ST L6935 User Manual

High performance 3 A ULDO linear regulator

Features

■ Up to 5 V input voltage range

■ 60 mΩ max R

■

35 µA shut-down current

■ 3 A maximum output current

■ Split bias and power supplies

■ Adjustable output voltage: 0.5 V to 3.0 V

■ Excellent load and line regulation: 1 %

accuracy (over temperature)

■ MLCC supported

■ Programmable soft-start

■ Short-circuit protection

■ 3.5 A overcurrent protection

■ Thermal shut-down

■ VFQFPN20 4 x 4 x 1.0 mm package

DS(on)

L6935

VFQFPN20

(4.0 x 4.0 x 1.0 mm)

Description

L6935 is an ultra low drop output linear regulator operating up to 5 V input and is able to support output current up to 3 A. Designed with an internal low-R be used for on-board DC-DC conversions saving in real estate, list of components and power dissipation.

Bias input and power input are split to allow linear conversion from buses lower than 1.2 V minimizing power losses.

N-channel MOSFET, it can

DS(on)

Applications

■ Motherboard

■ Mobile PC

■ Hand-held instruments

■ PCMCIA cards

■ Processors I/O

■ Chipset and RAM supply

voltage from 0.5 V to 3.0 V with a voltage regulation accuracy of 1 %. soft-start is available to program the output voltage rise-time according to the external capacitor connected.

Enable and Power Good functions make L6935 suitable for complex systems and programmable start-up sequencing.

The current limit at 3 A protects the system during a short circuit. The current is sensed in the power DMOS in order to limit the power dissipation. Thermal shut down limits the internal temperature at 150 °C with a hysteresis of 20 °C.

Table 1. Device summary

L6935 provides the application with an adjustable

Order codes Package Packing

L6935

VFQFPN20

Tu b e

L6935TR Tape and reel

May 2008 Rev 1 1/20

www.st.com

Contents L6935

Contents

1 Typical application circuit and block diagram . . . . . . . . . . . . . . . . . . . . 3

1.1 Application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.2 Block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2 Pins description and connection diagrams . . . . . . . . . . . . . . . . . . . . . . 5

2.1 Pin descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

3 Electrical specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

3.1 Absolute maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

3.2 Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

3.3 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

4 Typical performances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

5 Device description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

5.1 Soft-start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

5.2 Power Good . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

5.3 VIN vs VBIAS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

5.4 Protections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

5.4.1 Over-current protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

5.4.2 Thermal protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

6 Application information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

6.1 Components selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

6.1.1 Input capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

6.1.2 Output capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

6.2 VIN, VBIAS and sequencing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

7 Demonstration board description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

8 VFQFPN20 mechanical data and package dimensions . . . . . . . . . . . . 18

9 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

2/20

Typical application circuit and block diagram L6935

1 Typical application circuit and block diagram

1.1 Application circuit

Figure 1. Typical application circuit - VIN = VBIAS

VIN

VBIAS

L6935

VOUT

ADJ

OUT

= 0.5V to 3.0V

OUT

SS GND PGOOD

L6935 Reference Schematic

Figure 2. Typical application circuit - VIN

BIAS

VIN = 0.75V to V

BIAS

VIN

SS GND PGOOD

PAD

≠ VBIAS

VBIAS

L6935

PAD

VOUT

ADJ

PGOOD

OUT

> 0.5V (*)

OUT

PGOOD

L6935 Reference Schematic (*) Vin may decrease until the minimum drop is reached. Conversely, Vout can rise untile the minimum drop is reached.

3/20

Typical application circuit and block diagram L6935

1.2 Block diagram

Figure 3. Block diagram

VIN

VBIAS

GND

CHARGE

PUMP

VREF

0.9 VREF

ERROR AMPLIFIER

REFERENCE

0.500V

ENABLEEN

THERMAL

SENSOR

CURRENT

DRIVER

LIMIT

VOUT

ADJ

PGOOD

4/20

Pins description and connection diagrams L6935

2 Pins description and connection diagrams

Figure 4. Pins connection (top view)

2.1 Pin descriptions

Table 2. Pins descriptions

Pin # Name Function

1 N.C. Not internally connected.

2 GND Ground connection. Connect to PCB ground plane.

3, 4 N.C. Not internally connected.

N.C. N.C. N.C. N.C. N.C.

VIN

10987

L6935

16 17 18 19

VOUT

VBIAS

ADJ

PGOOD N.C. N.C. GND N.C.

Power Good output flag: the pin is open drain and it is forced low if the

5 PGOOD

6 VBIAS

7EN

8 to 10 VIN

11 to15 N.C. Not internally connected.

16 to 18 VOUT

5/20

output voltage is lower than 90 % of the programmed voltage. If not used, it can be left floating.

Input bias supply. This pin supplies the internal logic to drive the power N-channel MOSFET that realize the voltage conversion. Connect directly to

or to a different supply ranging from VIN to 5 V.

The voltage connected to this pin MUST always be higher or equal that V

Enables the device if a voltage higher than 1 V is applied. When pulled low, the device is in low-power consumption: everything inside

the controller is kept OFF. See Section 6.2 for details about EN signal and power sequencing.

Power supply voltage. This pin is connected to the drain of the internal N-channel MOSFET. Filter to GND with capacitor larger than the one used for V

Regulated output voltage. This pin is connected to the source of the internal N-mos. MLCC capacitor are supported. Filter to GND with capacitor smaller than the one used for V

OUT

Pins description and connection diagrams L6935

Table 2. Pins descriptions (continued)

Pin # Name Function

Feedback for the IC regulation.

19 ADJ

20 SS

PA D G ND

Connecting this pin through a voltage divider to V

, it is possible to

OUT

program the output voltage between 0.5 V and 3.0 V.

Soft-start pin. The soft-start time is programmed connecting an external capacitor C

from this pin to GND.

In steady state regulation, the voltage at this pin is 3.3 V.

Ground connection. Connect to PCB GND Plane with enough VIAs to improve thermal conductivity.

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+ 14 hidden pages