Supertex inc.
Isolated, Constant Current
LED Driver
►
Programmable true constant current operation
►
±3% LED current accuracy
►
Adaptive to external component tolerances and
parasitics
►
Primary-side current sensing
►
Output open circuit protection
►
Output short circuit protection
►
Input under voltage lockout
►
PWM dimming / enable
►
Universal 80-264VAC operation
►
Fixed frequency operation
HV9971
Features
General Description
The HV9971 is a peak-current mode PWM IC for controlling
constant current output of a discontinuous conduction mode
(DCM) flyback converter. The IC maintains the effective reference
voltage with ±3% accuracy,acheiving tight regulation of the LED
current. It is optimized for operation at a constant frequency
of 100kHz. However, the switching frequency is determined
by values of the current sense resistor, the inductance of the
transformer winding, the output voltage and the forward voltage
drop across the output rectifier. This patented approach allows
making the output current setting insensitive to most external
component tolerances and parasitics without use of an opto-
feedback.
The circuit is ideally suited for driving high-brightness LEDs. It
offers a low component count and excellent regulation of output
current. The HV9971 LED driver is fully protected against output
open and short circuit conditions and input under-voltage. It
also offers a logic input for dimming the LED light output by low-
frequency pulse-width modulation of the output current.
►
Low power lighting fixtures
Applications
Typical Application Circuit
I
O
V
IN
R
IN
2
4
PWMD
VIN
BIAS
1
R
BIAS
R
SN
C
SN
R
DD
HV9971
GATE
GND
VD
3
R
D
CS
VDD
8
7
5
R
S
6
C
DD
Supertex inc.
1235 Bordeaux Drive, Sunnyvale, CA 94089
Tel: 408-222-8888
www.supertex.com
HV9971
Ordering Information
Package Options
Device
HV9971
-G indicates package is RoHS compliant (‘Green’)
4.90x3.90mm body
1.75mm height (max) 1.27mm pitch
8-Lead SOIC
HV9971LG-G
Absolute Maximum Ratings*
Parameter
VIN, VD, BIAS current
VDD voltage
VDD current
GATE voltage
CS, PWMD voltage
(T
A
= +25°C) (derate 6.3mW/°C above +25°C)
Pin Configuration
Value
±5.0mA
-0.3V to V
SHUNT
10mA
-0.3V to V
DD
+0.3V
-0.3V to 6.0V
630mW
+150°C
-65°C to +150°C
BIAS
1
VIN
2
VD
3
PWMD
4
8
7
6
5
VDD
GATE
GND
CS
8-Lead SOIC (LG)
Continuous power dissipation
Product Marking
H9971
YWW
LLLL
Junction temperature
Storage temperature range
* All voltages referenced to GND pin.
Y = Last Digit of Year Sealed
WW = Week Sealed
L = Lot Number
= “Green” Packaging
Package may or may not include the following marks: Si or
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.
8-Lead SOIC (LG)
Electrical Characteristics
Sym
V
DD
V
DD, START
V
DD,STOP
I
DDQ
I
DDQ(START)
Description
Shunt voltage
Start voltage
Under voltage threshold
Supply standby current
Start-up current
(Specifications are at T
A
= 25°C, V
DD
= 10V, I
IN
= 200µA, C
GATE
= 750pF, BIAS open, unless otherwise noted).
Min
*
*
*
-
*
10.5
9.95
6.65
-
-
Typ
11.0
10.50
7.00
-
-
Max
11.5
11.45
7.70
1.0
65
Units
V
V
V
mA
μA
Conditions
---
V
DD
rising
V
DD
falling
Gate open
V
DD
= 10V
Power Supply (VDD)
Notes:
* Specifications which apply over the full operating ambient temperature range of -40
O
C < T
A
< +125
O
C.
† Parameters guaranteed by design
Supertex inc.
