Supertex inc.
Hysteretic, Buck, High Brightness LED Driver
with High-Side Current Sensing
Features
►
Hysteretic control with high-side current sensing
►
Integrated 40V 1.0Ω MOSFET
►
>90% Efficiency
►
Wide input voltage range: 4.5 to 40V
►
±5% LED current accuracy
►
Up to 2.0MHz switching frequency
►
Adjustable constant LED current
►
Analog or PWM control signal for PWM dimming
►
Over-temperature protection
►
-40ºC to +125ºC operating temperature range
HV9918
General Description
The HV9918 is a PWM controller IC designed to drive high
brightness LEDs using a buck topology. It operates from an input
voltage of 4.5 to 40VDC and employs hysteretic control with a
high-side current sense resistor to set the constant output current
up to 700mA. The device is well suited for applications requiring
a wide input voltage range. The high-side current sensing and an
integrated current-setting circuitry minimize the number of external
components while delivering an accurate average output.
Dedicated pulse-width modulation (PWM) input enables pulsed
LED dimming over a wide range of brightness levels. A hysteretic
control method ensures excellent input supply rejection and fast
response during load transients and PWM dimming.
The HV9918 offers an analog-controlled PWM dimming feature
that reduces the output current by applying an external DC voltage
below the internal 2.0V threshold voltage from ADIM to GND. ADIM
can also accept input from a resistor divider including a negative
temperature coefficient (NTC) thermistor connected between
ADIM and GND, or a positive temperature coefficient (PTC)
thermistor connected between ADIM and VDD thus providing a
PWM thermal-foldback feature that reduces the LED current when
the temperature of the LED string exceeds a specified temperature
point. Additional features include thermal-shutdown protection.
The high switching frequency up to 2.0MHz permits the use of
small inductors and capacitors, minimizing space and cost in the
overall system.
The HV9918 comes in a small 8-Lead DFN package and is ideal
for industrial and general lighting applications.
Applications
►
Low voltage industrial and architectural lighting
►
General purpose constant current source
►
Signage and decorative LED lighting
►
Indicator and emergency lighting
Typical Application Circuit
C
IN
R
SENSE
L
VIN
RAMP
CS
SW
VDD
GND
0 - 2.0V
ADIM
DIM
HV9918
Supertex inc.
●
1235 Bordeaux Drive, Sunnyvale, CA 94089
●
Tel: 408-222-8888
●
www.supertex.com
HV9918
Ordering Information
Package Options
Device
3.00x3.00mm body,
0.80mm height (max),
0.65mm pitch
Pin Description
8-Lead DFN
CS
VIN
RAMP
ADIM
1
2
3
4
8
7
6
5
SW
GND
VDD
DIM
HV9918
-G indicates package is RoHS compliant (‘Green’)
HV9918K7-G
GND
8-Lead DFN (K7)
(top view)
Product Marking
Absolute Maximum Ratings
Parameter
VIN, CS, SW to GND
VDD, RAMP, DIM, ADIM to GND
CS to VIN
Continuous power dissipation,
(T
A
= +25°C)
Operating temperature range
Junction temperature
Storage temperature range
Value
-0.3 to +45V
-0.3 to +6.0V
-1.0 to +0.3V
1.6W
-40°C to +125°C
+150°C
-65°C to +150°C
9918
YWLL
Y = Last Digit of Year Sealed
W = Code for Week Sealed
L = Lot Number
= “Green” Packaging
8-Lead DFN (K7)
Thermal Resistance
Package
8-Lead DFN (K7)
θ
ja
60
O
C/W
Mounted on FR-4 board, 25mm x 25mm x 1.57mm
Stresses beyond those listed under “Absolute Maximum Ratings” may cause
permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in
the operational sections of the specifications is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect device reliability.
