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July 2000 PRELIMINARY
ML4836* Compact Fluorescent Electronic Dimming Ballast Controller
GENERAL DESCRIPTION
The ML4836 is a complete solution for a dimmable or a non-dimmable high efficiency electronic ballast especially tailored for a compact fluorescent lamp (CFL). The Bi-CMOS ML4836 contains controllers for dimming ballast with end-of-life detection capability. The ballast controller section provides for programmable starting sequence with individual adjustable preheat and lamp out-of-socket interrupt times. The ML4836 provides latch type shut down comparator for ballast controllers in the event of end-of-life for the CFL.
FEATURES
s s
Programmable start scenario for rapid/instant start lamps Triple frequency control network for dimming or starting to handle various lamp sizes Programmable restart for lamp out condition to reduce ballast heating. Internal over-temperature shutdown Low start-up current; < 0.55mA (* Indicates Part is End Of Life as of July 1, 2000)
s
s s
BLOCK DIAGRAM
INTERRUPT CONTROL AND GATING LOGIC 7 LAMP FB 2 LEAO 3
ANTI-FLASH COMPENSATION AND DIMMING LEVEL INTERFACE RSET RT/CT RT2 VCO VARIABLE FREQUENCY OSCILLATOR THREE-FREQUENCY CONTROL SEQUENCER
OUT A 13 OUT B OUTPUT DRIVERS PGND 11 PRE-HEAT AND INTERRUPT TIMERS END-OF-LAMP DETECT AND POWER SHUTOFF UNDER-VOLTAGE AND THERMAL SHUTDOWN AGND REF 10 1 VCC 14 LAMP OUT DETECT AND AUTOMATIC LAMP RESTART RX/CX 8 12 4 6 5
PWDET 9
1
ML4836
PIN CONFIGURATION
ML4836 14-Pin SOIC (S14) 14-Pin DIP (P14)
REF LAMP FB LEAO RSET RT2 RT/CT INTERRUPT 1 2 3 4 5 6 7 14 13 12 11 10 9 8 VCC OUTA OUT B PGND AGND PWDET RX/CX
TOP VIEW
PIN DESCRIPTION
PIN NAME FUNCTION PIN NAME FUNCTION
1 2
REF LAMP FB
Buffered output for the 7.5V reference Inverting input of the lamp error amplifier, used to sense and regulate lamp arc current. Also the input node for dimmable control. Output of the lamp current error transconductance amplifier used for lamp current loop compensation External resistor which SETS oscillator FMAX, and RX/CX charging current Oscillator timing component to set start frequency Oscillator timing components
7
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. RX/CX PWDET AGND PGND OUT B OUT A VCC Sets the timing for preheat and interrupt. Lamp output power detection Analog ground Power ground. Ballast MOSFET driver output Ballast MOSFET driver output Positive supply voltage
8 9 10
3
LEAO
4 5 6
RSET RT2 RT/CT
11 12 13 14
2
ML4836
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 (ICC) ............................................................ 50mA Output Current, Source or Sink (OUT A, OUT B) DC ............................................ 250mA PIFB Input Voltage ............................................ -3V to 2V Maximum Forced Voltage (PEAO, LEAO) ............................................ -0.3V to 7.7V Maximum Forced Current (LEAO) ................................................................. 20mA Junction Temperature .............................................. 150C Storage Temperature Range...................... -65C to 150C Lead Temperature (Soldering, 10 sec) ...................... 260C Thermal Resistance (qJA) ML4836CP ............................................................... C/W ML4836CS ............................................................... C/W
OPERATING CONDITIONS
Temperature Range ........................................ 0C to 85C
ELECTRICAL CHARACTERISTICS
Unless otherwise specified, VCC = VCCZ -0.5V, RSET = 11.8kW, RT = 14.7kW, RT2 = 53.6kW, CT = 1.5nF, TA = Operating Temperature Range (Note 1)