1235 Bordeaux Drive, Sunnyvale, CA 94089
2
Tel: 408-222-8888
www.supertex.com
HV9971
Electrical Characteristics
Sym
I
IN
I
D
ΔQ
IN(MAX)
K
Osc
V
D
F
S(START)
V
BIAS
T
RISE
T
FALL
V
CS(TH)
T
DELAY
T
BLANK
I
IN(UVLO)
ΔI
IN(UVLO)
I
D(OV)
V
PWMD,HI
V
PWMD,LO
V
EFF
ΔV
EFF
/
V
EFF
Description
Operating current range
Operating current range
VIN Input charge swing
Oscillator coefficient
VD voltage
Start-up frequency
Output voltage
GATE output rise time
GATE output fall time
CS trip threshold
Propagation delay CS to GATE
Leading edge blanking delay
*
*
*
†
*
†
*
-
*
-
-
*
*
*
Min
0
0
-
0.32
2.406
-
1198
-
-
1198
-
200
Typ
-
-
-
0.33
2.440
10
1220
40
20
1220
-
300
Max
1000
1000
460
0.34
2.474
-
1242
75
40
1242
100
400
Units
μA
μA
pC
-
mV
kHz
mV
ns
ns
mV
ns
ns
Conditions
---
---
I
IN
= 400μA, I
D
= 0
---
---
---
---
---
---
---
(V
CS
- V
CS(TH)
) = 20mV
---
Feed Forward Inputs (VD, VIN) and Oscillator
Bias Current Generator (BIAS)
GATE Output
Current Sense Comparator
VIN Under Voltage Comparator
V
IN
undervoltage threshold current
V
DD
undervoltage lockout hysteresis
Output open circuit threshold
PWMD input high voltage
PWMD input low voltage
-
-
-
*
*
80
-
133
2.0
-
-
15
-
-
-
101
-
147
-
0.8
μA
μA
μA
V
V
V
IN
falling
V
IN
rising
---
---
---
I
IN
= 170μA, I
D
= 120μA,
See Note 1.
110μA ≤I
IN
≤ 350μA,
40μA ≤I
D
≤ 120μA
Open Circuit Protection
PWM Dimming
Effective Current Sense Reference Voltage
Effective reference voltage
I
IN
, I
D
regulation of V
EFF
-
†
195.5
-
-
3.0
207.6
-
mV
%
Notes:
* specifications which apply over the full operating ambient temperature range of -40
O
C < T
A
< +125
O
C.
†
Parameters guaranteed by design.
1. Effective output current V
EFF
= 0.5 • V
CS
• K
Osc
. Trimmed to the product of V
CS
• K
Osc
.
Supertex inc.
1235 Bordeaux Drive, Sunnyvale, CA 94089
3
Tel: 408-222-8888
www.supertex.com
HV9971
Functional Block Diagram
VD
VIN
UVLO
VDD
11V
Shunt
Reg.
i
D
2.44V
i
IN
Start-Up
Oscillator
S&H
Shutdown
PWMD
Current
Mirror
i
IN
i
IN
VIN
UVLO
UV
i
D
- i
BIAS
<i
D
- i
BIAS
>
(sampled)
GATE
UV Power-On Reset
Oscillator
&
Parasitics
Compensator
OVP
Shutdown
Q S
R
Power-On Reset
Q R
S
+
-
L/E
Blanking
1.22V
CLK
CS
i
UV
1.22V
BIAS
i
BIAS
BIAS
<i
D
- i
BIAS
>
(sampled)
i
OVP
GND
Supertex inc.
1235 Bordeaux Drive, Sunnyvale, CA 94089
4
Tel: 408-222-8888
www.supertex.com
HV9971
Functional Description
Power Topology and Control Method
The HV9971 regulates constant output current of a discon-
tinuous conduction mode (DCM) flyback converter. Although
it can be used in other applications, it is optimized for oper-
ating from a universal AC line input voltage of 85-264VAC.
The HV9971 is a fully integrated peak-current PWM control-
ler IC. It does not require an optocoupler feedback and in-
cludes protection from output open-circuit, short-circuit, and
input under-voltage conditions. A proprietary control scheme
permits accurate primary-side control of output current in-
sensitive to most circuit parasitics, external component toler-
ances and output voltage variation.
