Universal-Input/15 W 50 kHz
Flyback Switching Regulators
Data Sheet
28103.42b
STR-A6251
AND
STR-A6252
Sanken Power Devices
from Allegro MicroSystems
Switching
Regulators
ABSOLUTE MAXIMUM RATINGS
at T
A
= +25C
Control Supply Voltage, V
CC
. . . . 36 V
Drain-Source Voltage, V
DSS . . . . . .
650 V
Drain Switching Current, I
D
STR-A6251 . . . . . . . . . . . . . . 2.5 A*
STR-A6252 . . . . . . . . . . . . . . 3.0 A*
Peak Drain Switching Current, I
DM
STR-A6251 . . . . . . . . . . . . . . . 2.5 A
STR-A6252 . . . . . . . . . . . . . . . 3.0 A
Single-Pulse Avalanche Energy, E
AS
STR-A6251 . . . . . . . . . . . . . . 72 mJ
STR-A6252 . . . . . . . . . . . . . 123 mJ
S/OCP Voltage Range,
V
OCP
. . . . . . . . . . . . 0.3 V to +6 V
FB/CC/OLP Voltage Range,
V
FB/OLP
. . . . . . . . . . 0.3 V to +12 V
FM Voltage Range,
V
FM
. . . . . . . . . . . . . 0.3 V to +6 V
Package Power Dissipation, P
D
control (V
CC
I
CC(ON)
) . . . . . 0.15 W
MOSFET (V
DSS
I
D
) . . . . . . 1.35 W
total . . . . . . . . . . . . . . . . . . . . 1.5 W
MOSFET Channel Temp., T
J
. +150C
Internal Frame Temp., T
F
. . . . +125C
Storage Temperature Range,
T
S
. . . . . . . . . . . . -40C to +125C
* Drain switching current is limited by tem-
perature (page 2) and safe operating area
(page 4).
The STR-A6251 and STR-A6252 are 50 kHz PWM topology (with
5% frequency jittering for minimum EMI) regulators specifically
designed to satisfy the requirements for increased integration and
reliability in flyback converters. They incorporate a primary control and
drive circuit with avalanche-rated power MOSFETs. The STR-A6252
features higher allowable switching current and lower on-resistance.
The STR-A6251 is also available for 67 kHz operation.
Covering the power range from below 21 watts or 24 watts for a
230 VAC input, or to 15 or 20 watts for a universal (85 to 264 VAC)
input, these devices can be used in a wide range of applications, from
DVD players and VCR player/recorders to ac adapters for cellular
phones and digital cameras. An auto-burst standby function reduces
power consumption at light load, while multiple protections, including
the avalanche-energy guaranteed MOSFET, provide high reliability of
system design.
Cycle-by-cycle current limiting, undervoltage lockout with hyster-
esis, overvoltage protection, and thermal shutdown protect the power
supply during the normal overload and fault conditions. Overvoltage
protection and thermal shutdown are latched after a short delay. The
latch may be reset by cycling the input supply. Low start-up current and
a low-power standby mode selected from the secondary circuit completes
a comprehensive suite of features. Both devices are provided in an 8-pin
mini-DIP plastic package with pin 6 removed.
FEATURES
AND
BENEFITS
50 kHz PWM with 5% Frequency Jittering
Cost Reduction of EMI Noise Filtering
Rugged 650 V Avalanche-Rated MOSFET
Simplified Surge Absorption
No V
DSS
Derating Required
Choice of
r
DS(on)
(2.8
or 3.95 maximum)
Auto-Burst Mode for Stand-By Operation or Light Loads
Less Transformer Audible Noise
Built-In Leading Edge Blanking
Soft Start and Low Start-Up Current
Start-Up Circuit Disabled in Operation
Low Operating Current (4 mA max)
continued
Always order by complete part number, e.g.,
STR-A6251 .
STR-A6251 and STR-A6252
Universal-Input/15 W 50 kHz
Flyback Switching Regulators
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036
2
Switching
Regulators
Copyright 2005 Allegro MicroSystems, Inc.
FUNCTIONAL BLOCK DIAGRAM
FEATURES
AND
BENEFITS (cont'd)
Automatic Burst Stand-By (intermittent operation)
Input Power <0.1 W at No Load
Auto-Bias Function
Stable Burst Operation Without Generating Interference
Internal Off-Timer Circuit
Built-In Constant-Voltage/Constant Current
Multiple Protections:
Pulse-by-Pulse Overcurrent Protection (OCP)
Overload Protection (OLP) with Auto Restart
Latching Overvoltage Protection (OVP)
Undervoltage Lockout (UVLO) with Hysteresis
Latching Thermal Shutdown (TSD)
Molded Small-Size 8-Pin Package
For Low-Height SMPS
This data sheet is based on Sanken data sheet SSE-23297 and SSE-23298.
