Voltage Regulators
1
AN8028
Self-excited RCC pseudo-resonance type
AC-DC switching power supply control IC
s
Overview
The AN8028 is an IC developed for controlling the
self-excited switching power supply employing the RCC
pseudo-resonance type control method.
It is compact, equipped only with the necessary mini-
mum functions.
The maximum on-period and the minimum off-pe-
riod can be set separately by using the external capacitor
and resistor respectively.
It is suitable for the power supply of AV equipment.
s
Features
·
Operating supply voltage range:
Stop voltage (8.6 V typical) to 34 V
·
Output block employs the totem pole system.
·
Power MOSFET can be directly driven.
(output peak current:
±
1 A maximum)
·
Small pre-start operating current (95
µ
A typical) allows using a small size start resistor.
·
Built-in pulse-by-pulse overcurrent protection function
·
Incorporating the protection circuit against malfunction at low voltage (start/stop: 14.9 V/8.6 V)
·
Built-in overvoltage protection function (externally resettable)
·
Built-in timer latch function
·
Equipped with frequency (VF) control function.
·
9-pin single inline package expands the freedom of board design
s
Applications
·
Televisions, facsimiles, printers, scanners, video equipment
s
Block Diagram
SIP009-P-0000C
Unit: mm
9
8
7
6
5
4
3
2
1
0.3
+0.1
0.05
23.3±0.3
6.0±0.3
2.4±0.25
3.3±0.25
1.5±0.25
0.5±0.1
2.54
1.5±0.25
1.4±0.3
3.0±0.3
30
°
V
REF
(7.1 V)
U.V.L.O.
8.6
V
1.5
V
Current source
0.1 V
CLM
TIM
Q
I
FB
Switch
diode
Q
R
S
RS
latch
Signal
IN
IN
V
OUT
6
GND
5
CLM
4
TDL
1
FB
9
TIM/OVP
8
V
CC
7
T
OFF
2
TO
N
3
0.7 V
0.32 V
Low-side
clamp
0 V
High-side
clamp
2.8 V
2
AN8028
Voltage Regulators
s
Absolute Maximum Ratings
Parameter
Symbol
Rating
Unit
Supply voltage
V
CC
35
V
Peak output current
I
6PEAK
±
1
A
Power dissipation
P
D
874
mW
Operating ambient temperature
*
T
opr
-
30 to
+
85
°
C
Storage temperature
*
T
stg
-
55 to
+
150
°
C
Pin No.
Symbol
Description
1
TDL
Transformer reset detection
2
TOFF
Pin for connecting C and R to set minimum off-period
3
TON
Pin for connecting C to set minimum on-period
4
CLM
Input pin for overcurrent protection detection
5
GND
Grounding pin
6
V
OUT
Output pin
7
V
CC
Power supply voltage pin
8
TIM/OVP
Pin for use both overvoltage protection circuit and timer latch
9
FB
Photocoupler connection pin for error voltage feedback
s
Pin Descriptions
Note) *: Expect for the operating ambient temperature and storage temperature, all ratings are for T
a
=
25
°
C.
s
Recommended Operating Range
Parameter
Symbol
Range
Unit
Supply voltage
V
CC
From stop voltage to 34
V
s
Electrical Characteristics at V
CC
=
18 V, T
a
=
25
°
C
Parameter
Symbol
Conditions
Min
Typ
Max
Unit
U.V.L.O. start supply voltage
V
7START
13.4
14.9
16.4
V
U.V.L.O. operation stop supply voltage
V
7STOP
7.7
8.6
9.5
V
U.V.L.O. start to stop supply voltage
V
7
5.7
6.3
6.9
V
OVP operation threshold voltage
V
8OVP
6.1
7.3
8.5
V
OVP release voltage
V
7OVP
7.4
8.2
9
V
OVP operating circuit current 1
I
7OVP1
V
CC
=
9.1 V, V
OVP
=
8.5 V
0.56
0.79
1.02
mA
OVP operating circuit current 2
I
7OVP2
V
CC
=
20 V, V
OVP
=
8.5 V
5.9
7.7
9.5
mA
TDL threshold voltage
V
1TDL
0.22
0.32
0.42
V
TDL upper limit clamp voltage
V
1TDL/H
I
TDL
=
3mA
2
2.8
3.6
V
TDL lower limit clamp voltage
V
1TDL/L
I
TDL
= -
3mA
-
0.3
0
0.3
V
CLM threshold voltage
V
4CLM
-
220
-
200
-
180
mV
3
Voltage Regulators
AN8028
s
Electrical Characteristics at V
CC
=
18 V, T
a
=
25
°
C (continued)
Parameter
Symbol
Conditions
Min
Typ
Max
Unit
TON maximum on-period current
I
3TON
FB terminal
=
open
-
135
-
110
-
85
µ
A
TON terminal
=
GND
TON upper limit voltage
V
3TON/H
FB terminal
=
open
0.55
0.7
0.85
V
TON lower limit voltage
V
3TON/L
FB terminal
=
open
-
0.1
0.05
0.2
V
TOFF upper limit voltage
V
2TOFF/H
0.7
0.9
1.1
V
TOFF lower limit voltage
V
2TOFF/L
-
0.1
0.05
0.2
V
Output oscillation frequency
f
OSC
C
ON
=
2 200 pF, R
OFF
=
1.5 k
55
65
75
kHz
C
OFF
=
1 000 pF
