AP3785T

AP3785T
PRIMARY SIDE REGULATED SWITCHING MODE POWER SUPPLY CONTROLLER
Description
Pin Assignments
NEW PRODUCT
The AP3785T is a high performance AC/DC power supply controller
for battery charger and adapter applications. It can meet less than
10mW standby power for “Super Star” charger criteria. The device
uses Pulse Frequency Modulation (PFM) method to build
discontinuous conduction mode (DCM) flyback power supplies.
(Top View)
The AP3785T provides accurate constant voltage (CV), constant
current (CC) and outstanding dynamic performance without requiring
an opto-coupler. It also eliminates the need of loop compensation
circuitry while maintaining stability.
CS
1
8
FB
EM
2
7
CBC
VCC
3
6
OTP
OUT
4
5
GND
The AP3785T is equipped with both cable drop compensation
function to meet various cables with different lengths and gauges and
adjustable line voltage compensation function.
SO-8
When AP3785T is used with AP4341 or synchronous rectifier series
(for example APR343 + MOSFET, APR3415, APR34330), better
Features
under-shoot performance and higher conversion efficiency can be
achieved.
The AP3785T has internal over temperature protection for itself, and
also provides dedicated pin for external over temperature protection.
This IC is available in SO-8 package.

Primary Side Control for Eliminating Opto-coupler

10mW No-load Input Power

Flyback Topology in DCM Operation

External Adjustable Line Compensation for CC

External Adjustable Cable Compensation for CV

Multiple PWM/PFM Control Mode to Improve Audio Noise and
Efficiency

VCS Jitter to Reduce System EMI

Valley-on for the Higher Efficiency and Better EMI

Applications


Adapter/Chargers for Shaver, Cell/Cordless Phones, PDAs, MP3
and Other Portable Apparatus
Multiple Protections:

Over Voltage Protection (OVP)

Output Short Circuit Protection (SCP)

Transformer Saturation Protection (TSP) via Primary Peak
Standby and Auxiliary Power Supplies
Current Limitation

Notes:
OTP and External Over Temperature Protection (OTP)

Matching AP4341 with Schottky
Synchronous Rectifier Solution

SO-8 Package

Totally Lead-free & Fully RoHS Compliant (Notes 1 & 2)

