EM8800A
EM8800A
Constant Off Time, Current-Mode Controller for LED Applications
General Description
Applications
EM8800A is a constant off time current mode
controller. This device can operated with a fixed off
time of the power switch. The TOFF pin is provided
to set the off time. In addition, the PWMD pin
enables the user to use a PWM signal to modulate
LED Backlight or lighting
RGB Backlight or lighting
Organic Light-Emitting Diode Backlight or
lighting
AC-DC or DC-DC LED Driver applications.
Pin Configuration
the switching pattern and adjust the average
luminosity. The LD/SS pin enables the user to set
peak current by adjust the voltage of this pin.
This part includes internal soft start, maximum
on time protection, over current protection and
thermal shutdown function. This part is available in
SOP-8 package.
Typical Application Circuit
Ordering Information
Part Number
Package
EM8800AG
SOP-8
Remark
Features
Constant Off Time Current-Mode Control
Adjustable Off Time
Internal Leading Edge Blanking
Internal Start Up Delay
Maximum On Time Protection
Over Current Protection
Thermal Shutdown
VLED-in
FAULT
VCC
PWMD
EM8800A
GATE
CS
2011/09/06
Rev.A.3
LD/SS
TOFF
G
D
1
EM8800A
Pin Assignment
Pin Name Pin No.
TOFF
1
PWMD
2
VCC
3
CS
GATE
4
5
GND
6
LD/SS
7
FAULT
8
2011/09/06
Rev.A.3
Pin Function
OFF Time Setting. A resistor to ground to set off time. Pulling this pin to ground will disable
the device.
PWM Dimming. This pin is used for PWM dimming. When the voltage applied to this pin is
low, switching is inhibited. When the voltage applied to this pin is high, switching restarts.
Supply Voltage. This pin provides the bias supply for the EM8800A. The supply voltage is
internally regulated to 5VDD for internal control circuit. Connect a well-decoupled supply
voltage to this pin. Ensure that a decoupling capacitor is placed near the IC.
Current Sense Input. This pin senses the peak current.
Driver OUTPUT. The output of the driver is connected to the gate of the external MOSFET.
Signal and Power Ground for the IC. All voltages levels are measured with respect to this
pin. Tie this pin to the ground island/plane through the lowest impedance connection
available.
Linear Dimming and Soft Start. A capacitor connected to the pin sets the soft start period.
The voltage of this pin adjusts the peak current.
Fault. This pin is asserted high when a fault condition is detected.
2
EM8800A
Function Block Diagram
VCC
Internal VDD
OVP
22V
FAULT
Control
Logic
OCP
comparator
LEB
UVLO
9.75V/8.25V
OTP
+
1.5V
TOFF
Internal VDD
Internal VDD
Max
on
20uA
Toff
PWMD
/3
LD/SS
S
1V
PG
-
Q
R
Soft
Driver
GATE
+
CS
2011/09/06
Rev.A.3
LEB
Peak Current
comparator
G
D
3
EM8800A
Absolute Maximum Ratings (Note 1)
Supply voltage, VCC---------------------------------------------------------------
-0.3V to 24V
GATE---------------------------------------------------------------------------------- -0.3V to 24V
Other pins--------------------------------------------------------------------------- 0.3V to 6V
Power Dissipation, PD @ TA = 25°C, SOP-8 --------------------------------
0.909W
Package Thermal Resistance, ΘJA, SOP-8 (Note 2)------------------------
110°C/W