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS LAMP CURRENT AMPLIFIER (LAMP FB, LEAO) Input Bias Current Small Signal Transconductance Input Bias Voltage Output Low Output High Source Current Sink Current OSCILLATOR Initial Accuracy (FMIN) Total Variation (FMIN) Initial Accuracy (START) Total Variation (START) Ramp Valley to Peak Initial Accuracy (Preheat) Total Variation (Preheat) CT Discharge Current Output Drive Deadtime REFERENCE BUFFER Output Voltage Line Regulation Load Regulation Temperature Stability Total Variation Long Term Stabilty Line, Load, Temperature Tj = 125C, 1000 hrs 7.35 5 TA = 25C, IO = 0mA VCCZ - 4V < VCC < VCCZ - 0.5V 1mA < IO < 10mA 7.4 7.5 10 2 0.4 7.65 7.6 25 15 V mV mV % V mV TA = 25C Line, Temperature VRTCT = 2.5V CT = 1.5nF 60.8 60.8 6.0 TA = 25C Line, Temperature TA = 25C Line, Temperature 39.2 39.2 49 49 2.6 64 64 7.5 0.7 67.2 67.2 9.0 50 40 40.8 40.8 51 51 kHz kHz kHz kHz V kHz kHz mA us LAMP FB = 3V, RL = LAMP FB = 2V, RL = LAMP FB = 0V, LEAO = 6V LAMP FB = 5V, LEAO = 0.3V 7.1 -80 80 35 -0.3 0.2 7.5 -220 220 -0.3 75 -1.0 105 5.0 0.4 A
V V V A A
W
3
ML4836
ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER REFERENCE BUFFER (Continued) Short Circuit Current RSET Voltage PREHEAT AND INTERRUPT TIMER (RX = 346kW, CX = 10F) RX/CX Charging Current RX/CX Open Circuit Voltage RX/CX Maximum Voltage Preheat Lower Threshold Preheat Upper Threshold Start Period End Threshold Interrupt Disable Threshold Hysteresis Input Bias Current POWER SHUTDOWN Power Shutdown Voltage OUTPUTS (OUT A, OUT B, PFC OUT) Output Voltage Low IOUT = 20mA IOUT = 200mA Output Voltage High Output Voltage High Output Voltage Low in UVLO Output Rise and Fall Time UNDER VOLTAGE LOCKOUT AND BIAS CIRCUITS IC Shunt Voltage (VCCZ) Start-up Threshold (VCC START) Hysteresis Start-up Current Interrupt Current Operating Current Shutdown Temperature Hysteresis
Note 1: Limits are guaranteed by 100% testing, sampling, or correlation with worst case test conditions.
(Continued)
CONDITIONS MIN TYP MAX UNITS
40 2.4 2.5 2.6
mA V
-48 0.4 7.0 1.6 4.4 6.2 1.1 0.16
-52 0.7 7.3 1.75 4.65 6.6 1.25 0.26
-56 1.0 7.8 1.9 4.9 6.9 1.4 0.36 1
A V V V V V V V A
0.9
1.0
1.1
V
0.1 1.0 VCC - 0.2 VCC - 0.1 VCC - 2.0 VCC - 1.0
0.2 2.0
V V V V
IOUT = 20mA IOUT = 200mA IOUT = 20mA, VCC < VCC START CL = 1000pF
0.2 50
V ns
ICC = 15mA
14.0
14.8
15.5
V V V A A mA C C
VCCz - 1.5 VCCz - 1.0 VCCz - 0.5 3.0 VCC START - 0.2V (VCCz - 0.5V), INTERRUPT = 0V (VCCz - 0.5V) 3.7 350 500 4.0 140 30 4.4 550 750 8.0
4
ML4836
FUNCTIONAL DESCRIPTION
The ML4836 consists of 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 ML4836. The ML4836 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
REF 1 6.75V
+ -
REF_OK THERMAL SHUTDOWN
OUT A 13
OUT B
+
TEMP 140C/100C PGND
12 11
14
VCC
-
REF Q Q R S PWDET
+ - + -
9 1.05V 1.20V/1V INTERRUPT
AGND 10
Q Q
S R
COMP
7
- +
RX/CX 6.65V/1.25V
Q T
-
RT2
Q UVLO
+
5
14V
+
PREHEAT RT/CT LEAO 3 LAMP FB
- +
4.65V/ 1.75V
-
6
CLK RX/CX OSCILLATOR
8
2 2.5V
4
RSET
V TO I
V TO I
Figure 1. Detailed Block Diagram
5
ML4836
FUNCTIONAL DESCRIPTION (Continued)
The ML4836 implements a triple frequency operation scheme: programmable three-frequency sequence for preheat, 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). TRANSCONDUCTANCE AMPLIFIERS The Lamp 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 (<1F) can be used for AC coupling (C1) in the frequency compensation network. The compensation network shown in Figure 5 will introduce a zero and a pole at: fZ = 1 2p R 1C1 fP = 1 2p R 1C 2 (2)
