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PDF EM8635 Data sheet ( Hoja de datos )
| Número de pieza | EM8635 | |
| Descripción | PWM Controller | |
| Fabricantes | Excelliance MOS | |
| Logotipo |  |
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EM8635
Green mode PWM Flyback Controller with Brown-Out Protection
General Description
EM8635 is a high performance, low startup
current, low cost, current mode PWM controller
with green mode power saving. The EM8635
integrates functions of Soft Start(SS), Under Voltage
Lockout(UVLO), Leading Edge Blanking(LEB),
internal Over Temperature Protection(OTP),
internal slope compensation. The EM8635 also
features more protection like Over Load
Protection(OLP), Brown-out Protection(BNO) and
Over Voltage Protection(OVP) to prevent circuit
damage occurred under abnormal conditions.
The EM8635 provides the users a superior
AC/DC power application of high efficiency,
excellent EMI performance, low external
component counts and lower cost solution.
Ordering Information
Features
Ultra Low Start Up Current (6uA)
Current Mode Control
Soft Start Function
Built-in Slope Compensation
Internal Leading-edge Blanking
Over Voltage Protection (OVP) on VDD pin
Over Load Protection (OLP)
Cycle-by-cycle Current Limit
Feedback Open Protection
Brown-out Protection
Internal Over Temperature Protection (OTP)
Constant Output Power Limit (Full AC Input
Range)
Internal Frequency Jittering for Excellent
EMI performance
Part Number
EM8635J
Package
SOT-23-6
Remark
Applications
Switching AC/DC Adaptor and charger
Open-Frame SMPS
Typical Application Circuit
AC
INPUT
EMI
Filter
DC
+ OUTPUT
VDD
BNO
GATE
EM8635
COMP
CS
GND
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Electrical Characteristics
(VDD=15V, TA=25℃, unless otherwise specified)
Parameter
Symbol
Test Conditions
VDD Section
VDD OVP Protect voltage
Start up current
VDD On Threshold Voltage
VDD Off Threshold Voltage
Operating Supply Current 1
Operating Supply Current 2
Operating Supply Current 3
VOVP
ISTART1
ISTART2
VTH-ON
VTH-OFF
IDD-OP1
IDD-OP2
IDD-OP3
VDD=7V
VDD=VTH-ON-0.5V
VDD=15V, VCOMP=0V,
VDD=15V, VCOMP=3V,
CGATE=1nF
VDD=15V,
Protection triggerred
Gate Section
Rising Time
Falling Time
Current-Sense Section
TR CL = 1nF
TF CL = 1nF
Maximum Internal Current
Setpoint
Leading Edge Blanking Time
Propagation Delay Time
Soft-Start Period
Internal Oscillator
VCSLim
TLEB
TPD
TSS
VBNO=1V
VBNO=3V
Oscillation Frequency
fOSC
Maximum Duty
Dmax
Green mode minimum frequency
VCOMP=3V, VCS=0V
Frequency jittering
fjitter
Frequency variation vs. VDD
VDD=11V to 25V
Frequency variation vs.
Temperature
-20℃ to 105℃(Note4)
Min Typ
25 26
-1
-6
13.5 15
7.5 8.5
-2
- 2.5
- 0.4
- 150
- 30
0.8 0.85
0.65 0.7
200 300
100
2
60 65
70 75
22
±6
EM8635
Max Units
27 V
2 uA
15 uA
16.5 V
9.5 V
3 mA
- mA
- mA
200 nS
100 nS
0.9 V
0.75 V
400 nS
nS
mS
70 KHz
80 %
KHz
%
5%
3%
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Soft Start
The EM8635 has an internal soft-start circuit that
increases cycle-by-cycle current limit comparator
inverting input voltage slowly after it starts. The
typical soft-start time is 2mS. The pulse width to
the power MOSFET is progressively increased to
establish the correct working conditions for
transformers, rectifier diodes and capacitors. The
voltage on the output capacitors is progressively
increased with the intention of smoothly
establishing the required output voltage. It also
helps prevent transformer saturation and reduces
the stress on the secondary diode during startup.
Slope compensation
In the conventional application, the problem of the
stability is a critical issue for current mode
controlling, when it operates in high than 50% of
the duty cycle. The EM8635 built in saw-tooth
slope compensation. So it requires no extra
component.
Burst Mode Operation
At no load or light load condition, majority of the
power dissipation in switching power supply is
form switching loss on the power MOSFET, the
core loss of the transformer and the loss on the
snubber. The magnitude of power loss is in
proportion to the number of switching events
within a fixed period of time. Reducing switching
events leads reduction on the power loss and
conserves the energy.
The EM8635 adjusts the switching mode according
to the load condition, the COMP pin voltage drops
below burst mode threshold level. Device enters
Burst Mode Control. The Gate drive output remains
at off state to minimize the switching loss and
reduces the standby power consumption.
Protection
The EM8635 provides many protection functions
that intend to protect system from being damaged.
All the protection functions are listed as below:
EM8635
Cycle-by-cycle current limit
The EM8635 has over-current protection
thresholds (0.85V). It is for cycle-by-cycle
current limit, which turns off MOSFET for the
remainder of the switching cycle when the
sensing voltage of MOSFET current reaches the
threshold.
Over-load / Open-loop Protection (OLP)
When feedback loop is open, as shown in Fig. 17,
no current flows through the opto-coupler
transistor, the EM8635 pulls up the COMP pin
voltage to 5.2V.
When the COMP pin voltage is above 4.2V
longer than 56mS, OLP is triggered. This
protection is also triggered when the SMPS
output drops below the normal value longer
than 56mS due to the overload condition.
5.2V
-
R 2R
PWM +
compa rator
COMP
2
OLP 56mS
+
- 4.2V
Vout
Feedback
open loop
VCOMP
5.2V
4.2V
56mS
OLP triggers
t
Fig. 17
Over Voltage Protection (OVP) on VDD
The VGS ratings of the HV power MOSFETs are
often limited up to max 30V. To prevent the VGS
from the fault condition, the EM8635 are
implemented a Over-Voltage-Protection (OVP)
on VDD. Whenever the VDD voltage is high than
the OVP threshold voltage (26V), the output
gate drive will be shutdown to shop the
switching of the power MOSFET until the next
UVLO (on).
The Over-Voltage-Protection on VDD function in
EM8635 is an auto-restart type protection. If the
2013/05/13
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11
11 Page | ||
| Páginas | Total 13 Páginas | |
| PDF Descargar | [ Datasheet EM8635.PDF ] | |
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