HV9919 Supertex, Inc., HV9919 Datasheet - Page 4

• Manufacturer Part Number: HV9919
• Manufacturer: Supertex, Inc.

Block Diagram
Application Information
General Description
The HV9919 is a step-down, constant current, high-bright-
ness LED (HB LED) driver. The device operates from a 4.5
to 40V input voltage range and provides the gate drive out-
put to an external N-channel MOSFET. A high-side current
sense resistor sets the output current and a dedicated PWM
dimming input (DIM) allows for a wide range of diming duty
ratios. The PWM dimming could also be achieved by apply-
ing a DC voltage between 0 and 2V to the analog dimming
input (ADIM). In this case, the dimming frequency can be
programmed using a single capacitor at the RAMP pin. The
high-side current setting and sensing scheme minimizes the
number of external components while delivering LED cur-
rent with a ±8% accuracy, using a 1% sense resistor.
Undervoltage Lockout (UVLO)
The HV9919 includes a 3.7V under-voltage lockout (UVLO)
with 500mV hysteresis. When V
goes low, turning off the external n-channel MOSFET. GATE
goes high once V
5.0V Regulator
VDD is the output of a 5.0V regulator capable of sourcing
18mA. Bypass VDD to GND with a 1.0μF capacitor.
DD
is 4.2V or higher.
RAMP
ADIM
VIN
CS
DD
PWM RAMP
BANDGAP
0.1~1.9V
falls below 3.7V, GATE
REF
COMPARATOR
COMPARATOR
REGULATOR
CURRENT
+
+
-
SENSE
-
UVLO
+
-
4
DIM Input
The HV9919 allows dimming with a PWM signal at the DIM
input. A logic level below 0.8V at DIM forces the GATEoutput
low, turning off the LED current. To turn the LED current on,
the logic level at DIM must be at least 2.0V.
ADIM and RAMP Inputs
The PWM dimming scheme can be also implemented by ap-
plying an analog control signal to ADIM pin. If an analog con-
trol signal of 0~2.0V is applied to ADIM, the device compares
this analog input to a voltage ramp to pulse-width-modulate
the LED current. Connecting an external capacitor to RAMP
programs the PWM dimming ramp frequency.
Setting LED Current with External Resistor R
The output current in the LED is determined by the external
current sense resistor (R
CS. Disregarding the effect of the propagation delays, the
sense resistor can be calculated as:
F
R
PWM
SENSE
=
≈
HV9919
C
10
1
2
RAMP
-6
DRIVER
•
GATE
(V
RS,HI
SENSE
I
LED
+ V
) connected between VIN and
VDD
RS,LO
DIM
GATE
GND
)
=
200mV
HV9919
I
LED
SENSE