Figure 3 shows the output configuration for the operational transconductance amplifiers. A DC path to ground or VCC at the output of the transconductance amplifiers will introduce an offset error.
PREHEAT
SET TIME VALUES FOR PREHEAT, START AND OPERATION, AND RESTART
f1
ML4836
HIGH Q
LOW Q
f2
START
f3
OPERATION
Figure 2. Three Frequency Design Model
CURRENT MIRROR IN gmVIN 2 io = gmVIN OUT
IQ + IQ - gmVIN 2
IN
OUT CURRENT MIRROR
Figure 3. Output Configuration
6
ML4836
FUNCTIONAL DESCRIPTION (Continued)
The magnitude of the offset voltage that will appear at the input is given by VOS = io/gm. For an io of 1A and a gm of 0.05 W the input referred offset will be 20mV. Capacitor C1 as shown in Figure 4 is used to block the DC current to minimize the adverse effect of offsets. Slew rate enhancement is incorporated into all of the operational transconductance amplifiers in the ML4836. This improves the recovery of the circuit in response to power up and transient conditions. The response to large signals will be somewhat non-linear as the transconductance amplifiers change from their low to high transconductance mode, as illustrated in Figure 5. END OF LAMP LIFE At the end of a lamp's life when the emissive material is depleted, the arc current is rectified and high voltage occurs across the lamp near the depleted cathode. The ballast acts as a constant current source so power is dissipated near the depleted cathode which can lead to arcing and bulb cracking. Compact fluorescent lamps are more prone to cracking or shattering because their small diameter can't dissipate as much heat as the larger linear lamps. Compact fluorescents also present more of a safety hazard since they are usually used in downlighting systems without reflector covers.
iO
LAMP FB 1 2.5V - + R1 C1 LEAO
0 VIN DIFFERENTIAL LINEAR SLOPE REGION
C2
Figure 4. Compensation Network
Figure 5. Transconductance Amplifier Characteristics
PFC
LAMP NETWORK LAMP R9
ML4836
Figure 6. Simplified Model of ML4836 EOL Functionality
7
ML4836
FUNCTIONAL DESCRIPTION (Continued)
EOL and the ML4836 The ML4836 uses a circuit that creates a DC voltage representative of the power supplied to the lamps through the inverter when use in conjuction with PFC. This voltage is used by the ML4836 to latch off the ballast when it exceeds an internal threshold. An external resistor can be used as the "EOL latch resistor" to set the power level trip point, as shown in by R9 in Figure 6. BALLAST OUTPUT SECTION The IC controls output power to the lamps via frequency modulation with non-overlapping conduction. This means that both ballast output drivers will be low during the discharging time tDIS of the oscillator capacitor CT. OSCILLATOR The VCO frequency ranges are controlled by the output of the LFB amplifier (RSET). As lamp current decreases, LFB OUT falls in voltage, causing the CT charging current to increase, thereby causing the oscillator frequency to increase. Since the ballast output network attenuates high frequencies, the power to the lamp will be decreased. The oscillator frequency is determined by the following equations:
REF 1 DURING PREHEAT ICHG = 2.5V RSET AFTER PREHEAT LEA_ENB = HI ICHG = 5V - 7.5V RSET 8K25% LEA_ENB = LOW ICHG = 5V - LEAO RSET 8K25%
+
RT2
RT
ICHG
5
RT2
6 LEA_ENB
+
RT/CT 3.8/1.2V
-
INTERRUPT 7 1.20/1.0V VCC 0.625 RSET RX/CX 4.65/1.75V
- +
CT
7.5mA
14
7.5V
NOTE 1: RSET SHOULD BE SELECTED SUCH THAT AFTER PREHEAT WITH LEA_ENB "HI", ICHG MUST BE < 0. ICHG IS A UNI-DIRECTIONAL SOURCE CURRENT ONLY.
