HV9803LG-G Supertex, HV9803LG-G Datasheet - Page 5

• Manufacturer Part Number: HV9803LG-G
• Description: LED Lighting Drivers LED Driver w/Average Constant Current
• Manufacturer: Supertex

Specifications of HV9803LG-G

• Rohs: yes
• Input Voltage: 7 V to 13.2 V
• Maximum Supply Current: 2.5 mA
• Maximum Operating Temperature: + 125 C
• Mounting Style: SMD/SMT
• Package / Case: SOIC-8
• Minimum Operating Temperature: - 40 C
• Power Dissipation: 650 mW

OFF Timer
In the HV9803, the timing resistor connected to RT
determines the off-time of the gate driver, and it must be
wired to GND. The equation governing the off-time of the
GATE output is given by:
The R
condition at R
Current Sense Comparator and Timer Circuits
The function of the HV9803’s current sense comparator is
similar to that of a peak current controller. However, the GATE
pulse is not terminated immediately as the LD threshold is
met. The GATE turn off in the n
T
where T
two consequent switching cycles. This iterative control law is
needed for damping sub-harmonic oscillation.
Note, that the above control law is only valid up to a maximum
switching duty cycle D
reduction in the LED current.
Propagation delay in the current sense comparator is one
of the most significant contributors to the LED current error.
It must be noted that the control scheme described above
does not improve this deficiency of the peak-current control
scheme by itself. Moreover, it samples the propagation delay
during T
error introduced by this delay. In order to eliminate this error,
the reference voltage is corrected by an auto-zero circuit. In
essence, the HV9803 samples its CS signal when the current
sense comparator triggers, detects the difference between
the sampled CS level and the reference input of the current
sense comparator. The resulting difference is subtracted
from the reference level to generate a new reference in the
next switching cycle.
GATE Output
The GATE output of the HV9803 is used to drive an external
MOSFET. It is recommended that the gate charge Q
of the external MOSFET be less than 25nC for switching
frequencies ≤100kHz and less than 15nC for switching
frequencies >100kHz.
The resulting LED current is calculated from the equation:
Doc.# DSFP-HV9803
NR012313
2,n
determined by a timer circuit as follows:
T
T
T
1,n
I
input is protected from short circuit. Over-current
1
LED
OFF
2,n
and replicates it during T
and T
=
=
= R
T
2
1
0.49 • V
inhibits the IC.
T
• (T
1,n-1
• 40pF
1,n
are the times to the LD threshold in any
R
+ T
LD
max
CS
- 6mV
1,n-1
= 0.8. Exceeding D
)
th
cycle is delayed by a time
2
, essentially doubling the
max
will cause
G
5
Short Circuit Protection
The HV9803 is equipped with a protection comparator
having a CS threshold V
is triggered, the GATE output shuts off for the duration of
a restart delay, determined by the RC constant at UVLO.
The capacitor C
delay due to charging C
calculated as:
where k = R
Under-Voltage Shutdown
Under-voltage comparator input is provided to disable the
IC, when the UVLO input is below a threshold. Hysteresis is
provided to avoid oscillation.
Failure Modes and Effects Analysis (FMEA)
The HV9803 is designed to withstand short circuit between its
adjacent pins without damage. The following table describes
the effect of such incidental short circuit conditions.
Short Circuit
Mode
CS to VDD
VDD to GND
GND to GATE
RT to PWMD
PWMD to
UVLO
UVLO to LD
T
SKIP
2
= k • R
/(R
1
SKIP
+R
Effect
The IC triggers the short circuit
protection and operates in the auto-
restart mode continuously.
Short circuit across the 12V should
cause the external bias supply over-
current protection.
Should cause the external bias supply
over-current protection. The power
MOSFET Q1 is off.
Case 1 – PWMD = Lo: The RT pin
sources its maximum current.
GATE = 0V, and Q1 is off.
Case 2 – PWMD=Hi: The RT pin is
pulled up, shutting off the timer.
GATE is off.
This will overdrive the under-voltage
threshold. However, since V
condition is harmless to the IC, there is
no effect.
LD overdrives the UVLO. If LD is lower
than the UVLO threshold, the IC shuts
off. No effect otherwise.
1
2
).
is discharged below 200mV. A restart
• C
SKIP
SKIP
LIM
• ln
. When this second threshold
to the UVLO start threshold is
k • V
k • V
IN
IN
Supertex inc.
- 0.30V
- 1.17V
www.supertex.com
IN
HV9803
UV