CS5155 데이터 시트보기 (PDF) - ON Semiconductor

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CS5155

CPU 5−Bit Synchronous Buck Controller

ON Semiconductor 

CS5155

traces than occurs with constant current limit protection (see

Figures 12 and 13).

If the short circuit condition is removed, output voltage

will rise above the 1.0 V level, preventing the FAULT latch

from being set, allowing normal operation to resume.

Trace 1− Regulator Output Voltage (1.0 V/div.)

Trace 2− Inductor Switching Node (5.0 V/div.)

Trace 3− Output Current (13 to 0,5 Amps) (20 mV/div.)

Figure 11. CS5155 Demonstration Board Response to

13 A Load Turn Off (Output Set for 2.8 V). V2 Control

Topology Immediately Connects Inductor to Ground,

Providing 0% Duty Cycle. Regulation is Achieved in

Less Than 10 ms

PROTECTION AND MONITORING FEATURES

VCC1 Monitor

To maintain predictable startup and shutdown

characteristics an internal VCC1 monitor circuit is used to

prevent the part from operating below 3.75 V minimum

startup. The VCC1 monitor comparator provides hysteresis

and guarantees a 3.70 V minimum shutdown threshold.

Short Circuit Protection

A lossless hiccup mode short circuit protection feature is

provided, requiring only the Soft Start capacitor to

implement. If a short circuit condition occurs (VFFB < 1.0 V),

the VFFB low comparator sets the FAULT latch. This causes

the MOSFET to shut off, disconnecting the regulator from

it’s input voltage. The Soft Start capacitor is then slowly

discharged by a 2.0 μA current source until it reaches it’s

lower 0.7 V threshold. The regulator will then attempt to

restart normally, operating in it’s extended off time mode

with a 50% duty cycle, while the Soft Start capacitor is

charged with a 60 μA charge current.

If the short circuit condition persists, the regulator output

will not achieve the 1.0 V low VFFB comparator threshold

before the Soft Start capacitor is charged to it’s upper 2.5 V

threshold. If this happens the cycle will repeat itself until the

short is removed. The Soft Start charge/discharge current

ratio sets the duty cycle for the pulses (2.0 μA/60 μA =

3.3%), while actual duty cycle is half that due to the

extended off time mode (1.65%).

This protection feature results in less stress to the

regulator components, input power supply, and PC board

M 25.0 ms

Trace 4− 5.0 V Supply Voltage (2.0 V/div.)

Trace 3− Soft Start Timing Capacitor (1.0 V/div.)

Trace 2− Inductor Switching Node (2.0 V/div.)

Figure 12. CS5155 Demonstration Board Hiccup Mode

Short Circuit Protection. Gate Pulses are Delivered

While the Soft Start Capacitor Charges, and Cease

During Discharge

M 50.0 μs

Trace 4− 5.0 V from PC Power Supply (2.0 V/div.)

Trace 2− Inductor Switching Node (2.0 V/div.)

Figure 13. Startup with Regulator Output Shorted

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 100 ns, causing the top

MOSFET to shut off, disconnecting the regulator from it’s

input voltage. The bottom MOSFET is then activated,

resulting in a “crowbar” action to clamp the output voltage

and prevent damage to the load (see Figures 14 and 15 ). The

regulator will remain in this state until the overvoltage

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