8
- +
CLOCK
tDIS VTH = 3.8V
tCHG
CT VTL = 1.2V
Figure 7. Oscillator Block Diagram and Timing
8
ML4836
FUNCTIONAL DESCRIPTION (Continued)
FOSC = and
t CHG = R T C T In
1 t CHG + t DIS
(3)
2. The voltage at LFB OUT (lamp feedback amplifier output) In preheat condition, charging current is fixed at
V V
REF
REF
+ ICHG R T - VTL + IICHG R T - VTH

(4)
ICHG (PREHEAT ) =
The oscillator's minimum frequency is set when ICHG = 0 where: FMIN 1 0.54 x RT CT (5)
25 . R SET
(6)
In running mode, charging current decreases as the voltage rises from 0V to VOH at the LAMP FB amplifier. The charging current behavior can be expressed as: ICHG = 5V LEAO R SET 8k 25% (7)
The oscillator's start frequency can be expressed by: FSTART = 0.54 x RT RT 2 x CT
2
1
7
(5a)
The highest frequency is attained when ICHG is highest, which is attained when voltage at LFB OUT is at 0V: ICHG(0) = 5 R SET (8)
Both equations assume that tCHG >> tDIS. When LFB OUT is high, ICHG = 0 and the minimum frequency occurs. The charging current varies according to two control inputs to the oscillator: 1. The output of the preheat timer
Highest lamp power, and lowest output frequency are attained when voltage at LFB OUT is at its maximum output voltage (VOH).
VCC VCCZ V(ON) V(OFF)
ICC 5.5mA
t
0.34mA t
Figure 8. Typical VCC and ICC Waveforms when the ML4836 is Started with a Bleed Resistor from the Rectified AC Line and Bootstrapped from an Auxiliary Winding.
9
ML4836
FUNCTIONAL DESCRIPTION (Continued)
In this condition, the minimum operating frequency of the ballast is set per equation 5 above. For the IC to be used effectively in dimming ballasts with higher Q output networks a larger CT value and lower RT value can be used, to yield a smaller frequency excursion over the control range (voltage at LFB OUT). The discharge current is set to 7.5mA. The operation of the oscillator is hown in Figure 7. Assuming that IDIS >>IRT: ballast cost, the ML4836 includes a temperature sensor which will inhibit ballast operation if the IC's junction temperature exceeds 140C. In order to use this sensor in lieu of an external sensor, care should be taken when placing the IC to ensure that it is sensing temperature at the physically appropriate point in the ballast. The ML4836's die temperature can be estimated with the following equation:
TJ @ TA + (PD + 65 C / W)
STARTING, RE-START, PREHEAT AND INTERRUPT
(10)
t DIS( VCO) @ 600 C T
IC BIAS, UNDER-VOLTAGE LOCKOUT AND THERMAL SHUTDOWN
(9) The lamp starting scenario implemented in the ML4836 is designed to maximize lamp life and minimize ballast heating during lamp out conditions. The circuit in Figure 9 controls the lamp starting scenarios: Filament preheat and lamp out interrupt. CX is charged with a current of IR(SET)/4 and discharged through RX. The voltage at CX is initialized to 0.7V (VBE) at power up. The time for CX to rise to 4.65V is the filament preheat time. During that time, the oscillator charging current (ICHG) is 2.5/RSET. This will produce a high frequency for filament preheat, but will not produce sufficient voltage to ignite the lamp or cause significant glow current.
