ST MICROELECTRONICS L 6920 D Datasheet

L6920

Fi

1V HIGH EFFICIENCY SYNCRONOUS STEP UP CONVERTER

1 Features

■ 0.6 TO 5.5V OPERATING INPUT VOLTAGE

■ 1V START UP INPUT VOLTAGE

■ INTERNAL SYNCHRONOUS RECTIFIER

■ ZERO SHUT DOWN CURRENT

■ 3.3V AND 5V FIXED OR ADJUSTABLE

OUTPUT VOLTAGE (2V UP TO 5.2V)

■ 120mΩ INTERNAL ACTIVE SWITCH

■ LOW BATTERY VOLTAGE DETECTION

■ REVERSE BATTERY PROTECTION

1.1 Applications

■ ONE TO THREE CELL BATTERY DEVICES

■ PDA AND HAND HELD INSTRUMENTS

■ CELLULAR PHONES - DIGITAL CORDLESS

PHONE

■ PAGERS

■ GPS

■ DIGITAL CAMERAS

gure 1. Package

TSSOP8

Table 1. Order Codes

Part Number Package

L6920D TSSOP8 Tube

L6920DTR Tape & Reel

2 Description

The L6920 is a high efficiency step-up controller re­quiring only three external components to realize the
conversion from the battery voltage to the selected
output voltage.

The start up is guaranteed at 1V and the device is op­erating down to 0.6V.

Internal synchronous rectifier is implemented with a
120m

Ω

P-channel MOSFET and, in order to improve
the efficiency, a variable frequency control is imple­mented.

Figure 1. Application Circuit

L1

V

CC

2.5V 3.3V

February 2005

C2

LX

SHDN

LBI

REF

7

5

L6920D

2

4

OUT

8

V

OUT

FB

1

500mA

C3 C1

LBO

3

GND

6

Rev. 2

1/13

L6920

8

Table 1. Pin Description

Pin Name Function

1FB

Output voltage selector. Connect FB to GND for Vout=5V or to OUT for Vout=3.3V. Connect FB to an
external resistor divider for adjustable output voltage (from 2V to 5.2V) [see R4 and R5, fig. 7].

2 LBI Battery low voltage detector input. The internal threshold is set to 1.23V.

A resistor divider is needed to adjust the desired low battery threshold:

R1

V

LBI

3

LBO

Battery low voltage detector output. If the voltage at the LBI pin drops below the internal

⎛⎞

1.23V= 1

⋅

⎝⎠

[see R1 and R2, fig. 7]

------- -+

R2

threshold typ. 1.23V, LBO goes low.

LBO is an open drain output and so a pull-up resistor (about 200KΩ) has to be added for

The
correct output setting [see R3, fig. 7].

4 REF 1.23V reference voltage. Bypass this output to GND with a 100nF capacitor for filtering high

frequency noise. No capacitor is required for stability

5

SHDN

Shutdown pin. When pin 5 is below 0.2V the device is in shutdown, when pin 5 is above 0.6V the
device is operating.

6 GND Ground pin

7 LX Step-up inductor connection

8 OUT Power OUTPUT pin

Figure 2. Pin Connection (Top view)

FB

LBI

LBO

REF

8

2

3

4

TSSOP

7

6

5

OUT1

LX

GND

SHDN

Table 2. Absolute Maximum Ratings

Symbol Parameter Value Unit

V

ccmax

Vcc to GND 6 V

LBI, SHDN, FB to GND 6 V

V

out max

Vout to GND 6 V

Table 3. Thermal Data

Symbol Parameter Value Unit

R

th j-amb

T

Thermal Resistance Junction to Ambient 250 °C/W

Maximum Junction Temperature 150 °C

j

2/13

L6920

Table 4. Electrical Characteristcs

= 2V, FB = GND, T

(V

in

Symbol Parameter Test Condition Min. Typ. Max. Unit

SECTION

V

CC

V

Minimum operating Input Voltage 0.6 V

in

V

Minimum Start Up Input Voltage 1 V

in

= -40°C to 85°C and Tj < 125°C unless otherwise specified)