Output current feedback current gain
G
IFB
I
FB
=
-
1 mA
5.05
6.8
8.55
Pre-start low-level output voltage
V
6STB/L
V
CC
=
10 V, I
OUT
=
10 mA
1
1.25
V
Low-level output voltage 1
V
6L(1)
I
OUT
=
10 mA
0.9
2
V
Low-level output voltage 2
V
6L(2)
I
OUT
=
100 mA
1.1
2.2
V
High-level output voltage 1
V
6H(1)
I
OUT
=
-
10 mA
15.7
16.5
V
High-level output voltage 2
V
6H(2)
I
OUT
=
-
100 mA
15.5
16.3
V
Pre-start circuit current
I
7STB
V
CC
=
12V
55
95
135
µ
A
Circuit current 1
I
7OPR(1)
V
CC
=
18 V
8.55
11.5
14.3
mA
TON terminal
=
GND
FB terminal
=
open
Circuit current 2
I
7OPR(2)
V
CC
=
34 V
9.6
12.5
15.4
mA
TON terminal
=
GND
FB terminal
=
open
TDL flowing-out current
I
1TDL
V
TDL
=
0.5 V
-
5
0
µ
A
Pin No.
Equivalent circuit
Description
I/O
1
TDL:
I
Transformer reset detection terminal.
When the transformer reset is detected and low
is inputted into the terminal, the output of the IC
(V
OUT
) becomes high. However, low-level sig-
nal under the minimum off-period determined
by the T
OFF
is ignored.
2
TOFF:
Terminal for connecting the resistor and capaci-
tor for determining the minimum off-period (low)
of the IC output (V
OUT
).
An equation for approximate calculation of the
minimum off-period (T
OFF
) is as follows:
T
OFF
=
2.2
×
C
×
R
C: External capacitance
R: External resistance
s
Terminal Equivalent Circuits
V
REF
High-
side
clamp
Low-
side
clamp
1
V
CC
Comp.
0.1 V
2
4
AN8028
Voltage Regulators
Pin No.
Equivalent circuit
Description
I/O
3
TON:
Terminal for connecting the capacitor for deter-
mining the maximum on-period (high) of the IC
output (V
OUT
). An equation for approximate
calculation of the maximum on-period (T
ON
) is
as follows:
T
ON
=
6 500
×
C
C: External capacitance
4
CLM:
I
Input terminal for detection of the pulse-by-
pulse overcurrent protection.
Normally, it is recommended that a filter be
attached externally.
5
GND:
Grounding terminal.
6
V
OUT
:
O
Output terminal for directly driving the power
MOSFET.
It uses the totem pole type output.
The maximum rating of the output current:
Peak:
±
1 A
DC:
±
150 mA
7
V
CC
:
Terminal for applying power supply voltage.
It monitors the supply voltage and has the opera-
tion threshold of start/stop/OVP reset.
s
Terminal Equivalent Circuits (continued)
FB
Comp.
0.7 V
3
V
CC
V
REF
(
-
)
Comp.
4
V
REF
5
6
V
CC
7
5
Voltage Regulators
AN8028
Pin No.
Equivalent circuit
Description
I/O
8
TIM/OVP:
I
Terminal for use both OVP (overvoltage protec-
tion circuit) and timer latch.
[OVP]
When overvoltage signal of the power supply is
detected and high is inputted to the terminal, it
turns off the internal circuit. At the same time, it
holds that condition (latch). To reset the OVP
latch, the V
CC
should be decreased to a voltage
lower than the release voltage.
[Timer latch]
It detects the output voltage fall due to the
overcurrent condition of the power supply out-
put through the current level inputted to IFB.
When the I
IFB
decreases under the current of
certain value, the charge current flows in the
capacitor which is connected to this terminal.
Then, when the capacitor is charged up to the
threshold voltage of the OVP, the OVP works so
that the IC could keep the operation stop condi-
tion.
9
FB:
I
Terminal for connecting the photocoupler for
error voltage feedback of the power supply out-
put.
It is possible to cancel about 180
µ
A of the dark
current of photocoupler.
s
Terminal Equivalent Circuits (continued)
5
µ
A
7.3 V
Comp.
8
V
CC
TON
9
V
CC
s
Application Notes
[1] 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 start resistor, the IC starts opera-
tion. 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 gen-
erated 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 (C8) connected to V
CC
.
Start
voltage
Stop
voltage
a
b
Start condition
Start failure
c
Voltage supplied
from bias coil
Before start
Start
V
CC
V
OUT
GND
After AC rectification
Figure 1
Start resistance
R1
C8
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