PWM, three voltages are input: the voltage to which the current feedback level is converted (hereinafter referred
to as VFB), the voltage determining the maximum duty (hereinafter referred to as VDTC). This voltage is determined
inside the IC), and the triangular wave oscillation voltage (hereinafter referred to as VCT). VSS , VFB and VDTC are
input in the non-reverse input (+) of the PWM comparator and VCT is input in the reverse input (−). Among the three
signals of the non-reverse input, the lowest one is selected for input to the PWM comparator.
The external capacitor (hereinafter referred to as CSS) is connected to the SS terminal. In the pre-start condition,
this capacitor is set to be sufficiently discharged by the transistor inside the IC.
When the supply voltage exceeds the start voltage to start the IC operation, charging is started in the CSS by
the constant current source inside the IC. Therefore VSS gradually rises from 0 V.
11
AN8022L, AN8022SB
Voltage Regulators
■ Application Notes (continued)
[2] Operation descriptions (continued)
5. Soft start (continued)
On the other hand, the VFB has high voltage because the power supply output is low. And, the VDTC is positioned
at the medium voltage of the triangular wave oscillation waveform as constant voltage. Therefore, at operation
starting, the VSS is input to the PWM comparator as the lowest voltage and is compared with the triangular wave
oscillation waveform.
As the result, the output of the IC generates the pulse of duty which gradually becomes large with the rise of
VSS from the minimum duty. (Refer to figure 7.)
However, when the VSS exceeds the VFB or VDTC , the duty of the output pulse depends on the VFB or VDTC .
The soft start function works only up to that point and after that the normal control comes.
VFB
VCT
VCT
VSS
VSS
VDTC
VFB
VFB
VDTC
0V
VOUT
0V
Figure 7. Soft start operation waveform
6. Timer latch
When the short-circuit or overload of the power supply output continues for a certain period, the pulse-by-pulse
overcurrent protection is not sufficient for protection of the transformer, Fast Recovery Diode (FRD), Schottky
Diode in the secondary side and the power MOSFET. For this reason, the timer latch function is employed, which
stops the power supply by hitting the OVP, when the overcurrent condition continues for a certain period.
The short-circuit or overload of the power supply output is monitored as the decrease of the power supply output
(at this time the pulse-by-pulse overcurrent protector is in the operating condition). The decrease of the power
supply output is detected as the decrease of current amount from the current feedback terminal of the normal
PWM control. When the decrease amount of this current exceeds a certain value, the comparator inside the IC
reverses to flow the constant current to the TIM/OVP terminal.
The external capacitor is connected to the TIM/OVP terminal. Electric charges are accumulated in this capacitor
to rise the OVP terminal voltage. When the OVP operating threshold voltage (6 V typical) is reached, the OVP starts
operation to stop the IC and keeps this stop condition. (Refer to Figure 8.)
• Timer period
The period from the time when an error of the power supply output is detected to the time when the OVP starts
operation (hereinafter referred to as timer period) should be longer than the rise time of the power supply. Since
at operation start the IC is in the same condition as the overload or output short-circuit condition, if the timer
period is shorter, the power supply works latch and can not start.
Therefore, the IC is designed so that the timer period can be set to any desired value with capacitance value of
the external capacitor connected to the TIM/OVP terminal. However, particular care should be taken, because too
large value of this capacitance may cause the breakdown of the power supply.
12
Voltage Regulators
AN8022L, AN8022SB
■ Application Notes (continued)
[2] Operation descriptions (continued)
6. Timer latch (continued)
VO
Power supply stop
Power supply
output voltage
Time
0
Power supply stop
IDS
Power MOSFET
current
Time
0
Power supply stop
VOVP
TIM/OVP
terminal
voltage
OVP
VTH = 6 V (typ.)
Time
0
Figure 8. Timer latch basic operation
7. Output Block
The AN8022L and AN8022SB employ the
output circuit using the totem pole (push-pull)
method, by which sink/source of current is performed with the NPN transistor as shown in figure
9, in order to drive the power MOSFET at high
Schottky barrier
speed.
diode
The maximum sink/source current is ±0.1 A
(DC) and ±1.0 A (peak). Even when the supply
voltage VCC is under the stop voltage, the sink
function works to ensure that the power MOSFET
Figure 9
be turned off.
For the current capability, the peak current is major concern, and the particularly large current is not required
normally: The power MOSFET which works as load on the output is capacitive load. Therefore, in order to drive
it at high speed, the large peak current is required. However, after charge/discharge particularly large current is not
required to keep that condition.
For the AN8022L or AN8022SB, capacitance value of the power MOSFET used is taking into account, and
the capability of peak value ±1 A is ensured.