amb

Quiescent Current Il =0 mA, FB = 1.4V, V

I

q

I

Shut Down Current Vin = 5V, Il =0 mA 0.1 1 µA

sd

Irev Reverse battery current V

LBI = SHDN = 2V, T

Il =0 mA, FB = 1.4V, V
LBI = SHDN = 2V, T

= -4V, Tj = T

in

amb

= T

j

= T

j

= 3.3V

out

amb

= 5V

out

amb

915µA

11 18 µA

0.1 2 µA

POWER SECTION

on-N

on-P

Active switch ON resistance 120 250 mΩ

Synchronous switch ON

120 250 mΩ

R

R

resistance

CONTROL SECTION

V

t Output voltage FB = OUT, Il =0 mA 3.2 3.3 3.4 V

ou

FB = GND, I

=0 mA 4.955.1V

l

Output voltage range External divider 2 5.2 V

V

V

LBI threshold 1.18 1.23 1.27 V

LBI

< 70°C 1.205 1.23 1.255 V

j

< 250µA 0.20.4V

sink

LBO

LBO logic LOW

0°C < T

I

I

LX switch current limit 0.8 1 1.2 A

lim

T

onmax

T

offmin

Maximum on time V

Minimum off time V

SHDN SHDN logic LOW

SHDN logic HIGH

V

Reference Voltage 1.18 1.23 1.27 V

ref

= 2V to 5.3V 3.75 5 6.25 µs

out

= 2V to 5.3V 0.75 1 1.25 µs

out

0.2 V

0.6 V

3/13

L6920

Figure 3.

Efficiency vs. Output Current

100

90

80

Vin = 1.2V

70

60

η [%]

50

EFFICIENCY

40

30

20

10

0

0.01 0.1 1 10 100 1000

Figure 4.

Efficiency vs. Output Current

100

90

80

LOAD CURRENT [ mA]

Vout = 3.3V
L = 47µH
C = 100µF

Vin = 1.2V

70

Vin = 2.4V

Vin = 3.6V

Vin = 2.4V

Figure 5. Startup Voltage vs Output Current

1.4

1.2

1

0.8

0.6

Startup voltage (V)

0.4

0.2

0

30 60 90 120 150 180

Output current (mA)

L = 47µH
C = 22µF

60

50

η [%]

EFFICIENCY

40

30

20

10

0

0.01 0.1 1 10 100 1000

f

Vout = 5V
L = 47µH
C = 100µF

LOAD CURRENT [mA]

4/13

L6920

3 Detailed Description

The L6920 is a high efficiency, low voltage step-up DC/DC converter particularly suitable for 1 to 3 cells (Li-Ion/
polymer, NiMH respectively) battery up conversion.

µ

These performances are achieved via a strong reduction of quiescent current (10
chronous rectification, that implies also a reduced cost in the application (no external diode required).

Operation is based on maximum ON time - minimum OFF time control, tailored by a current limit set to 1A. A
simplified block diagram is shown here below.

Figure 6. Simplified Block Diagram

A only) and adopting a syn-

V

REF

SHDN

LBO

-

+

VBG

FB Y

V

OUT

GND
R1,R

Y

VBG

2

-

+

Toff min

1µsec

VBG

A

B

C

-

+

4 Principle of Operation

A
B
C

OPAMP

(CR)

LBI

ZERO CROSSING

RQS

Ton max

5µsec

-

+

- +

CURRENT LIMIT

OUT

VOUT

LX

-

+

GND

FB

D99IN1041

V

OUT

V

IN

In L6920 the control is based on a comparator that continuously checks the status of output voltage.
If the output voltage is lower than the expected value, the control function of the L6920 directs the energy stored

in the inductor to be transferred to the load. This is accomplished by alternating between two basic steps:

- TON phase: the energy is transferred from the battery to the inductor by shorting LX node to ground via the N­channel power switch. The switch is turned off if the current flowing in the inductor reaches 1A or after a max­imum on time set to 5

µ

s.

- TOFF phase: the energy stored in the inductor is transferred to the load through the synchronous switch for at

least a minimum off time equal to 1

µ

s. After this, the synchronous switch is turned off as soon as the output

voltage goes lower than the regulated voltage or the current flowing in the inductor goes down to zero.

So, in case of light load, the device works in PFM mode, as shown in figures 7 to 10.

5/13

L6920

Figure 7.

PFM mode Condition: V

= 5V; Vin =1.5V.

out

Trace1: Vout (50mV~/div) Trace 4: IL (100mA/div)
Time div.: 5µs/div

Figure 8.
Trace1: V

Heavier load - Train pulses overlapping.

(100mV~/div) Trace 4: IL (200mA/div)

out

Time div.: 10 µs/div

Figure 9.
below I

Heavy load - Inductor current ripples

Trace1: V

lim

(100mV~/div)

out

Trace 4: IL

(200mA/div) Time div.: 20 µs/div

Figure 10.

