CS5165A View Datasheet(PDF) - ON Semiconductor
Part Name
Description
MFG CO.
'CS5165A' PDF : 18 Pages View PDF
CS5165A
capacitor begins charging. The GATE(H) output will remain
on, enabling the NFET switch, until terminated by either the
PWM comparator, or the maximum on time timer.
If the maximum on time is exceeded before the regulator
output voltage achieves the 1.0 V level, the pulse is terminated.
The GATE(H) pin drives low, and the GATE(L) pin drives high
for the duration of the extended off time. This time is set by the
time out timer and is approximately equal to the maximum on
time, resulting in a 50% duty cycle. The GATE(L) pin will then
drive low, the GATE(H) pin will drive high, and the cycle
repeats.
When regulator output voltage achieves the 1.0 V level
present at the COMP pin, regulation has been achieved and
normal off time will ensue. The PWM comparator terminates
the switch on time, with off time set by the COFF capacitor. The
V2 control loop will adjust switch duty cycle as required to
ensure the regulator output voltage tracks the output of the
error amplifier.
The Soft−Start and COMP capacitors will charge to their
final levels, providing a controlled turn on of the regulator
output. Regulator turn on time is determined by the COMP
capacitor charging to its final value. Its voltage is limited by the
Soft−Start COMP clamp and the voltage on the Soft−Start pin.
Power Supply Sequencing
The CS5165A offers inherent protection from undefined
startup conditions, regardless of the 12 V and 5.0 V supply
power up sequencing. The turn on slew rates of the 12 V and
5.0 V power supplies can be varied over wide ranges without
affecting the output voltage or causing detrimental effects to
the buck regulator.
M 250 ms
Trace 1− Regulator Output Voltage (1.0 V/div.)
Trace 2− Inductor Switching Node (2.0 V/div.)
Trace 3− 12 V Input (VCC) (5.0 V/div.)
Trace 4− 5.0 V Input (1.0 V/div.)
Figure 10. Demonstration Board Startup in
Response to Increasing 12 V and 5.0 V Input
Voltages. Extended Off Time is Followed by Normal
Off Time Operation when Output Voltage Achieves
Regulation to the Error Amplifier Output.
Trace 1− Soft−Start Pin (2.0 V/div.)
Trace 2− COMP PIn (error amplifier output) (1.0 V/div.)
Trace 4− Regulator Output Voltage (1.0 V/div.)
Figure 11. Demonstration Board Startup Waveforms
M 10.0 ms
Trace 1− Regulator Output Voltage (1.0 V/div.)
Trace 2− Inductor Switching Node (5.0 V/div.)
Figure 12. Demonstration Board Enable Startup
Waveforms
Normal Operation
During normal operation, switch off time is constant and
set by the COFF capacitor. Switch on time is adjusted by the
V2 control loop to maintain regulation. This results in changes
in regulator switching frequency, duty cycle, and output
ripple in response to changes in load and line. Output voltage
ripple will be determined by inductor ripple current working
and the ESR of the output capacitors (see Figures 13 and 14).
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