July 2000
PRELIMINARY
ML4835
*
Compact Fluorescent Electronic Dimming
Ballast Controller
1
GENERAL DESCRIPTION
The ML4835 is a complete solution for a dimmable or a
non-dimmable, high power factor, high efficiency
electronic ballast especially tailored for a compact
fluorescent lamp (CFL). The Bi-CMOS ML4835 contains
controllers for “boost” type power factor correction as
well as for a dimming ballast with end-of-lamp life
detection.
The PFC circuits uses a new , simple PFC topology which
requires only one loop for compensation. In addition,
this PFC can be used with either peak- or average-current
mode. This system produces a power factor of better than
0.99 with low input current THD.
The ballast controller section provides for programmable
starting sequence with individual adjustable preheat and
lamp out-of-socket interrupt times. The ML4835 provides
a shut down for both PFC and ballast controllers in the
event of end-of-life for the CFL.
BLOCK DIAGRAM
FEATURES
s
Power detect for end-of-lamp-life detection
s
Low distortion , high efficiency continuous boost, peak
or average current sensing PFC section
s
Leading- and trailing-edge synchronization between
PFC and ballast
s
One to one frequency operation between PFC and
ballast
s
Programmable start scenario for rapid/instant start lamps
s
Triple frequency control network for dimming or
starting to handle various lamp sizes
s
Programmable restart for lamp out condition to reduce
ballast heating.
s
Internal over-temperature shutdown
s
PFC over-voltage comparator eliminates output
“runaway” due to load removal
s
Low start-up current; < 0.55mA
7
RSET
9
RT/CT
8
RT2
13
CRAMP
4
PIFBO
3
PIFB
2
PEAO
1
PVFB/OVP
12
PWDET
10
INTERRUPT
5
LAMP FB
6
LEAO
17
OUT A
16
OUT B
18
PFC OUT
15
PGND
11
RX/CX
19
VCC
20
REF
14
AGND
OUTPUT
DRIVERS
PRE-HEAT AND
INTERRUPT TIMERS
LAMP OUT DETECT
AND
AUTOMATIC LAMP
RESTART
UNDER-VOLTAGE
AND
THERMAL SHUTDOWN
END-OF-LAMP DETECT
AND
POWER SHUTOFF
ANTI-FLASH
COMPENSATION
AND
POWER DIMMING LEVEL
INTERFACE
CONTROL
AND
GATING
LOGIC
THREE-FREQUENCY
CONTROL SEQUENCER
VCO
VARIABLE FREQUENCY
OSCILLATOR
POWER
FACTOR
CONTROLLER
(* Indicates Part is End Of Life as of July 1, 2000)
ML4835
2
PIN CONFIGURATION
PIN DESCRIPTION
PIN
NAME
FUNCTION
1
PVFB/OVP
Inverting input to the PFC error
amplifier and OVP comparator input.
2
PEAO
PFC error amplifier output and
compensation node
3
PIFB
Senses the inductor current and peak
current sense point of the PFC cycle
by cycle current limit
4
PIFBO
Output of the current sense amplifier.
Placing a capacitor to ground will
average the inductor current.
5
LAMP FB
Inverting input of the lamp error
amplifier, used to sense and regulate
lamp arc current. Also the input node
for dimmable control.
6
LEAO
Output of the lamp current error
transconductance amplifier used for
lamp current loop compensation
7
R
SET
External resistor which SETS oscillator
F
MAX
, and R
X
/C
X
charging current
8
R
T2
Oscillator timing component to set
start frequency
9
R
T
/C
T
Oscillator timing components
PIN
NAME
FUNCTION
10
INTERRUPT Input used for lamp-out detection and
restart. A voltage less than 1V will
reset the IC and cause a restart after a
programmable interval.
11
R
X
/C
X
Sets the timing for preheat and
interrupt.
12
PWDET
Lamp output power detection
13
C
RAMP
Integrated voltage of the error
amplifier out
14
AGND
Analog ground
15
PGND
Power ground.
16
OUT B
Ballast MOSFET driver output
17
OUT A
Ballast MOSFET driver output
18
PFC OUT
Power factor MOSFET driver output
19
V
CC
Positive supply voltage
20
REF
Buffered output for the 7.5V reference
1
2
3
4
5
6
7
8
9
10
20
19
18
17
16
15
14
13
12
11
ML4835
20-Pin SOIC (S20)
20-Pin DIP (P20)
PVFB/OVP
PEAO
PIFB
PIFBO
LAMP FB
LEAO
RSET
RT2
RT/CT
INTERRUPT
REF
VCC
PFC OUT
OUT A
OUT B
PGND
AGND
CRAMP
PWDET
RX/CX
ML4835
3
ABSOLUTE MAXIMUM RATINGS
Absolute maximum ratings are those values beyond which
the device could be permanently damaged. Absolute
maximum ratings are stress ratings only and functional
device operation is not implied.
