C1 =

1

(2 x 5 x RFB1 x 45 x 10

3)

VOUT = VFB x

RFB1

RFB2

1+

©

§

LP8720

www.ti.com

SNVS575B – JULY 2008 – REVISED MAY 2013

The formula for output voltage selection is

•

VOUT – output voltage

•

VFB – feedback voltage (0.5V)

(1)

For any out voltage greater than or equal to 0.8V a transfer function zero should be added by the addition of a

capacitor C1. The formula for calculation of C1 is:

(2)

For recommended component values see the table below.

VOUT [V]

RFB1 [kΩ]

RFB2 [kΩ]

C1 [pF]

L [µH]

COUT [µF]

1.0

200

200

18

2.2

10

1.2

280

200

12

2.2

10

1.4

360

200

10

2.2

10

1.5

360

180

10

2.2

10

1.6

440

200

8.2

2.2

10

1.85

540

200

6.8

2.2

10

LDO’s

There are, all together, 5 LDO’s in the LP8720 grouped as:

•

A-type LDO’s (LDO2, 3)

•

D-type LDO’s (LDO1, 5)

•

LO-type LDO (LDO 4)

The A-type LDO’s are optimized for supplying of analog loads and have ultra low noise (15 µVRMS) and excellent

PSRR (70 dB) performance.

The D-type LDO’s are optimized for good dynamic performance to supply different fast changing (digital) loads.

The LO-type LDO is optimized for low output voltage and for good dynamic performance to supply different fast

changing (digital) loads.

All LDO’s can be programmed through serial interface for 32 different output voltage values, which are

summarized in the Ouput Voltage Programming tables below.

At the PMU power on, LDO’s start up according to the selected startup sequence, and the default voltages after

startup sequence depend on startup setup. See section Power-On and Power-Off Sequences for details.

For stability all LDO’s have to be connected to output an external capacitor COUT with recommended value of 1

µF. It is important to select the type of capacitor which capacitance will in no case (voltage, temperature, etc) be

outside of limits specified in the LDO Electrical Characteristics.

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