DIODES 744770933

A Product Line of
Diodes Incorporated
ZXLD1370
60V HIGH ACCURACY BUCK/BOOST/BUCK-BOOST LED DRIVER CONTROLLER
Description
Pin Assignments
The ZXLD1370 is an LED driver controller IC for driving
external MOSFETs to drive high current LEDs. It is a multitopology controller enabling it to efficiently control the current
through series connected LEDs. The multi-topology enables
it to operate in buck, boost and buck-boost configurations.
The 60V capability coupled with its multi-topology capability
enables it to be used in a wide range of applications and
drive in excess of 15 LEDs in series.
The ZXLD1370 is a modified hysteretic controller using a
patent pending control scheme providing high output current
accuracy in all three modes of operation. High accuracy
dimming is achieved through DC control and high frequency
PWM control.
The ZXLD1370 uses two pins for fault diagnosis. A flag
output highlights a fault, while the multi-level status pin gives
further information on the exact fault.
TSSOP-16 EP
Features
•
•
•
•
•
•
•
0.5% typical output current accuracy
6 to 60V operating voltage range
LED driver supports Buck, Boost and Buck-boost
configurations
Wide dynamic range dimming
o 20:1 DC dimming
o 1000:1 dimming range at 500Hz
Up to 1MHz switching
High temperature control of LED current using TADJ
Typical Application Circuit
Buck-boost diagram utilizing thermistor and Tadj
ZXLD1370
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ZXLD1370
Pin Descriptions
Pin Name
Pin
Type‡
ADJ
1
I
REF
2
O
TADJ
3
I
SHP
4
I/O
STATUS
5
O
SGND
6
P
Signal ground (Connect to 0V)
PGND
7
P
Power ground - Connect to 0V and pin 8 to maximize copper area
N/C
8
-
Not Connected internally – recommend connection to pin 7, (PGND), to maximize PCB
copper for thermal dissipation
N/C
9
GATE
10
Not Connected internally – recommend connection pin 10 (GATE) to permit wide copper
trace to gate of MOSFET
O
VAUX
11
P
VIN
12
P
ISM
13
I
FLAG
14
O
PWM
15
I
GI
16
I
EP
PAD
P
Notes:
Description
Adjust input (for dc output current control)
Connect to REF to set 100% output current.
Drive with dc voltage (125mV<VADJ< 2.5V) to adjust output current from 10% to 200%
of set value. The ADJ pin has an internal clamp that limits the internal node to less than
3V. This provides some failsafe should they get overdriven
Internal 1.25V reference voltage output
Temperature Adjust input for LED thermal current control
Connect thermistor/resistor network to this pin to reduce output current above a preset
temperature threshold.
Connect to REF to disable thermal compensation function. (See section on thermal
control.)
Shaping capacitor for feedback control loop
Connect 100pF ±20% capacitor from this pin to ground to provide loop compensation
Operation status output (analog output)
Pin is at 4.5V (nominal) during normal operation.
Pin switches to a lower voltage to indicate specific operation warnings or fault
conditions. (See section on STATUS output.)
Status pin voltage is low during shutdown mode
Gate drive output to external NMOS transistor – connect to pin 9
Auxiliary positive supply to internal switch gate driver
Connect to VIN, or auxiliary supply from 6V to 15V supply to reduce internal power
dissipation (Refer to application section for more details)
Decouple to ground with capacitor close to device (refer to Applications section)
Input supply to device (6V to 60V)
Decouple to ground with capacitor close to device (refer to Applications section)
Current monitor input. Connect current sense resistor between this pin and VIN
The nominal voltage across the resistor is 225mV
Flag open drain output
Pin is high impedance during normal operation
Pin switches low to indicate a fault, or warning condition
Digital PWM output current control
Pin driven either by open Drain or push-pull 3.3V or 5V logic levels.
Drive with frequency higher than 100Hz to gate output ‘on’ and ‘off’ during dimming
control
The device enters standby mode when PWM pin is driven with logic low level for more
than 15ms nominal (Refer to application section for more details)
Gain setting input
Used to set the device in Buck mode or Boost, Buck-boost modes
Connect to ADJ in Buck mode operation
For Boost and Buck-boost modes, connect to resistive divider from ADJ to SGND. This
defines the ratio of switch current to LED current (see application section). The GI pin
has an internal clamp that limits the internal node to less than 3V. This provides some
failsafe should they get overdriven
Exposed paddle. Connect to 0V plane for electrical and thermal management
‡
. Type refers to whether or not pin is an Input, Output, Input/Output or Power supply pin.
ZXLD1370
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Absolute Maximum Ratings (Voltages to GND Unless Otherwise Stated)
Symbol
VIN
VAUX
VISM
VSENSE
VGATE
IGATE
VFLAG
VPWM, VADJ,
VTADJ, VGI,
VPWM
TJ
TST
Parameter
Input supply voltage relative to GND
Auxiliary supply voltage relative to GND
Current monitor input relative to GND
Current monitor sense voltage (VIN-VISM)
Gate driver output voltage
Gate driver continuous output current
Flag output voltage
Rating
-0.3 to 65
-0.3 to 65
-0.3 to 65
-0.3 to 5
-0.3 to 20
18
-0.3 to 40
Unit
V
V
V
V
V
mA
V
Other input pins
-0.3 to 5.5
V
Maximum junction temperature
Storage temperature
150
-55 to 150
°C
°C
These are stress ratings only. Operation outside the absolute maximum ratings may cause device failure.
Operation at the absolute maximum rating for extended periods may reduce device reliability.
Recommended Operating Conditions
Symbol
Parameter
Performance/Comment
Normal operation
Functional (Note 1)
Normal operation
Functional
VIN
Input supply voltage range
VAUX
Auxiliary supply voltage range (Note 2)
VISM
VSENSE
Current sense monitor input range
Differential input voltage
External dc control voltage applied to ADJ
pin to adjust output current
Reference external load current
Recommended switching frequency range
(Note 3)
Temperature adjustment (TADJ) input voltage
range
Recommended PWM dimming frequency range
(Note 4)
PWM pulse width in dimming mode
PWM pin high level input voltage
PWM pin low level input voltage
Operating Junction Temperature Range
Gain setting ratio for boost and buck-boost modes
VADJ
IREF
fmax
VTADJ
fPWM
tPWMH/L
VPWMH
VPWML
TJ
GI
Notes:
VVIN-VISM, with 0 ≤ VADJ ≤ 2.5
DC brightness control mode
from 10% to 200%
REF sourcing current
To achieve 1000:1 resolution
To achieve 500:1 resolution
PWM input high or low
Ratio= VGI/VADJ
Min
8
6.3
8
6.3
6.3
0
Max
Unit
60
V
60
V
60
450
V
mV
0.125
2.5
V
1
mA
300
1000
kHz
0
VREF
V
100
100
0.002
2
0
-40
0.20
500
1000
10
5.5
0.4
125
0.50
Hz
Hz
ms
V
V
°C
1. The functional range of VIN is the voltage range over which the device will function. Output current and device parameters may deviate from their
normal values for VIN and VAUX voltages between 6V and 8V, depending upon load and conditions.
2. VAUX can be driven from a voltage higher than VIN to provide higher efficiency at low VIN voltages, but to avoid false operation; a voltage should not
be applied to VAUX in the absence of a voltage at VIN.
3. The device contains circuitry to control the switching frequency to approximately 400kHz. The maximum and minimum operating frequency are not
tested in production.