Halogen and Antimony Free. “Green” Device (Note 3)
or
APR343/APR3415
1. No purposely added lead. Fully EU Directive 2002/95/EC (RoHS) & 2011/65/EU (RoHS 2) compliant.
2. See http://www.diodes.com/quality/lead_free.html for more information about Diodes Incorporated’s definitions of Halogen- and Antimony-free, "Green"
and Lead-free.
3. Halogen- and Antimony-free "Green” products are defined as those which contain <900ppm bromine, <900ppm chlorine (<1500ppm total Br + Cl) and
<1000ppm antimony compounds.
AP3785T
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AP3785T
Typical Applications Circuit (Note 4)
FR1
L1
TR1
C4
R1
D1,D2,
D3,D4
+
C1
C2
D8
R9
R11
D7
+
R12
R10
NEW PRODUCT
D6
C3
+
C6
IC2
AP4341
R2
L2
+
C5
OUT VCC
GND
VO
R7
Q1
IC1
AP3785T
R8
VCC
OTP
NTC1
R5
OUT
CBC
CY1
D5
FB
GND
EM
CS
R6
R4
R3
With Schottky (VOUT=5V/1A or 2A)
FR1
L1
T1
C4
R1
C2
C9
D7
+
C5
R2
L2
D6
C3
R7
CBC
GND
OUT
R5
IC2
VDET
VCC
D5
FB
C6
C7
R13
APR343
DRISR
OTP
R8
+
Q2
R12
Q1
IC1
AP3785T
NTC1
+
R14
R10
AREF
C1
VCC
+
GND
D1,D2,
D3,D4
R9
R11
EM
CS
R6
R4
R3
C8
CY1
With Synchronous Rectifier (VOUT=5V/2A)
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AP3785T
Typical Applications Circuit (Note 4, Cont.)
FR1
L1
T1
C4
R1
D1,D2,
D3,D4
NEW PRODUCT
+
C1
C2
R9
C5
+
D7
+
C9
R10
D6
C3
R7
R12
Q1
IC1
AP3785T
OTP
VCC
CBC
NTC1
GND
R8
OUT
D5
R14
IC2
APR34XX
R2
L2
C6
+
DRAIN
GND
DRAIN
GND
VDET
VCC
DRISR
AREF
C7
C8
R13
R5
FB
R 11
CY1
EM
CS
R6
R4
R3
With Synchronous Rectifier (i.e. APR34330 for VOUT=5V/1.5A, APR3415 for VOUT=5V/2A and APR34309 for VOUT=5V/3A)
Note 4: If the OTP pin is not connected to the NTC resistor, the external OTP function will not work and the IC can still work normally with internal OTP.
Pin Descriptions
Pin Number
Pin Name
Function
1
CS
Sense primary side current for turning off the external power MOSFET and deliver a voltage
proportional to the line voltage for compensation from FB pin
2
EM
Connected to the source of external power MOSFET
3
VCC
The power supply for the IC. In order to get the correct operation of the IC, a capacitor with low
ESR should be placed as close as possible to the VCC pin
4
OUT
Turn on and turn off the external power MOSFET
5
GND
The ground of the IC
6
OTP
The external over temperature protection
7
CBC
This pin connects a resistor to GND for output cable voltage drop compensation
8
FB
AP3785T
Document number: DS37552 Rev. 4 - 2
Voltage feedback. The CV and CC regulation are realized based on the voltage sampling of this
pin
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AP3785T
Functional Block Diagram
VCC
OTP
6
External OTP/
OTP/VCC OVP/
FB OVP/CBC short
OTP
Dmin
OCKP
SCP
FB up_resistance open
RCS Short Protection
Transformer Saturation
Protection
NEW PRODUCT
3
Fast Auto-recovery
Transformer Saturation
Protection
0.1V
Regulator
&
Bias
&
Latch
Auto-recovery
UVLO
RCS Short Protection
COMP
tONS
Detector
PFM
tONS
LVCC
NL
Pro
VDD
Dynamic
Response
8
FB
Dyn
Pro
Constant Voltage
Control
EA
tDELAY
Dyn
VREF
Q
R
VCABLE
PFM
CV_CTRL
Valley
ON
CC_CTRL
S
4
OUT
Peak Current
Control & LEB
Line
Compensation
Shutdown
2
Driver
EM
VLINE
1
VCS_REF
VCS
tONP
tONS
Transformer Saturation
Protection
tDELAY
Enable
Constant Current
Control
R
Q
CC_ CTRL
S
RCS Short Protection
5
DAC
GND
tDELAY
VLOAD
Cable
Compensation
DAC
VCS
COMP
COMP
VCS(MAX)
0.1V
CS
No Load
Detection
NL
VLOAD
7
CBC
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AP3785T
Absolute Maximum Ratings (Note 5)
Symbol
Rating
Unit
Voltage at VCC to GND
-0.3 to 30
V
–
Voltage at OUT, EM to GND
-0.3 to 22
V
–
Voltage at CS, CBC,OTP to GND
-0.3 to 7.4
V
VFB
FB Input Voltage
-0.7 to 7.4
V
TJ
Operating Junction Temperature
-40 to +150
ºC
TSTG
Storage Temperature
-65 to +150
ºC
TLEAD
Lead Temperature (Soldering, 10 sec)
+300
ºC
θJC
Thermal Resistance (Junction to Case)
20
ºC/W
θJA
Thermal Resistance (Junction to Ambient)
(Note 6)
100
ºC/W
–
ESD (Human Body Model)
4000
V
–
ESD (Machine Model)
200
V
NEW PRODUCT
VCC
Notes:
Parameter
5. Stresses greater than those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and
functional operation of the device at these or any other conditions beyond those indicated under “Recommended Operating Conditions” is not implied.
Exposure to “Absolute Maximum Ratings” for extended periods may affect device reliability.
6. The device is mounted on FR-4 substrate PCB, 2 oz copper, with 1 inch2 pad.
Electrical Characteristics (@VCC=15V, TA=+25°C, unless otherwise specified.)
Symbol
Parameter
Conditions
Min
Typ
Max
Unit
STARTUP AND UVLO SECTION
VTH_ST
VOPR(MIN)
Startup Threshold
–
11
13
15
V
Minimum Operating Voltage
–
5.5
5.9
6.3
V
STANDBY CURRENT SECTION
IST
Startup Current
VCC=VTH_ST-1V before
startup
0
0.2
0.6
ICC_NL
Standby Current
At no load
5
17.5
30
ICC_OPR
Operating Current
Static current
350
450
550
A
DRIVING OUTPUT SECTION
VGATE
ISOURCE_PEAK
RDS(ON)
Gate Voltage
–
9
10.5
12
V
Peak Driver Source Current
–
15
20.5
26
mA
Sink Resistance
–
2
2.3
2.6

