Supertex inc.
3-Pin Switch-Mode
LED Lamp Driver IC
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►
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HV9922
Features
Constant output current: 50mA
Universal 85 - 265VAC operation
Fixed off-time buck converter
Internal 475V power MOSFET
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Decorative lighting
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Low power lighting fixtures
Applications
The HV9922 is a pulse width modulated (PWM) high-efficiency
LED driver control IC. It allows efficient operation of LED strings
from voltage sources ranging up to 400VDC. The HV9922
includes an internal high voltage switching MOSFET controlled
with fixed off-time (T
OFF
) of approximately 10.5μs. The LED string
is driven at constant current, thus providing constant light output
and enhanced reliability. The output current is internally fixed at
50mA for HV9922. The peak current control scheme provides
good regulation of the output current throughout the universal
AC line voltage range of 85 to 265VAC or DC input voltage of
20 to 400V.
General Description
Typical Application Circuit
AC
LED
1
-
LED
n
HV9922
3 VDD
GND
2
DRAIN 1
Supertex inc.
1235 Bordeaux Drive, Sunnyvale, CA 94089
Tel: 408-222-8888
www.supertex.com
HV9922
Ordering Information
Device
HV9922
Package Options
TO-92
HV9922N3-G
SOT-89
HV9922N8-G
-G indicates package is RoHS compliant (‘Green’)
Absolute Maximum Ratings
Parameter
Supply voltage, V
DD
Supply current, I
DD
Operating ambient temperature range
Operating junction temperature range
Storage temperature range
Power dissipation @ 25°C, TO-92
Power dissipation @ 25°C, SOT-89
Value
-0.3 to +10V
+5.0mA
-40°C to +85°C
-40° to +125°C
-65° to +150°C
740mW
1600mW
*
Pin Configurations
VDD
DRAIN
GND
VDD
GND
DRAIN
TO-92 (N3)
SOT-89 (N8)
Product Marking
SiHV
9 9 2 2
YYWW
YY = Year Sealed
WW = Week Sealed
= “Green” Packaging
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.
Package may or may not include the following marks: Si or
TO-92 (N3)
W = Code for week sealed
Y = Code for year sealed
= “Green” Packaging
Package may or may not include the following marks: Si or
H22YW
Electrical Characteristics
Sym
Regulator (V
DD
)
V
DD
V
DRAIN
V
UVLO
I
DD
V
BR
R
ON
C
DRAIN
I
SAT
I
TH
T
BLANK
V
DD
regulator output
V
DRAIN
supply voltage
V
DD
undervoltage threshold
Operating supply current
Breakdown voltage
On-resistance
Output capacitance
Parameter
(Specifications are at T
A
= 25
°
C and V
DRAIN
= 50V, unless otherwise noted.)
SOT-89 (N8)
Typ
7.5
-
-
200
200
-
-
1.0
150
-
300
-
10.5
Max
-
-
-
-
350
-
210
5.0
-
63
400
650
13
Units Conditions
V
V
V
mV
µA
V
Ω
pF
mA
mA
ns
ns
µs
---
---
---
---
V
DD(EXT)
= 8.5V, V
DRAIN
= 40V
---
I
DRAIN
= 50mA
V
DRAIN
= 400V
---
---
---
---
---
Min
- -
- -
- -
- -
* -
- -
- #
- #
* -
* #
- -
- -
-
20
5.0
-
-
475
-
-
100
49
200
-
8.0
∆V
UVLO
V
DD
undervoltage lockout hysteresis - -
Output (DRAIN)
MOSFET saturation current
Threshold current
Leading edge blanking delay
Current Sense Comparator
T
ON(MIN)
Minimum on-time
OFF-Time Generator
T
OFF
Off-time
Note:
* Denotes the specifications which apply over the full operating ambient temperature range of -40°C
< T
A
< +85°C.
# Denotes guaranteed by design.
Supertex inc.