4. This gives maximum resolution at the expense of accuracy. To ensure accuracy the following equation should be used: 2*Resolution *fPWM < fSWH
ZXLD1370
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Electrical Characteristics
(Test conditions: VIN = VAUX = 12V, TA = 25°C, unless otherwise specified.)
Symbol
Parameter
Supply and reference parameters
Under-Voltage detection threshold
VUVNormal operation to switch disabled
Under-Voltage detection threshold
VUV+
Switch disabled to normal operation
IQ-IN
Quiescent current into VIN
IQ-AUX
Quiescent current into VAUX
ISB-IN
Standby current into VIN.
ISB-AUX
Standby current into VAUX.
Internal reference voltage
VREF
Change in reference voltage with output
ΔVREF
current
Conditions
Min
Typ
Max
VIN or VAUX falling
5.2
5.6
6.3
VIN or VAUX rising
5.5
6
6.5
1.5
150
90
0.7
1.25
3
300
150
10
1.263
PWM pin floating.
Output not switching
PWM pin grounded
for more than 15ms
No load
Sourcing 1mA
Sinking 100 µA
VREF_LINE Reference voltage line regulation
VIN = VAUX , 6.5V<VIN = <60V
Reference
temperature
coefficient
VREF-TC
DC-DC converter parameters
External dc control voltage applied to ADJ DC brightness control mode
VADJ‡
pin to adjust output current
10% to 200%
VADJ ≤ 2.5V
ADJ input current
IADJ
†
VADJ = 5.0V
GI Voltage threshold for boost and buckVGI‡
VADJ = 1.25V
boost modes selection
VGI ≤ 2.5V
GI input current
IGI
†
VGI = 5.0V
PWM input current
IPWM
VPWM = 5.5V
PWM pulse width
PWM input low
tPWMoff
(to enter shutdown state)
Thermal shutdown upper threshold
Temperature rising.
TSDH
(GATE output forced low)
Thermal shutdown lower threshold
Temperature falling.
TSDL
(GATE output re-enabled)
High-Side Current Monitor (Pin ISM)
Measured into ISM pin and
Input Current
IISM
VISM = 12V
Accuracy of nominal VSENSE threshold
VSENSE_acc
voltage
VADJ = 1.25V
Over-current
sense threshold voltage
VSENSE-OC
Notes:
†
1.237
-5
-90
+/-50
0.125
1.25
10
300
V
V
mA
µA
µA
µA
V
mV
5
-60
Units
dB
ppm/°C
2.5
V
100
5
nA
µA
0.8
V
100
5
nA
µA
36
100
µA
15
25
ms
150
ºC
125
ºC
11
20
µA
±0.25
±2
%
350
375
mV
The ADJ and GI pins have an internal clamp that limits the internal node to less than 3V. This provides some failsafe should those
pins get overdriven.
ZXLD1370
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ZXLD1370
Electrical Characteristics
(Test conditions: VIN = VAUX = 12V, TA = 25°C, unless otherwise specified.)
Symbol
Parameter
Output Parameters
VFLAGL FLAG pin low level output voltage
IFLAGOFF FLAG pin open-drain leakage current
STATUS Flag no-load output voltage
VSTATUS (Note 5)
RSTATUS Output impedance of STATUS output
Driver output (PIN GATE)
Conditions
VFLAG=40V
Normal operation
Out of regulation (VSHP out of range)
(Note 6)
VIN under-voltage (VIN < 5.6V)
Switch stalled (tON or tOFF> 100µs)
Over-temperature (TJ > 125°C)
Excess sense resistor current
(VSENSE > 0.32V)
Normal operation
No load Sourcing 1mA
(Note 7)
Low level output voltage
Sinking 1mA, (Note 8)
VGATECL High level GATE CLAMP voltage
IGATE
Dynamic peak current available during
rise or fall of output voltage
Typ
Max
Units
V
µA
4.2
4.5
0.5
1
4.8
3.3
3.6
3.9
3.3
3.3
1.5
3.6
3.6
1.8
3.9
3.9
2.1
0.6
0.9
1.2
Output sinking 1mA
VGATEH High level output voltage
VGATEL
Min
10
VIN = VAU X= VISM = 18V
IGATE = 1mA
Charging or discharging gate of
external switch with QG = 10nC and
400kHz
Time to assert ‘STALL’ flag and
warning on STATUS output
GATE low or high
(Note 9)
LED Thermal control circuit (TADJ) parameters
Upper threshold voltage
Onset of output current reduction
VTADJH
(VTADJ falling)
Lower threshold voltage
Output current reduced to <10% of
VTADJL
set value (VTADJ falling)
TADJ pin Input current
ITADJ
VTADJ = 1.25V
10
kΩ
11
V
12.8
0.5
V
15
V
±300
mA
100
170
µs
560
625
690
mV
380
440
500
mV
1
µA
tSTALL
Notes:
V
5. In the event of more than one fault/warning condition occurring, the higher priority condition will take precedence. E.g. ‘Excessive coil current’ and
‘Out of regulation’ occurring together will produce an output of 0.9V on the STATUS pin. The voltage levels on the STATUS output assume the
Internal regulator to be in regulation and VADJ<=VREF. A reduction of the voltage on the STATUS pin will occur when the voltage on VIN is near the
minimum value of 6V.
6. Flag is asserted if VSHP<2.5V or VSHP>3.5V
7. GATE is switched to the supply voltage VAUX for low values of VAUX (i.e. between 6V and approximately 12V). For VAUX>12V, GATE is clamped
internally to prevent it exceeding 15V.
8. GATE is switched to PGND by an NMOS transistor
9. If tON exceeds tSTALL, the device will force GATE low to turn off the external switch and then initiate a restart cycle. During this phase, ADJ is
grounded internally and the SHP pin is switched to its nominal operating voltage, before operation is allowed to resume. Restart cycles will be
repeated automatically until the operating conditions are such that normal operation can be sustained. If tOFF exceeds tSTALL, the switch will remain
off until normal operation is possible.