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AP3785T
Electrical Characteristics (Cont.) (@VCC=15V, TA=+25°C, unless otherwise specified.)
Symbol
Parameter
Conditions
Min
Typ
Max
Unit
–
–
80
kHz
40% to 100% full load
4.8
5.2
5.7
s
NL Mode to 8% full load
2.4
2.7
3.0
s
OPERATING FREQUENCY SECTION (NL MODE TO FULL LOAD)
fS(MAX)
The Maximum Operating Frequency
tsample_H
100% full load
Sample Time
tsample_L
NEW PRODUCT
OPERATING FREQUENCY SECTION (NL MODE)
VCBC(EN)
CBC Pin Voltage to Enter NL Mode
–
55
60
65
mV
tOFF(EN)
Off Time to Enter NL Mode
From the end of tONS
168
224
280
s
tOFF(EX)
Off Time to Exit NL Mode
From the end of tONS
168
224
280
s
4.5
5
5.5
%
1.8
2
2.2
kHz
40% to 100% full load
537
565
593
mV
0% to 8% full load
243
255
267
mV
FREQUENCY JITTER
ΔVCS/VCS
VCS Modulation
NL to full load
fMOD
VCS Modulation Frequency
CURRENT SENSE SECTION
VCS_H
VCS_L
Peak Current Sense Threshold
Voltage
RLINE
Built-in Line Compensation Resistor
(Note 8)
108
120
132