Heavy load and High ESR. Regulation

falls in continuous mode of operation. Trace1:

(100mV~/div) Trace 4: IL (200mA/div). Time

V

out

div.: 5 µs/div

When Iload is heavier, the pulse trains are overlapped. Figures 7 - 8 show some possible behaviors.
Considering that current in the inductor is limited to 1A, the maximum load current is defined by the following

relationship:

Where

η

is the efficiency and I

I

load_lim

lim

=1A.

V

in

⎛⎞

-----------

V

out

–

I

limToff min

⎝⎠

–

V

outVin

------------------------- -

⋅

2L⋅

η⋅⋅=

eq. (1)

Of course, if Iload is greater than Iload_lim the regulation is lost (figure 11).

6/13

L6920

Figure 11. No regulation. I

V

Trace1:

(100mV~/div) Trace 4: IL (200mA/div).

out

load

> I

load_lim

Time div.: 5 µs/div

4.1 Start-up

One of the key features of L6920 is the startup at sup­ply voltage down to 1V (please see the diagram in
Figure 5. in case of heavy load).

The device leaves the startup mode of operation as
soon as VOUT goes over 1.4V. During startup, the
synchronous switch is off and the energy is trans­ferred to the load through its intrinsic body diode.

The N-channel switches with a very low RDSon
thanks to an internal charge pump used to bias the
power mos gate. Because of this modified behavior,
TON/TOFF times are lengthened. Current limit and
zero crossing detection are still available.

4.2 Shutdown

In shutdown mode (

SHDN

pulled low) all internal cir­cuitries are turned off, minimizing the current provid­ed by the battery (I

< 100 nA, in typical case).

SHDN

Both switches are turned off, and the low battery
comparator output is forced in high impedance state.

The synchronous switch body diode causes a para­sitic path between power supply and output that can't
be avoided also in shutdown.

4.3 Low battery detection

The L6920 includes a low battery detector compara­tor. Threshold is VREF voltage and a 1.3% hystere­sis is added to avoid oscillations when input crosses
the threshold slowly. The

LBO

is an open drain out-

put so a pull up resistor is required for a proper use.

4.4 Reverse polarity

A protection circuit has been implemented to avoid
that L6920 and the battery are destroyed in case of
wrong battery insertion.

In addition, this circuit has been designed so that the
current required by the battery is zero also in reverse
polarity.

5 Application Information

5.1 Output voltage selection

Output voltage must be selected acting on FB pin.
Three choices are available: fixed 3.3V, 5V or adjust­able output set via an external resistor divider.

Table 5. Output Voltage Selection

V

= 3.3V FB pin connected to OUT (see

OUT

= 5V FB pin connected to GND

V

OUT

2V ≤ V

≤ 5.2V FB pin connected to a resistive

OUT

application circuit)

divider

V

OUT

=

⎛⎞

1.23V 1

⎝⎠

R4

------- -+

R5

7/13

L6920

Figure 12. Demoboard Circuit

+VBATT

R1

N.C.

LBI

R2

N.C.

VREF

C4

100nF

GND

not mounted components

VBATT

2

4

6

L6920

F.B.

Panasonic

ELL6RH100M

L1 10µH

7

VOUT

8

R3

N.C.

LBO

3

SHDN

5

1

J1

C3

N.C.

1
2

3

1

2

J2

3

C2

47µF

C1

47µF

R4 N.C.

R5 N.C.

Panasonic

EEFCDJ470R

Panasonic

EEFCDJ470R

D01IN1310

+VBATT

GND

VOUT

GND

LBO

SHDN

Table 6.

Jumper Position Function

1-2 Device enabled

J1

2-3 Device disabled

None Adjustable using R4 and R5 [not mounted]

J2

1-2 3.3V output voltage

2-3 5V output voltage

R4, R5 should be selected in the range of 100kΩ - 10MΩ to minimize consumption and error due to current sunk
by FB pin (few nA).

5.2 Output capacitor selection

The output capacitor affects both efficiency and output ripple so its choice has to be considered with particular
care.

The capacitance value should be in the range of about 10

µ

F-100µF.

An additional, smaller, low ESR capacitor can be in parallel for high frequency filtering. A typical value can be
around 1

µ

F.

If very high performances, in terms of efficiency and output voltage ripple, are required, a very low ESR capac­itor has to be chosen.