Junction Temperature------------------------------------------------------------
150°C
Lead Temperature (Soldering, 10 sec.)----------------------------------------
260°C
Storage Temperature Range-----------------------------------------------------
-65°C to 150°C
ESD susceptibility (Note3)
HBM (Human Body Mode)------------------------------------------------------ 2kV
MM (Machine Mode)------------------------------------------------------------ 200V
Recommended Operating Conditions (Note4)
Junction Temperature
------------------------------------------------------
-40°C to 125°C
Ambient Temperature
------------------------------------------------------
-40°C to 85°C
Electrical Characteristics
VCC=12V, RTOFF=40kohm, TA=25℃, unless otherwise specified
Parameter
Symbol
Test Conditions
Pin
Min
Typ
Max
Units
21
9.0
22
9.75
1.5
0.6
0.05
23.5
10.5
1.2
0.1
V
V
V
mA
mA
0.6
1.2
mA
1.5
2.35
mA
80
30
140
60
1
ns
ns
V
V
0.97
1
1.03
V
400
550
700
ns
100
150
200
ns
VCC Section
VCC OVP Protect voltage
VCC On Threshold Voltage
VCC Off Hysteresis Voltage
Current Consumption in Latch Mode
Current Consumption in Start-up
VOVP
VTH-ON
VTH-HY
ICC-LATCH
ICC-OP1
Current Consumption in Device Disable
ICC-OP2
Current Consumption in Device Switching
ICC-OP3
Gate Section
Rising Time
Falling Time
Output Voltage Low
Output Voltage High
Current-Sense Section
TR
TF
VSource
VSink
Maximum Internal Current Set-point
VCSLim
Leading Edge Blanking Time
TLEB
Propagation Delay Time
TPD
Internal Soft-Start Period
TSS
2011/09/06
Rev.A.3
VCC=VTH-ON-0.2V
VCC=12V,
VPWMD=0V
CGATE=1nF
FSW=60KHz
CL = 1nF
CL = 1nF
20mA
20mA
VCS=VCSLim to Vgate=1V,
Cgate=1nF
11
2
ms
4
EM8800A
TOFF section
Off Time
TOFF
Minimum Off Time
Maximum Off Time
TOFF Short Protection Trigger Level
Off Time Variation vs. VCC
Off Time Variation vs. Temperature
TOFF-min
TOFF-max
VTOFF-SHORT
PWMD Section
PWMD ON Voltage Threshold
PWMD OFF Voltage Threshold
PWMD Pin Open Voltage
R_TOFF=30K ohm
R_TOFF=10K ohm
R_TOFF=1K ohm
R_TOFF=60K ohm
1.8
0.3
6
2
0.435
12
0.4
VCC=9.5V to 16V
-20°C to 105°C
VPWMD-ON VPWMD increasing
VPWMD-OFF VPWMD decreasing
VPWMD-OPE
2.2
0.5
2
5
2.2
0.8
5
us
us
us
us
V
%
%
V
V
V
N
PWMD Pin Internal Pull High Current
Dimming Wake-up Time
LD/SS Section
LD/SS Pin Open Voltage
LD/SS Pin Internal Pull High Current
LD/SS Pin Voltage to Peak Current Ratio
FAULT Section
FAULT Internal Pull Low Current
FAULT Pull high Voltage
FAULT Pull high Capability
Protection Section
Maximum On Time
Over Current Trigger Level
Suspend mode Vcs over voltage protection
OCP Leading Edge Blanking Time
Start-up Delay
Thermal Shutdown
Thermal Shutdown Hysteresis
IPWMD
TWAKE
VLD-OPEN
ILD
IFA
VFA_HIGH
IFA_HIGH
TON-MAX
VOCP1
VOCP2
TLEB-OCP
TSTART-DELAY
TSD
TSD-HYS
2
4
VPWMD= VPWMD-ON to
VGATE=10V
18
2.85
5
20
3
1
6
5
2
1.45
1.45
80
135
50
1.5
1.5
550
130
155
40
6
uA
1
us
22
3.15
V
uA
V/V
10
1.6
1.6
160
uA
V
mA
us
V
V
ns
ms
°C
°C
Note 1.
Stresses listed as the above “Absolute Maximum Ratings” may cause permanent damage to the device. These are for
stress ratings. Functional operation of the device at these or any other conditions beyond those indicated in the
operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended
periods may remain possibility to affect device reliability.