Output current of an HV9971 flyback converter can be ex-
pressed as:
I
O
=
I
PK
• n • K
Osc
2
(1)
where:
V
OR
= n • (V
O
+ V
F
)
(6)
In the equation (5), L
m
is magnetizing inductance of the
transformer primary winding, and V
F
is the forward voltage
drop at the output rectifier diode. (Note that the switching
frequency is not a function of the internal timing components
of the HV9971 or the absolute value of R
IN
and R
D
).
Proper selection of maximum switching frequency F
S(MAX)
at
full load in combination with maximum V
OR(MAX)
is critical for
proper operation of the HV9971. The oscillator circuit ramp
may saturate when the maximum charge swing ΔQ
IN(MAX)
=
400pC is exceeded at V
IN
. Therefore, the circuit components
should be selected such that:
ΔQ
IN
=
V
IN
• T
ON
R
IN
≤ ΔQ
IN(MAX)
(7)
Where K
Osc
= 0.33 is an oscillator coefficient, n is flyback
transformer turns ratio of primary to secondary winding, and
where I
PK
is peak primary winding current given by:
V
CS(TH)
I
PK
=
(2)
R
S
In (2), V
CS(TH)
is the reference voltage of the current sense
comparator at CS, and R
S
is the current sense resistance.
Combining (1) and (2), we can write the output current as:
I
O
=
V
CS(TH)
• n • K
Osc
2
•
R
S
=
n • V
EFF
R
S
(3)
(Note, that the HV9971 is protected against careless oscil-
lator setup. When saturation of the oscillator ramp occurs,
the HV9971 shuts off and attempts to go through a start-up
cycle again.)
The transformer magnetic flux equals the volt-seconds at
the transformer winding in the DCM flyback converter:
V
IN
• T
ON
≈ L
M
• I
PK
(8)
Therefore, the charge swing ΔQ
IN
varies only as a function
of external component tolerances and circuit parasitic, and it
is the same for all V
IN
and V
O
operating conditions. Combin-
ing equations (5), (7) and (8), and taking into consideration
tolerances for L
m
, R
S
and V
CS(TH)
, we get the following design
criterion:
V
OR(MAX)
•
K
Osc(MAX)
L
m(MAX)
V
CS(TH)MAX
R
S(MAX)
•
•
•
≤ ΔQ
IN(MAX)
F
S(MAX)
•
R
IN(MIN)
L
m(MIN)
V
CS(TH)MIN
R
S(MIN)
(9)
The equation (9) gives the condition for selecting proper
ratio of V
OR(max)
/F
S(MAX)
, which guarantees ΔQ
IN
≤ Q
IN(MAX)
.
Selection of the resistor R
IN
is dictated by the desired input
under-voltage (UV) and output over-voltage (OV) protection
thresholds. The recommended selection of R
IN
= 1MΩ pro-
duces a UV shutdown at V
IN
< 90V, adequate for a universal
AC line voltage range of 85-265VAC, and an OV shutdown
at V
OR
> 140V. As an example, we can assume the toleranc-
es of L
m
and R
S
as ±10% and ±1% correspondingly. We shall
also limit the switching frequency under F
S(MAX)
= 130KHz.
The effective reference voltage V
EFF
= 202mV. Hence, the
desired LED current is programmed by merely selecting the
current sense resistor as:
R
S
=
n
•
V
EFF
I
O
(4)
Note that the output current of the HV9971 LED driver is
independent of the input and output voltage, the switching
frequency or the transformer inductance.
The switching frequency at a given output voltage V
O
can be
estimated as:
n • (V
O
+ V
F
) • K
Osc
V
OR
• K
Osc
F
S
=
=
(5)
L
m
• I
PK
L
m
• I
PK
Supertex inc.
1235 Bordeaux Drive, Sunnyvale, CA 94089
5
Tel: 408-222-8888
www.supertex.com
实时操作系统RTOS
京公网安备 11010802033920号
Copyright © 2005-2026 EEWORLD.com.cn, Inc. All rights reserved
电子工程世界