Ceramic capacitors are the lowest ESR but they are very expensive.
Other possibilities are low-ESR tantalum capacitors, available from KEMET, AVX and other sources. POSCAP

capacitors from SANYO and polymeric capacitors from PANASONIC are also good.
Below there is a list of some capacitors suppliers. The cap values and rated voltages are only a suggested pos-

sibility

8/13

Table 7. Capacitors distributors main list

Manufacturer Series Cap Value (µF) Rated Voltage (V) ESR (mΩ)

AVX TPS 15 to 470 6.3 50 to 1500

L6920

KEMET T510/T494/

T495

PANASONIC EEFCD 22 to 47 6.3 50 to 700

SANYO POSCAP TPA/B/C 22 to 230 6.3 40 to 80

SPRAGUE 595D 100 to 390 6.3 160 to 700

10 to 470 6 30 to 1000

5.3 Inductor selection

Usually, inductors ranging between 5µH to 40µH satisfy most of the applications.
Small value inductors have smaller physical size and guarantee a faster response to load transient but in steady

state condition a bigger ripple on output voltage is generated. In fact the output ripple voltage is given by Ipeak
multiplied by ESR. Furthermore, as shown in equation (1), inductor size affects also the maximum current de­liverable to the load. Lastly, a low series resistance is suggested if very high efficiency values are needed. Any­way, the saturation current of the choke should be higher than the peak current limit of the device (1A).

Good surface mounting inductors are available from COILCRAFTS, COILTRONICS, MURATA and other souc­es. In the following table are listed some suggested components.

Table 8. Inductors distributors main list

Manufacturer Series Inductor Value (uH) Saturation Current (A)

Coilcraft DO1813HC 22 to 33 1 to 1.2

DO1608 4.7 to 15 0.9 to 1.5

Coiltronics UP1B 22 to 33 1 to 1.2

TP3 4.7 to 15 0.97 to 1.6

BI HM76-2 22 to 33 1 to 1.2

HM76-1 4.7 to 10 1 to 1.5

Murata LQN6C 10 to 22 1.2 to 1.7

Panasonic ELL6SH 10 to 22 0.9 to 1.5

ELL6RH 5.1 to10 11 to 1.55

Sumida CR43 4.7 to 10 0.84 to 1.15

5.4 Layout Guidelines

The board layout is very important in order to minimize noise, high frequency resonance problems and electro­magnetic interference.

It is essential to keep as small as possible the high switching current circulating paths to reduce radiation and
resonance problems. So, the output and input cap should be very close to the device.

The external resistor dividers, if used, should be as close as possible to the pins of the device (FB and LBI) and
as far as possible from the high current circulating paths, to avoid pick up noise.

Large traces for high current paths and an extended groundplane, help to reduce the noise and increase the
efficiency.

For an example of recommended layout see the following evaluation board.

9/13

L6920

Figure 13. Demoboard Components (Top side).

Figure 14. Demoboard Layout (Top side).

4.5cm

4cm

Figure 15. Demoboard Layout (Bottom side).

4.5cm

4cm

4.5cm

4cm

10/13

6 Package Information

Figure 16. TSSOP8 Mechanical Data & Package Dimensions

L6920

DIM.

A 1.20 0.047

A1 0.050 0.150 0.002 0.006

A2 0.800 1.000 1.050 0.031 0.039 0.041

b 0.190 0.300 0.007 0.012

c 0.090 0.200 0.003 0.008

D (1) 2.900 3.000 3.100 0.114 0.118 0.122

E 6.200 6.400 6.650 0.244 0.252 0.260

E1 (1) 4.300 4.400 4.500 0.169 0.173 0.177

e 0.650 0.026

L 0.450 0.600 0.750 0.018 0.024 0.027

L1 1.000 0.039

k 0˚ (min.) 8˚ (max.)

aaa 0.100 0.004

Note: 1. D and F does n ot include mold flash o r protrusio ns.

mm inch

MIN. TYP. MAX. MIN. TYP. MAX.

Mold flash or potrusions shall not excee d 0.15mm
(.006inch) per side .

OUTLINE AND

MECHANICAL DATA

TSSOP8

(Body 4.4mm)

0079397 (Jedec MO-153-AA)

11/13

L6920

7 Revision History

Table 9. Revision History

Date Revision Description of Changes

May 2003 1 First Issue.

February 2005 2 Modified the max. value of the I

parameter in the Table 4 pag. 3.

sd

12/13

L6920

Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences
of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is granted
by implication or otherwise under any patent or patent rights of STMicroelectronics. Specifications mentioned in this publication are subject
to change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products are not
authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics.

The ST logo is a registered trademark of STMicroelectronics.

All other names are the property of their respective owners

© 2005 STMicroelectronics - All rights reserved

Australia - Belgium - Brazil - Canada - China - Czech Republic - Finland - France - Germany - Hong Kong - India - Israel - Italy - Japan -

Malaysia - Malta - Morocco - Singapore - Spain - Sweden - Switzerland - United Kingdom - United States of America

STMicroelectronics group of companies

www.st.com

13/13