The IC includes a shunt clamp which will limit the voltage at VCC to 14.5V (VCCZ). The IC should be fed with a current limited source, typically derived from the ballast transformer auxiliary winding. When VCC is below VCCZ - 1.1V, the IC draws less than 0.55mA of quiescent current and the outputs are off. This allows the IC to start using a "bleed resistor" from the rectified AC line. The ICC start-up condition is shown in Figure 7. To help reduce
0.625 RSET RX/CX 10 RX CX 1.75/4.65
+ -
HEAT
INTERRUPT 9 1.0/1.20
+ -
LEA_ENB OR DIMMING LOCKOUT
S
+
Q
INHIBIT
1.25/6.65
-
R
Figure 9. Lamp Preheat and Interrupt Timers
10
ML4836
FUNCTIONAL DESCRIPTION (Continued)
After cathode heating, the inverter frequency drops to FSTART causing a high voltage to appear to ignite the lamp. If lamp current is not detected when the lamp is supposed to have ignited, the CX charging current is shut off and the inverter is inhibited until CX is discharged by RX to the 1.25V threshold. Shutting off the inverter in this manner prevents the inverter from generating excessive heat when the lamp fails to strike or is out of socket. Typically this time is set to be fairly long by choosing a large value of RX. LFB OUT is ignored by the oscillator until INTERRUPT is above 1.20V The CX pin is clamped to about 7.5V. Care should also be taken not to turn on the VCCZ clamp so as not to dissipate excessive power in the IC. This will cause the temp sensor to become active at a lower ambient temperature. A summary of the operating frequencies in the various operating modes is shown below. OPERATING MODE Preheat After Preheat Dimming Control OPERATING FREQUENCY [F(MAX) to F(MIN)] 2 F(START) F(MIN) to F(MAX)
7.5 6.75 RX/CX 4.75 1.25 .7 0
HEAT LEA_ENB OR DIMMING LOCKOUT
INTERRUPT
INHIBIT
Figure10. Lamp Starting and Restart Timing
11
ML4836
TYPICAL APPLICATIONS
The ML4836 can be used for a variety of lamp types: T4 or compact fluorescent lamps IEC T8 (linear lamps) T5 linear lamps T12 linear lamps The ML4836 can also be used for dimming applications. For example, 20:1 dimming can be achieved using the ML4836 with external dimming units. The applications schematics shown in Figures 11 and 12 are examples of the various uses of the ML4836.