ZXLD1370
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Typical Characteristics – Buck Mode – RS = 150mΩ – L = 33µH - ILED = 1.5A
1.500
1 LED
3 LEDs
5 LEDs
7 LEDs
9 LEDs
11 LEDs
13 LEDs
15 LEDs
LED Current (A)
1.490
1.480
1.470
1.460
1.450
1.440
1.430
6.5
11
15.5
20
24.5
29
33.5
38
42.5
47
51.5
Input Voltage (V)
Figure 1: Load Current vs. Input Voltage & Number of LED
56
60.5
1000
1 LE D
3 LE Ds
5 LE Ds
7 LE Ds
9 LE Ds
11 LE Ds
13 LE Ds
15 LE Ds
Switching Frequency (kHz)
900
800
TA = 25°C
VAU X = VIN
700
600
500
400
300
200
100
0
6.5
11
15.5
11
15.5
20
24.5
29
33.5
38
42.5
47
51.5
Input Voltage (V)
Figure 2: Frequency vs. Input Voltage & Number of LED
20
24.5
56
60.5
56
60.5
100%
95%
Efficiency
90%
85%
80%
75%
70%
65%
60%
6.5
ZXLD1370
Document number: DS32165 Rev. 2 - 2
29
33.5
38
42.5
47
Input Voltage (V)
Figure 3: Efficiency vs. Input & Number of LED
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ZXLD1370
Typical Characteristics – Buck Mode – Rs = 300mΩ - L = 47µH - ILED = 750mA
0.740
0.735
LED Current (A)
TA = 25°C
V AUX = VIN
0.730
0.725
0.720
2 LEDs
0.715
6.5
11
3 LEDs
15.5
5 LEDs
20
7 LEDs
9 LEDs
11 LEDs
24.5
29
33.5
38
42.5
Input Voltage (V)
Figure 4: I LED vs. Input & Number of LED
13 LEDs
47
51.5
15 LEDs
56
60.5
1000
2 LEDs
3 LEDs
5 LEDs
7 LEDs
9 LEDs
11 LEDs
13 LEDs
15 LEDs
900
Switching Frequency (kHz)
800
TA = 25°C
VAU X = VIN
700
600
500
400
300
200
100
0
6.5
11
15.5
20
24.5
29
33.5
38
42.5
47
Input Voltage (V)
Figure 5: Frequency ZXLD1370 - Buck Mode - L47 μH
51.5
56
60.5
100%
95%
Efficiency
90%
85%
80%
75%
TA = 25°C
VAU X = VIN
70%
2 LEDs
3 LEDs
5 LEDs
7 LEDs
9 LEDs
11 LEDs
13 LEDs
15 LEDs
65%
60%
6.5
11
ZXLD1370
Document number: DS32165 Rev. 2 - 2
15.5
20
24.5
29
33.5
38
42.5
47
Input Voltage (V)
Figure 6: Efficiency vs. Input Voltage & Number of LED
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51.5
56
60.5
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ZXLD1370
Typical Characteristics – Boost mode – ILED = 350mA – RS = 150mΩ – GIRATIO = 0.23
0.400
0.350
TA = 25°C
VAU X = VIN
LED Current (A)
0.300
0.250
0.200
0.150
0.100
0.050
3 LEDs
0.000
6.5
10
4 LEDs
13.5
17
6 LEDs
8 LEDs
10 LEDs
12 LEDs
20.5
14 LEDs
24
27.5
31
34.5
38
Input Voltage (V)
Figure 7: ILED vs. Input Voltage & Number of LED
16 LEDs
41.5
45
48.5
500
3 LEDs
4 LEDs
6 LEDs
8 LEDs
10 LEDs
12 LEDs
14 LEDs
16 LEDs
Switching Frequency (kHz)
450
TA = 25°C
VAU X = VIN
400
350
300
250
200
150
100
50
Boosted voltage across
LEDs approaching VIN
6.5
100%
10
3 LEDs
13.5
17
24
27.5
31
34.5
38
41.5
Input Voltage (V)
Figure 8: Frequency vs. Input Voltage & Number of LED
4 LEDs
20.5
6 LEDs
8 LEDs
10 LEDs
12 LEDs
14 LEDs
45
48.5
16 LEDs
95%
Efficiency
90%
85%
80%
TA = 25°C
VAU X = VIN
75%
70%
65%
60%
6.5
10
ZXLD1370
Document number: DS32165 Rev. 2 - 2
13.5
17
20.5
24
27.5
31
34.5
38
41.5
Input Voltage (V)
Figure 9: Efficiency vs. Input Voltage & Number of LED
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48.5
May 2010
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ZXLD1370
Typical Characteristics – Buck-Boost mode – RS=150mΩ - ILED = 350mA - GIRATIO = 0.23
0.370
3 LEDs
4 LEDs
5 LEDs
6 LEDs
7 LEDs
8 LEDs
0.365
LED Current (A)
0.360
0.355
0.350
0.345
0.340
0.335
0.330
6.5
8
9.5
11
12.5
14
Input Voltage (V)
Figure 10: LED Current vs. Input Voltage & Number of LED
15.5
17
800
3 LEDs
4 LEDs
5 LEDs
6 LEDs
7 LEDs
8 LEDs
Switching Frequency (kHz)
700
600
500
400
300
200
100
0
6.5
8
9.5
11
12.5
14
15.5
Input Voltage (V)
Figure 11: Switching Frequency vs. Input Voltage & Number of LED
17
100%
3 L EDs
4 L EDs
5 L EDs
6 L EDs
7 L EDs
8 L EDs
95%
Efficiency
90%
85%
80%
75%
70%
65%
60%
6.5
ZXLD1370
Document number: DS32165 Rev. 2 - 2
8
9.5
11
12.5
14
Input Voltage (V)
Figure 12: Efficiency vs. Input Voltage & Number of LED
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17
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ZXLD1370
Applications Information
The ZXLD1370 is a high accuracy hysteretic inductive buck/boost/buck-boost controller designed to be used with an
external NMOS switch for current-driving single or multiple series-connected LEDs. The device can be configured to
operate in buck, boost, or buck-boost modes by suitable configuration of the external components as shown in the
schematics shown in the device operation description.
DEVICE OPERATION
a) Buck mode – the most simple buck circuit is shown in Figure 13
LED current control in buck mode is achieved by sensing
the coil current in the sense resistor Rs, connected
between the two inputs of a current monitor within the
control loop block. An output from the control loop drives
the input of a comparator which drives the gate of the
external NMOS switch transistor M1 via the internal Gate
Driver. When the switch is on, current flows from VIN, via
Rs, LED, coil and switch to ground. This current ramps up
until an upper threshold value is reached. At this point
GATE goes low, the switch is turned off and the current
flows via Rs, LED, coil and D1 back to VIN. When the coil
current has ramped down to a lower threshold value, GATE
goes high, the switch is turned on again and the cycle of
events repeats, resulting in continuous oscillation.
Figure 13: Buck configuration
The average current in the LED and coil is equal to the average of the maximum and minimum threshold currents. The ripple
current (hysteresis) is equal to the difference between the thresholds. The control loop maintains the average LED current at
the set level by adjusting the thresholds continuously to force the average current in the coil to the value demanded by the
voltage on the ADJ pin. This minimizes variation in output current with changes in operating conditions. The control loop also
attempts to minimize changes in switching frequency by varying the level of hysteresis. The hysteresis has a defined minimum
(typ 5%) and a maximum (typ 30%), the frequency may deviate from nominal in extreme conditions. Loop compensation is
achieved by a single external capacitor C2, connected between SHP and SGND.
Gate Voltage
~15V
0V
V
VIN
V -225 mV
VIN
ISM Voltage
Coil/LED current
225mV/R s
0A
t
OFF
t
ON
Figure 14: Operating waveforms (Buck mode)
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b) Boost and Buck-Boost modes
Control in Boost and Buck-boost mode is achieved by
sensing the coil current in the series resistor Rs, connected
between the two inputs of a current monitor within the
control loop block. An output from the control loop drives
the input of a comparator which drives the gate of the
external NMOS switch transistor M1 via the internal Gate
Driver. In boost and buck-boost modes, when the switch is
on, current flows from VIN, via Rs, coil and switch to
ground. This current ramps up until an upper threshold
value is reached. At this point GATE goes low, the switch
is turned off and the current flows via Rs, coil, D1 and LED
back to VIN (Buck-boost mode), or GND (Boost mode).
When the coil current has ramped down to a lower
threshold value, GATE goes high, the switch is turned on
again and the cycle of events repeats, resulting in
continuous oscillation. The average current in the coil is
equal to the average of the maximum and minimum
threshold currents and the ripple current (hysteresis) is
Figure 15: Boost and Buck-Boost configuration
equal to the difference between the thresholds.
