HV9930 Supertex, Inc., HV9930 Datasheet - Page 6

• Manufacturer Part Number: HV9930
• Description: Hysteretic Boost-buck ?uk Led Driver Ic
• Manufacturer: Supertex, Inc.

Design Example
The resistors can be chosen using the following equations:
I x R
ΔI x R
Where I is the current (either I
peak ripple in the current (either ΔI
For the input side, the current level used in the equations
should be larger than the maximum input current so that it
does not interfere with the normal operation of the circuit.
The peak input current can be computed as:
I
Assuming a 30% peak-to-peak ripple when the converter is
in input current limit mode, the minimum value of the input
current will be:
I
Setting
I
The current level to limit the converter can then be com-
puted.
I
Using I
R
R
Pin Description
IN,PK
LIN,MIN
LIN,MIN
IN,LIN
CS2
S2
Pin #
/R
1
2
3
4
5
6
7
8
= I
CS
= (1.05/0.85) x I
= 1.78Ω
REF2
= 0.85 x I
= 1.05 x I
CS
= 12V x (R
IN,MAX
O
= 0.1V x (R
= 0.35A and ΔI
= 0.5625
PWMD
Name
GATE
GND
VDD
CS1
CS2
REF
VIN
+ (I
IN,LIN
IN,PK
IN
/2) = 1.706A
S
/R
Description
This pin is the input of a 8.0 - 200V voltage regulator.
This pin is used to sense the input and output currents of the boost-buck converter. It is the non-inverting input of
the internal comparators.
Ground return for all the internal circuitry. This pin must be electrically connected to the ground of the power train.
This pin is the output gate driver for an external N-channel power MOSFET.
When this pin is left open or pulled to GND, the gate driver is disabled. Pulling the pin to a voltage greater than 2.0V
will enable the gate drive output.
This is a power supply pin for all internal circuits. It must be bypassed to GND with a low ESR capacitor to GND.
This pin is used to sense the input and output currents of the boost-buck converter. It is the non-inverting input of
the internal comparators.
This pin provides accurate reference voltage. It must be bypassed with a 0.01 - 0.1µF capacitor to GND.
S
INPK
REF
/R
REF
) - 0.05V
O
= 2.1A
(cont.)
= 0.0875A in (1) and (2),
) + 0.1V
O
or I
O
in
or ΔI
) and ΔI is the peak-to-
in
).
(1)
(2)
(3)
(4)
(5)
(6)
6
Before the design of the output side is complete, over voltage
protection has to be included in the design. For this applica-
tion, choose a 33V zener diode. This is the voltage at which
the output will clamp in case of an open LED condition. For
a 350mW diode, the maximum current rating at 33V works
out to about 10mA. Using a 2.5mA current level during open
LED conditions, and assuming the same R
R
Choose the following values for the resistors:
R
R
R
R
The current sense resistor needs to be at least a 1/4W, 1%
resistor.
Similarly, using I
and (2),
R
R
P
Choose the following values for the resistors:
R
R
R
RCS1
CS2
CS2
REF2
S2A
S2B
S1
CS1
CS1
REF1
S1
/R
= 4.42kΩ, 1/8W, 1%
= 100Ω, 1/8W, 1%
= 5.23Ω, 1/8W, 1%
+ R
= 1.65Ω, 1/4W, 1%
= 0.228Ω
= parallel combination of three 0.68Ω, 1/2W, 5%
REF1
= 10kΩ, 1/8W, 1%
= I
= 10kΩ, 1/8W, 1%
2
S2A
IN,LIM
= 0.442
= 120Ω
x R
IN
CS1
= 2.1A and ΔI
= 1.0W
IN
= 0.3 x I
S2
IN
/R
HV9930
= 0.63A in (1)
REF2
ratio,