tLEB
Leading Edge Blanking
–
400
625
850
ns
Feedback Threshold Voltage
Closed loop test of VOUT
2.45
2.50
2.55
V
Maximum CBC Voltage for Cable
Compensation
–
1.4
1.45
1.5
V
Tested @ VFB=2V
–
4/8
–
–
From the end of tONS
20
27
34
Trigger Voltage for Dynamic
Function
Delay Time for Dynamic
Function
–
40
62.5
85
mV
From the end of tONS
99
127
155
s
Under Voltage of FB Pin for VCS_H
–
2.23
2.27
2.32
V
CONSTANT VOLTAGE SECTION
VFB
VCBC(MAX)
CONSTANT CURRENT SECTION
tONS/tSW
Secondary Winding Conduction
Duty
VALLEY-ON SECTION
tVAL-ON
Valid Off Time of Valley-on
s
DYNAMIC SECTION
VTRIGGER
tDELAY
VUV_H
PROTECTION FUNCTION SECTION
VFB(OVP)
Over Voltage Protection at FB Pin
–
3.5
3.75
4
V
VCC(OVP)
Over Voltage Protection at VCC Pin
–
27
28.5
30
V
tONP(MAX)
Maximum Turn-on Time
–
14
18
22
s
tOFF(MAX)
Maximum Off Time
–
11
14
17
ms
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AP3785T
Electrical Characteristics (Cont.) (@VCC=15V, TA=+25°C, unless otherwise specified.)
Symbol
Min
Typ
Max
Unit
–
135
150
165
mV
(Note 7)
1.8
2
2.2
V
Conditions
1.57
1.61
1.65
V
–
32
43
54
ms
Maximum Typical Time under VFB(SCP)
–
43
57
71
ms
VOTP
External OTP Shutdown Threshold
–
0.49
0.52
0.55
V
VOTP_REC
External OTP Recovery Threshold
–
0.99
1.05
1.11
V
IOTP
External OTP Shutdown Current
–
94
102
110
µA
TOTP
Shutdown Temperature
–
+125
+135
+145
ºC
THYS
Temperature Hysteresis
–
+37
+40
+43
ºC
VFB(SCP)
Short Circuit Protection
VFB @ Hiccup
tSCP(MIN)
Minimum Typical Time under VFB(SCP)
tSCP(MAX)
VCS(MIN)
VEM(MAX)
NEW PRODUCT
Parameter
Minimum Peak Current Sense Voltage
at tONP(MAX)
Maximum EM Voltage for Transformer
Saturation Protection
Notes:
7. These parameters are not 100% tested, guaranteed by design and characterization.
8. Line compensation voltage on CS reference: Δ VCS _ REF  0.35 
RLINE
 VAUX
RFB1  RLINE
Operation Principle Description
1.
Start-up Circuit
VBULK
VBULK
R13
R13
R15
R15
C3
D8
R9
C3
D8
Q1
VCC
Q1
I SOURCE
OUT
OUT
EM
VDD
R9
VCC
OUT
OUT
EM
CS
CS
(a)
(b)
Figure 1. Start-up Circuit
Figure 1 (a) shows the Startup Phase
•
Before VCC reaches VTH(ST), VDD is zero and EM to CS pin is open.
•
C3 is charged by ISOURCE.
•
The resistance of R13 and R15 should be high enough to reduce the power dissipation.
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Operation Principle Description (Cont.)
Figure 1 (b) shows the Normal Operation Phase
•
When VCC reaches VTH(ST), VDD is high and EM to CS pin is short.
•
•
The voltage of EM pin is lower than 1V so that the four diodes in chip are open.
C3 is supplied by Aux. winding of transformer.
NEW PRODUCT
2. Operation Mode
The typical application circuit of AP3785T is a conventional Flyback converter with a 3-winding transformer---primary winding (NP), secondary
winding (NS) and auxiliary winding (NAUX), as shown in typical application with AP4341. The auxiliary winding is used for providing VCC supply
voltage for IC and sensing the output voltage feedback signal to FB pin.
Figure 2 shows the typical waveforms which demonstrate the basic operating principle of AP3785T application. And the parameters are defined
as following.
•
IP---The primary side current
•
IS ---The secondary side current
•
IPK---Peak value of primary side current
•
IPKS---Peak value of secondary side current
•
VSEC---The transient voltage at secondary winding
•
VS---The stable voltage at secondary winding when rectification diode is in conducting status, which equals the sum of output voltage VO
•
•
and the forward voltage drop of diode
VAUX---The transient voltage at auxiliary winding
VA--- The stable voltage at auxiliary winding when rectification diode is in conducting status, which equals the sum of voltage V CC and the
•
•
•
•
•
forward voltage drop of auxiliary diode
tSW ---The period of switching frequency
tONP ---The conduction time when primary side switch is “ON”
tONS ---The conduction time when secondary side diode is “ON”
tOFF ---The dead time when neither primary side switch nor secondary side diode is “ON”
tOFFS --- The time when secondary side diode is “OFF”
IPK
IP
IPKS
tOFFS
IS
VAUX
VA
tSW
VSEC
VS
tONP
tONS
tOFF
Figure 2. The Operation Waveform of Flyback PSR System
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Operation Principle Description (Cont.)
3.
Constant Voltage Operation
As to constant-voltage (CV) operation mode, the AP3785T detects the auxiliary winding voltage at FB pin to regulate the output voltage. The
auxiliary winding voltage is coupled with secondary side winding voltage, so the auxiliary winding voltage during the conduction time of
secondary rectification diode D1 is:
NEW PRODUCT
VAUX 
N AUX
 VOUT  Vd 
NS
(1)
Where Vd is the diode forward voltage drop.
0V
tSAMPLE
tONS
Figure 3. Auxiliary Voltage Waveform
The voltage detection point is at the tSAMPLE of the D1 on-time. The voltage detection point is changed with the different primary peak current. The
CV loop control function of AP3785T then generates a D1 off-time to regulate the output voltage.
4.
Constant Current Operation
The AP3785T can work in constant-current (CC) mode. Figure 2 shows the secondary current waveforms.
In CC operation mode, the CC control loop of AP3785T will keep a fixed proportion between D1 on-time tONS and D1 off-time tOFFS. The fixed
proportion is
t ONS 4

t OFFS 4
(2)
The relationship between the output current and secondary peak current I PKS is given by:
t ONS
1
I OUT   I PKS 
2
t ONS  t OFFS
(3)
As to tight coupled primary and secondary winding, the secondary peak current is
I PKS 
NP
 I PK
NS
(4)
Thus the output constant-current is given by:
I OUT 
t ONS
1 NP
2 N