The average current in the LED is always less than the average current in the coil and the ratio between these currents is
set by the values of external resistors RGI1 and RGI2. The peak LED current is equal to the peak coil current. The control
loop maintains the average LED current at the set level by adjusting the thresholds and the hysteresis continuously to force
the average current in the coil to the value demanded by the voltage on the ADJ and GI pins. This minimises variation in
output current with changes in operating conditions. Loop compensation is achieved by a single external capacitor C2,
connected between SHP and SGND.
Gate Voltage
~15V
0V
VVIN
VVIN -225mV
ISM Voltage
Coil current
225mV/Rs
0A
LED current
225mV/Rs
Average
LED current
0A
tOFF
tON
Figure 16 - Operating waveforms (Boost and Buck-boost modes)
Note: In Boost and Buck-boost modes, average ILED= average ICOIL x RGI1/(RGI1+RGI2)
For more detailed descriptions of device operation and for choosing external components, please refer to the application
circuits and descriptions in the later sections of this specification.
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Application Information
A basic ZXLD1370 application circuit is shown in Figure 13 and 15.
External component selection is driven by the characteristics of the load and the input supply, since this will determine the
kind of topology being used for the system.
Component selection starts with the current setting procedure, the inductor/frequency setting and the MOSFET selection.
Finally after selecting the freewheeling diode and the output capacitor (if needed), the application section will cover the PWM
dimming and thermal feedback.
Setting the output current
The first choice when defining the output current is whether the device is operating with the load in series with the sense
resistor (buck mode) or whether the load is not in series with the sense resistor (boost and buck-boost modes).
The output current setting depends on the choice of the sense resistor Rs, the voltage on the ADJ pin and the voltage on the
GI pin, according to the device working mode. The sense resistor Rs sets the coil current IRS.
The ADJ pin may be connected directly to the internal 1.25V reference (VREF) to define the nominal 100% LED current. The
ADJ pin can also be overdriven with an external dc voltage between 125mV and 2.5V to adjust the LED current proportionally
between 10% and 200% of the nominal value.
ADJ and GI are high impedance inputs within their normal operating voltage ranges. An internal 2.6V clamp protects the
device against excessive input voltage and limits the maximum output current to approximately 4% above the maximum
current set by VADJ if the maximum input voltage is exceeded.
Below are provided the details of the LED current calculation both when the load in series with the sense resistor (buck mode)
and when the load is not in series with the sense resistor (boost and buck-boost modes).
RS
In Buck mode, GI is connected to ADJ giving the ratio of
average LED current (ILED) to average sense resistor/coil
current (IRS).
=
ILED
IRs =
VIN
225mV VADJ
R S VREF
REF
ADJ
If the ADJ and GI pins are connected to VREF directly, this
becomes:
=
ILED
IRs =
GI
225mV
RS
SGND
Therefore:
225mV
ILED
Rs =
Figure 17: Buck configuration
In Boost and Buck-boost mode GI is connected to ADJ
through a voltage divider.
RS
VIN
With VADJ equal to VREF, the ratio defined by the resistor
divider at the GI pin determines the ratio of average LED
current (ILED) to average sense resistor/coil current (IRS).
ILED
Where
ISM
=
IRs =
VGI
R GI1
IRs =
IRs
VADJ
(R GI1 + R GI2 )
=
R GI2
225mV VADJ
RS VREF
GI
R GI1
225mV
RS
ZXLD1370
Document number: DS32165 Rev. 2 - 2
REF
ADJ
When the ADJ pin is connected to VREF directly, this
becomes:
IRs
ISM
SGND
Figure 18: Boost and Buck-boost connection
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Therefore:
Rs =
R GI1
225mV
(R GI1 + R GI2 ) ILED
Note that the average LED current for a boost or buck-boost converter is always less than the average sense resistor
current. For the ZXLD1370, the recommended potential divider ratio is given by:
0. 2 ≤
RGI1
≤ 0.50
(RGI1 + RGI2 )
It is possible to use a different combination of GI pin voltages and sense resistor values to set the LED current.
In general the design procedure to follow is:
-
Define input conditions in terms of VIN and IIN
-
Set output conditions in terms of LED current and the number of LEDs
-
Define controller topology – Buck, Boost or Buck-boost
Calculate the maximum duty-cycle as:
Buck mode
D MAX =
VLEDs
VINMIN
Boost mode
DMAX =
VLEDS − VIN MIN
VLEDS
Buck-boost mode
DMAX =
VLEDS
VLEDS + VIN MIN
Set the appropriate GI ratio according to the circuit duty and the max switch current admissible cycle limitations
VGI
R GI1
=
≤ 1 − D MAX
VADJ
(R GI1 + R GI2 )
10kΩ ≤ R GI1 ≤ 200kΩ
- Set RGI1 as:
- Calculate RGI2 as:
R GI2 ≈
-
D MAX
x R GI1
1 − D MAX
Calculate the sense resistor as:
Rs =
R GI1
225mV
(R GI1 + R GI2 ) ILED
If the potential divider ratio is greater than 0.64, the device detects that buck-mode operation is desired and the output current
will deviate from the desired value.
For example, as in the typical application circuit, in order to get ILED= 350mA with IRS=1.5A the ratio has to be set as:
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ILED
VGI
RGI1
=
=
≈ 0.23
IRS
VADJ
(RGI1 + RGI2)
Setting RGI1= 33kΩ it results
R GI2 = R GI1(
VADJ
− 1) = 110kΩ
VGI
This will result in:
Rs =
R GI1
225mV
= 150mΩ
(R GI1 + R GI2 ) ILED
Table 1 shows typical resistor values used to determine GIRATIO with E24 series resistors
Table 1
GI ratio
0.2
0.25
0.3
0.35
0.4
0.45
0.5
RGI1
30kΩ
33kΩ
39kΩ
30kΩ
100kΩ
51kΩ
30kΩ
RG2
120kΩ
100kΩ
91kΩ
56kΩ
150kΩ
62kΩ
30kΩ
INDUCTOR/FREQUENCY SELECTION
Recommended inductor values for the ZXLD1370 are in the range 22 μH to 100 μH. The chosen coil should have a
saturation current higher than the peak sensed current and a continuous current rating above the required mean sensed
current by at least 50%.
The inductor value should be chosen to maintain operating duty cycle and switch 'on'/'off' times within the recommended
limits over the supply voltage and load current range.
The frequency compensation mechanism inside the chip tends to keep the frequency within the range 300kHz – 400kHz in
most of the operating conditions. Nonetheless, the controller allows for higher frequencies when either the number of LEDs
or the input voltage increases.
The graphs below can be used to select a recommended inductor to maintain the ZXLD1370 switching frequency within a
predetermined range when used in different topologies.
Buck inductor selection:
ZXLD1370 Buck Mode 1.5A Minimum Recommended Inductor
Target Switching frequency - 400kHz
15
Number of LEDs
13
11
9
L=47uH
7
5
L=33uH
3
L=22uH
L=10uH
1
0
10
20
30
40
50
60
Supply Voltage (V)
Figure 19: 1.5A Buck mode inductor selection for target frequency of 400 kHz
ZXLD1370
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ZXLD1370 Buck Mode 1.5A Minimum Recommended Inductor
Target Switching frequency > 500kHz
15
13
Number of LEDs
11
9
L=47uH
7
5
L=33uH
L=22uH
3
L=10uH
1
0
10
20
30
40
50
60
Supply Voltage (V)
Figure 20: 1.5A Buck mode inductor selection for target frequency > 500kHz
For example, in a buck configuration (VIN =24V and 6 LEDs), with a load current of 1.5A; if the target frequency is around
400 kHz, the Ideal inductor size is L= 33µH.
