AVAILABLE
EVALUATION KIT AVAILABLE
Functional Diagrams
Pin Configurations appear at end of data sheet.
Functional Diagrams continued at end of data sheet.
UCSP is a trademark of Maxim Integrated Products, Inc.
For pricing, delivery, and ordering information, please contact Maxim Direct
at 1-888-629-4642, or visit Maxim’s website at www.maximintegrated.com.
Controller IC for Dimmable Offline LED Lamps
19-6028; Rev 0; 10/11
Ordering Information appears at end of data sheet.
For related parts and recommended products to use with this part,
refer to www.maxim-ic.com/MAX16841.related.
Typical Operating Circuits appear at end of data sheet.
General Description
The MAX16841 is an LED driver for AC line (100V, 120V,
220V, and 230V AC) input lamps. It features proprietary
control of the input current that allows lamps to dim
smoothly from full to zero light intensity, while providing
active power factor correction (PFC). It is a very flexible
product that can be used in isolated (e.g., flyback) and
nonisolated (e.g., buck) configurations. The conventional
use of an optocoupler in isolated configurations can be
avoided in MAX16841-based designs.
The constant frequency-control technique of the
device allows maximization of the conversion efficien-
cy at both low and high AC line by operating at the
conduction mode that minimizes total conduction and
switching losses.
The device can be configured for universal input (90V to
264V AC) dimmable applications, allowing the design of an
LED lamp that can be operated and dimmed worldwide.
This device can be used without electrolytic capacitors,
thus maximizing the lamp lifetime. In this case, the LED
current is a rectified sinusoid with a frequency that is
twice the AC line frequency.
The device also features thermal shutdown, current limit,
open LED protection, and VCC undervoltage lockout.
The MAX16841 is available in an 8-pin SO package and
operates over the -40NC to +125NC temperature range.
Applications
Retrofit LED Lamps with Triac Dimming
Universal Input LED Retrofit Lamps
Industrial and Commercial Lighting
Residential LED Lighting
Features
S Smooth Dimming with Leading-Edge (Triac) and
Trailing-Edge Dimmers
S Active Power Factor Correction
S Nonisolated (e.g., Buck) and Isolated
(e.g., Flyback) Topologies
S Universal 90V to 264V AC Input Range
S Constant Frequency-Control Scheme Maximizes
Efficiency at High and Low AC Line Voltage
S Constant Power Control with No Need for
Optocouplers
S Very-Low Quiescent Current
S Output Open and Short Protection
S Thermal Shutdown
S Available in an 8-Pin SO Package
MAX16841
Controller IC for Dimmable Offline LED Lamps
IN to GND .............................................................. -0.3V to +26V
NDRV, DIMOUT to GND ........................... -0.3V to (VIN + 0.3V)
All Other Pins to GND .............................................-0.3V to +6V
NDRV Continuous Current .............................................. Q10mA
DIMOUT Continuous Current ............................................ Q2mA
Continuous Power Dissipation (TA = +70NC)
8 SO (derate 7mW/NC above +70NC) ..................588.2mW
Operating Temperature Range ........................ -40NC to +125NC
Junction Temperature .....................................................+150NC
Storage Temperature Range ............................ -65NC to +150NC
Lead Temperature (soldering, 10s) ................................+300NC
Soldering Temperature (reflow) ......................................+260NC
8 SO
Junction-to-Ambient Thermal
Resistance (BJA) (based on S8+2) ...........................136NC/W
Junction-to-Case Thermal
Resistance (BJC) (based on S8+2) .............................38NC/W
ABSOLUTE MAXIMUM RATINGS
Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-
layer board. For detailed information on package thermal considerations, refer to www.maxim-ic.com/thermal-tutorial.
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional opera-
tion 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 affect device reliability.
