RT2810A/B
trip threshold (1.2 times regulation level) for longer than
5μs (typical), the IC's OVP is triggered. RT2810AL chip
enters latch mode.
Thermal Considerations
For continuous operation, do not exceed absolute
maximum junction temperature. The maximum power
dissipation depends on the thermal resistance of the IC
package, PCB layout, rate of surrounding airflow, and
difference between junction and ambient temperature. The
maximum power dissipation can be calculated by the
following formula :
For RT2810BH, if the output voltage remains high, the
synchronous rectifier remains on until the inductor current
reaches the low side current limit. If the output voltage
still remains high, the synchronous rectifier turns on and
high-side MOSFET keeps off to operate at typical 500kHz
switching protection, again if inductor current reaches low
side current limit, the synchronous rectifier will turn off
until next protection clock. RT2810BH is without OVP
latch function and recover when OV condition release.
PD(MAX) = (TJ(MAX) − TA) / θJA
where TJ(MAX) is the maximum junction temperature, TA is
the ambient temperature, and θJA is the junction to ambient
thermal resistance.
For RT2810AH, if the output voltage remains high, the
synchronous rectifier remains on until the inductor current
reaches zero current. If the output voltage still remains
high, then IC's switches remain off. RT2810AH is without
OVP latch function and recover when OV condition release.
For recommended operating condition specifications, the
maximum junction temperature is 125°C. The junction to
ambient thermal resistance, θJA, is layout dependent. For
UQFN-16JL 3x3 (FC) package, the thermal resistance,
θJA, is 27.6°C/W on a standard four-layer thermal test
board. The maximum power dissipation at TA = 25°C can
be calculated by the following formula :
Switching Frequency Setting
The switching frequency can be set by using extra resister
RRT. Switching frequency range is from 300kHz to 700kHz.
Through extra resister RRT connect to RT pin to setting
the switching frequency fSW as Figure 8, below offer
approximate formula equation :
PD(MAX) = (125°C − 25°C) / (27.6°C/W) = 3.623W for
UQFN-16JL 3x3 (FC) package
The maximum power dissipation depends on the operating
ambient temperature for fixed TJ(MAX) and thermal
resistance, θJA. The derating curve in Figure 9 allows the
designer to see the effect of rising ambient temperature
on the maximum power dissipation.
Setting Frequency = fSW (kHz)
106
R
RT
=
f
1.374105 1.541104
SW
Frequency vs. RRT Resistor
4.0
700
650
600
550
500
450
400
350
300
Four-Layer PCB
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0
25
50
75
100
125
100 115 130 145 160 175 190 205 220 235 250
Ambient Temperature (°C)
RRT (k )
Ω
Figure 9. Derating Curve of Maximum PowerDissipation
Figure 8. Frequency vs. RRT Resistor
Copyright 2016 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
DS2810A/B-06 November 2016
www.richtek.com
15
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