The same kind of graphs can be used to select the right inductor for a buck configuration and a LED current of 750mA, as
shown in figures 21 and 22.
ZXLD1370 Buck Mode 750mA Minimum Recommended Inductor
Target Switching frequency 400kHz
15
Number of LEDs
13
11
9
7
L=100uH
5
L=68uH
L=47uH
3
L=33uH
1
0
10
20
30
40
50
60
Supply Voltage (V)
Figure 21: 750mA Buck mode inductor selection for target frequency 400kHz
ZXLD1370
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ZXLD1370 Buck Mode 750mA Minimum Recommended Inductor
Target Switching frequency > 500kHz
15
Number of LEDs
13
11
9
L=100uH
7
5
L=68uH
L=47uH
3
L=33uH
1
0
10
20
30
40
50
60
Supply Voltage (V)
Figure 22: 750mA Buck mode inductor selection for target frequency > 500kHz
In the case of the Buck-boost topology, the following graphs guide the designer to select the inductor for a target frequency
of 400kHz (figure 23) or higher than 500kHz (figure 24).
ZXLD1370 Buck-Boost Mode 350mA Minimum Recommended Inductor
Target Switching frequency - 400kHz
15
Number of LEDs
13
11
9
L=47uH
7
5
L=33uH
3
L=22uH
1
0
10
20
30
40
50
60
Supply Voltage (V)
Figure 23: 350mA Buck-Boost mode inductor selection for target frequency 400kHz
ZXLD1370
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ZXLD1370 Buck-Boost Mode 350mA Minimum Recommended Inductor
Target Switching frequency > 500kHz
15
Number of LEDs
13
11
L=47uH
9
7
5
L=33uH
3
L=22uH
1
0
10
20
30
40
50
60
Supply Voltage (V)
Figure 24: 350mA Buck-Boost mode inductor selection for target frequency > 500kHz
For example, in a Buck-bust configuration (VIN =10-18V and 4 LEDs), with a load current of 350mA; if the target frequency
is around 400kHz, the Ideal inductor size is L= 33uH. The same size of inductor can be used if the target frequency is higher
than 500kHz driving 6LEDs with a current of 350mA from a VIN =12-24V.
In the case of the Boost topology, the following graphs guide the designer to select the inductor for a target frequency of
400kHz (figure 25) or higher than 500kHz (figure 26).
ZXLD1370 Boost Mode 350mA Minimum Recommended Inductor
Target Switching frequency - 400kHz
L=47uH
15
Number of LEDs
13
11
L=33uH
9
7
L=22uH
5
3
1
0
10
20
30
40
50
60
Supply Voltage (V)
Figure 25: 350mA Boost mode inductor selection for target frequency 400kHz
ZXLD1370
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ZXLD1370 Boost Mode 350mA Minimum Recommended Inductor
Target Switching frequency > 500kHz
L=47uH
15
Number of LEDs
13
L=33uH
11
9
7
L=22uH
5
3
1
0
10
20
30
40
50
60
Supply Voltage (V)
Figure 26: 350mA Buck-Boost mode inductor selection for target frequency > 500kHz
Suitable coils for use with the ZXLD1370 may be selected from the MSS range manufactured by Coilcraft, or the NPIS range
manufactured by NIC components.
The following websites may be useful in finding suitable components
www.coilcraft.com
www.niccomp.com
www.wuerth-elektronik.de
MOSFET Selection
The ZXLD130 requires an external NMOS FET as the main power switch with a voltage rating at least 15% higher than the
maximum transistor voltage to ensure safe operation during the ringing of the switch node. The current rating is
recommended to be at least 10% higher than the average transistor current. The power rating is then verified by calculating
the resistive and switching power losses.
P = Presistive + Pswitching
Resistive power losses
The resistive power losses are calculated using the RMS transistor current and the MOSFET on-resistance.
Calculate the current for the different topologies as follows:
Buck mode
IMOSFET −MAX = D MAX x ILED
Boost / Buck-boost mode
IMOSFET −MAX =
D MAX
x ILED
1 − DMAX
The approximate RMS current in the MOSFET will be:
Buck mode
IMOSFET −RMS =ILED D
Boost / Buck-boost mode
IMOSFET −RMS =
D
x ILED
1− D
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The resistive power dissipation of the MOSFET is:
Presistive = IMOSFET−RMS x RDS −ON
2
Switching power losses
Calculating the switching MOSFET's switching loss depends on many factors that influence both turn-on and turn-off. Using
a first order rough approximation, the switching power dissipation of the MOSFET is:
Pswitching =
CRSS x V 2 IN x fsw x ILOAD
IGATE
where
CRSS is the MOSFET's reverse-transfer capacitance (a data sheet parameter),
fSW is the switching frequency,
IGATE is the MOSFET gate-driver's sink/source current at the MOSFET's turn-on threshold.
Matching the MOSFET with the controller is primarily based on the rise and fall time of the gate voltage. The best rise/fall
time in the application is based on many requirements, such as EMI (conducted and radiated), switching losses, lead/circuit
inductance, switching frequency, etc. How fast a MOSFET can be turned on and off is related to how fast the gate
capacitance of the MOSFET can be charged and discharged. The relationship between C (and the relative total gate
charge Qg), turn-on/turn-off time and the MOSFET driver current rating can be written as:
dt =
dV ⋅ C Qg
=
I
I
where
dt = turn-on/turn-off time
dV = gate voltage
C = gate capacitance = Qg/V
I = drive current – constant current source (for the given voltage value)
Here the constant current source” I ” usually is approximated with the peak drive current at a given driver input voltage.
Example 1)
Using the DMN6068 MOSFET (VDS(MAX) = 60V, ID(MAX) = 8.5A):
Æ QG = 10.3nC at VGS = 10V
ZXLD1370 IPEAK = I GATE = 300mA
dt =
Qg
IPEAK
=
10.3nC
= 35ns
300mA
Assuming that cumulatively the rise time and fall time can account for a maximum of 10% of the period, the maximum
frequency allowed in this condition is:
tPERIOD = 20*dt
Æ
f = 1/ tPERIOD = 1.43MHz
This frequency is well above the max frequency the device can handle, therefore the DNM6068 can be used with the
ZXLD1370 in the whole spectrum of frequencies recommended for the device (from 300kHz to 1MHz).
Example 2)
Using the ZXMN6A09K (VDS(MAX) = 60V, ID(MAX) = 12.2A):
Æ QG = 29nC at VGS = 10V
ZXLD1370 IPEAK = 300mA
dt =
Qg
IPEAK
=
29nC
= 97ns
300mA
Assuming that cumulatively the rise time and fall time can account for a maximum of 10% of the period, the maximum
frequency allowed in this condition is:
tPERIOD = 20*dt
Æ
f = 1/ tPERIOD = 515kHz
This frequency is within the recommended frequency range the device can handle, therefore the ZXMN6A09K is
recommended to be used with the ZXLD1370 for frequencies from 300kHz to 500kHz).
The recommended total gate charge for the MOSFET used in conjunction with the ZXLD1370 is less than 30nC.
