
CS5160
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12
Figure 15. CS5160 OVP Response to an
Input–to–Output Short Circuit by Pulling the Input
Voltage to Ground
M 5.00 ms
Trace 1– Regulator Output Voltage (1.0 V/div.)
Trace 4– 5.0 V from PC Power Supply (5.0 V/div.)
External Output Enable Circuit
On/off control of the regulator can be implemented
through the addition of two additional discrete components
(see Figure 14). This circuit operates by pulling the Soft
Start pin high, and the VFFB pin low, emulating a short
circuit condition.
Figure 16. Implementing Shutdown
with the CS5160
Shutdown
Input
5.0 V
MMUN2111T1 (SOT–23)
5
8
VFFB
SS
IN4148
CS5160
External Power Good Circuit
An optional Power Good signal can be generated through
the use of four additional external components (see Figure
17). The threshold voltage of the Power Good signal can be
adjusted per the following equation:
VPower Good +
(R1
) R2)
0.65 V
R2
This circuit provides an open collector output that drives
the Power Good output to ground for regulator voltages less
than VPower Good.
Figure 17. Implementing Power Good
with the CS5160
5.0 V
Power Good
10 k
VOUT
PN3904
6.2 k
R1
R2
PN3904
10 k
R3
CS5160
Figure 18. CS5160 During Power Up. Power
Good Signal is Activated when Output
Voltage Reaches 1.70 V
M 2.50 ms
Trace 4– 5.0 V Input (2.0 V/div.)
Trace 3 – 12 V Input (VCC1) and (VCC2) (10 V/div.)
Trace 1– Regulator Output Voltage (1.0 V/div.)
Trace 2– Power Good Signal (2.0 V/div.)
Slope Compensation
The V2 control method uses a ramp signal, generated by
the ESR of the output capacitors, that is proportional to the
ripple current through the inductor. To maintain regulation,
the V2 control loop monitors this ramp signal, through the
PWM comparator, and terminates the switch on–time.
The stringent load transient requirements of modern
microprocessors require the output capacitors to have very
low ESR. The resulting shallow slope presented to the PWM
comparator, due to the very low ESR, can lead to pulse width
jitter and variation caused by both random or synchronous
noise.
Adding slope compensation to the control loop, avoids
erratic operation of the PWM circuit, particularly at lower
duty cycles and higher frequencies, where there is not
enough ramp signal, and provides a more stable switchpoint.
The
scheme
that
prevents
that
switching
noise
prematurely triggers the PWM circuit consists of adding a
positive voltage slope to the output of the Error Amplifier
(COMP pin) during an off–time cycle.