The parasitic LC of the power MOSFET may produce ringing which makes the output pin go under the GND
potential. When the decrease of the output pin becomes larger than the voltage drop of diode and its voltage
becomes negative, the parasitic diode consisting of the substrate and collector of the output NPN turns on. This
phenomenon may cause the malfunction of the device. In such a case, the Schottky barrier diode should be
connected between the output and GND.
13
AN8022L, AN8022SB
Voltage Regulators
■ Application Notes (continued)
[3] Design reference data
1. Setting the output frequency
The output is controlling the triangular oscillation with PWM control: Triangular oscillation frequency =
Output frequency
CT (C6) = Capacitor terminal for triangular oscillation
RT (C7) = Resistor terminal for triangular oscillation
[Reference calculation formula]
VOSC − H−
C6 · V
T1 = T 2 =
2IRT (charge/discharge current)
V
Since the IRT is given by rough calculation of 2.5 V/RT and
V becomes approximately 3 V, the output frequency is obtained
VOSC − L−
in the following equation:
1
IRT
5
fOUT =
=
=
T1
T2
C6 · V
6 · C6 · R7
T1 + T2
However, it may deviate a little from the design value due to delay of the internal circuit.
(Reference value)
fOUT = approximately 200 kHz
at CT (C6) = 220 pF and RT (R7) = 19 kΩ
2. Setting the timer latch period
The timer latch period t, the period from the time when an abnormality of the power supply output is detected
to the time when the overvoltage protector is activated, can be set to any desired value by using the external
capacitance CTIM (C2) based on the following equation:
TIM/OVP = Capacitor terminal for timer latch period setting
[Reference calculated value]
C2 · VTIM
t=
[s]
ITIM
VTIM = 6 V (typ.): Over voltage protection threshold value
ITIM = Timer latch charge current
(Varies depending on R7 value, at R7 = 19 kΩ)
ITIM = 30 µA (typ.)
3. Setting the soft start time
• Soft start charge current
Most of the conventional ICs are charged by using the internal resistor from the internal reference voltage, or
by using the constant current source which is determined by the internal resistance. However, the above charging
method suffers from problems on dispersion or temperature change and can not ensure the soft start time. For this
reason, the AN8022L and AN8022SB use the following method: The soft start charge current is given from the
constant current source used in the internal triangular wave oscillation circuit. In addition, the above constant
current source is stable with respect to dispersion or fluctuation with temperature because it has the current value
which is determined by the external resistor and the terminal voltage given from the resistor-divider of internal
reference voltage. However, for this method, particular care should be taken on the application: Since each time
the setting of oscillation frequency is changed, the soft start constant should be also changed.
SS (C5) = Capacitor terminal for soft start
[Reference calculation formula]
t=
C5 · VSS
ISS
[s]
ISS = Soft start charging current
(Varies depending on R7 value, at R7 = 19 kΩ)
ISS = 30 µA (typ.)
VSS = 2.0 V, at duty = 0%
VSS = 4.1 V, at maximum duty
14
Voltage Regulators
AN8022L, AN8022SB
■ Application Notes (continued)
[3] Design reference data (continued)
4. Start circuit
The start time from the power-on to the actual start can be set by using the values of R1 and C1. Too long start
time makes the power supply to rise slowly.
[Setting the start resistor R1]
1) When the overload shutting-off condition is kept, the shut-off bias current (OVP operating bias current) of the
AN8022L and AN8022SB is 550 µA (typical) at VCC = 10 V. Therefore, set the R1 as shown in the following
equation :
VIN − 10 V
R1 <
550 µA
2) When automatic reset is desired after the overload shut-off, the standby current of the AN8022L and AN8022SB
is 70 µA (typical) at VCC = 12 V. Therefore, set the R1 as shown in the following equation :
VIN − 10 V
VIN − 12 V
< R1 <
550 µA
70 µA
[Setting the C1]
When the AN8022L or AN8022SB is started, the operating supply current of 7.5 mA is required at VCC = 18 V.
The current should be supplied with the discharge current of the C1 during the period from the soft start time
up to the time when the supply current is supplied from the auxiliary bias coil. Therefore, set the C1 as shown in
the following equation:
(VCC(START) − VCC(STOP)) · C1
> Soft start time
7.5 mA
15
AN8022L, AN8022SB
Voltage Regulators
■ Application Circuit Example
R8
C1
TIM/
8 OVP
6 VOUT
C2
DZ1
Start-up resistor
R1
VIN
R2
R3
DI
FRD
Photocoupler
FRD
Filter
2 RT
AC input
C4
C6
3 CT
C5
1 SS
R6
9 IFB
R7
AN8022L
R4
R5
4 CLM
VCC 7
C3
5 GND
16
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