 I PK 
  P  I PK
2 NS
t ONS  t OFFS 8 N S
(5)
Therefore, AP3785T can realize CC mode operation by constant primary peak current and fixed diode conduction duty cycle.
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Operation Principle Description (Cont.)
5.
Multiple Segment Peak Current
As to the original PFM PSR system, the switching frequency decreases with decreasing of output current, which will encounter audible noise
issue since switching frequency decreases to audio frequency range, about less than 20kHz.
In order to avoid audible noise issue, AP3785T uses 3-segment primary peak current control method at constant voltage (CV) mode, the current
sense threshold voltage is multiple segments with different loading, as shown in Figure 4, which are VCS_H for high load, varied VCS_M for
medium load and VCS_L for light load. In no load and ultra light load condition (NL mode), the current reference is also VCS_L. But the operation in
NEW PRODUCT
NL mode is different, which will be described in next section.
At constant current (CC) mode, the peak current is still VCS_H when VO> VFB(SCP), if not, the peak current is 2/3* VCS_H。
It can be seen from the following figure that with multiple segment peak current control, AP3785T power system can keep switching frequency
above 20kHz from light load to heavy load and guarantee the audible noise free performance, and the maximum system switching frequency is
not less than 50kHz.
FM
FM
AM
50/80KHz
45/72KHz
fSW
VCSMAX
VCS
20/32KHz
1/2.25*VCSMAX
8%
40%
100%
IO/IOMAX
Figure 4. Segment Peak Current and Operating Frequency at CV Mode
6. Operating Frequency
For primary-side regulation, the primary current ip(t) is sensed by a current sense resistor RCS (R3 as shown in Typical Applications). The current
rises up linearly at a rate of:
dip ( t ) VIN ( t )