R
R
B
B
C13
C15
5
6
7
8
1
2
Q3
C16
C14
Q2
D9
D7
D8
R14
R15
C13
C12
3
2
T2
6
R4
C10
R5
7
R6
C9
R13
1
8
C12
R16 14 13 12 11 10 9 D6 VCC OUTA AGND PGND PWDET OUTB RX/CX 8
R2
R3
ML4836
C2
C3
INTRPT
D1
D2
RT/CT
LEAO
RSET
R7
RT2
REF
LFB
R11
1
2
3
4
5
6
L1
C1
D5
C8
D3
D4
R1
F1
R9
7
NEUTRAL
L2
R8
HOT
Figure11. 120V CFL Ballast
12
C4
R10
C5
C6
R12
C7
C17
D10
L2
R17
+ R4 D7 C10 T2 3 1 R 6 D8 Q3 B 8 C15 R15 1 8 C8 C12 C14 D5 R13 C16 R1 2 7 B 6 R3 7 R6 C9 2 R14 5 R R5 Q2 L2 R2
-
L2
D3
D4
R7 D6
C18
ML4836
VCC OUTA OUTB PGND AGND PWDET RX/CX R11 8 9 C12 10 11 C13 12 13 14
1
REF
R8
R9
2
LFB
Figure12. DC Input CFL Ballast
D9 R16 R12 C7 C17 D10 R17
3
LEAO
4
C4
RSET
5
RT2
6
R10
RT/CT
7
INTRPT
C5
C6
ML4836
13
ML4836
PHYSICAL DIMENSIONS
inches (millimeters)
Package: S14 14-Pin SOIC
0.337 - 0.347 (8.56 - 8.81) 14
PIN 1 ID
0.148 - 0.158 0.228 - 0.244 (3.76 - 4.01) (5.79 - 6.20)
1 0.017 - 0.027 (0.43 - 0.69) (4 PLACES) 0.050 BSC (1.27 BSC) 0.059 - 0.069 (1.49 - 1.75) 0 - 8
0.055 - 0.061 (1.40 - 1.55)
0.012 - 0.020 (0.30 - 0.51)
SEATING PLANE
0.004 - 0.010 (0.10 - 0.26)
0.015 - 0.035 (0.38 - 0.89)
0.006 - 0.010 (0.15 - 0.26)
Package: P14 14-Pin PDIP
0.740 - 0.760 (18.79 - 19.31) 14
PIN 1 ID
0.240 - 0.260 0.295 - 0.325 (6.09 - 6.61) (7.49 - 8.25)
0.070 MIN (1.77 MIN) (4 PLACES)
1 0.050 - 0.065 (1.27 - 1.65) 0.100 BSC (2.54 BSC) 0.015 MIN (0.38 MIN)
0.170 MAX (4.32 MAX)
0.125 MIN (3.18 MIN)
0.016 - 0.022 (0.40 - 0.56)
SEATING PLANE
0 - 15
0.008 - 0.012 (0.20 - 0.31)
14
ML4836
ORDERING INFORMATION
PART NUMBER ML4836CP (End Of Life) ML4836CS (End Of Life) TEMPERATURE RANGE 0C to 70C 0C to 70C PACKAGE 14-Pin DIP (P14) 14-Pin SOIC (S14)
(c) Micro Linear 1999.
is a registered trademark of Micro Linear Corporation. All other trademarks are the property of their respective owners.
DS4836-01
Products described herein may be covered by one or more of the following U.S. patents: 4,897,611; 4,964,026; 5,027,116; 5,281,862; 5,283,483; 5,418,502; 5,508,570; 5,510,727; 5,523,940; 5,546,017; 5,559,470; 5,565,761; 5,592,128; 5,594,376; 5,652,479; 5,661,427; 5,663,874; 5,672,959; 5,689,167; 5,714,897; 5,717,798; 5,742,151; 5,747,977; 5,754,012; 5,757,174; 5,767,653; 5,777,514; 5,793,168; 5,798,635; 5,804,950; 5,808,455; 5,811,999; 5,818,207; 5,818,669; 5,825,165; 5,825,223; 5,838,723; 5.844,378; 5,844,941. Japan: 2,598,946; 2,619,299; 2,704,176; 2,821,714. Other patents are pending. Micro Linear reserves the right to make changes to any product herein to improve reliability, function or design. Micro Linear does not assume any liability arising out of the application or use of any product described herein, neither does it convey any license under its patent right nor the rights of others. The circuits contained in this data sheet are offered as possible applications only. Micro Linear makes no warranties or representations as to whether the illustrated circuits infringe any intellectual property rights of others, and will accept no responsibility or liability for use of any application herein. The customer is urged to consult with appropriate legal counsel before deciding on a particular application.
2092 Concourse Drive San Jose, CA 95131 Tel: (408) 433-5200 Fax: (408) 432-0295 www.microlinear.com
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