Instrukcja obsługi Microchip HV9912DB1

Microchip nieskategoryzowany HV9912DB1

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Supertex inc.
Supertex inc.
www.supertex.com
HV9912DB1
Doc.# DSDB-HV9912DB1
A032913
The HV9912DB1 is an LED driver demoboard capable of driving up
to 20 one-watt LEDs in series from an input of 21 - 27VDC. It uses
the Supertex HV9912 in a boost topology. The converter has very
good initial regulation (+/-5%) and excellent line and load regulation
over the entire input and output voltage range (<+/- 1%). The full
load efciency of the converter is typically greater than 90%.
The HV9912DB1 is protected against open LED and output short
circuit conditions. It is also protected under input under-voltage
conditions by limiting the input current. It has an excellent PWM
dimming response, with typical rise and fall times less than 1.0μs,
which allows high PWM dimming ratios. The switching frequency of
the HV9912DB1 can be synchronized to other HV9912 boards or
to an external 200kHz clock by connecting the clock to the SYNC
pin of the HV9912DB1.
The HV9912DB1 features hiccup mode short circuit and open LED
protection. Upon detection of either fault condition, the IC shuts
down the driver and periodically attemps to restart until the fault
condition ends. The HV9912DB1 also features a built-in 500ns
blanking to prevent false tripping of the over-current comparator
due to parasitic capacitance spikes during PWM dimming.
Board Layout and Connection Diagram
High Brightness Boost LED Driver Demoboard
with 1:3000 Dimming Ratio and Hiccup Mode Protection
Parameter Value
Input voltage (steady state): 21 - 27VDC
Output LED string voltage: 35V min - 80V max
Output current: 350mA +/-5%
Output current ripple: 10% typical
Switching frequency: 200kHz
Full load efciency: 93% (at 24V input)
Open LED protection: Shuts down at 92V
Output short circuit
protection: Included
Input under voltage
protection: Included
PWM dimming: 1:3000 dimming ratio
at 200Hz
Connections
Input - The input is connected between the terminals of
connector J1 as shown in the Connection Diagram.
Output - The output is connected between the terminals of
connector J2 as shown.
Enable/PWM Dimming - To just enable the board, short pins
PWMD and VDD of connector J3 as shown by the dashed
lines. To PWM dim the board, connect the external push-
pull waveform source between terminals PWMD and GND
of connector J3 as shown by the solid lines.
SYNC - To synchronize two or more boards, connect the
SYNC pins of all the boards together. To synchronize the
HV9912DB1 to an external 200kHz clock, connect the clock
between the SYNC and GND pins of terminal J3.
Note:
During PWM dimming, pin 2 of connector J3 should be left
open. Also, the PWM signal must have the proper polarity
with the positive connected to pin 3 of J3. Note that pin 4
of J3 is internally connected to the return path of the input
voltage.
Actual size: 64.0mm x 34.5mm
V
IN
+
General Description Specications
2
HV9912DB1
Supertex inc.
www.supertex.com
Doc.# DSDB-HV9912DB1
A032913
Testing The Demoboard
Normal Operation: Connect the input source and the output
LEDs as shown in the Connection Diagram and enable the
board. The LEDs will glow with a steady intensity. Connecting
an ammeter in series with the LEDs will allow measurement
of the LED current. The current will be 350mA +/- 5%.
Current Regulation: With the input power to the converter
disconnected, change the LED string voltage within
the specications mentioned. The current output of the
HV9912DB1 will remain very steady over the entire load
range. Vary the input voltage while the circuit is operational.
The current will be regulated over the entire line range.
Open LED test: Connect a voltmeter across the output
terminals of the HV9912DB1. Start the demoboard normally,
and once the LED current reaches steady state, unplug
one end of the LED string from the demoboard. The output
voltage will rise to about 92V and the HV9912DB1 will shut
down. Once the LED string is reconnected, the driver will
start regulating current.
Short Circuit Test: When the HV9912DB1 is operating in
steady state, connect a jumper across the terminals of the
LED string. Notice that the output current will immediately
go to zero and the converter will shut down. Removing the
jumper will cause the HV9912DB1 to restart and continue to
