HV9821K7-G Supertex, HV9821K7-G Datasheet - Page 4

• Manufacturer Part Number: HV9821K7-G
• Description: LED Lighting Drivers LED Driver, 264Vac- 10Vdc Wide Input IC
• Manufacturer: Supertex

Specifications of HV9821K7-G

• Rohs: yes
• Input Voltage: 80 VAC to 264 VAC
• Maximum Supply Current: 800 uA
• Output Current: Adjustable
• Maximum Operating Temperature: + 125 C
• Mounting Style: SMD/SMT
• Package / Case: DFN-19
• Minimum Operating Temperature: - 40 C
• Power Dissipation: 3.3 W

Power Topology
The HV9821 is a clamped-mode buck converter for driving
a low-voltage LED load at a fixed current up to 50mA (or
higher, as permitted by power dissipation, voltage drop and
saturation current) from a wide range of input voltage of 10
to 700V. The IC generates a switching waveform of program-
mable amplitude V
cycle limitation. Since the input current can be determined
as I
to the clamped mode are manageable:
where V
200µA(max), I
The inductor value can be chosen in accordance with:
where ∆I
The LED current is programmed by selecting the current
sense resistor in accordance with the following equation:
At low input voltage, parasitic resistances such as R
HV9821, DCR of the inductor, and sense resistor R
playing a major role. The 0.50V reference voltage can no
longer develop at RS, and the HV9821 high-voltage switch
remains in the on-state. At this condition, the internal regula-
tor cannot power the IC, and the VDD voltage ramps down
at the rate of I
high-voltage switch turns off. The capacitor C
to 3.4V. (See Figure 3.) Thus, at the described low input volt-
age condition, the HV9821 no longer maintains constant
LED current, but rather enters a resistive mode of operation
with periodical brief interruption to replenish charge in C
The on-time between such interruptions is determined as
T
Doc.# DSFP-HV9821
NR032113
P
ON
COND
IN
= 0.4V • C
= I
= V

 

O
L
R



OUT
L
V
• D, where D = V
O
CS
V
is the desired inductor current peak-to-peak ripple.
O
OUT
=
IN
= V
• I
=
V
- 1 + V
VZ(+)
O
OUT
DD
I
DD(Q)
Z
OUT
+ V
∆I
- 2V, I
/I

 

0.50V
• T
DD(Q)
L
= 13mA(max), and T
- ½∆I
OUT
O
/C
OFF
• I
DD
.
DD(Q)
IN
VZ(BIAS)
to accommodate the minimum duty
. When V
L
• I
O
DD(Q)
= 800µA(max), I
/V
+ I
OUT
VZ(+)
, the conduction losses due
DD
• (V
drops below 3.0V, the
BL
OUT
= 400ns(max).
- V
VZ(BIAS)
DD
O
) •
is charged
=
T
T
ON
BL
OFF
S
of the
start



DD
•
.
4
Voltage Clamp
The voltage limit at OUT is determined by breakdown volt-
age V
gate drive current of the internal power MOSFET is diverted
into VZ, when the voltage reaches V
OUT becomes clamped to ~V
ing-edge blanking delay of 300ns, this current can be up to
10mA. The current is further reduced to 100µA to minimize
power dissipation in the Zener diode.
Connection of a Schottky diode between OUT and VZ pre-
vents latch-up conditions due to parasitic charge redistribu-
tion in the switching circuit.
The VZ pin can be left open. In this case, the circuit shall
function as a switching converter with the OUT voltage
V
Regulator
The off state of the switch is used by an internal voltage
regulator to derive the 9.0V supply at VDD from VIN for the
control circuits.
Current Sense Comparator
The comparator terminates the gate driver on-state to pull
the gate of the cascoded internal switching transistor to
OUT, when the voltage at RS exceeds 0.50V. The 300ns
leading-edge blanking delay prevents false tripping of the
comparator.
OFF Timer
The IC operates with fixed off time of the power switch. This
time duration is programmed with an external resistor at R
in accordance with the equation T
Over-Temperature Protection
The HV9821 is protected from over-temperature by turning
the internal voltage regulator off at a temperature threshold
greater than 125
the IC until the junction temperature falls by 20
OUT
= V
Z
of an external Zener diode connected at VZ. The
IN
.
O
C. Minimum current shall be consumed by
Z
. For the duration of the lead-
OFF
Z
. Hence, the voltage at
= R
Supertex inc.
T
• 100pF.
www.supertex.com
HV9821
O
C.
T