PACKAGE THERMAL CHARACTERISTICS (Note 1)
ELECTRICAL CHARACTERISTICS
(VIN = 12V, TA = TJ = -40NC to +125NC, unless otherwise noted. Typical values are at TA = +25NC.) (Note 2)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
IN Operating Range VIN 11 20 V
IN Undervoltage Threshold UVLORIN VIN rising, VHYST = 1V 9.5 10 10.5 V
IN Overvoltage Threshold OVLORIN VIN rising, VHYST = 1.8V 21 22 23 V
IN Input Supply Current IIN
NDRV not switching, VTH = 0V 0.7 1.3 2.6
mA
NDRV switching, 177.5kW/330pF on
NDRV, VTH = 5V, VCOMP = 2V,
VCS = 0V, VREFI = 2.35V
1.7 2.7 4.2
VIN = 8V 1.6
TH
TH Operating Range 0 4 V
TH Threshold Voltage VTH VTH rising, hysteresis = 150mV 1.17 1.215 1.26 V
TH Input Supply Current VTH = 0V 0.16 0.3 FA
REFI
REFI Operating Range VREFI 0.5 3.25 V
REFI Input Supply Current VREFI = 2V 48.5 50 51.5 FA
DIMOUT
DIMOUT On-Resistance DIMOUT = IN 20 40 I
DIMOUT = GND 20 40
TH to DIMOUT Propagation
Delay
VTH rising 40 80 ns
VTH falling 40 80
INTERNAL OSCILLATOR
Oscillator Frequency
RT = 47.5KI50
kHz
RT = 177.5kI160 180 200
RT = 297.5kI270 300 330
MAX16841
2
Maxim Integrated
Controller IC for Dimmable Offline LED Lamps
Note 2: All parameters are tested at TA = +25NC only. Limits over temperature are guaranteed by design.
ELECTRICAL CHARACTERISTICS (continued)
(VIN = 12V, TA = TJ = -40NC to +125NC, unless otherwise noted. Typical values are at TA = +25NC.) (Note 2)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
RT Resistance Range 47.5 297.5 kW
Oscillator Decode Resolution 6 Bits
Dither Frequency Range 45kHz to 330kHz 1.875 %
Frequency Dither Ramping DAC 7 Bits
Dither Frequency 1.5 kHz
CURRENT SENSE
CS Input Bias Current VCS = 2V, VCOMP = 4V -1 0 +1
FA
VCS = 2V, VCOMP = 0.7V 60 90 130
CS Voltage at Current Limit VCS_LIMIT 2.1 2.2 2.3 V
CS Voltage at Current Limit
Soft-Start 10 ms
CS Voltage at Hiccup Current
Limit 2.6 2.7 2.8 V
CS Hiccup Shutdown CS > hiccup 1.2 s
Hiccup Detection Cycles 3 Times
CS Regulation Voltage VCOMP = 2V, VREFI = 2.35V,
VCS = 0.45V 448 450 462 V
TRANSCONDUCTANCE AMPLIFIER
Transconductance GmVCOMP = 2.2V, VREFI = 2.35V,
VCS = 0.45V Q0.05V 95 135 175 FS
COMP Sink Current ISINK VCOMP = 2V, VREFI = 2.35V, VCS = 0V 45 65 85 FA
COMP Source Current ISOURCE VCOMP = 2V, VREFI = 2.35V,
VCS = 0.9V 45 65 85 FA
NDRV
NDRV Operating Range 0 VIN V
NDRV On-Resistance INDRV = 50mA to 100mA 2 5.0 I
INDRV = -50mA to -100mA 1.25 2.5
NDRV Dead Time Rising or falling 5 Ns
NDRV Rise Time NDRV = 1nF, 10% to 90% 15 ns
NDRV Fall Time NDRV = 1nF, 90% to 10% 15 ns
NDRV Reference Current Startup only 7.5 8 8.5 FA
THERMAL SHUTDOWN
Thermal-Shutdown Threshold TJ rising 164 NC
Thermal Hysteresis 20 NC
MAX16841
Maxim Integrated
3
Controller IC for Dimmable Offline LED Lamps
Typical Operating Characteristics
(TA = TJ = +25NC, 12 series LED load.)