dt
LM
(6)
As illustrated in Figure 2, when the current ip(t) rises up to IPK, the switch Q1 turns off. The constant peak current is given by:
I PK 
VCS
R CS
(7)
The energy stored in the magnetizing inductance LM each cycle is therefore:
Eg 
1
2
 L M  I PK
2
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Operation Principle Description (Cont.)
So the power transferring from the input to the output is given by:
P
1
2
 L M  I PK  f SW
2
(9)
1
2
   L P  I PK  f SW  PO  VO  I O
2
(10)
NEW PRODUCT
Where, fSW is the switching frequency, η is the transferring efficiency.
In AP3785T, the high load mode and light load mode adopt the frequency modulation (FM), and the middle load mode uses the amplitude
modulation (AM).
During FM, the peak current IPK is constant, the output power depends on the switching frequency fSW.
During AM, the frequency is fixed, VCS_M is varied. Below is the analysis of VCS_M。
The square root equation can be got from the following equation:
2
V 
1
1
2
   L P  I PK  f SW     L P   CS   f SW  VO  I O
2
2
 R CS 
(11)
2  R CS  VO  I O
  L p  f SW
2
So, V 
CS
(12)
During AM, the frequency is fixed, assume VO and η are constants, then
VCS  k  I O
7.
2  R CS  VO )
  L p  f SW
2
( k
(13)
NL Mode Operation (Typical Application with APR3415)
At no load and ultra light load, the AP3785T works at no load mode (NL mode) and the output voltage is detected by APR3415. In order to
achieve ultra low standby power at NL mode, the static current is reduced to ICC_NL.
• The conditions of exiting NL mode---VCBC> VCBC(EN) or tOFF< tOFF(EX)
• The conditions of entering NL mode-- VCBC< VCBC(EN) and tOFF≥tOFF(EN)
At NL mode, the internal reference voltage VDD is pulled to ground. For normal NL working state, when the APR3415 detects the output voltage is
lower than its trigger voltage. The APR3415 VDET pin emits a periodical pulse current. This pulse current will generate a pulse voltage on
feedback winding through the transformer coupling. When the FB pin detects this pulse (>VTRIGGER is valid), the AP3785T re-establishes the VDD
and turns on primary switch to provide one energy pulse to supply output terminal and primary VCC voltage.
8.
Leading Edge Blanking
When the power switch is turned on, a turn-on spike will occur on the sense-resistor. To avoid false-termination of the switching pulse, a leadingedge blanking (from power MOSFET on) is built in. During this blanking period, the current sense comparator is disabled and the gate driver can’t
be switched off.
9.
Valley Turn-on
When the off time (tOFF) is lower than tVAL-ON, AP3785T power system can work with valley turn-on. It can reduce MOSFET switching on power
losses which is resulted from the equivalent output capacitance to achieve highest overall efficiency. At the same time, because of valley turn-on
the switching frequency has the random jitter feature, which will be benefit for conductive EMI performance. And valley turn-on can also reduce
the power switch turn on spike current and then achieve the better radiative EMI performance.
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Operation Principle Description (Cont.)
10. Adjustable Line Compensation
Since there is a constant delay time from the CS pin voltage reaching the given VCS reference to the power MOSFET turning off, the real primary
peak current value always has a gap with the ideal value. The gap value changes with different input line voltage, which is caused by different
current rising slope, results in different system constant current value.
NEW PRODUCT
In order to eliminate the constant current deviation due to line voltage, the adjustable line compensation is introduced to design. The negative
voltage of FB pin which is linear to the line voltage is added up to VCS reference by a certain proportion and create an adjustable compensation
voltage to clear up the primary current gap, so that the excellent line regulation of output current will be achieved.
VSAMPLE
R1
VCS
VAUX
R2
RFB1
PFM
Vx
FB
RM
RLC
RFB2
Figure 5. Adjustable Line Compensation Circuit
VCS  
N
R LC
R1
 AUX 
 VLINE
R 1  R 2 N P R LC  R M  R FB1
(14)
So, the AP3785T can change the line compensation capability by adjusting the upper resistor at FB pin (R FB1). Higher resistance means lower
line compensation capability.
11. Adjustable Cable Compensation
To meet the voltage drop of different output cables, the AP3785T can realize the adjustable cable compensation.
As shown in Figure 6, VCBC follows the VLOAD that reflects the power system loading percentage.
RFB1
VAUX
FB RFB2
ICBC
VLOAD
VCBC
RCBC
Figure 6. Adjustable Cable Compensation Circuit
AP3785T
Document number: DS37552 Rev. 4 - 2
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AP3785T
Operation Principle Description (Cont.)
If the CBC resistance (RCBC) and RFB1 are fixed, the current (ICBC) flowing through the CBC resistance (RCBC) also follows the changing of the
VLOAD:
ICBC 
VLOAD
R CBC
(15)
NEW PRODUCT
The voltage change (VAUX) of auxiliary winding (VAUX) is varied with the VLOAD:
VAUX  R FB1  ICBC 
R FB1
 VLOAD
R CBC
(16)
The VO changing (VO) which VAUX reflects is also changed with VLOAD:
VO 
NS
N
R
 VAUX  S  FB1  VLOAD
N AUX
N aux R CBC
(17)