Electrical Characteristics
Sym
V
IN
V
DD
I
IN
I
IN, SDN
I
IN, LIM
f
SW
UVLO
ΔUVLO
Description
(V
IN
= 12V, V
DIM
= V
DD
, V
RAMP
= GND, C
VDD
= 1.0µF, R
CS
= 0.5Ω, T
A
= T
J
= -40
O
C to +125
O
C* unless otherwise noted)
Min
4.5
4.5
-
-
-
-
-
-
-
Typ
-
-
-
-
30
8.0
-
-
500
Max
40
5.5
1.5
900
-
-
2.0
4.5
-
Units
V
V
mA
µA
mA
MHz
V
mV
Conditions
DC input voltage
V
IN
= 6.0 to 40V
SW = GND
DIM < 0.7V
V
IN
= 4.5V, V
DD
= 0V
V
IN
= 4.5V, V
DD
= 4.0V
---
V
DD
rising
V
DD
falling
Input DC supply voltage range
Internally regulated voltage
Supply current
Shutdown supply current
Current limit
Switchingr frequency
V
DD
Undervoltage lockout threshold
V
DD
Undervoltage lockout hysteresis
*
Guaranteed by design and characterization, 100% tested at T
A
= 25
O
C. Typical characteristics are given at T
A
= 25
O
C.
Supertex inc.
●
1235 Bordeaux Drive, Sunnyvale, CA 94089
●
Tel: 408-222-8888
●
www.supertex.com
2
HV9918
Electrical Characteristics
Sym
V
RS(HI)
V
RS(LO)
t
DPDL
Description
Sense voltage threshold high
Sense voltage threshold low
Propagation delay to SW off
(V
IN
= 12V, V
DIM
= V
DD
, V
RAMP
= GND, C
VDD
= 1.0µF, R
CS
= 0.5Ω, T
A
= T
J
= -40
O
C to +125
O
C* unless otherwise noted)
Min
213
158
-
Typ
-
-
70
Max
246
182
-
Units
mV
mV
ns
Conditions
(V
IN
- V
CS
) rising
(V
IN
- V
CS
) falling
Rising edge of
(V
IN
- V
CS
) = V
RS(HI)
+70mV to
V
SW
= 0.9 • V
IN
Falling edge of
(V
IN
- V
CS
) = V
RS(LO)
-70mV to
V
SW
= 0.1 • V
IN
(V
IN
- V
CS
) = 200mV
---
---
---
DIM rising edge to
V
SW
= 0.9 • V
IN
DIM falling edge to
V
SW
= 0.1 • V
IN
---
---
V
IN
= 40V
---
---
C
RAMP
= 47nF
C
RAMP
= 10nF
---
---
---
Sense Comparator
t
DPDH
I
CS
I
CS(HYS)
Propagation delay to SW on
Current-sense input current
Current-sense threshold hysteresis
Pin DIM input high voltage
Pin DIM input low voltage
Turn-on time
Turn-off time
-
-
-
2.2
-
-
-
70
-
56
-
-
100
100
-
1.0
70
-
0.7
-
-
ns
µA
mV
V
V
ns
ns
DIM Input
V
IH
V
IL
t
ON
t
OFF
Output Switch
I
DC
R
ON
I
LEAK
T
OT
∆T
HYST
SW continuous current
ON resistance
SW leakage current
Over temperature trip limit
Temperature hysteresis
-
-
-
128
-
130
550
-
1.8
-35
-
1.0
10
140
60
-
-
0.1
-
-
0.7
2.0
-
-
-
300
1250
-
2.1
35
A
Ω
µA
ºC
ºC
Over-Temperature Protection
Analog Control of PWM Dimming
f
RAMP
V
LOW
V
HiGH
V
OS
Dimming frequency
RAMP threshold, Low
RAMP threshold, High
ADIM offset voltage
Hz
V
V
mV
*
Guaranteed by design and characterization, 100% tested at T
A
= 25
O
C. Typical characteristics are given at T
A
= 25
O
C.
Supertex inc.
●
1235 Bordeaux Drive, Sunnyvale, CA 94089
●
Tel: 408-222-8888
●
www.supertex.com
3
HV9918
Block Diagram
VIN
REGULATOR
VDD
SW
CS
+
-
CURRENT
SENSE
COMPARATOR
BANDGAP
REF
+
-
UVLO
COMPARATOR
DIM
GND
RAMP
ADIM
PWM RAMP
0.1~1.9V
-
+
HV9918
Application Information
The HV9918 is a step-down, constant current, high-bright-
ness LED (HB LED) driver. The device operates from a 4.5
to 40V input voltage range, and includes an internal 40V
1.0Ω N-channel MOSFET. A high-side current sense resistor
sets the output current and a dedicated PWM dimming input
(DIM) allows for a wide range of diming duty ratios. PWM
dimming can also be achieved by applying a DC voltage be-
tween 0 and 2.0V to the analog dimming input (ADIM). In
this case, the dimming frequency can be programmed using
a single capacitor at the RAMP pin. The high-side current
setting and sensing scheme minimizes the number of ex-
ternal components while delivering LED current with ±5%
accuracy using a 1% sense resistor.