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Junction temperature estimation
Finally, the ZXLD1370 junction temperature can be estimated using the following equations:
Total supply current of ZXLD1370:
IQTOT ≈ IQ + f • QG
Where IQ = total quiescent current IQ-IN + IQ-AUX
Power consumed by ZXLD1370
PIC = VIN • (IQ + f • Qg)
Or in case of separate voltage supply, with VAUX < 15V
PIC = VIN • IQ-IN + Vaux • (IQ-AUX + f • Qg)
TJ =
TA + PIC • RTH(JA)=
TA + PIC • (RTH(JC)+ RTH(CA))
Where the total quiescent current IQTOT consists of the static supply current (IQ) and the current required to charge and
discharge the gate of the power MOSFET. Moreover the part of thermal resistance between case and ambient depends on
the PCB characteristics.
DIODE SELECTION
For maximum efficiency and performance, the rectifier (D1) should be a fast low capacitance Schottky diode* with low
reverse leakage at the maximum operating voltage and temperature. The Schottky diode also provides better efficiency
than silicon PN diodes, due to a combination of lower forward voltage and reduced recovery time.
It is important to select parts with a peak current rating above the peak coil current and a continuous current rating higher
than the maximum output load current. In particular, it is recommended to have a voltage rating at least 15% higher than
the maximum transistor voltage to ensure safe operation during the ringing of the switch node and a current rating at least
10% higher than the average diode current. The power rating is verified by calculating the power loss through the diode.
The higher forward voltage and overshoot due to reverse recovery time in silicon diodes will increase the peak voltage on
the Drain of the external MOSFET. If a silicon diode is used, care should be taken to ensure that the total voltage appearing
on the Drain of the external MOSFET, including supply ripple, does not exceed the specified maximum value.
*A suitable Schottky diode would be PDS3100 (Diodes Inc).
OUTPUT CAPACITOR
An output capacitor may be required to limit interference or for specific EMC purposes. For boost and buck-boost
regulators, the output capacitor provides energy to the load when the freewheeling diode is reverse biased during the first
switching subinterval. An output capacitor in a buck topology will simply reduce the LED current ripple below the inductor
current ripple. In other words, this capacitor changes the current waveform through the LED(s) from a triangular ramp to a
more sinusoidal version without altering the mean current value.
In all cases, the output capacitor is chosen to provide a desired current ripple of the LED current (usually recommended to
be less than 40% of the average LED current).
Buck:
C OUTPUT =
8 x fSW
ΔIL −PP
x rLED x ΔILED −PP
Boost and Buck-boost
C OUTPUT =
fSW
D x ILED −PP
x rLED x ΔILED −PP
where:
•
ΔIL is the ripple of the inductor current, usually ± 20% of the average sensed current
•
ΔILED is the ripple of the LED current, it should be <40% of the LEDs average current
•
fsw is the switching frequency (From graphs and calculator)
•
rLED is the dynamic resistance of the LEDs string (n times the dynamic resistance of the single LED from the
datasheet of the LED manufacturer).
The output capacitor should be chosen to account for derating due to temperature and operating voltage. It must also have
the necessary RMS current rating. The minimum RMS current for the output capacitor is calculated as follows:
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Buck
ICOUTPUT − RMS =
ILED −PP
12
Boost and Buck-boost
ICOUTPUT −RMS = ILED
D MAX
1 − D MAX
Ceramic capacitors with X7R dielectric are the best choice due to their high ripple current rating, long lifetime, and
performance over the voltage and temperature ranges.
INPUT CAPACITOR
The input capacitor can be calculated knowing the input voltage ripple ΔVIN-PP as follows:
Buck
CIN =
D x(1 − D)x ILED
fSW x ΔVIN−PP
CIN =
ΔIL −PP
8 x fSW x ΔVIN−PP
Use D = 0.5 as worst case
Boost
Buck-boost
CIN =
D x ILED
fSW x ΔVIN−PP
Use D = DMAX as worst case
The minimum RMS current for the output capacitor is calculated as follows:
Buck
ICIN−RMS = ILED x Dx(1 − D)
use D=0.5 as worst case
Boost
ICIN−RMS =
IL −PP
12
Buck-boost
ICIN−RMS = ILED x
D
(1 − D)
Use D=DMAX as worst case
PWM OUTPUT CURRENT CONTROL & DIMMING
The ZXLD1370 has a dedicated PWM dimming input that allows a wide dimming frequency range from 100Hz to 1kHz with
up to 1000:1 resolution; however higher dimming frequencies can be used – at the expense of dimming dynamic range and
accuracy.
Typically, for a PWM frequency of 1kHz, the error on the current linearity is lower than 5%; in particular the accuracy is
better than 1% for PWM from 5% to 100%. This is shown in the graph below:
ZXLD1370
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Buck mode - L=33uH - Rs = 150mΩ - PWM @ 1kHz
1500.00
10%
9%
8%
7%
1000.00
6%
750.00
5%
4%
500.00
Error
LED current [mA]
1250.00
3%
2%
250.00
1%
0.00
0
10
20
30
40
50
60
70
80
90
0%
100
PWM
PWM @ 1kHz
Error
Figure 27: LED current linearity and accuracy with PWM dimming at 1kHz
For a PWM frequency of 100Hz, the error on the current linearity is lower than 2.5%; it becomes negligible for PWM greater
than 5%. This is shown in the graph below:
Buck mode - L=33uH - Rs = 150mΩ - PWM @ 100Hz
10%
1500.00
9%
8%
7%
1000.00
6%
5%
750.00
4%
500.00
Error
LED current [mA]
1250.00
3%
2%
250.00
1%
0.00
0
10
20
30
40
50
60
70
80
90
0%
100
PWM
PWM @ 100Hz
Error
Figure 28: LED current linearity and accuracy with PWM dimming at 100Hz
The PWM pin is designed to be driven by both 3.3V and 5V logic levels. It can be driven also by an open drain/collector
transistor. In this case the designer can either use the internal pull-up network or an external pull-up network in order to
speed-up PWM transitions, as shown in the Boost/ Buck-Boost section.
Figure 30: PWM dimming from MCU
Figure 29: PWM dimming from open collector switch
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LED current can be adjusted digitally, by applying a
low frequency PWM logic signal to the PWM pin to
turn the controller on and off. This will produce an
average output current proportional to the duty
cycle of the control signal. During PWM operation,
the device remains powered up and only the output
switch is gated by the control signal.
The PWM signal can achieve very high LED current
resolution. In fact, dimming down from 100% to 0, a
minimum pulse width of 2µs can be achieved
resulting in very high accuracy. While the maximum
recommended pulse is for the PWM signal is10ms.
2µs
< 10 ms
Gate
0V
PWM
< 10 ms
0V
2µs
Figure 31:PWM dimming minimum and maximum pulse
The device can be put in standby by taking the PWM pin to ground, or pulling it to a voltage below 0.4V with a suitable open
collector NPN or open drain NMOS transistor, for a time exceeding 15ms (nominal). In the shutdown state, most of the
circuitry inside the device is switched off and residual quiescent current will be typically 90µA. In particular, the Status pin
will go down to GND while the FLAG and REF pins will stay at their nominal values.
Fig 32: Stand-by state from PWM signal
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TADJ pin - Thermal control of LED current
The ‘Thermal control’ circuit monitors the voltage on the TADJ pin and reduces output current if the voltage on this pin falls
below 625mV. An external NTC thermistor and resistor can therefore be connected as shown below to set the voltage on
the TADJ pin to 625mV at the required temperature threshold. This will give 100% LED current below the threshold
temperature and a falling current above it as shown in the graph. The temperature threshold can be altered by adjusting the
value of Rth and/or the thermistor to suit the requirements of the chosen LED.
The Thermal Control feature can be disabled by connecting TADJ to REF.