So, the right cable compensation can be achieved by adjusting RCBC. The 43kΩ resistance can ensure about 350mV cable compensation from
no load to full load.
12. Protection
The AP3785T has multiple built-in fault protection functions: FB over voltage protection, VCC over voltage protection, output short circuit
protection, FB open circuit protection, transformer saturation protection, current sense resistor fault (short or open) protection and external over
temperature protection. The different fault conditions trigger the different protection modes.
Protection Mode
The AP3785T has three protection modes: Dmin, auto-recovery and fast auto-recovery, which the operation principles are different.
When FB down-resistance short protection is triggered, the AP3785T enters the Dmin mode whereby the AP3785T immediately shuts down and
keeps a duration time tOFF(MAX) to output a pulse for turning on the primary switch, which is used to detect whether the fault condition is removed
and provide VCC supply. If the fault condition is removed before VCC decreases below VOPR(MIN), the device will enter normal operation mode. If
not, the AP3785T will repeat another Dmin mode action. When VCC drops below VOPR(MIN), AP3785T will enter the restart process, and VCC
voltage changes between VTH(ST) and VOPR(MIN) until FB down-resistance short condition is removed.
When FB open circuit protection, output short circuit protection, transformer saturation protection and current sense resistor fault (short or open)
protection are triggered, the device enters the auto-recovery mode. Once the AP3785T enters the auto-recovery mode, the device shuts down
immediately and doesn’t signal any pulse, the VCC static current is decreased from operating current (ICC_OPR) to standby current (ICC_NL). Until
VCC voltage drops to VOPR(MIN), the AP3785T will enter the restart process, and VCC voltage changes between VTH(ST) and VOPR(MIN) until the
fault condition is removed. The slope of VCC voltage to discharge is very small, and the time to drop to VOPR(MIN) is very long. It can decrease the
average power dissipation at a fault condition.
When VCC over voltage protection, FB over voltage protection, CBC short to GND protection, internal over temperature and external over
temperature protection are activated, the device enters the fast auto-recovery mode. The only difference with auto-recovery is that the VCC to
discharge current is kept operating current and the system can fast restart.
12.1
Short Circuit Protection (SCP)
Short Circuit Protection (SCP) detection principle is similar to the normal output voltage feedback detection by sensing FB pin voltage. When the
detected FB pin voltage is below VFB(SCP) for a duration of about tSCP, the SCP is triggered. Then the AP3785T enters auto-recovery mode that
the IC immediately shuts down and then restarts, so that the VCC voltage changes between VTH_ST and UVLO threshold until VFB(SCP) condition
is removed.
As to the normal system startup, the time duration of FB pin voltage below VFB(SCP) should be less than tSCP to avoid entering SCP mode. But for
the output short condition or the output voltage below a certain level, the SCP mode will be triggered.
AP3785T
Document number: DS37552 Rev. 4 - 2
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AP3785T
Operation Principle Description (Cont.)
Figure 7 is the AP3785T normal start-up waveform that the voltage of FB pin is above VFB(SCP) during tSCP after VCC gets to the VTH_ST, which
doesn’t enter the SCP mode. As shown in Figure 8, VOUT is short and the voltage of FB pin is lower than VFB(SCP) during tSCP, the AP3785T
triggers the SCP and enters auto-recovery mode.
tSCP
VTH_ST
VCC
NEW PRODUCT
VFB(SCP)
VFB
5V
VOUT(SCP)
VOUT
Figure 7. Normal Start-up
tSCP
VTH_ST
VCC
VOPR(MIN)
VFB(SCP)
VFB
VOUT
0V
Figure 8. Short Circuit Protection (SCP) and Auto-recovery Mode
12.2
Transformer Saturation Protection via Primary Peak Current Limitation
When the transformer saturation happens, the voltage of EM pin will increase promptly and be over the reference voltage VEM(MAX). If two
consecutive pulses exceed the value, the device shuts down and enters into auto-recovery mode.
12.3
External Over Temperature Protection (External OTP)
The AP3785T provides external over-temperature protection (OTP) by connecting a Negative-Temperature-Coefficient (NTC) resistor from OTP
pin to GND. Internally, a current source IOTP is injected to the OTP pin, which generates a voltage proportional to the NTC resistance. At high
ambient temperature, the NTC resistance gets lower and results in the OTP pin voltage decreasing. If the OTP pin voltage drops below an
internally-set threshold VOTP, then the OTP is triggered, and the AP3785T shuts down immediately and enters the fast auto-recovery mode. The
power system will keep fast auto-recovery mode until the ambient temperature decreases and OTP pin voltage increases over the voltage VOTP_REC,
which the AP3785T can recover to normal operation.
If the OTP pin is not connected to the NTC resistor, the external OTP function will not work and the IC can still work normally with internal OTP.
AP3785T
Document number: DS37552 Rev. 4 - 2
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AP3785T