AVERAGE VCS vs. TEMPERATURE
MAX16841 toc01
TEMPERATURE (°C)
AVERAGE VCS (mV)
1008040 600 20-20
301
302
303
304
305
306
307
308
309
310
300
-40 120
CS (mV)
CURRENT-SENSE
RESISTOR = 3.3I
VCS vs. VREFI
MAX16841 toc02
VREFI (V)
VCS (mV)
321
100
200
300
400
500
600
700
800
0
04
CS (mV)
CURRENT-SENSE
RESISTOR = 3.3I
QUIESCENT CURRENT vs. VIN
MAX16841 toc03
VIN (V)
QUIESCENT CURRENT
1917151311
0.5
1.0
1.5
2.0
2.5
3.0
0
9
IQ mA (VTH = 5V)
IQ mA (VTH = 0V)
MAX16841
4
Maxim Integrated
Controller IC for Dimmable Offline LED Lamps
Pin Description
Pin Configuration
PIN NAME FUNCTION
1 REFI Current Reference Input. The IC sources 50FA current out of this pin. Connect a resistor from REFI to
GND to set the input-current reference.
2 COMP Compensation Component Connection for the Switching Stage. Connect a suitable RC network to
ground. This is the output of the Gm amplifier.
3 TH Sets the Voltage Threshold on the Input at Which Switching Starts. This threshold is set at 1.24V.
Connect a resistor-divider from the bridge rectifier output, TH, and GND.
4DIMOUT
DIMOUT Drives an External FET to Provide a Resistive Path for the Triac when Input is Low. DIMOUT is
also used to drive an external FET that sets the programmed current to zero when the input voltage is
low.
5 GND Ground
6 CS Switch Current-Sense Input
7 NDRV Gate Drive for the Switching MOSFET. Connect a resistor across NDRV and GND to set the
switching frequency.
8 IN Input. Bypass with a 0.1FF or a higher value ceramic capacitor to ground.
REFI +
COMP
TH
1
2
3
4
8
7
6
5DIMOUT
IN
NDRV
CS
GND
SO
TOP VIEW
MAX16841
MAX16841
Maxim Integrated
5
Controller IC for Dimmable Offline LED Lamps
Functional Diagram
MAX16841
10ms
SOFT-START
OSCILLATOR
THERMAL SHUTDOWN
2.2V
2.7V
1.24V
CS LIMIT
COMPARATOR
2.4VP-P
NDRV
HICCUP
COMPARATOR
200ns
BLANKING
100mV
1s TIMER
1/5
SQ
RQ
CLR
SET
GND
IN
VIN UVLO
VIN OV
BIAS
IN
COMP
TH
GND
DIMOUT
REFI
CS
NDRV
Gm
VCC 2.2V 2.3V 1.24V
50µA
VCC
MAX16841
6
Maxim Integrated
Controller IC for Dimmable Offline LED Lamps
Detailed Description
The MAX16841 is a fixed-frequency offline LED driver
IC that is compatible with both leading-edge triac dim-
mers and trailing-edge transistor dimmers. The device
uses a fixed-frequency average current-mode control
scheme to control the switching current in the MOSFET.
In addition, a peak-limit comparator is used to limit the
peak switching current during overload and transient
conditions. The peak-limit comparator has a threshold of
2.2V. For the active PFC, the device uses a proprietary
current-control scheme where the averaged switch cur-
rent on a cycle-by-cycle basis is set to a programmed
DC value. This maximizes the efficiency of the converter
by operating in continuous-conduction mode (CCM) at
low AC line voltage (100V to 120V) and in discontinuous-
conduction mode (DCM) at high AC line voltage (220V
to 240V). Switching is initiated when the voltage on the
TH pin exceeds a threshold of 1.24V. In the case of the
buck configuration, the VTH falling threshold should be
set in such a way so that the input voltage exceeds the
maximum forward voltage of the LED string. In the case
of the buck-boost or flyback configuration, this threshold
can be set lower.