2
Note 2. θJA SOP-8 packages is 52°C /W on JEDEC 51-7 (4 layers,2S2P) thermal test board with 50mm copper area.
Note 3. Devices are ESD sensitive. Handling precaution is recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.
2011/09/06
Rev.A.3
5
EM8800A
Typical start-up sequence and possible type of steady-state operation.
Toff(us) time vs Rtoff(kohm) Adjustment Resistor
2011/09/06
Rev.A.3
6
EM8800A
Functional Description
EM8800A is a constant off time current mode
controller. The PWMD pin enables the user to use
a PWM signal to modulate the switching pattern
and adjust the average luminosity. The LD/SS pin
enables the user to set peak current by adjust the
voltage of this pin. A capacitor connected to the
LD/SS pin sets the soft start period.
Supply Voltage
The VCC pin provides the bias supply of EM8800A
control circuit, as well as MOSFET’s gate. A
minimum 0.1uF ceramic capacitor is recommended
to bypass the supply voltage.
Power ON Reset
To let EM8800A start to operation, VCC voltage
must be higher than its POR voltage. Typical POR
voltage is 9.75V.
Start Up Delay
When VCC reaches POR threshold, start-up-delay
timer begins to count. When start-up-delay is
finished, the current source of LD/SS pin is enabled
and the soft-start sequence begins.
Soft Start
A capacitor connected to the LD/SS pin sets the
soft start period.
Dimming
The device is able to perform both linear and PWM
dimming. Two separate inputs are provided (LD/SS
pin for linear dimming, PWMD pin for PWM
dimming). The two functions can be used
simultaneously and independently to one another.
Linear dimming can be performed by applying a dc
voltage between 0.3V and 3V. This voltage is
internally processed, generating the reference level
VCS_LD. The relationship between VLD and VCS_LD
is:
2011/09/06
Rev.A.3
VCS_LD=VLD/3, when VLD>0.3V
VCS_LD=0.1V, when VLD<=0.3V
PWM dimming can be achieved by driving the
PWMD pin with a low frequency square wave
signal. When the PWMD signal is lower than 0.8V,
switching is inhibited. When the PWMD signal is
higher than 2V, the switching is enabled.
Constant Off-Time Generator
The off-time generator begins at the end of each
on time. Once the off time generator has elapsed,
it begins the next GATE pulse. The off-time is
programmed by connecting a resistor from the
TOFF pin to ground.
Protections and Fault Flag
In case the LED string fails short, the inductor
current will rise cycle by cycle without control. To
prevent the current from exceeding levels that
might lead to catastrophic failure of the power
MOSFET, EM8800A detects if VCS exceeds 1.5V. If
this occurs for eight consecutive switching cycles, a
latched shutdown function is tripped: the device is
stopped in an idle state and it is necessary to
recycle its supply voltage to make it restart.
In case the LED string fails open, the current will
drop to zero and the inductor current will never
reach the programmed level. To detect this
situation, an internal timer checks the ON time of
the power MOSFET and, if it exceeds 30us for eight
consecutive switching cycles, a latched shutdown
function is tripped: the device is stopped in an idle
state and it is necessary to recycle its supply
voltage to make it restart.
In either case, the activation of the protection
functions is signaled by FAULT pin asserted high,
becoming a 5V voltage source able to provide up to
5mA source current.
7
EM8800A
Ordering & Marking Information
Device Name: EM8800AG for SOP-8
EM
8800A
ABCDEFG
EM8800A: Device Name
ABCDEFG: Date Code
Outline Drawing
J
F
I
I
G
D
K
H
E
B
C
A
Dimension in mm
Dimension
Min.
Typ.
Max.
2011/09/06
Rev.A.3
A
4.70
B
3.70
C
5.80
D
0.33
5.10
4.10
6.20
0.51
E
F
1.20
G
0.08
H
0.40
I
0.19
J
0.25
K
0∘
1.62
0.28
0.83
0.26
0.50
8∘
1.27
8
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