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FAN5631/FAN5632 Rev. 1.0.2

Switch Configuration

Figure 5. Mode 2:1 Configuration

control the rate of the output voltage ramp-up to its final value.

Typical start-up time is 1ms. Since the rate of the output voltage

ramp-up is controlled by an internally generated slow ramp,

pulse-skipping occurs and in-rush current is automatically lim-

ited.

Shutdown, UVLO, Short Circuit Current Limit

and Thermal Shutdown

The device has an active-low shutdown pin to decrease supply

current to less than 1

µA. In shutdown mode, the supply is dis-

connected from the output. UVLO triggers when supply voltage

drops below 2V. When the output voltage is lower than 150mV, a

short circuit protection is triggered. In this mode 15 out of 16

pulses during the switching will be skipped and the supply cur-

rent is limited. Thermal shutdown triggers at 150ºC.

Efficiency Optimizer (FAN5632)

ground to enable the efficiency optimizer feature. To achieve an

optimized efficiency, the switch mode configuration transition

point is shifted from a 2:1 to a 1:1 mode until the output voltage

falls to 20% of its nominal value. For example, when the nominal

output voltage is 1.5V, the output voltage is allowed to drop to

1.2V. This will maintain a peak efficiency of 85% for the input

should be tied high.

Figure 6. Mode 1:1 Configuration

Applications Information

The FAN5631/FAN5632 requires one ceramic bucket capacitor

in the 0.1µF to 1µF range; one 10µF output bypass capacitor

and one 10µF input bypass capacitor. To obtain optimum output

ripple and noise performance, use of low ESR (<0.05

Ω) ceramic

input and output bypass capacitors is recommended. The X5R-

and X7R-rated capacitors provide adequate performance over

the -40°C to 85°C temperature range.

The bucket capacitor’s value is dependent on load current

requirements. A 1µF bucket capacitor will work well in all appli-

cations at all load currents, while a 0.1µF capacitor will support

most applications under 100mA of load current. The choice of

bucket capacitor values should be verified in the actual applica-

tion at the lowest input voltage and highest load current. A 30%

margin of safety is recommended in order to account for the tol-

erance of the bucket capacitor and the variations in the on-resis-

tance of the internal switches.

One of the key benefits of the ScalarPump™ architecture is that

the dynamically scaled on-resistance of the switches effectively

reduces the peak current in the bucket capacitor and therefore

input and output ripple currents are also reduced. Nevertheless,

due to the ESR of the input and output bypass capacitors, these

current spikes generate voltage spikes at the input and output

pins. However, these ESR spikes can be easily filtered because

their frequencies lie at up to 12 times the clock frequencies. In

S1

S3

S4

V

IN

GND

C+

VOUT

C-

C

OUT

C

B

S2

S1

S2

S3

S4

V

IN

GND

C+

VOUT

C-

C

OUT

C

B

This configuration shows the switches in the charging

This configuration shows the S1 and S2 swithces in phase 1 position.

phase position. For the pumping phase, reverse all

switch positions.

For phase 2, reverse the positions of the S1 and S2 switches.

The S3 switch is always OFF, and the S4 switch is always ON.