Supply Current (I
CC) .............................................................
65mA
Output Current, Source or Sink
(OUT A, OUT B, PFC OUT) DC ........................... 250mA
PIFB Input Voltage ............................................–3V to 2V
Maximum Forced Voltage
(PEAO, LEAO) ............................................ –0.3V to 7.7V
Maximum Forced Current
(PEAO, LEAO) ...................................................... ±20mA
Junction Temperature .............................................. 150ºC
Storage Temperature Range ...................... –65ºC to 150ºC
Lead Temperature (Soldering, 10 sec) ..................... 260ºC
Thermal Resistance (
q
JA
)
ML4835CP .......................................................... 65ºC/W
ML4835CS .......................................................... 80ºC/W
OPERATING CONDITIONS
Temperature Range ....................................... 0°C to 85°C
ELECTRICAL CHARACTERISTICS
Unless otherwise specified, V
CC
= V
CCZ
–0.5V, R
SET
= 11.8k
W, R
T
= 15.4k
W, R
T2
= 67.5k
W, C
T
= 1.5nF,
T
A
= Operating Temperature Range (Note 1)
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
LAMP CURRENT AMPLIFIER (LAMP FB, LEAO)
Input Bias Current
-0.3
-1.0
µA
Small Signal Transconductance
35
75
105
µ
W
Input Bias Voltage
-0.3
5.0
V
Output Low
LAMP FB = 3V, R
L
=
¥
0.2
0.4
V
Output High
LAMP FB = 2V, R
L
=
¥
7.1
7.5
V
Source Current
LAMP FB = 0V, LEAO = 6V
-80
-220
µA
Sink Current
LAMP FB = 5V, LEAO = 0.3V
80
220
µA
PFC VOLTAGE FEEDBACK AMPLIFIER ( PEAO, PVFB/OVP)
Input Bias Current
-0.3
-1.0
µA
Small Signal Transconductance
35
75
105
µ
W
Input Bias Voltage
-0.3
5.0
V
Output Low
PVFB = 3V, R
L
=
¥
0.2
0.4
V
Output High
PVFB = 2V, R
L
=
¥
6.4
6.8
V
Source Current
PVFB = 0V, PEAO = 6V
-80
220
µA
Sink Current
PVFB = 5V, PEAO = 0.3V
80
220
µA
PFC CURRENT-LIMIT COMPARATOR (PIFB)
Current-Limit Threshold
-0.9
-1.0
-1.1
V
Propagation Delay
100mV Step and 100mV Overdrive
100
ns
PFC OVP COMPARATOR
OVP Threshold
2.65
2.75
2.85
V
Hysteresis
0.14
0.20
0.30
V
Propagation Delay
1.4
µs
ML4835
4
ELECTRICAL CHARACTERISTICS
(Continued)
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
OSCILLATOR
Initial Accuracy (F
MIN
)
T
A
= 25ºC
39.2
40
40.8
kHz
Voltage Stability (F
MIN
)
V
CCZ
– 4V < V
CC
< V
CCZ
– 0.5V
0.3
%
Temperature Stability (F
MIN
)
0.3
%
Total Variation (F
MIN
)
Line, Temperature
39.2
40.8
kHz
Initial Accuracy (START)
T
A
= 25ºC
49
50
51
kHz
Voltage Stability (START)
0.3
%
Temparature Stability (START)
0.3
%
Total Variation (START)
Line, Temperature
49
51
kHz
Ramp Valley to Peak
2.5
V
Initial Accuracy (Preheat)
TA = 25ºC
60.8
64
67.2
kHz
Total Variation (Preheat)
Line, Temperature
60.8
64
67.2
kHz
C
T
Discharge Current
V
RTCT
= 2.5V
6.0
7.5
9.0
mA
Output Drive Deadtime
C
T
= 1.5nF
0.7
us
REFERENCE BUFFER
Output Voltage
T
A
= 25ºC, I
O
= 0mA
7.4
7.5
7.6
V
Line Regulation
V
CCZ
– 4V < V
CC
< V
CCZ
– 0.5V
10
25
mV
Load Regulation
1mA < I
O
< 10mA
2
15
mV
Temperature Stability
0.4
%
Total Variation
Line, Load, Temperature
7.35
7.65
V
Long Term Stabilty
Tj=125ºC, 1000 hrs
5
mV
Short Circuit Current
40
mA
R
SET
Voltage
2.4
2.5
2.6
V
ML4835
5
ELECTRICAL CHARACTERISTICS
(Continued)
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
PREHEAT AND INTERRUPT TIMER (R
X
= 346k
W, C
X
= 10µF)
Initial Preheat Period
0.86
s
Subsequenct Preheat Period
0.72
s
Interrupt Period
5.9
s
R
X
/C
X
Charging Current
-50