Here is a simple procedure to design the thermal feedback circuit:
1)
Select the temperature threshold Tthreshold at which the current must start to decrease
2)
Select the Thermistor TH1 (both resistive value at 25˚C and beta)
3)
Select the value of the resistor Rth as Rth = TH at Tthreshold
Figure 33: Thermal feedback network
For example,
1)
Temperature threshold Tthreshold = 70˚C
2)
TH1 = 10kΩ at 25˚C and beta= 3500
3)
Rth = TH at Tthreshold = 3.3kΩ
Æ TH = 3.3kΩ @ 70˚C
Over-Temperature Shutdown
The ZXLD1370 incorporates an over-temperature shutdown circuit to protect against damage caused by excessive die
temperature. A warning signal is generated on the STATUS output when die temperature exceeds 125°C nominal and the
output is disabled when die temperature exceeds 150°C nominal. Normal operation resumes when the device cools back
down to 125°C.
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FLAG/STATUS Outputs
The FLAG/STATUS outputs provide a warning of extreme operating or fault conditions. FLAG is an open-drain logic output,
which is normally off, but switches low to indicate that a warning, or fault condition exists. STATUS is a DAC output, which is
normally high (4.5V), but switches to a lower voltage to indicate the nature of the warning/fault.
Conditions monitored, the method of detection and the nominal STATUS output voltage are given in the following table:
Table 2
Warning/Fault condition
Severity
(Note 9)
Monitored
parameters
FLAG
Nominal STATUS voltage
H
4.5
4.5
Normal operation
1
VAUX<5.6V
L
2
VIN<5.6V
L
3.6
Output current out of regulation
(Note 10)
2
VSHP outside normal
voltage range
L
3.6
Driver stalled with switch ‘on’, or
‘off’ (Note 11)
2
tON, or tOFF>100µs
L
3.6
Device temperature above
maximum recommended
operating value
3
TJ>125°C
L
1.8
Sense resistor current IRS above
specified maximum
4
VSENSE>0.32V
L
0.9
Supply under-voltage
9. Severity 1 denotes lowest severity.
10. This warning will be indicated if the output power demand is higher than the available input power; the loop may not be able to maintain
regulation.
11. This warning will be indicated if the gate pin stays at the same level for greater than 100us (e.g. the output transistor cannot pass enough current
to reach the upper switching threshold).
FLAG VOLTAGE
Notes:
VREF
0V
4.5V
Normal
Operations
VAUX
UVLO
STATUS VOLTAGE
3.6V
- VIN UVLO
- STALL
- OUT of REG
2.7V
1.8V
Over
Temperature
0.9V
Over
Current
0A
0
1
2
3
4
SEVERITY
Fig 34: Status levels
In the event of more than one fault/warning condition occurring, the higher severity condition will take precedence. E.g.
‘Excessive coil current’ and ‘Out of regulation’ occurring together will produce an output of 0.9V on the STATUS pin.
If VADJ>1.7V, VSENSE may be greater than the excess coil current threshold in normal operation and an error will be
reported. Hence, STATUS and FLAG are only guaranteed for VADJ<=VREF.
ZXLD1370
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VR EF
FLAG
Diagnostic signals should be ignored during the device
start – up for 100μs. The device start up sequence will
be initiated both during the first power on of the device
or after the PWM signal is kept low for more than 15ms,
initiating the standby state of the device.
0V
O ut of
STATUS
In particular, during the first 100μs the diagnostic is
signaling an over-current then an out-of-regulation
status. These two events are due to the charging of the
inductor and are not true fault conditions.
r e g u la t io n
O ver
C u rre n t
Coil current
2 2 5 m V /R 1
0A
100us
Fig 35: Diagnostic during Start-up
Boosting VAUX supply voltage in Boost and Buck-Boost mode
When the input voltage is lower than 8V, the gate voltage will also be lower 8V. This means that depending on the
characteristics of the external MOSFET, the gate voltage may not be enough to fully enhance the power MOSFET. This
boosting technique is particularly important when the output MOSFET is operating at full current, since the boost circuit
allows the gate voltage to be higher than 12V. This guarantees that the MOSFET is fully enhanced reducing both the power
dissipation and the risk of thermal runaway of the MOSFET itself. An extra diode D2 and decoupling capacitor C3 can be
used, as shown below in figure 36, to generate a boosted voltage at VAUX when the input supply voltage at VIN is below 8V.
This enables the device to operate with full output current when VIN is at the minimum value of 6V. In the case of a low
voltage threshold MOSFET, the bootstrap circuit is generally not required.
Fig 36: Bootstrap circuit for Boost and Buck-boost low voltage operations
The resistor R2 can be used to limit the current in the bootstrap circuit in order to reduce the impact of the circuit itself on the
LED accuracy. The impact on the LED current is usually a decrease of maximum 5% compared to the nominal current
value set by the sense resistor.
The Zener diode D3 is used to limit the voltage on the VAUX pin to less than 60V.
Due to the increased number of components and the loss of current accuracy, the bootstrap circuit is recommended only
when the system has to operate continuously in conditions of low input voltage (between 6 and 8V) and high load current.
Other circumstances such as low input voltage at low load current, or transient low input voltage at high current should be
evaluated keeping account of the external MOSFET power dissipation.
Over-voltage Protection
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The ZXLD1370 is inherently protected against open-circuit load when used in Buck configuration. However care has to be
taken with open-circuit load conditions in Buck-Boost or Boost configurations. This is because in these configurations there
is no internal open-circuit protection mechanism for the external MOSFET. In this case an Over-Voltage-Protection (OVP)
network should be provided externally to the MOSFET to avoid damage due to open circuit conditions. This is shown in
Figure 33 below, highlighted in the dotted blue box.
Fig 37: OVP circuit
The zener voltage is determined according to: Vz = VLEDMAX +10%
Take care of the max voltage drop on the Q2 MOSFET gate.
PCB Layout considerations
PCB layout is a fundamental activity to get the most of the device in all configurations. In the following section it is possible
to find some important insight to design with the ZXLD1370 both in Buck and Buck-Boost/Boost configurations.
SHP pin
Inductor, Switch
and
Freewheeling
diode
VIN / VAUX
decoupling
Figure 38: Circuit Layout
Here are some considerations useful for the PCB layout:
ƒ
In order to avoid ringing due to stray inductances, the inductor L1, the anode of D1 and the drain of Q1 should be
placed as close together as possible.
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ƒ
ƒ
The shaping capacitor C1 is fundamental for the stability of the control loop. To this end it should be placed no more
than 5mm from the SHP pin.
Input voltage pins, VIN and VAUX, need to be decoupled. It is recommended to use two ceramic capacitors of
2.2uF, X7R, 100V (C3 and C4). In addition to these capacitors, it is suggested to add two ceramic capacitors of
1uF, X7R, 100V each (C2, C8), as well as a further decoupling capacitor of 100nF close to the VIN/VAUX pins (C9).
VIN and VAUX pins can be short-circuited when the device is used in buck mode, or can be driven from a separate
supply.
APPLICATION EXAMPLES
Example 1:
2.8A Buck LED driver
In this application example, the ZXLD1370 is connected as a buck LED driver. The schematic and parts list are shown
below. The LED driver is able to deliver 2.8A of LED current with an input voltage range of 8V to 24V. In order to achieve
high efficiency at high LED current, a Super Barrier Rectifier (SBR) with a low forward voltage is used as the free wheeling
rectifier.
