TLV62090 Datasheet, PDF(11/23 Page) Texas Instruments – 3A High Efficient Synchronous Step Down Converter with DCS™ Control

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TLV62090 Datasheet, PDF (11/23 Pages) Texas Instruments – 3A High Efficient Synchronous Step Down Converter with DCS™ Control

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TLV62090

www.ti.com

SLVSBB9B â MARCH 2012 â REVISED APRIL 2012

Where

RDS(on) = High side FET on-resistance

RL = DC resistance of the inductor

VOUT(max) = nominal output voltage plus maximum output voltage tolerance

Softstart (SS)

To minimize inrush current during start up, the device has an adjustable softstart depending on the capacitor

value connected to the SS pin. The device charges the softstart capacitor with a constant current of typically 7.5

ÂµA. The feedback voltage follows this voltage with a fraction of 1.56 until the internal reference voltage of 0.8 V is

reached. The softstart operation is completed once the voltage at the softstart capacitor has reached typically

1.25 V. The soft-start time can be calculated using Equation 3. The larger the softstart capacitor the longer the

softstart time. The relation between softstart voltage and feedback voltage can be estimated using Equation 4.

tSS

= CSS

1.25V

7.5Î¼A

(3)

VFB

VSS

1.56

(4)

This is also the case for the fixed output voltage option having the internal regulation voltage. Leaving the

softstart pin floating sets the minimum start-up time.

Start-up Tracking (SS)

The softstart pin can also be used to implement output voltage tracking with other supply rails. The internal

reference voltage follows the voltage at the softstart pin with a fraction of 1.56 until the internal reference voltage

of 0.8 V is reached. The softstart pin can be used to implement output voltage tracking as shown in Figure 20.

Vin

2.5V to 5.5V

22mF

TLV62090

1mH

12 PVIN

11 PVIN

SW 2

10 AVIN

VOS 16

3 DEF

FB 5

10nF

13 EN

7 CP

PG 4

SS 9

Output of external

DC DC converter

8 CN

AGND 6

PGND PGND

14 15

59k

140k

Vout

1.5V/3A

22mF

160k

500k

Power Good

43k

Figure 20. Output Voltage Tracking

In Figure 20, the output V2 tracks the voltage applied to V1. The voltage tracks simultaneously when following

conditions are met:

R3 R1

= x 1.56

R4 R2

(5)

As the fraction of R3/R4 becomes larger the voltage V1 ramps up faster than V2, and if it gets smaller then the

ramp is slower than V2. R4 needs to be determined first using Equation 6.

Product Folder Link(s): TLV62090

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