-54
-58
µA
R
X
/C
X
Open Circuit Voltage
0.4
0.7
1.0
V
R
X
/C
X
Maximum Voltage
7.0
7.3
7.8
V
Preheat Lower Threshold
1.6
1.75
1.9
V
Preheat Upper Threshold
4.4
4.65
4.9
V
Start Period End Threshold
6.2
6.6
6.9
V
Interrupt Disable Threshold
1.1
1.25
1.4
V
Hysteresis
0.16
0.26
0.36
V
Input Bias Current
1
µA
POWER SHUTDOWN
Power Shutdown Voltage
0.9
1
1.1
V
OUTPUTS (OUT A, OUT B, PFC OUT)
Output Voltage Low
I
OUT
= 20mA
0.1
0.2
V
I
OUT
= 200mA
1.0
2.0
V
Output Voltage High
I
OUT
= 20mA
V
CC
-0.2
V
CC
-0.1
V
Output Voltage High
I
OUT
= 200mA
V
CC
-2.0
V
CC
-1.0
V
Output Voltage Low in UVLO
I
OUT
= 10mA, V
CC
< V
CC START
0.2
V
Output Rise and Fall Time
CL=1000pF
50
ns
UNDER VOLTAGE LOCKOUT AND BIAS CIRCUITS
IC Shunt Voltage (V
CCZ
)
ICC=15mA
14.0
14.8
15.5
V
Start-up Threshold (V
CC START
)
V
CCZ
-1.5 V
CCZ
-1.0 V
CCZ
-0.5
V
Hysteresis
3.0
3.7
4.4
V
Start-up Current
V
CC START
–0.2V
350
550
µA
Interrupt Current
(V
CC
–0.5V), INTERRUPT = 0V
500
750
µA
Operating Current
(V
CC
–0.5V)
5.5
8.0
mA
Shutdown Temperature
130
ºC
Hysteresis
30
ºC
Note 1:
Limits are guaranteed by 100% testing, sampling, or correlation with worst case test conditions.
ML4835
6
FUNCTIONAL DESCRIPTION
The ML4835 consists of peak or average current
controlled continuous boost power factor front end section
with a flexible ballast control section. Start-up and lamp-
out retry timing are controlled by the selection of external
timing components, allowing for control of a wide variety
of different lamp types. The ballast section controls the
lamp power using frequency modulation (FM) with
additional programmability provided to adjust the VCO
frequency range. This allows for the IC to be used with a
variety of different output networks. Figure 1 depicts a
detailed block diagram of ML4835.
The ML4835 provides several safety features. See the
corresponding sections for more details:
• End-of-lamp life detection to detect EOL and shut-off
lamps; See End Of Life Section.
• Thermal shutdown for temperature sensing extremes;
See IC Bias, Under-Voltage Lockout and Thermal
Shutdown Section.
• Relamping starting with anti-flash for programmable
restart for lamp out conditions while minimizing
“flashing” when powering from full power to dimming
levels; See Starting, Re-Start, Preheat and Interrupt
Section
Figure 1. Detailed Block Diagram
VCC
19
REF
20
AGND
14
CRAMP
13
PVFB/OVP
1
PEAO
2
PIFB
PIFBO
4
PFC OUT
18
RSET
7
LAMP FB
5
LEAO
6
RT2
8
INTERRUPT
10
PWDET
12
PGND
15
OUT B
16
OUT A
17
REF
–
+
14V
+
–
6.75V
Q
Q
R
S
Q
Q
T
+
–
TEMP
130ºC/100ºC
+
–
1.25V/1V
RX/CX
6.75V/1.25V
2.5V
+
–
1.0V
Q
Q
S
R
–
+
–
+
+
–
4.75V/
1.75V
+
–
PVFB
2.75V
+
–
–1V
+
–
3
R
S
Q
Q
R
S
Q
Q
–
+
2.5V
V
TO
I
÷2
CLK1
CLK
RX/CX
11
PFC CONTROLLER
OVP
ILIM
UVLO
REF_OK
PREHEAT
THERMAL SHUTDOWN
RT/CT
9
OSCILLATOR
V
TO
I
V
TO
I
COMP
ML4835
7
Figure 3. ML4835 PFC Controller Section
FUNCTIONAL DESCRIPTION
(Continued)
The ML4835 implements a triple frequency operation
scheme: programmable three-frequency sequence for pre-
heat, ignition, and dimming, that extends lamp life,
simplifies lamp network design, and starts lamps at any
dimming level without flashing. This addresses the need
for a high-Q network for starting sequence and low-Q
network for operation, minimizing parasitic losses and
improving overall power efficiency. The values for the
pre-heat, start, operation, and restart can be programmed
or selected (Figure 2).