regulate the LED current.
PWM Dimming: With the input voltage to the board
disconnected, apply a TTL compatible, push-pull square wave
signal between PWMD and GND terminals of connector J3
as shown in the Connection Diagram. Turn the input voltage
back on and adjust the duty cycle and/or frequency of the
PWM dimming signal. The output current will track the PWM
dimming signal. Note that although the converter operates
perfectly well at 1.0kHz PWM dimming frequency, the widest
PWM dimming ratio can be obtained at lower frequencies
like 100 or 200Hz.
Typical Results
1. Ef฀ciency: The efciency of the converter at various LED
string voltages are shown in Fig.1 (measured at the nominal
input voltage of 24V). Fig.2 shows the full load efciency
of the converter at varying input voltages. The minimum ef-
ciency of 93% for the converter occurs at 21V input and full
load output.
2. Current Regulation: Figs. 3 and 4 show the output cur-
rent regulation vs. output voltage and input voltage respec-
tively. The total current regulation (line and load combined)
is found to be less than 1%.
90
91
92
93
94
95
35 40 45 50 55 60 65 70 75 80
Output ltage (V)Vo
Efficiency (%)
Fig. 1 Efficiency evs. Output Voltag
90
91
92
93
94
95
20 22 24 26 28
Input ltage (V)Vo
Efficiency (%)
Fig. 2 Efficiency evs. Input Voltag
0.346
0.348
0.350
0.352
0.354
35 40 45 50 55 60 65 70 75 80
Output ltage (V)Vo
Output Current (A)
Fig. 3 Output Current tput Voltagvs. Ou e
Fig. 4 Output Current put Voltagevs. In
0.346
0.348
0.350
0.352
0.354
20 22 24 26 28
Input ltage (V)Vo
Output Current (A)
3
HV9912DB1
Supertex inc.
www.supertex.com
Doc.# DSDB-HV9912DB1
A032913
3. Input Under Voltage Protection: Input under voltage
protection is provided by limiting the input current at low in-
put voltages. Fig. 5 shows the output and input currents at
voltages less than the minimum rated voltage. The LED cur-
rent will decrease as the input voltage falls and the input
current limits to about 1.4A. Note that the input current limit
is not a hard limit as the slope compensation added to the
peak current sense signal will allow a small change in the
input current with a decrease in the input voltage.
4. Open LED Protection: Figs 6 and 7 show the hiccup-
mode over voltage protection. Fig. 6 shows the open LED
condition occurs when the LED current goes to zero. At
that point, the inductor current charges the output capacitor
and the COMP voltage rails to VDD. Once the output volt-
age reaches the over voltage threshold, the converter shuts
down and the output voltage slowly decays because the out-
put capacitor is discharged by the over-voltage sensing re-
sistor network. Once the output voltage falls to 90% of its trip
point, the converter tries to restart. Since the fault conditions
still persists, the converter shuts down almost immediately.
Thus, the HV9912 maintains the output voltage in a band
until the LED reconnects.
Fig. 7 shows the recovery of the HV9912DB1 from an over
voltage condition. In this case, the LED has reconnected
at some point when the converter is turned off. When the
converter attempts to restart, if nds the fault condition has
disappeared and it starts up normally. There is no overshoot
in the LED current .
Short Circuit Protection: Figs 8 and 9 show the operation
of the short circuit protection in the HV9912DB1. In Fig. 8,
the onset of the output short circuit is indicated by the rst
spike in the LED current. At this point, the HV9912DB1 shuts
down and the hiccup mode protection takes over. A constant
current source charges the COMP pin to 5.0V and then an-
other current source discharges it to 1.0V. This charge/dis-
charge cycle determines the hiccup time. When the COMP
pin reaches 1.0V, the converter attempts to restart and nd-
ing the fault condition still present, shuts down again.
1.0
1.2
1.4
1.6
10152025
Input Voltage (V), Sweep
Input Current (A)
0.1
0.2
0.3
0.4
Output Current (A)
Input Current Output Current
Fig. 5 Input Under-Voltage Behavior
Output ltageVo
COM VoltageP
LED Current
Fig. 6 Open LED Condition
Output ltageVo
Fig. 7 Recovery from an Open LED Condition
COMP Voltage
LED Current
Output ltageVo
Fig. 8 Short Circuit Condition
COMP ltageVo
LED Current

Specyfikacje produktu

Marka: Microchip
Kategoria: nieskategoryzowany
Model: HV9912DB1

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