CS5165GDWR16 View Datasheet(PDF) - Cherry semiconductor

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CS5165GDWR16

Fast, Precise 5-Bit Synchronous Buck Controller for the Next Generation Low Voltage Pentium® II Processors

Cherry semiconductor 

Application Information: continued

Overvoltage Protection

Overvoltage protection (OVP) is provided as result of the

normal operation of the V2™ control topology and requires

no additional external components. The control loop

responds to an overvoltage condition within 100ns, causing

the top MOSFET to shut off, disconnecting the regulator

from its input voltage. The bottom MOSFET is then activat-

ed, resulting in a “crowbar” action to clamp the output

voltage and prevent damage to the load (see Figures 12

and 13). The regulator will remain in this state until the

overvoltage condition ceases or the input voltage is pulled

low. The bottom FET and board trace must be properly

designed to implement the OVP function. If a dedicated

OVP output is required, it can be implemented using the

circuit in figure 14. In this figure the OVP signal will go

high (overvoltage condition), if the output voltage (VCORE)

exceeds 20% of the voltage set by the particular DAC code

and provided that PWRGD is low. It is also required that

the overvoltage condition be present for at least the

PWRGD delay time for the OVP signal to be activated. The

resistor values shown in figure 14 are for VDAC = +2.8V

(DAC = 10111). The VOVP (overvoltage trip-point) can be

set using the following equation:

Trace 4 = 5V from PC Power Supply (2V/div.)

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

Figure 13: OVP response to an input-to-output short circuit by pulling

the input voltage to ground.

VCORE

( )R2

VOVP = VBEQ3 1 + R1

+5V

5K

15K

R1

56K

R2

Q3

2N3906

OVP

20K

+5V

Q2

10K

CS5165

2N3904

10K

10K

Q1

PWRGD

2N3906

Figure 14: Circuit to implement a dedicated OVP output using the

CS5165.

Trace 4 = 5V from PC Power Supply (5V/div.)

Trace1 = Regulator Output Voltage (1V/div.)

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

Figure 12: OVP response to an input-to-output short circuit by immedi-

ately providing 0% duty cycle, crow-barring the input voltage to

ground.

Output Enable Circuit

The Enable pin (pin 8) is used to enable or disable the regu-

lator output voltage, and is consistent with TTL DC specifi-

cations. It is internally pulled-up. If pulled low (below

0.8V), the output voltage is disabled. At the same time the

Power Good and Soft Start pins are pulled low, so that

when normal operation resumes power-up of the CS5165

goes through the Soft Start sequence. Upon pulling the

Enable pin low, the internal IC bias is completely shut off,

resulting in total shutdown of the Controller IC.

Power Good Circuit

The Power Good pin (pin 13) is an open-collector signal

consistent with TTL DC specifications. It is externally

pulled -up, and is pulled low (below 0.3V) when the regu-

lator output voltage typically exceeds ± 8.5% of the nomi-

nal output voltage. Maximum output voltage deviation

before Power Good is pulled low is ± 12%.

11

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