BD81A24MUV-M Datasheet, PDF (23/40 Pages) Rohm – 4ch White LED Driver with Buck-Boost

BD81A24MUV-M/EFV-M
8. Phase Characteristics adjustment
Vout
Datasheet
LED1~4
Internal IC
A
COMP
RPC
CPC
Figure 25. COMP terminal Application Circuit Diagram
About Application Stability Condition
The stability in LED voltage feedback system is achieved when the following conditions are met.
(1) The phase delay when gain is 1(0dB) is below 150°C (or simply, phase margin >30°C).
(2) The frequency (Unity Gain Frequency) when gain is 1(0dB) is <1/10 of switching frequency.
One way to assure stability based on phase margin adjustment is setting the Phase-lead fz close to switching frequency. In
addition, the Phase-lag fp1 shall be decided based on COUT and Output impedance RL.
Respective formula shall be as follows.
Phase-lead [ ] = 1/(2
[Ω] [ ] )
Phase-lag 1[ ] = 1/(2 [Ω] [ ])
(Note) The output impedance calculated from
=
/
Good stability would be obtained when the fz is set between 1kHz to 10kHz.
It is important to keep in Mind that these are very loose guidelines, and adjustments may have to be made to ensure stability
in the actual circuitry. It is also important to note that stability characteristics can change greatly depending on factors such
as substrate layout and load conditions. Therefore, when designing for mass-production, stability should be thoroughly
investigated and confirmed in the actual physical design.
9. Setting of Over Voltage Protection(OVP)
Over voltage protection (OVP) is set from the external resistance ROVP1 and ROVP2.
The setting described below will be important in the either boost, buck, buck-boost applications.
Vout
Internal IC
ROVP2
OVP
ROVP1
2.0V/1.94V
1.0V/0.57V
Figure 26. OVP Application Circuit
The OVP terminal detects the over voltage when at >2.0V (Typ) and stops the DC/DC switching. In addition, it detects the
open condition when OVP terminal is at >2.0V (Typ) and LED1 to 4 pin voltage is at <0.3V (Typ), and the circuit is latched to
OFF (Please refer to page 6, Protect Function). In preventing error in detection of OPEN, it is necessary that the resistor
divide voltage of the maximum value of output voltage shall be less than the MIN value of OPEN detection voltage. Please
set the ROVP1 and ROVP2 is such a way the formula shown below can be met.
( )[ ] × {
1[ ]⁄(
1[ ] +
2[ ])} <
( )[ ] …(1)
Vout: DC/DC Output Voltage
Sample 1: When VF=3.2V±0.3V LED is used in 8series
( )[ ] = 1.1 (
VOVPopen: OVP Pin Open Detection Voltage
) + (3.2 + 0.3 ) × 8 = 29.1
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TSZ02201-0T3T0C600070-1-2
2016.10.19 Rev.003