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PDF HV9961 Data sheet ( Hoja de datos )
| Número de pieza | HV9961 | |
| Descripción | LED Driver ICs | |
| Fabricantes | Supertex | |
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LED Driver with Average-Mode
Constant Current Control
HV9961
Features
► Fast average current control
► Programmable constant off-time switching
► Linear dimming input
► PWM dimming input
► Output short circuit protection with skip mode
► Ambient operating temperature -40OC to +125OC
► Pin-compatible with the HV9910B
Applications
► DC/DC or AC/DC LED driver applications
► LED backlight driver for LCD displays
► General purpose constant current source
► LED signage and displays
► Architectural and decorative LED lighting
► LED street lighting
General Description
The HV9961 is an average current mode control LED driver
IC operating in a constant off-time mode. Unlike HV9910B,
this control IC does not produce a peak-to-average error, and
therefore greatly improves accuracy, line and load regulation
of the LED current without any need for loop compensation or
high-side current sensing. The output LED current accuracy
is ±3%.
The IC is equipped with a current limit comparator for hiccup-
mode output short circuit protection.
The HV9961 can be powered from an 8.0 - 450V supply.
A PWM dimming input is provided that accepts an external
control TTL compatible signal. The output current can be
programmed by an internal 272mV reference, or controlled
externally through a 0 - 1.5V dimming input.
HV9961 is pin-to-pin compatible with HV9910B and it can
be used as a drop-in replacement for many applications to
improve the LED current accuracy and regulation.
Typical Application Circuit
8.0 - 450VDC
1
VIN
5 PWMD GATE 4
HV9961
6 VDD
CS 2
7 LD
GND RT 8
3
LED
Load
Sets
LED
Current
● 1235 Bordeaux Drive, Sunnyvale, CA 94089 ● Tel: 408-222-8888 ● www.supertex.com
1 page  
HV9961
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Application Information
General Description
Peak-current control (as in HV9910B) of a buck converter is
the most economical and simple way to regulate its output
current. However, it suffers accuracy and regulation prob-
lems that arise from the so-called peak-to-average current
error, contributed by the current ripple in the output inductor
and the propagation delay in the current sense compara-
tor. The full inductor current signal is unavailable for direct
sensing at the ground potential in a buck converter when
the control switch is referenced to the same ground poten-
tial because the control switch is only conducting for small
periods. While it is very simple to detect the peak current in
the switch, controlling the average inductor current is usu-
ally implemented by level translating the sense signal from
+VIN. Though this is practical for relatively low input voltage
VIN, this type of average-current control may become exces-
sively complex and expensive in the offline AC or other high-
voltage DC applications.
The HV9961 employs Supertex’ proprietary control scheme,
achieving fast and very accurate control of average current
in the buck inductor through sensing the switch current only.
No compensation of the current control loop is required. The
LED current response to PWMD input is similar to that of the
HV9910B. The inductor current ripple amplitude does not af-
fect this control scheme significantly, and therefore, the LED
current is independent of the variation in inductance, switch-
ing frequency or output voltage. Constant off-time control of
the buck converter is used for stability and to improve the
LED current regulation over a wide range of input voltages.
(Note that, unlike HV9910B, the HV9961 does not support
the constant-frequency mode of operation.)
OFF Timer
The timing resistor connected to RT determines the off-time
of the gate driver, and it must be wired to GND. (Wiring this
resistor to GATE as with HV9910B is no longer supported.)
The equation governing the off-time of the GATE output is
given by:
TOFF (µs) =
RT (kΩ)
25
+
0.3
(1)
within the range of 30kΩ ≤ RT ≤ 1.0MΩ.
Average Current Control Feedback and Output
Short Circuit Protection
The current through the switching MOSFET source is aver-
aged and used to give constant-current feedback. This cur-
rent is detected using a sense resistor at the CS pin. The
feedback operates in a fast open-loop mode. No compensa-
tion is required. Output current is programmed simply as:
ILED =
0.272V
RCS
(2)
when the voltage at the LD input VLD ≥ 1.5V. Otherwise:
ILED =
VLD • 0.181
RCS
(3)
The above equations are only valid for continuous conduc-
tion of the output inductor. It is a good practice to design the
inductor such that the switching ripple current in it is 30~40%
of its average peak-to-peak, full load, DC current. Hence,
the recommended inductance can be calculated as:
LO =
VO(MAX) • TOFF
0.4 • IO
(4)
The duty-cycle range of the current control feedback is lim-
ited to D ≤ 0.75. A reduction in the LED current may occur
when the LED string voltage VO is greater than 75% of the
input voltage VIN of the HV9961 LED driver.
Reducing the output LED voltage VO below VO(MIN) = VIN •
DMIN, where DMIN = 1.0µs/(TOFF +1.0µs), may also result in
the loss of regulation of the LED current. This condition,
however, causes an increase in the LED current and can
potentially trip the short-circuit protection comparator.
The typical output characteristic of the HV9961 LED driver is
shown in Fig.1. The corresponding HV9910B characteristic
is given for the comparison.
Output Characteristics
0.60
0.55 VIN = 170VDC
0.50
0.45
0.40
HV9961
0.35
0.30
0.25
0
HV9910B
10 20 30 40 50 60
Output Voltage (V)
Fig.1. Typical output characteristic of an HV9961 LED
driver.
● 1235 Bordeaux Drive, Sunnyvale, CA 94089 ● Tel: 408-222-8888 ● www.supertex.com
5
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| PDF Descargar | [ Datasheet HV9961.PDF ] | |
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