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POWER MANAGEMENT

SC4624

Operation

Application Information (Cont.)

Application Information (Cont.)

5

15

25

35

45

55

65

75

85

95

105

115

125

135

145

200

400

600

800

1000

1200

1400

1600

1800

2000

5VIN

2.5VIN

The operation frequency can be programmed up to 2MHz,

but there is a minimum on-time limitation which is around

110ns. Users should take care of minimum limitation

on the operating duty cycle under high frequency

application.

Synchronization Frequency

Synchronization operation mode is invoked by using an

external clock signal and is activated when the SYNC/EN

is pulled and held above 2V and held below 0.8V. The

range of synchronization frequency is from 200kHz to

2MHz.

A jitter happens when sync pulse clock edge is less than

120ns before the phase switches. It is caused by the

ground bounce of synchronization pulse coupled to PWM

comparator. Users try to avoid this application. (refer to

Figure 9).

Power Good Indicator

The PGOOD pin is an open-drain and incorporated window

comparators output. It’s is necessary that a pull-up

resistor from the PGOOD pin to the input supply for setting

the logic high level of the PGOOD signal. When FB voltage

is within +10% setting output voltages typical, the output

of power good comparator becomes high impedance after

delay time. The PGOOD signal delay time is around 1024/

F

pulled low.

For example, 1MHz switching frequency applications, the

PGOOD delay time is around 1ms.

Thermal Shutdown

When the junction temperature rises up around 160°C,

the internal soft start voltage is held low, the internal high

side and low side MOSFETs are turned off and the output

voltage will fall to zero. Once the junction temperature

goes below hysteresis temperature around 10°C, the

regulator will restart. (refer to Figure 8).

Linear Mode Operation (100% duty)

The SC4624 can allows 100% duty cycle operation. The

Vout is,

where

R

R

(refer to Figure11).

As Vin drops gradually and close to Vout, the buck regulator

will go into 100% duty cycle ratio. A matter needing

attention is internal high side PMOS has minimum off time

makes the working duty cycle perform at randon with the

output ripple increasing and a poor transient response.

Above phenomenon can be improved by larger output

capacitor and smaller output inductor. Users need to

verify whether above application condition has opposite

influence on entire circuit.

Over Current Protection

A over current setting is programmed by an external

resistor (R

generates a voltage.

where

I : The current is generated by R

by internal current amplifier.

R

Output inductor current goes through internal high side

P-MOSFET and generate a voltage.

where

I

R

Switching Frequency Setting

F

Figure 15. Switching Frequency vs. R

FS