The first range is 2.125V to 3.525V in 100mV steps, the sec-

ond is 1.325V to 2.075V in 50mV steps, depending on the

digital input code. If all five bits are left open, the CS5166

enters adjust mode. In adjust mode, the designer can

choose any output voltage by using resistor divider feed-

CS5166 is specifically designed to meet or exceed Intel’s

Start-up

monitor threshold, the Soft Start and Gate pins are held

low. The Fault latch is Reset (no Fault condition). The out-

put of the Error Amp (COMP) is pulled up to 1V by the

threshold, the GATE(H) output is activated, and the Soft

Start 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 1V level, the pulse is terminat-

ed. 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 1V level pre-

sent at the Comp pin, regulation has been achieved and

normal Off-Time will ensue. The PWM comparator termi-

Cycle as required to ensure the regulator output voltage

tracks the output of the Error Amp.

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.

Figure 3: Demonstration board startup in response to increasing 12V

and 5V input voltages. Extended off time is followed by normal off

time operation when output voltage achieves regulation to the error

amplifier output.

Figure 4: Demonstration board startup waveforms.

Figure 5: Demonstration board enable startup waveforms.

Normal Operation

During Normal operation, Switch Off-Time is constant and

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 rip-

ple current and the ESR of the output capacitors (see

Figures 6 and 7).

Trace 1 - Regulator Output Voltage (5V/div.)

Trace 2 - Inductor Switching Node (5V/div.)

Trace 1 - Regulator Output Voltage (1V/div.)

Trace 3 - COMP Pin (error amplifier output) (1V/div.)

Trace 4 - Soft Start Pin (2V/div.)

Trace 1 - Regulator Output Voltage (1V/div.)

Trace 2 - Inductor Switching Node (2V/div.)

Trace 4 - 5V Input (1V/div.)

8

Application Information: continued