The device also uses a proprietary current-sense scheme
to regulate the LED current.
The device switching frequency is adjustable from 50kHz
to 300kHz using a single resistor from NDRV to ground.
The device operates over a wide 11V to 20V supply
voltage. The device’s switching MOSFET gate driver
sources and sinks up to 1A, making it capable of driving
high-voltage MOSFETs in offline LED driver applica-
tions for power ranges up to 25W. The device allows for
dimming with leading-edge and trailing-edge dimmers.
Additional features include thermal shutdown and
overvoltage protection.
IN
The device is powered up by the voltage at IN. All the
internal regulators derive power from IN. The operational
voltage is between 11V and 20V.
TH
TH sets the threshold for switching. Switching is initiated
once TH crosses 1.24V. The TH comparator has a 150mV
hysteresis. In a buck configuration, the VTH falling thresh-
old should be set in such a way so that the input voltage
exceeds the maximum forward voltage of the LED string.
In a buck-boost configuration, the VTH falling threshold
can be set to a lower level.
DIMOUT
For proper operation with triac dimmers, the load con-
nected to the dimmer should draw at least the startup
current when the dimmer is in the off state. For proper
operation of the timing circuit of the dimmer, there should
always be a close-current path. To ensure this, a bleeder
resistor is connected across IN and GND with the help
of an external FET. DIMOUT drives this external FET on
when VTH goes below the falling threshold. The bleeder
resistor is disconnected when VTH crosses its rising
threshold, resulting in better performance and efficiency.
Internal Oscillator
The internal oscillator of the device is programmable
from 50kHz to 300kHz. Connect a single resistor from
NDRV to GND to set the oscillator frequency. Upon
power-up, an 8FA of current sinks into this resistor. An
internal ramp is then compared against the voltage on
NDRV to determine the oscillator frequency.
Frequency Dithering
The device incorporates a frequency-dithering feature.
This feature helps to reduce EMI.
n-Channel MOSFET Switch Driver (NDRV)
The NDRV driver drives the gate of an external n-channel
switching MOSFET. NDRV switches between IN and
GND. NDRV is capable of sourcing/sinking 1A of peak
current, allowing the device to switch MOSFETs in an
offline LED driver application. The average current drawn
from the supply to drive the external MOSFET depends
on the MOSFET gate charge and switching frequency.
Use the following equation to calculate the MOSFET
driver supply current:
NDRV G SW
I Qf= ×
Switching MOSFET Current Sense (CS)
The switching MOSFET current-sense resistor should be
connected to the CS pin of the device. The device con-
trols the average of the CS signal to a level determined
by the REFI voltage. Internal leading-edge blanking of
200ns (typ) is provided to avoid premature turn-off of
the switching MOSFET in each switching cycle. A peak-
limit comparator is used to limit the peak switch current
during overload and transient conditions. The peak-limit
comparator has a threshold of 2.2V (typ).
MAX16841
Maxim Integrated
7
Controller IC for Dimmable Offline LED Lamps
Input-Current Setting (REFI)
REFI is the external reference for programming the input
current of the LED driver. The input current is proportinal
to the REFI voltage. The IC sources 50FA current out of
this pin and the voltage at the REFI pin can also be set
by connecting a resistor from REFI to GND. Internally, the
REFI signal is downshifted by 100mV and then attenua-
ted by a factor of 5. The attenuated signal is applied to
the positive terminal of the internal error amplifier and this
signal sets the reference for the controller.
Error-Amplifier Output (COMP)
The device includes an internal transconductance
current error amplifier with a typical Gm of 150FS. The
output of the error amplifier is controlled by the TH
comparator output. When the TH comparator is high,
the output of the error amplifier connects to COMP.
When the TH comparator is low, the error amplifier is
disconnected from COMP, preserving the charge on
the compensation capacitor. COMP is connected to the
positive terminal of the PWM comparator.
