CS5158
Applications Information: continued
Trace1 - Regulator Output Voltage (10mV/div.)
Trace 2 - Inductor Switching Node (5V/div.)
Trace 1 - Regulator Output Voltage (100mV/div.)
Trace 2 - Inductor Switching Node (5V/div.)
Trace 3 - Output Current (0.5 to 13 Amps) (10A/div.)
Figure 6: Peak-to-peak ripple on V
OUT
= 2.8V, I
OUT
= 13A (heavy load).
Transient Response
The CS5158 V
2
TM
control loop’s 100ns reaction time pro-
vides unprecedented transient response to changes in input
voltage or output current. Pulse by pulse adjustment of
duty cycle is provided to quickly ramp the inductor current
to the required level. Since the inductor current cannot be
changed instantaneously, regulation is maintained by the
output capacitor(s) during the time required to slew the
inductor current.
For best transient response, a combination of a number of
high frequency and bulk output capacitors are usually
used.
If the maximum on time is exceeded while responding to a
sudden increase in load current, a normal off time occurs to
prevent saturation of the output inductor.
Figure 8: CS5158 demonstration board response to 13A load turn on
(output set for 2.8V). Upon completing a normal off time, the V
2
TM
con-
trol loop immediately connects the inductor to the input voltage, pro-
viding 100% duty cycle. Regulation is achieved in less than 20µs.
Trace1 - Regulator Output Voltage (100mV/div.)
Trace 2 - Inductor Switching Node (5V/div.)
Trace 3 - Output Current (13 to 0.5 Amps) (10A/div.)
Figure 9: CS5158 demonstration board response to 13A load turn off
(output set for 2.8V). V
2
TM
control topology immediately connects
inductor to ground, providing 0% duty cycle. Regulation is achieved in
less than 10µs.
Protection and Monitoring Features
V
CC1
Monitor
To maintain predictable startup and shutdown characteris-
tics an internal V
CC1
monitor circuit is used to prevent the
part from operating below 3.75V minimum startup. The
V
CC1
monitor comparator provides hysteresis and guaran-
tees a 3.70V minimum shutdown threshold.
Trace 1 - Regulator Output Voltage (100mV/div.)
Trace 3 - Regulator Output Current (10A/div.)
Figure 7: CS5158 demonstration board response to a 0.5 to 13A load
pulse (output set for 2.8V).
8
CHERRY [ CHERRY SEMICONDUCTOR CORPORATION ]