POWER FACTOR SECTION
The ML4835 power factor section is a peak or average
current sensing boost mode PFC control circuit in which
only voltage loop compensation is needed. It is simpler
than a conventional average current control method. It
consists of a voltage error amplifier, a current sense
amplifier (no compensation is needed), an integrator, a
comparator, and a logic control block. In the boost
topology, power factor correction is achieved by sensing
the output voltage and the current flowing through the
current sense resistor. Duty cycle control is achieved by
comparing the integrated voltage signal of the error
amplifier and the voltage across R
SENSE
. The duty cycle
control timing is shown in Figure 3.
+
–
–
+
LAMP
NETWORK
INVERTER
LAMP
LAMP
RA
SW2
L
SW1
R
SENSE
RB
V
OUT
EMI
FILTER
18
3
PIFB
PIFBO
C
RAMP
C1
C2
R1
C
RAMP
PFC OUT
PVFB/OVP
1
–A
S
VREF1
OSC
PIFBO
RAMP
CLK
PFC OUT
CLK
R
Q
V
TO
I
PEAO
13
PEAO
2
4
START
HIGH Q
LOW Q
OPERATION
PREHEAT
f3
f2
f1
ML4835
SET TIME VALUES
FOR PREHEAT,
START AND OPERATION,
AND RESTART
Figure 2. Three Frequency Design Model
ML4835
8
Setting minimum input voltage for output regulation can
be achieved by selecting C
RAMP
as follows for peak
current mode:
C
PEAO
K
D Ts
t
P
V
V
V
L
D Ts
R
RAMP
MAX
OUT
IN
OUT
IN
SENSE
=
-
-
-
-
-
!
"
$##
´
22
1
1
2
2
2
1
8
(
)
(
)
D
:
?
(1)
And for average current mode:
C
PEAO
K
D Ts
t
P
V
V
L
D Ts
R
RAMP
MAX
OUT
IN
OUT
SENSE
=
-
-
-
-
!
"
$##
´
22
1
1
2
2
1
8
(
)
(
)
D
:
?
(1a)
Where
Dt is the dead time.
OVERVOLTAGE PROTECTION AND INHIBIT
The OVP pin serves to protect the power circuit from
being subjected to excessive voltages if the load should
change suddenly (lamp removal). A divider from the high
voltage DC bus sets the OVP trip level. When the voltage
on PVFB/OVP exceeds 2.75V, the PFC transistor are
inhibited. The ballast section will continue to operate.
TRANSCONDUCTANCE AMPLIFIERS
The PFC voltage feedback amplifier is implemented as an
operational transconductance amplifier. It is designed to
have low small signal forward transconductance such that
a large value of load resistor (R1) and a low value
ceramic capacitor (<1µF) can be used for AC coupling
FUNCTIONAL DESCRIPTION
(Continued)
Figure 5. Compensation Network
Figure 6. Output Configuration
Figure 7. Transconductance Amplifier Characteristics
–
+
1
2.5V
PVFB/OVP
R1
C1
C2
CURRENT
MIRROR
IN
OUT
CURRENT
MIRROR
IN
OUT
gmV
IN
io = gmV
IN
IQ +
2
gmV
IN
IQ –
2
V
IN
DIFFERENTIAL
LINEAR SLOPE REGION
0
i
O
Figure 4. Simplified Model of ML4835 EOL Functionality
ML4835
POWER LEVEL
TRIP POINT
POWER DETECT
POWER SHUTOFF
ML4835
9
CLOCK
C
T
V
TH
= 3.75V
V
TL
= 1.25V