HV9805 Datasheet, PDF (11/34 Pages) Microchip Technology – Off-Line LED Driver with True DC Output Current

HV9805
3.0 PIN DESCRIPTION
The descriptions of the pins are listed in Table 3-1.
TABLE 3-1: PIN FUNCTION TABLE
Pin Symbol
1
V_DD
2
CSL
3
CSH
4
HVS
5
HVR
6
CRS
7
CRG
8
BVS
9
GND
10
DRV
I/O
Description
—
Pin for support of the V_DD supply
I
Non-inverting input pin of the current sense amplifier of the first stage
I
Inverting input pin of the current sense amplifier of the first stage
I
Input pin of the headroom voltage sense amplifier
O
Output pin of the headroom voltage regulator control amplifier
I
Input pin of the current sense amplifier of the second stage
O
Output pin of the constant current regulator control amplifier
I
Input pin of the bus voltage sense amplifier
—
Ground pin
O
Drive pin for control of the boost converter switch
3.1 V_DD Supply Support Pin (V_DD)
The V_DD supply is not capable of sourcing a significant
current to external circuitry. A significant source of sup-
ply current can be created by means of an auxiliary
winding on the boost inductor.
Connect a 10 μF ceramic capacitor between the V_DD
and GND pins to provide V_DD supply filtering and V_DD
supply holdup.
A sizable holdup capacitor is required to maintain an
adequate V_DD supply voltage near the zero crossings
of the AC line voltage, where the supply of current to
the V_DD supply circuit drops off significantly.
3.2 Input Pins of the First-Stage
Current Sense Amplifier (CSL,
CSH)
The Current Sense Amplifier senses the boost inductor
current for line current-waveform shaping and
detecting the drain voltage valley.
The sense amplifier is arranged as a differential
amplifier featuring unity gain and an output voltage
offset of 1.25V, as seen in Figure 4-3. The offset allows
a negative boost inductor sense voltage to be
processed as a positive voltage. Note that positive
boost inductor current produces negative sense
voltage at the current sense resistor R_LBS.
The resistance of each gain setting resistor R_CSA is
nominally 10 kΩ. Two of the gain setting resistors are
provided internally to the HV9805, and two are
provided externally. Complete the differential amplifier
setup by adding two R_CSA resistors of 10 kΩ and of 1%
tolerance, as indicated in Figure 4-3.
To improve drain voltage valley detection, a second set
of resistors R_VAL and a capacitor C_VAL can be added to
the amplifier setup, as shown in the Typical Application
Circuit and Block Diagram. Detection signal amplitude
can be adjusted freely by the C_VAL and R_VAL selection,
with larger values generating a larger detection signal
from the drain voltage swing. Starting values of 100Ω
and 10pF for R_VAL and C_VAL are suggested. Provide
detection resistors in both legs of the sense amplifier to
keep the amplifier setup balanced.
The combination of resistors R_VAL and R_CSA at the
CSH pin can be replaced by a single resistor, R_CSH.
Refer to the Typical Application Circuit and to the Block
Diagram for more details.
3.3 Input Pin of the Headroom Voltage
Sense Amplifier (HVS)
Connect the HVS pin to the drain of the constant
current regulator FET with a resistive divider.
The addition of a Zener diode at the HVS pin is required
to protect the HVS pin from an overvoltage condition at
shutdown of the LED driver. Overvoltage at the HVS pin
can occur as the bus capacitor remains charged for a
significant time after shutdown. The headroom voltage
rises significantly as the forward voltage drop across
the LED load drops towards zero. Consequently, the
voltage at the HVS pin rises as well, and may take the
voltage at the HVS pin above its absolute maximum
rating without an external Zener diode in place.
 2015 Microchip Technology Inc.
DS20005374A-page 11