The device incorporates an average current-mode
control scheme to regulate the input current. The
control loop regulates the average of the CS signal to a
level determined by the REFI voltage. The control loop
consists of the current-sense resistor (RCS) connected
across CS and GND, the transconductance current error
amplifier, an oscillator providing a 2.4V ramp at switching
frequency, the control voltage on the positive input of the
Gm amplifier, and the PWM comparator.
Overvoltage-Protection Input (OVP)
This is the protection feature in a flyback converter during
an open LED condition. The IN pin is connected to the
auxiliary winding of the flyback transformer. During an
open LED condition, the IN voltage increases and NDRV
is disabled once the IN voltage reaches 22.5V (typ).
When the IN voltage drops by 2V, NDRV is enabled.
Short-Circuit Protection
During an output short condition, the inductor current
keeps increasing with input voltage as there is no nega-
tive voltage across the inductor during the off period of
the switching cycle. During this condition, the CS voltage
signal peak is at a higher level because the inductor
current is at a higher level than during the normal condi-
tion. Once the CS signal exceeds the hiccup threshold
of 2.7V (typ),
the internal hiccup block gets activated.
Switching is disabled for 1s (typ) if CS exceeds 2.7V (typ)
for three times.
Thermal Protection
The device enters into thermal-shutdown mode when
junction temperature exceeds +160NC. During thermal
shutdown, NDRV is disabled. The device recovers from
thermal-shutdown mode once the junction temperature
drops by 20NC.
Applications Information
Figure 1 shows a MAX16841-based, triac-dimmable,
PFC, nonisolated-buck offline LED driver. Components
L1, L2, L3, and C1 provide EMI filtering. During the turn-
on instant of triac dimming, there would be significant
ringing due to high inrush current to charge the input
capacitor (C9). The ringing could cause the line current
to fall to zero and this would turn off the triac. R3, R22,
and C14 act as a damper and help to limit the inrush
current and ringing. Due to R3, the efficiency of the sup-
ply decreases. The damper circuit can be omitted in
nondimming applications. The circuit, consisting of D4,
R5, C2, D3, R6, R4, and Q5, bypasses R3 with Q1 after
1ms of dimming instant, thereby reducing the power
dissipation in R3 and improving efficiency. During the
turn-on instant, capacitor C2 is charged by a constant-
current source formed by D3, R6, R4, and Q5. Within
1ms time, sufficient voltage develops across C2 to fire
the SCR Q1. Diode D4 provides fast discharge of C2.
Resistors R8, R9, and R10 program the switching thresh-
old. The rising threshold should be set at a voltage higher
than the maximum LED string voltage. When the input
voltage is below the falling threshold, DIMOUT drives
the Q3 FET on, connecting R7 across the diode-bridge
positive and GND. Thus, a close circuit is formed for the
timing circuit of the triac. Diode D2 blocks capacitors C9
and C14 to discharge through R7. This helps to reduce
the inrush current during the triac turn-on instant.
The circuit consisting of R23, R24, D6, and Q2 is a linear
regulator and provides bias to the device.
The buck-converter circuit is formed by C9, LED+, LED-,
C10, L5, Q4, D10, D11, and R20. Capacitor C9 provides
a path for the switching frequency currents. Maximum
value of this capacitor is limited by the input power-factor
requirements. The higher the value of C9, the lower the
input power factor.
Since the input-voltage waveform to the buck converter is
a rectified sinusoid at line frequency, the LED current has
a ripple at double-line frequency. Electrolytic capacitors
C11 and C12 filter this double-line frequency ripple.
