5

LTC1516

higher ripple due to higher output voltage dV/dt. High ESR

capacitors (ESR > 0.5

Ω) on the output pin cause high

There are several ways to reduce the output voltage ripple.

charging and discharging dV/dt and the lower ESR typi-

cally found with higher value (larger case size) capacitors.

A low ESR ceramic output capacitor will minimize the high

frequency ripple, but will not reduce the low frequency

ripple unless a high capacitance value is chosen. A reason-

able compromise is to use a 10

µF to 22µF tantalum

capacitor in parallel with a 1

µF to 3.3µF ceramic capacitor

An RC filter may also be used to reduce high frequency

voltage spikes (see Figure 2).

and C2 may be used to reduce output ripple. The smaller

C1 and C2 flying capacitors (0.022

µF to 0.1µF) deliver less

charge per clock cycle to the output capacitor resulting in

lower output ripple. However, the smaller value flying caps

efficiency.

Short-Circuit/Thermal Protection

During short-circuit conditions, the LTC1516 will draw

the junction temperature. On-chip thermal shutdown

circuitry disables the charge pump once the junction

temperature exceeds 135

°C, and reenables the charge

pump once the junction temperature falls back to 115

°C.

The LTC1516 will cycle in and out of thermal shutdown

is removed.

Capacitor Selection

For best performance, it is recommended that low ESR

ceramic or tantalum and should be 10

µF or greater. If the

reduce output voltage ripple.

Ceramic or tantalum capacitors are recommended for the

flying caps C1 and C2 with values in the range of 0.1

µF to

1

µF. Note that large value flying caps (> 0.22µF) will

very low load applications, C1 and C2 may be reduced to

0.01

µF to 0.047µF. This will reduce output ripple at the

expense of efficiency and maximum output current.

Output Ripple

Normal LTC1516 operation produces voltage ripple on the

to regulate. Low frequency ripple exists due to the hyster-

esis in the sense comparator and propagation delays in the

charge pump enable/disable circuits. High frequency ripple

is also present mainly due to ESR (Equivalent Series

Resistance) in the output capacitor. Typical output ripple

output capacitor.

The magnitude of the ripple voltage depends on several

cycle. Large C1 and C2 flying capacitors (> 0.22

µF) also

increase ripple for the same reason. Large output current

load and/or a small output capacitor (< 10

µF) results in

Inrush Currents

sients in the 100mA to 200mA range whenever the charge

pump is enabled. During start-up, these inrush currents

may approach 500mA. For this reason, it is important to

minimize the source resistance between the input supply

input voltage transients.

5V

LTC1516

3

15

µF

TANTALUM

1

µF

CERAMIC

5V

+

LTC1516

3

1516 F02

2

Ω

10

µF

+

10

µF

+

Figure 2. Output Ripple Reduction Techniques