This LED driver is suitable for applications which require high LED current such as LED projector, automatic LED lighting
etc.
Figure 39: Application circuit: 2.8A Buck LED driver
Table 3: Bill of Material
Ref No.
U1
Q1
D1
L1
C1
C2
C3 C4 C5
R1 R2 R3
R4
R5
Value
60V LED driver
60V MOSFET
45V 10A SBR
33uH 4.2A
100pF 50V
1uF 50V X7R
4.7uF 50V X7R
300mΩ 1%
400mΩ 1%
0Ω
ZXLD1370
Document number: DS32165 Rev. 2 - 2
Part No.
ZXLD1370
ZXMN6A09K
SBR10U45SP5
744770933
SMD 0805/0603
SMD1206
SMD1210
SMD1206
SMD1206
SMD 0805/0603
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Manufacturer
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Diodes Inc
Diodes Inc
Wurth Electronik
Generic
Generic
Generic
Generic
Generic
Generic
May 2010
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A Product Line of
Diodes Incorporated
ZXLD1370
Typical Performance
LED Current vs Input Voltage
Efficiency vs Input Voltage
3000
100%
90%
2500
80%
LED Current (mA)
Efficiency (%)
70%
60%
50%
40%
30%
1 LED
2 LED
20%
2000
1500
1000
500
10%
0%
10
12
14
16
18
20
22
24
Input Voltage (V)
0
10
12
14
16
18
20
22
24
Input Voltage (V)
Figure 41: Line regulation
Figure 40: Efficiency
Example 2:
400mA Boost LED driver
In this application example, the ZXLD1370 is connected as a boost LED driver. The schematic and parts list are shown
below. The LED driver is able to deliver 400mA of LED current into 12 high-brightness LEDs with an input voltage range of
16V to 32V.
The overall high efficiency of 92%+ makes it ideal for applications such as solar LED street lighting and general LED
illuminations.
Figure 42: Application circuit - 400mA Boost LED driver
ZXLD1370
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Table 4: Bill of Material
Ref No.
U1
Q1
Q2
D1
Z1
L1
C1
C3 C9
C2
R1 R2
R9 R10
R12
R15
Value
60V LED driver
60V MOSFET
60V MOSFET
100V 3A Schottky
47V 410mW Zener
68uH 2.1A
100pF 50V
4.7uF 50V X7R
1uF 50V X7R
560mΩ 1%
33KΩ 1%
0Ω
2.7KΩ
Part No.
ZXLD1370
ZXMN6A25G
2N7002A
PDS3100-13
BZT52C47
744771168
SMD 0805/0603
SMD1210
SMD1206
SMD1206
SMD 0805/0603
SMD 0805/0603
SMD 0805/0603
Manufacturer
Diodes Inc
Diodes Inc
Diodes Inc
Diodes Inc
Diodes Inc
Wurth Electronik
Generic
Generic
Generic
Generic
Generic
Generic
Generic
Typical Performance
Efficiency vs Input Voltage
LED Current vs Input Voltage
100%
450
90%
400
80%
350
300
60%
LED Current
Efficiency
70%
50%
40%
30%
250
200
150
20%
100
10%
50
0%
0
16
18
20
22
24
26
28
30
32
Input Voltage
16
18
20
22
24
26
28
30
32
Input Voltage
Figure 43: Efficiency
Figure 44: Line regulation
Example 3:
700mA Buck-Boost LED driver
In this application example, the ZXLD1370 is connected as a buck-boost LED driver. The schematic and parts list are
shown below. The LED driver is able to deliver 700mA of LED current into 4 high-brightness LEDs with an input voltage
range of 7V to 20V.
Since the Buck-boost LED driver handles an input voltage range from below and above the total LED voltage, the versatile
input voltage range make it ideal for automotive lighting applications.
ZXLD1370
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Figure 45: Application circuit - 700mA Buck-Boost LED driver
Table 5: Bill of Material
Ref No.
U1
Q1
Q2
D1
Z1
L1
C1
C3 C9
C2
R1 R2 R3
R9
R10
R12
R15
Value
60V LED driver
60V MOSFET
60V MOSFET
100V 5A Schottky
47V 410mW Zener
22uH 2.1A
100pF 50V
4.7uF 50V X7R
1uF 50V X7R
300mΩ 1%
33KΩ 1%
15KΩ 1%
0Ω
2.7KΩ
Part No.
ZXLD1370
ZXMN6A25G
2N7002A
PDS5100-13
BZT52C47
744771122
SMD 0805/0603
SMD1210
SMD1206
SMD1206
SMD 0805/0603
SMD 0805/0603
SMD 0805/0603
SMD 0805/0603
Manufacturer
Diodes Inc
Diodes Inc
Diodes Inc
Diodes Inc
Diodes Inc
Wurth Electronik
Generic
Generic
Generic
Generic
Generic
Generic
Generic
Generic
Typical Performance
Efficiency vs Input Voltage
LED Current vs Input Voltage
100%
800
90%
80%
700
70%
600
LED Current
Efficiency
60%
50%
40%
30%
500
400
300
200
20%
100
10%
0%
0
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Input Voltage
Document number: DS32165 Rev. 2 - 2
8
9
10
11
12
13
14
15
16
17
18
19
20
Input Voltage
Figure 46: Efficiency
ZXLD1370
7
Figure 47: Line regulation
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Ordering Information
Device
Packaging
Status
ZXLD1370EST16TC
TSSOP-16 EP
Active
Part
Marking
ZXLD1370
Reel
Quantity
2500
Tape Width
16mm
Reel
Size
13”
Package Thermal Data
Thermal Resistance
Junction-to-Case, θJC
Package
TSSOP-16 EP
Unit
23
°C/W
Package Thermal Data
TSSOP-16 EP
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IMPORTANT NOTICE
DIODES INCORPORATED MAKES NO WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, WITH REGARDS TO THIS DOCUMENT,
INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
PURPOSE (AND THEIR EQUIVALENTS UNDER THE LAWS OF ANY JURISDICTION).
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without further notice to this document and any product described herein. Diodes Incorporated does not assume any liability arising out of the
application or use of this document or any product described herein; neither does Diodes Incorporated convey any license under its patent or
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assume all risks of such use and will agree to hold Diodes Incorporated and all the companies whose products are represented on Diodes
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Diodes Incorporated does not warrant or accept any liability whatsoever in respect of any products purchased through unauthorized sales
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Diodes Incorporated products are specifically not authorized for use as critical components in life support devices or systems without the
express written approval of the Chief Executive Officer of Diodes Incorporated. As used herein:
A. Life support devices or systems are devices or systems which:
1. are intended to implant into the body, or
2. support or sustain life and whose failure to perform when properly used in accordance with instructions for use provided in the
labeling can be reasonably expected to result in significant injury to the user.
B. A critical component is any component in a life support device or system whose failure to perform can be reasonably expected to cause
the failure of the life support device or to affect its safety or effectiveness.
Customers represent that they have all necessary expertise in the safety and regulatory ramifications of their life support devices or systems,
and acknowledge and agree that they are solely responsible for all legal, regulatory and safety-related requirements concerning their products
and any use of Diodes Incorporated products in such safety-critical, life support devices or systems, notwithstanding any devices- or systemsrelated information or support that may be provided by Diodes Incorporated. Further, Customers must fully indemnify Diodes Incorporated and
its representatives against any damages arising out of the use of Diodes Incorporated products in such safety-critical, life support devices or
systems.
Copyright © 2010, Diodes Incorporated
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