MAX16841
8
Maxim Integrated
Controller IC for Dimmable Offline LED Lamps
Circuit components R11, R12, C15, Q6, Q7, R13, and
R14 are used to control the input current. Q6 and Q7
are matched transistors. The voltage on C15 represents
the average input voltage. The average voltage is then
used to control the current in the current-mirror circuit
formed by R12, R13, R14, Q6, and Q7. The current
flowing into R12 is approximately proportional to the
voltage across C15 and is now reflected on the collector
of Q6, and sinks the same amount of current from the
collector of Q7 that flows into R12. Inside the device is
a 50FA current source. The current flowing into R16 sets
the input current, or the average current flowing into R20.
The circuit tries to keep the input power over the line volt-
age almost constant.
Figure 1. Nonisolated (Buck) Topology
Q2
D6
D10
15V
D3
18V
Q3
F1 L1
L3
D1
D2
1
3
DB+
4
2
R1
R2
AC2
AC1
LED+
LED-
R3
R5
R22 R23
R24
R34
C14
C13 L5
C10 C11 C12
C8
C9
D4
Q1
L2
R26 C1
C2
R20R18
R17
R16
R10
R13
R12
R6
R4
R11
R14
Q7Q6
Q5
R9
R7
R8 DIMOUT
TH
REFI
COMP GND
CS
NDRV
IN
IN
8
7
6
52
1
REFI
REFI 3
4
U1
Q4
C5
C4C3
C16
D12
R21
MAX16841
DB+
DB+
DB+
DB-
G
C15
G
DB-
MAX16841
Maxim Integrated
9
Controller IC for Dimmable Offline LED Lamps
Resistors R16 and R20
The average current in resistor R16 is the average input
current of the buck converter.
If POUT is the output power, then the input power is given by:
OUT
IN
IN
IN M
M INrms
IN
CS
CS P
LP IN Lmax
P
P
P
I2V
V 2V
I R20 0.1V
R16 10µA
V 80%
RIL
I I 0.5 I
=η
×π
=×
= ×
×+
=
×
=
= + ×∆
ILP is the switch peak current. Maximum peak in the
switch current occurs at the peak level of the highest
input voltage.
VCS is 2.2V. Allow 80% margin for tolerances.
Inductor Selection
For optimum efficiency, inductor L5 must be operated in
continuous-conduction mode.
The current in the inductor would be at its maximum level
at peak of the highest input voltage. LED string voltage
is assumed constant. Calculate the duty cycle at peak of
the highest input voltage.
LED
INmax
V
D2V
=×
The percentage peak-to-peak ripple is considered
between 30% and 60% of the inductor current. Assuming
60% peak-to-peak inductor current ripple, the maximum
inductor current is given by:
OUT
Lmax LED
P
I2V
×π
=×
The minimum value of the inductor is given by:
( )
INmax LED
Lmax SW
2V V D
Lmin 0.6 I f
× −×
=××
Figure 2 shows a PFC triac, dimmable, isolated (flyback
topology) offline LED driver.
Here the current through the Q4 MOSFET is controlled.
Current through Q4 is the same as the input current
of the flyback converter. The input-side circuitry is the
same as in the nonisolated buck LED driver that was
previously described. During startup, the device is
powered up from Q2, R10, R11, and D8. Bootstrap from
the bias winding on the transformer turns off the Q2
MOSFET, thus saving power from high-voltage line. Here
the switching threshold programmed by R15, R16, and
R18 can be lower than the LED string voltage.
Output-side electrolytic capacitors C8 and C9 are used
for filtering the double-line frequency current ripple in
LED current.
During an open LED condition, the voltage across the
output capacitors increases and is reflected on the bias-
winding side.
Once the bias-winding voltage goes above 22.5V (typ),
NDRV is disabled and the Q4 MOSFET turns off.
Choose the transformer turns ratio based on the voltage
rating of the MOSFET. Use the following expression to
calculate primary-secondary turns ratio:
DSmax INmax
PS LEDmax
0.8 V V
NV
×−
=
where:
NPS is the primary-secondary turns ratio
VDSmax is the voltage rating of the Q4 MOSFET
VINmax is the maximum peak input voltage
VLEDmax is the maximum voltage of the LED string
Factor 0.8 is taken into account for the voltage spikes,
due to transformer-leakage inductance.