1235 Bordeaux Drive, Sunnyvale, CA 94089
2
Tel: 408-222-8888
www.supertex.com
HV9922
Typical Performance Characteristics
(T
1.10
J
= 25°C
unless otherwise noted)
200
180
160
Normalized Threshold Current
1.05
ON Resistance (Ohm)
-15
10
35
60
85
110
140
120
100
80
60
40
20
1.00
0.95
0.90
0.85
0.80
-40
0
-40
-15
10
35
60
85
110
Junction Temperature, °C
Junction Temperature (°C)
12
1000
10
OFF Time (uS)
8
DRAIN Capacitance (pF)
-15
10
35
60
85
110
100
6
4
10
2
0
-40
1
Junction Temperature (°C)
0
10
20
30
40
DRAIN Voltage (V)
580
180
160
140
DRAIN Breakdown Voltage (V)
570
560
550
540
530
520
510
500
490
-40
T
J
= 25°C
T
J
= 125°C
DRAIN Current, mA
-15
10
35
60
85
110
120
100
80
60
40
20
0
0
10
20
30
40
Junction Temperature, °C
DRAIN Voltage (V)
Supertex inc.
1235 Bordeaux Drive, Sunnyvale, CA 94089
3
Tel: 408-222-8888
www.supertex.com
HV9922
Functional Description
where I
TH
is the current sense comparator threshold. The
ripple current introduces a peak-to-average error in the
output current setting that needs to be accounted for. Due to
the constant off-time control technique used in the HV9922,
the ripple current is independent of the input AC or DC line
voltage variation. Therefore, the output current will remain
unaffected by the varying input voltage.
Adding a filter capacitor across the LED string can reduce
the output current ripple even further, thus permitting a
reduced value of L1. However, one must keep in mind that
the peak-to-average current error is affected by the variation
of T
OFF
. Therefore, the initial output current accuracy might
be sacrificed at large ripple current in L1.
Another important aspect of designing an LED driver with
the HV9922 is related to certain parasitic elements of the
circuit, including distributed coil capacitance of L1, junction
capacitance and reverse recovery of the rectifier diode D1,
capacitance of the printed circuit board traces C
PCB
and output
capacitance C
DRAIN
of the controller itself. These parasitic
elements affect the efficiency of the switching converter and
could potentially cause false triggering of the current sense
comparator if not properly managed. Minimizing these
parasitics is essential for efficient and reliable operation of
the HV9922.
Coil capacitance of inductors is typically provided in the
manufacturer’s data books either directly or in terms of the
self-resonant frequency (SRF).
SRF = 1 / [2π √(L • C
L
)]
where L is the inductance value, and C
L
is the coil capacitance.
Charging and discharging this capacitance every switching
cycle causes high-current spikes in the LED string. Therefore,
connecting a small capacitor C
O
(~10nF) is recommended to
bypass these spikes.
Using an ultra-fast rectifier diode for D1 is recommended to
achieve high efficiency and reduce the risk of false triggering
of the current sense comparator. Using diodes with shorter
reverse recovery time
t
rr
and lower junction capacitance C
J
achieves better performance. The reverse voltage rating V
R
of the diode must be greater than the maximum input voltage
of the LED lamp.
The total parasitic capacitance present at the DRAIN pin of
the HV9922 can be calculated as:
C
P
= C
DRAIN
+ C
PCB
+C
L
+C
J
(3)
The HV9922 is a PWM peak current controller for controlling
a buck converter topology in continuous conduction mode
(CCM). The output current is internally preset at 50mA.
When the input voltage of 20 to 400V appears at the
DRAIN pin, the internal high-voltage linear regulator seeks
to maintain a voltage of 7.5VDC at the VDD pin. Until this
voltage exceeds the internally programmed under-voltage
threshold, the output switching MOSFET is non-conductive.
When the threshold is exceeded, the MOSFET turns on. The
input current begins to flow into the DRAIN pin. Hysteresis
is provided in the under-voltage comparator to prevent
oscillation.
When the input current exceeds the internal preset level,
a current sense comparator resets an RS flip-flop, and the
MOSFET turns off. At the same time, a one-shot circuit is
activated that determines the duration of the off-state (10.5µs
typ.). As soon as this time is over, the flip-flop sets again.
The new switching cycle begins.
A “blanking” delay of 300ns is provided that prevents false
triggering of the current sense comparator due to the leading
edge spike caused by circuit parasitics.
Application Information
The HV9922 is a low-cost off-line buck converter IC
specifically designed for driving multi-LED strings. It can
be operated from either universal AC line range of 85 to
265VAC, or 20 to 400VDC, and drives up to tens of high
brightness LEDs. All LEDs can be run in series, and the
HV9922 regulates at constant current, yielding uniform
illumination. The HV9922 is compatible with triac dimmers.
