NCP3101CMNTXG Datasheet, PDF (21/26 Pages) ON Semiconductor – Wide Input Voltage Synchronous Buck Converter

NCP3101C
I_{ICinrush_PK}
+
V_IN
CIN_ESR
(eq. 51)
120 A + ¹²
0.1
I_{ICin_RMS}
+
V_IN
CINESR
*
Ǹ 0.316 * 5 * CINESR * CIN
t_{DELAY_TOTAL}
Ǹ ^{12 V}
5 * 0.1 W * 330 mF
5.92 A +
* 0.316 *
0.1 W
6.76 ms
(eq. 52)
C_IN
= Input capacitor
CIN_ESR
= Input capacitor ESR
t_{DELAY_TOTAL} = Total delay interval
V_CC
= Input voltage
Once the t_{DELAY_TOTAL} has expired, the buck converter
starts to switch and a second inrush current can be
calculated:
ǒ_{COUT ) CLOAD}Ǔ _{* VOUT}
I_{OCinrush_RMS} +
t_SS
(eq. 53)
*
D
Ǹ₃
)
I_CL
*
D
C_OUT
C_LOAD
D
= Total converter output capacitance
= Total load capacitance
= Duty ratio of the load
I_CL
= Applied load at the output
I_{OCinrush_RMS} = RMS inrush current during start−up
t_SS
= Soft start interval
V_OUT
= Output voltage
From the above equation, it is clear that the inrush current
is dependant on the type of load that is connected to the
output. Two types of load are considered in Figure 33: a
resistive load and a stepped current load.
Inrush
Current
Load
I_CLR_RMS
+
1
Ǹ₃
*
V_OUT
R_OUT
I_{CR_PK}
+
V_OUT
R_OUT
191 mA +
1
3.3 V
*
Ǹ_{3 10 W}
3.3 V
330 mA +
10 W
R_OUT
V_OUT
I_{CLR_RMS}
I_{CR_PK}
= Output resistance
= Output voltage
= RMS resistor current
= Peak resistor current
3.3V
(eq. 54)
Output
Voltage
Output
Current
tss
Figure 34. Resistive Load Current
Alternatively, if the output has an under voltage lockout,
turns on at a defined voltage level, and draws a consistent
current, then the RMS connected load current is:
Ǹ I_CLKI +
V_OUT * V_{OUT_TO}
V_OUT
* I_OUT
(eq. 55)
Ǹ^{3.3 V * 1.0 V}
835 mA +
*1A
3.3 V
I_OUT
V_OUT
V_{OUT_TO}
= Output current
= Output voltage
= Output voltage load turn on
OR
Figure 33. Load Connected to the Output Stage
If the load is resistive in nature, the output current will
increase with soft start linearly which can be quantified in
Equation 54.
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