Undervoltage Lockout (UVLO)
The HV9918 includes a 3.7V under-voltage lockout (UVLO)
with 500mV hysteresis. When V
IN
falls below 3.7V, switching
of SW is disabled. Switching of SW resumes once V
IN
is 4.5V
or higher.
5.0V Regulator
VDD is the output of a 5.0V regulator capable of sourcing
8mA. Bypass VDD to GND with a 1.0μF capacitor.
General Description
DIM Input
The HV9918 allows dimming with a PWM signal at the DIM
input. A logic level below 0.7V at DIM halts SW switching,
turning the LED current off. To turn the LED current back on,
the logic level at DIM must be at least 2.2V.
ADIM and RAMP Inputs
The PWM dimming scheme can be also implemented by
applying an analog control signal to ADIM pin. If an ana-
log control signal of 0 ~ 2.0V is applied to ADIM, the device
compares this analog input to a voltage ramp to pulse-width-
modulate the LED current. Connecting an external capacitor
to RAMP programs the PWM dimming ramp frequency.
f
PWM
=
1
C
RAMP
• 120kΩ
DIM and ADIM inputs can be used simultaneously. In such
case, f
PWM(MAX)
must be selected lower than the frequency of
the dimming signal at DIM. The smaller dimming duty cycle
of ADIM and DIM will determine the SW signal.
When the analog control of the PWM dimming feature is not
used, RAMP must be wired to GND, and ADIM should be
connected to VDD.
Supertex inc.
●
1235 Bordeaux Drive, Sunnyvale, CA 94089
●
Tel: 408-222-8888
●
www.supertex.com
4
HV9918
One possible application of the ADIM feature of the HV9918
may include protection of the LED load from over-tempera-
ture by connecting an NTC thermistor at ADIM, as shown in
Figure 1.
VDD
the inductor ramps up and the voltage across the sense re-
sistor reaches the upper threshold, the internal MOSFET at
SW turns off. The MOSFET turns on again when the inductor
current ramps down through the freewheeling diode until the
voltage across the sense resistor equals the lower threshold.
Use the following equation to determine the inductor value
for a desired value of operating frequency f
S
:
L=
(V
IN
- V
OUT
)V
OUT
f
S
V
IN
∆I
O
-
(V
IN
- V
OUT
)t
DPDL
V
OUT
t
DPDH
-
∆I
O
∆I
O
HV9918
ADIM
NTC
GND
where:
∆I
O
=
V
RS(HI)
- V
RS(LO)
R
SENSE
Figure 1
Setting LED Current with External Resistor R
SENSE
The output current in the LED is determined by the external
current sense resistor (R
SENSE
) connected between VIN and
CS. Disregarding the effect of the propagation delays, the
sense resistor can be calculated as:
1
2
(V
RS(HI)
+ V
RS(LO)
)
I
LED
200mV
I
LED
and t
DPDL
, t
DPDH
are the propagation delays. Note, that the cur-
rent ripple ∆I in the inductor L is greater than ∆I
O
. This ripple
can be calculated from the following equation:
(V
IN
- V
OUT
)t
DPDL
L
V
OUT
t
DPDH
L
R
SENSE
≈
•
=
∆I = ∆I
O
+
+
Selecting Buck Inductor L
The HV9918 regulates the LED output current using an input
comparator with hysteresis (Figure 2). As the current through
For the purpose of the proper inductor selection, note that
the maximum switching frequency occurs at the highest V
IN
and V
OUT
= V
IN
/2.
V
RS(HI)
R
SENSE
I
LED
t
DPDL
T
S
=
1
f
S
V
RS(LO)
R
SENSE
t
DPDH
ΔI
ΔI
O
t
V
DIM
Figure 2
Supertex inc.
●
1235 Bordeaux Drive, Sunnyvale, CA 94089
●
Tel: 408-222-8888
●
www.supertex.com
5
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