Use the following equation to calculate bias-secondary
turns ratio:
AS LEDmax
18V
NV
=
where NAS is the bias-secondary turns ratio and 18V is
the bias voltage for the device.
MAX16841
Maxim Integrated
Controller IC for Dimmable Offline LED Lamps
Figure 2. Flyback Configuration
Q2
D8
D2
D11
15V
D3
18V Q3
F1 L1
L3
D1
D6
DB-
R1
R2
AC2
AC1
R3
R5
R7 R10 R9
R11
R12
C6
C15
C10
C7
C14 C8 C9
C12
C5
D4
D7
Q1
L2
R24 C1
C2 G
R20R23
R17
R21
R18
R6
Q5 R16
R15
R4
R19
TH
REFI
COMP GND
CS
NDRV
IN
U1
Q4
C13
C4
C3
D12
R14
DIMOUT
MAX16841
DB-
G
REFI
REFI
D9
T1
4
3
1
2
8
7
6
5
DB+
Q6 Q7
DB+
R12
C15
R11
MAX16841
Maxim Integrated
11
Controller IC for Dimmable Offline LED Lamps
Choose the transformer’s magnetizing inductance (Lm)
in such a way so that the transformer operates in DCM
above 120V AC input. DCM operation at higher voltages
reduces switching losses in the Q4 MOSFET. Use the fol-
lowing equation to calculate Lm:
2
IN SW
IN
IN
170V D
Lm If 2
P
I340V
×
=××
×π
=
where D is the switching duty cycle at 170V DC and fSW
is the switching frequency.
In DCM conditions, the peak current in Lm can be
calculated with the help of the following equation:
IN INmax
PSW
2I V
ILm f
××
=×
where VINmax is the maximum peak input voltage.
Feedback Compensation
Loop Compensation for
Nonisolated Buck (R17, C3, C4)
The switching converter small-signal transfer function
contains a pole at origin and a zero. The zero location
is inversely related to inductor current and inductance
value. The minimum frequency of the zero location is:
LED
Zmin Lmax
V
f2 LI
=×π× ×
Design the loop compensation in such a way so that the
loop crossover is near fZmin. Place the compensation
zero formed by R17 and C4 at fZmin/5. R20 is given by:
Lmax
m PP
Zmin
I R20
R17 GV
5
C4 2 f R17
−
×
=×
=×π× ×
where Gm is the transconductance of the internal error
amplifier and VP-P is 2.4V.
Place the compensation pole formed by R17 and
C3 at 5 x fZmin:
Zmin
1
C3 2 5 f R17
=×π× × ×
Loop Compensation
for Flyback Driver (R17, C3, C4)
The switching converter small-signal transfer function is
identical to the buck transfer function. The zero location
is inversely related to primary-magnetizing inductance
and its current. The minimum frequency of the zero
location is:
LED P
Zmin Lmax S
VN
f2 Lm I N
= ×
×π× ×
Design the loop compensation in such a way so that the
loop crossover is near fZmin. Place the compensation
zero formed by R17 and C4 at fZmin/5. R20 is given by:
Lmmax
m PP
Zmin
I R20
R17 GV
5
C4 2 f R17
−
×
=×
=×π× ×
where Lm is the magnetizing inductance of the flyback
transformer, Gm is the transconductance of the internal
error amplifier, and VP-P is 2.4V.
Place the compensation pole formed by R17 and
C3 at 5 x fZmin:
Zmin
1
C3 2 5 f R17
=×π× × ×
MAX16841
Maxim Integrated
Controller IC for Dimmable Offline LED Lamps
Layout Recommendations
Careful PCB layout is critical to achieve low switching
losses, and clean, stable operation. The switching-
converter portion of the circuit has nodes with very fast
voltage changes that could lead to undesirable effects
on the sensitive parts of the circuit.
Follow the guidelines below to reduce noise as much
as possible:
1) Ensure that all heat-dissipating components have
adequate cooling.
