RT9202BGS RICHTEK [Richtek Technology Corporation], RT9202BGS Datasheet - Page 10

• Manufacturer Part Number: RT9202BGS
• Description: Single Synchronous Buck PWM DC-DC Controller
• Manufacturer: RICHTEK [Richtek Technology Corporation]

RT9202B
Both V
capacitor across R
variations of V
current function will be tripped at a peak inductor current
(I
The OC trip point varies with MOSFET's R
temperature variations. The temperature coefficient of
I
temperature variations. To avoid over-current tripping in
the normal operating load range, determine the R
resistor value from the equation above with:
1.The maximum R
2.The minimum I
3.Determine I
where
Under Voltage and Over Voltage Protection
The voltage at FB pin is monitored and protected against
OC (over current), UV (under voltage), and OV (over
voltage). The UV threshold is 0.5V and OV-threshold is
1.0V. Both UV/OV detection have 30 s triggered delay.
When OC or UV trigged, a hiccup re-start sequence will
be initialized, as shown in Figure 4. Only 3 times of trigger
are allowed to latch off. Hiccup is disabled during soft-
start interval.
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10
OCSET
PEAK
temperature
I
PEAK
OC
PWM
) determined by :
is 2500ppm that is used to compensate R
SET
I is the output inductor ripple current.
+
-
I
OCSET
and V
OVER-CURRENT TRIP:
V
i
D
CONTROL
DS
PEAK
GATE
R
IN
R
> V
DS(ON)
DS(ON)
due to MOSFET switching. The over-
DS
OCSET
SET
for I
I
20uF
OCSET
R
DRIVE
OCSET
are referenced to V
OCSET
> I
OCSET
SD(ON)
PEAK
OCSET
from the characteristics
Figure 3
> I
helps V
VCC
at the highest junction
R
OUT(MAX)
OCSET
V
V
UGATE
PHASE
OCSET
R
V
OCSET
OCSET
PHASE
SET+
+ ( I)/2
= V
= V
IN
IN
tracking the
IN
and a small
- V
- V
V
V
IN
DS
SET
i
DS+
D
= +5V
DS(ON)
DS(ON)
OCSET
Shutdown
Pulling low the OCSET pin can shutdown the RT9202B
PWM controller as shown in typical application circuit.
Inductor Selection
The RT9202B was designed for V
application mainly. Figure 5 shows the typical topology
and waveforms of step-down converter.
The ripple current of inductor can be calculated as follows:
Because operation frequency is fixed at 300kHz,
The V
ESR is output capacitor equivalent series resistor
Table 1 shows the ripple voltage of V
T
IL
V
ON
OUT RIPPLE
RIPPLE
OUT
0A
= 3.33 × V
4V
2V
0V
= (5V - V
ripple is
COUNT = 1 COUNT = 2 COUNT = 3
= IL
T0
OUT
RIPPLE
OUT
T1
/5V
)/L × T
Figure 4
× ESR
OVERLOAD
APPLIED
T2
ON
DS9202B-03 March 2007
TIME
IN
OUT
= 5V, step-down
: VIN = 5V
T3