The output current is internally fixed at 50mA. This part is
available in space saving TO-92 and SOT-89 packages.
Selecting L1 and D1
There is a certain trade-off to be considered between
optimal sizing of the output inductor L1 and the tolerated
output current ripple. The required value of L1 is inversely
proportional to the ripple current ∆I
O
in it.
L1 = (V
O
•
T
OFF
) / ΔI
O
(1)
V
O
is the forward voltage of the LED string. T
OFF
is the off-
time of the HV9922. The output current in the LED string (I
O
)
is calculated then as:
I
O
= I
TH
- (ΔI
O
/ 2)
(2)
Supertex inc.
1235 Bordeaux Drive, Sunnyvale, CA 94089
4
Tel: 408-222-8888
www.supertex.com
HV9922
When the switching MOSFET turns on, the capacitance C
P
is discharged into the DRAIN pin of the IC. The discharge
current is limited to about 150mA typically. However, it
may become lower at increased junction temperature. The
duration of the leading edge current spike can be estimated
as:
T
SPIKE
= [(V
IN
• C
P
) / (I
SAT
)] +t
r
(4)
Conduction power loss in the HV9922 can be calculated as:
P
COND
= (D • I
O2
• R
ON
) + [I
DD
• V
IN
• (1 - D)]
(9)
where D = V
O
/ηV
IN
is the duty ratio, R
ON
is the on-resistance,
I
DD
is the internal linear regulator current.
When the LED driver is powered from the full-wave
rectified AC line input, the exact equation for calculating the
conduction loss is more cumbersome. However, it can be
estimated using the following equation:
P
COND
= (K
C
• I
O2
• R
ON
) + (K
d
• I
DD
• V
AC
)
(10)
In order to avoid false triggering of the current sense
comparator, C
P
must be minimized in accordance with the
following expression:
C
P
< I
SAT
•
(T
BLANK(MIN)
- t
rr
)
V
IN(MAX)
(5)
where V
AC
is the input AC line voltage. The coefficients K
C
and K
d
can be determined from the minimum duty ratio of
the HV9922.
0.7
where T
BLANK(MIN)
is the minimum blanking time of 200ns, and
V
IN(MAX)
is the maximum instantaneous input voltage.
Estimating Power Loss
Discharging the parasitic capacitance C
P
into the DRAIN pin of
the HV9922 is responsible for the bulk of the switching power
loss. It can be estimated using the following equation:
P
SWITCH
= [(V
IN
• C
P
) / 2 + V
IN
• I
SAT
• t
rr
] • F
S
2
0.6
0.5
Kd(Dm)
Kc(Dm)
0.4
(6)
0.3
where F
S
is the switching frequency, I
SAT
is the saturated
DRAIN current of the HV9922. The switching loss is the
greatest at the maximum input voltage.
The switching frequency is given by the following:
F
S
= (V
IN
- η
-1
• V
O
) / V
IN
• T
OFF
where η is the efficiency of the power converter.
When the HV9922 LED driver is powered from the full-wave
rectified AC input, the switching power loss can be estimated
as:
P
SWITCH
≈
1
(V
AC
• C
P
+ 2 • I
SAT
• t
rr
)(V
AC
- η
-1
• V
O
)
2 • T
OFF
V
AC
is the input AC line voltage.
The switching power loss associated with turn-off transitions
of the DRAIN pin can be disregarded. Due to the large amount
of parasitic capacitance connected to this switching node,
the turn-off transition occurs essentially at zero-voltage.
(8)
(7)
0.2
0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Dm
Fig. 1.
Conduction Loss Coefficients K
C
and K
d
EMI Filter
As with all off-line converters, selecting an input filter is critical
to obtaining good EMI. A switching side capacitor, albeit of
small value, is necessary in order to ensure low impedance
to the high frequency switching currents of the converter. As
a rule of thumb, this capacitor should be approximately 0.1-
0.2 µF/W of LED output power. A recommended input filter is
shown in Figure 2 for the following design example.
Design Example
Let us design an HV9922 LED lamp driver meeting the
following specifications:
Input:
Universal AC, 85 - 135VAC
Output Current: 50mA
Load:
String of 12 LED (Power TOPLED OSRAM
®
V
F
= 2.5V max. each)
Supertex inc.
1235 Bordeaux Drive, Sunnyvale, CA 94089
5
Tel: 408-222-8888
www.supertex.com
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