STR-A6251 and STR-A6252
Universal-Input/15 W 50 kHz
Flyback Switching Regulators
www.allegromicro.com
3
Switching
Regulators
ELECTRICAL CHARACTERISTICS at T
A
= 25C, V
CC
= 18 V (unless otherwise specified).
Pin
Ratings
Characteristic
No.
Symbol
Test Conditions
Min
Typ
Max
Units
Drain-to-Source Breakdown Volt.
8 - 1
V
(BR)DSS
I
D
= 300 A,
650
-
-
V
V
1
V
3
= 0 V (short)
Drain Leakage Current
8
I
DSS
V
DS
= 650 V,
-
-
300
A
V
1
V
3
= 0 V (short)
On-State Resistance
8 - 1
r
DS(on)
STR-A6251, I
D
= 0.4 A
-
-
3.95
STR-A6252, I
D
= 0.4 A
-
-
2.8
MOSFET Switching Time
8 - 3
t
f
-
-
-
250
ns
Operation-Start Voltage
5 - 3
V
CC(ON)
V
CC
= 0
15.7 V
12.9
14.3
15.7
V
Operation-Stop Voltage
5 - 3
V
CC(OFF)
V
CC
= 15.7
9 V
9.0
10
11
V
Maximum Switching Frequency
8 - 3
f
osc(max)
-
45
50
55
kHz
Frequency-Jitter Deviation
8 - 3
f
osc
-
3.0
5.0
7.0
kHz
Maximum ON Duty Cycle
8 - 3
D max
-
70
76
82
%
Circuit Current in Operation
5
I
CC(ON)
-
-
-
4.0
mA
Circuit Current in Non-Operation
5
I
CC(OFF)
V
CC
= 12 V
-
14
25
A
FM Voltage
2 - 3
V
FMH
fosc = f
osc(max)
4.0
4.5
5.0
V
V
FML
fosc < f
osc(max)
3.2
3.6
4.0
V
FM Current
2
I
FMH
-7.7
-11.0
-14.3
A
I
FML
7.7
11.0
14.3
A
OCP Threshold Voltage
1 - 3
V
OCP
-
0.67
0.74
0.81
V
Leading Edge Blanking Time
8 - 3
t
bw
-
220
320
420
ns
Burst Threshold Voltage
4 - 3
V
burst
-
1.00
1.12
1.24
V
OLP Threshold Voltage
4 - 3
V
OLP
-
7.3
8.6
9.9
V
Current at OLP Operation
4
I
OLP
-
-12
-17
-22
A
OLP Delay Time
4 - 3
t
OLP
-
0.84
1.20
1.56
s
Maximum FB Current
4
I
FB(MAX)
-
220
310
400
A
CC Set Voltage
4 - 3
V
SET(CC)
-
4.9
5.8
6.7
V
CC Reset Voltage
4 - 3
V
RES(CC)
V
CC
= 25 V
3.5
3.9
4.3
V
Start-Up Current
5
I
startup
V
CC
= 13 V
0.77
1.10
1.43
mA
OVP Operation Voltage
5 - 3
V
CC(OVP)
V
CC
= 18
35.2 V
28.8
32.0
35.2
V
OVP/TSD Latch Sustaining Current
5
I
CC(H)
V
CC
=35.2
8.6 V
-
-
270
A
OVP/TSD Latch Release Voltage
5 - 3
V
CC
V
CC
=35.2
5.9 V
5.9
7.2
8.6
V
Thermal Shutdown
-
T
J
-
125
140
-
C
Thermal Resistance
-
R
JF
-
-
-
52
C/W
Typical values are given for circuit design information only.
Negative current is defined as coming out of (sourcing) the specified terminal.
STR-A6251 and STR-A6252
Universal-Input/15 W 50 kHz
Flyback Switching Regulators
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036
4
Switching
Regulators
Avalanche energy is measured at V
DD
= 99 V,
L = 20 mH, I
L
= 2.5 A.
MOSFET TYPICAL CHARACTERISTICS
STR-A6252
STR-A6251
Avalanche energy is measured at V
DD
= 99 V,
L = 20 mH, I
L
= 3.0 A.
Recommended Operating Conditions
Operating Ambient Temperature ....... -20C to +100C
Operating Junction Temperature ....... -20C to +125C
Maximum Frame Temperature ........................ +115C
For the availability of parts meeting -40C requirements, contact
Allegro's Sales Representative.
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