HV9967B
Reducing the output LED voltage VO below VO(MIN) =VIN • DMIN
,
SW Input and Linear Regulator
where DMIN = 0.8µs/(TOFF + 0.8µs), may also result in the loss
of regulation of the LED current. This condition, however,
causes increase in the LED current and can potentially trip
the short-circuit protection comparator threshold.
HV9967B includes an integrated 60V, 0.8Ω switching
MOSFET at the SW input. The power for the IC is supplied
from a linear 5.0V regulator that is also derived from the SW
input.
The short circuit protection comparator trips when the volt-
age at RSENSE exceeds 0.4V. When this occurs, the SW
off-time THICCUP = 800µs is generated to prevent stair-casing
of the inductor current and potentially its saturation due to
insufficient output voltage. The typical short-circuit current is
shown in the waveform of Fig. 1.
PWM Dimming
The HV9967B features a TTL compatible dimming input
PWMD. Applying a square-wave voltage to PWMD will mod-
ulate the duty ratio of the LED current accordingly. The rising
and falling edges are limited by the current slew rate in the
inductor. The first switching cycle is terminated upon reach-
ing the 250mV level at RSENSE. The circuit will reach the
steady state within 3~4 switching cycles regardless of the
switching frequency.
0.44V/RSENSE
800µs
Over-Temperature Protection
The HV9967B includes over-temperature protection. Typi-
cally, when the junction temperature exceeds 145OC, switch-
ing of the SW input is disabled. The switching resumes when
the temperature falls by approximately 20OC from the trip
point.
Fig.1. Short-circuit inductor current.
A leading-edge blanking delay is provided at RSENSE to
prevent false triggering of the current feedback and the short
circuit protection.
Pin Description
Pin #
Function Description
1
SW
Drain of 60V 0.8Ω NDMOS switch and input of H/V regulator.
Source of NDMOS switch and current sense input.
2
RSENSE
Connect a resistor to GND to program the output current and short circuit thresholds.
Power ground. Must be wired to AGND on PCB.
3
4
5
6
7
PGND
PWMD
NC
PWM dimming input. This TTL input enables switching of SW when in high state.
No connection.
RT
Resistor connected between RT and VDD programs the off-time of SW.
Analog ground (0V).
AGND
Power supply for all internal circuits. Bypass with a low ESR capacitor to PGND (>0.5μF).
Connect GATE of external depletion-mode NFET for high-voltage operation.
8
VDD
Doc.# DSFP-HV9967B
B060712
Supertex inc.
www.supertex.com
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