CS5166GDWR16 View Datasheet(PDF) - ON Semiconductor
Part Name
Description
MFG CO.
'CS5166GDWR16' PDF : 25 Pages View PDF
CS5166
Trace 1 = Output voltage ripple.
Trace 2 = Buck regulator #1 inductor switching node.
Trace 3 = Buck regulator #2 inductor switching node.
Figure 33. 15 A Load Transient Waveforms
Trace 1 = Output voltage ripple.
Trace 2 = Buck regulator #1 inductor switching node.
Trace 3 = Buck regulator #2 inductor switching node.
Figure 34. 30 A Load Waveforms
Figure 33 shows supply response to a 15 A load step with
a 30 A/μs slew rate. The V2 control loop immediately forces
the duty cycle to 100%, ramping the current in both
inductors up. A voltage spike of 136 mV due to output
capacitor impedance occurs. The inductive component of
the spike due to ESL recovers within several microseconds.
The resistive component due to ESR decreases as inductor
current replaces capacitor current.
The benefit of adaptive voltage positioning in reducing
the voltage spike can readily be seen. The difference in DC
voltage and duty cycle can also be observed. This particular
transient occurred near the beginning of regulator off time,
resulting in a longer recovery time and increased voltage
spike.
Output Inductor
The inductor should be selected based on its inductance,
current capability, and DC resistance. Increasing the
inductor value will decrease output voltage ripple, but
degrade transient response.
Inductor Ripple Current
Ripple
Current
+
[(VIN * VOUT)
(Switching Frequency
VOUT]
L VIN)
Example: VIN = +5.0 V, VOUT = +2.8 V, ILOAD = 14.2 A,
L = 1.2 μH, Freq = 200 kHz
Ripple
Current
+
[(5.0 V *
[200 kHz
2.8 V)
1.2 mH
2.8 V]
5.0 V]
+
5.1
A
Output Ripple Voltage
VRIPPLE + Inductor Ripple Current Output Capacitor ESR
Example:
VIN = +5.0 V, VOUT = +2.8 V, ILOAD = 14.2 A, L = 1.2 μH,
Switching Frequency = 200 kHz
Output Ripple Voltage = 5.1 A × Output Capacitor ESR
(from manufacturer’s specs)
ESR of Output Capacitors to limit Output Voltage Spikes
ESR
+
DVOUT
DIOUT
This applies for current spikes that are faster than
regulator response time. Printed Circuit Board resistance
will add to the ESR of the output capacitors.
In order to limit spikes to 100 mV for a 14.2 A Load Step,
ESR = 0.1/14.2 = 0.007 Ω
Inductor Peak Current
ǒ Ǔ Peak Current + Maximum Load Current )
Ripple Current
2
Example: VIN = +5.0 V, VOUT = +2.8 V, ILOAD = 14.2 A,
L = 1.2 μH, Freq = 200 kHz
Peak Current + 14.2 A ) (5.1ń2) + 16.75 A
A key consideration is that the inductor must be able to
deliver the Peak Current at the switching frequency without
saturating.
Response Time to Load Increase
(limited by Inductor value unless Maximum On−Time is
exceeded)
Response
Time
+
L
(VIN
DIOUT
* VOUT)
Example: VIN = +5.0 V, VOUT = +2.8 V, L = 1.2 μH, 14.2 A
change in Load Current
Response
Time
+
1.2 mH
(5.0 V
*
14.2 A
2.8 V)
+
7.7
ms
Response Time to Load Decrease
(limited by Inductor value)
Response Time + L
Change in IOUT
VOUT
Example: VOUT = +2.8 V, 14.2 A change in Load Current,
L = 1.2 μH
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