2) Isolate the power components and high-current paths
from the sensitive analog circuitry.
3) Have a power ground plane for the switching-
converter power circuit under the power compo-
nents (input filter capacitor, output filter capacitor,
inductor, MOSFET, rectifier diode, and current-sense
resistor). Connect GND to the power ground plane as
close as possible to GND. Connect all other ground
connections to the power ground plane using vias
close to the terminals
4) There are two loops in the power circuit that carry
high-frequency switching currents. One loop is when
the MOSFET is on (from the input filter capacitor posi-
tive terminal, through the output capacitor, inductor,
switching MOSFET, and current-sense resistor, to the
input capacitor negative terminal). The other loop is
when the MOSFET is off (from the output capacitor
negative terminal, through the inductor, the rectifier
diode, and output filter capacitor positive terminal).
Analyze these two loops and make the loop areas as
small as possible. Wherever possible, have a return
path on the power ground plane for the switching
currents on the top-layer copper traces or through
power components. This reduces the loop area con-
siderably and provides a low-inductance path for
the switching currents. Reducing the loop area also
reduces radiation during switching.
MAX16841
Maxim Integrated
13
Controller IC for Dimmable Offline LED Lamps
Figure 3. Flyback LED Driver
Typical Operating Circuits
L1
AC1
D2
C1
Q1
Q2
R1
D4
D5
D7
R8R7
R6
R5
R4
TH
REFI
COMP GND
CS
NDRV
IN
4
3
1
2
8
7
6
5
R3
R2
Q3
T1
LED+
LED-
C5
C4
C2
D3
AC2
D1
MAX16841
DIMOUT
MAX16841
Maxim Integrated
Controller IC for Dimmable Offline LED Lamps
Figure 4. Buck LED Driver
Typical Operating Circuits (continued)
TH
REFI
COMP GND
CS
NDRV
IN
4
3
1
2
8
7
6
5
MAX16841
DIMOUT
L1
L2
AC1
D2
C1
Q1
Q2
R1
D4
D3
R8R7
R6
R5
R4
R3
R2
Q3
LED+
LED-
C5
C4
C2
AC2
D1
MAX16841
Maxim Integrated
15
Controller IC for Dimmable Offline LED Lamps
Figure 5. Buck-Boost LED Driver
Typical Operating Circuits (continued)
L1
D3
AC1
D2
C1
Q1
Q2
R1
D4
L2
R8R7
R6
R5
R4
R3
R2
Q3
LED-
LED+
C5
C4
C2
AC2
D1
TH
REFI
COMP GND
CS
NDRV
IN
4
3
1
2
8
7
6
5
MAX16841
DIMOUT
MAX16841
Maxim Integrated
Controller IC for Dimmable Offline LED Lamps
Ordering Information
+Denotes a lead(Pb)-free/RoHS-compliant package.
Chip Information
PROCESS: BiCMOS
Package Information
For the latest package outline information and land patterns
(footprints), go to www.maxim-ic.com/packages. Note that a
“+”, “#”, or “-” in the package code indicates RoHS status only.
Package drawings may show a different suffix character, but
the drawing pertains to the package regardless of RoHS status.
PART TEMP. RANGE PIN-PACKAGE
MAX16841ASA+ -40NC to +125NC8 SO
PACKAGE
TYPE
PACKAGE
CODE
OUTLINE
NO.
LAND
PATTERN NO.
8 SO S8+2 21-0041 90-0096
MAX16841
Maxim Integrated
17
Controller IC for Dimmable Offline LED Lamps
Revision History
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
0 10/11 Initial release —
MAX16841
18
Maxim Integrated 160 Rio Robles, San Jose, CA 95134 USA 1-408-601-1000
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied.
Maxim reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max limits) shown in the Electrical
Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
© 2011 Maxim Integrated The Maxim logo and Maxim Integrated are trademarks of Maxim Integrated Products, Inc.