Ordering Information
AP3785T X XX - G1
NEW PRODUCT
Product Name
Package
Packing
RoHS/Green
M : SO-8
TR : Tape & Reel
G1 : Green
Package
Temperature Range
SO-8
-40 to +85°C
Part Number
AP3785TMTR-G1
Marking ID
3785TM-G1
Packing
4000/Tape & Reel
Marking Information
(Top View)
3785TM
-G1
YWWAXX
AP3785T
Document number: DS37552 Rev. 4 - 2
First and Second Lines: Logo and Marking ID
Third Line: Date Code
Y: Year
WW: Work Week of Molding
A: Assembly House Code
XX: 7th and 8th Digits of Batch No.
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AP3785T
Package Outline Dimensions (All dimensions in mm(inch).)
(1)
Package Type: SO-8
4.700(0.185)
5.100(0. 201)
7°
~ 9°
0.320(0. 013)
TYP
1.350(0. 053)
1.750(0. 069)
NEW PRODUCT
8°
8°
~ 9°
7°
0.600(0. 024)
0.725(0. 029)
D
5.800(0. 228)
6.200(0. 244)
1.270(0. 050)
TYP
D
20:1
0.300(0. 012)
R0.150(0.006)
0.100(0. 004)
1.000(0. 039)
TYP
3.800(0. 150)
Option 1
4.000(0. 157)
0.300(0. 012)
0.150(0. 006)
0.250(0. 010)
Option 1
0°
8°
1°
7°
0.510(0. 020)
R0.150(0.006)
0.450(0. 017)
0.820(0. 032)
Option 2
0.350(0. 014)
TYP
Note: Eject hole , oriented hole and mold mark is optional .
AP3785T
Document number: DS37552 Rev. 4 - 2
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AP3785T
Suggested Pad Layout
(1)
Package Type: SO-8
NEW PRODUCT
Grid
placement
courtyard
G
Z
Y
E
Dimensions
Value
Z
(mm)/(inch)
6.900/0.272
AP3785T
Document number: DS37552 Rev. 4 - 2
G
(mm)/(inch)
3.900/0.154
X
X
(mm)/(inch)
0.650/0.026
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Y
(mm)/(inch)
1.500/0.059
E
(mm)/(inch)
1.270/0.050
September 2015
© Diodes Incorporated
AP3785T
IMPORTANT NOTICE
DIODES INCORPORATED MAKES NO WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, WITH REGARDS TO THIS DOCUMENT,
INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
(AND THEIR EQUIVALENTS UNDER THE LAWS OF ANY JURISDICTION).
NEW PRODUCT
Diodes Incorporated and its subsidiaries reserve the right to make modifications, enhancements, improvements, corrections or other changes
without further notice to this document and any product described herein. Diodes Incorporated does not assume any liability arising out of the
application or use of this document or any product described herein; neither does Diodes Incorporated convey any license under its patent or
trademark rights, nor the rights of others. Any Customer or user of this document or products described herein in such applications shall assume
all risks of such use and will agree to hold Diodes Incorporated and all the companies whose products are represented on Diodes Incorporated
website, harmless against all damages.
Diodes Incorporated does not warrant or accept any liability whatsoever in respect of any products purchased through unauthorized sales channel.
Should Customers purchase or use Diodes Incorporated products for any unintended or unauthorized application, Customers shall indemnify and
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indirectly, any claim of personal injury or death associated with such unintended or unauthorized application.
Products described herein may be covered by one or more United States, international or foreign patents pending. Product names and markings
noted herein may also be covered by one or more United States, international or foreign trademarks.
This document is written in English but may be translated into multiple languages for reference. Only the English version of this document is the
final and determinative format released by Diodes Incorporated.
LIFE SUPPORT
Diodes Incorporated products are specifically not authorized for use as critical components in life support devices or systems without the express
written approval of the Chief Executive Officer of Diodes Incorporated. As used herein:
A. Life support devices or systems are devices or systems which:
1. are intended to implant into the body, or
2. support or sustain life and whose failure to perform when properly used in accordance with instructions for use provided in the
labeling can be reasonably expected to result in significant injury to the user.
B. A critical component is any component in a life support device or system whose failure to perform can be reasonably expected to cause the
failure of the life support device or to affect its safety or effectiveness.
Customers represent that they have all necessary expertise in the safety and regulatory ramifications of their life support devices or systems, and
acknowledge and agree that they are solely responsible for all legal, regulatory and safety-related requirements concerning their products and any
use of Diodes Incorporated products in such safety-critical, life support devices or systems, notwithstanding any devices- or systems-related
information or support that may be provided by Diodes Incorporated. Further, Customers must fully indemnify Diodes Incorporated and its
representatives against any damages arising out of the use of Diodes Incorporated products in such safety-critical, life support devices or systems.
Copyright © 2015, Diodes Incorporated
www.diodes.com
AP3785T
Document number: DS37552 Rev. 4 - 2
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