STMICROELECTRONICS L6920DC

L6920DC
Synchronous rectifier step up converter
General features
■
0.8V start up input voltage
■
Up to 5.5V operating input voltage
■
Internal synchronous rectifier
■
Adjustable output voltage from 1.8V to 5.5V
■
3.3V and 5V fixed output voltages
■
Low battery voltage detection
Description
■
Reverse battery protection
■
550mA minimum input current limit
■
Switching frequency up to 1MHz
The L6920DC is a high efficiency monolithic step
up switching converter IC especially designed for
battery powered application.
■
1.23V reference voltage available
Applications
■
Conversion from 1 to 3 alkaline,
■
NiMH, NiCd battery cells or 1 lithium ION
■
PDA and handheld instruments
■
Digital cameras
■
Cellular phones
■
GPS
■
Distributed power
MSOP8
Package is MSOP8 in order to minimize PCB
space. It requires only three external components
to realize the conversion from the battery voltage
to the selected output voltage.
The minimum output voltage is 1.8V: suitable to
supply the most advanced ASIC and µP.
High switching frequency allows for a low profile,
small sized inductor and output capacitor to be
used.
Reference voltage, low battery detection and
Shutdown are provided together with over current,
over voltage.
Application circuit
L6920DC
June 2006
Rev 1
3.3V
1/16
www.st.com
16
Contents
L6920DC
Contents
1
2
Pin settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1
Pin connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2
Pin description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Electrical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1
Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2
Thermal data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3
Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4
Typical performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5
Detailed description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5.1
Principle of operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5.2
Start-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
5.3
Shutdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.4
Low battery detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.5
Low battery input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.6
Reverse polarity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.7
Output voltage selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
6
Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
7
Order code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
8
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2/16
L6920DC
Pin settings
1
Pin settings
1.1
Pin connection
Figure 1.
1.2
Pin connection (top view)
Pin description
Table 1. Pin description
N°
Type
Description
1
FB
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
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.
3
LBO
Battery low voltage detector output. If the voltage at the LBI pin drops
below the internal threshold typ. 1.23V, LBO goes low.
The LBO is an open drain output and so a pull-up resistor (about
200KΩ) has to be added for correct output setting .
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
8
OUT
Step-up inductor connection
Power OUTPUT pin
3/16
Electrical data
L6920DC
2
Electrical data
2.1
Maximum ratings
Table 2. Absolute maximum ratings
Symbol
Vccmax
Vout max
2.2
Parameter
Value
Unit
Vcc to GND
6
V
LBI, SHDN, FB to GND
6
V
Vout to GND
6
V
Value
Unit
Maximum thermal resistance junction-ambient
180
° C/W
Maximum junction temperature
150
°C
Thermal data
Table 3. Thermal data
Symbol
RthJA
TJ
4/16
Parameter
L6920DC
3
Electrical characteristics
Electrical characteristics
Table 4. Electrical characteristcs
(VIN = 2V, FB = GND, TJ = 25°C unless otherwise specified)
Symbol
Parameter
Test condition
Min
Typ
Max
Unit
VCC Section
VIN
Iq
Minimum Start Up Input
Voltage
Vout = 3.3V
0.8
V
Il = 0 mA, FB = 1.4V, Vout = 3.3V
LBI = SHDN = 2V
9
12
µA
Il = 0 mA, FB = 1.4V, Vout = 5V
LBI = SHDN = 2V
11
15
µA
Quiescent Current
Isd
Shut Down Current
Vin = 5V, Il = 0 mA
0.1
1
µA
Irev
Reverse battery current
Vin = -4V
0.1
1
µA
Power section
Ron-N
Active switch ON resistance
300
mΩ
Ron-P
Synchronous switch ON
resistance
300
mΩ
Control section
Vout
Output voltage
Output voltage range
VLBI
LBI threshold
VLBO
LBO logic LOW
Ilim
FB = OUT, Il = 0 mA
3.2
3.3
3.4
V
FB = GND, Il = 0 mA
4.9
5
5.1
V
External divider
1.8
5.5
V
1.23
Isink = 1mA
LX switch current limit
0.2
0.55
V
0.4
V
0.9
A
Tonmax
Maximum on time
Vout = 3.3V
3.75
5
6.25
µs
Toffmin
Minimum off time
Vout = 3.3V
0.75
1
1.25
µs
SHDN
SHDN logic LOW
0.2
V
SHDN logic HIGH
Vref
Reference Voltage
0.6
1.18
V
1.23
1.27
V
5/16
Typical performance
4
L6920DC
Typical performance
Figure 2.
Efficiency vs output current @ VOUT = 3.3V
95
Vin=2.4V
90
85
80
Vin=1.2V
75
70
65
60
L6920DC
L
6920DB
Vout=3.3V
L=10µH
Cout=47µF
Cin=10µF
55
50
45
40
0.1
Figure 3.
1
10
1000
100
Efficiency vs output current @ VOUT = 5V
100
Vin=3.6V
90
80
Vin=2.4V
Vin=1.2V
70
60
50
40
L6920DC
L
6920DB
Vout=5V
L=10µH
Cout=47µF
Cin=10µF
30
20
10
0
0.1
Figure 4.
1
10
100
Start up voltage vs output current @ Vout = 5V & Vout = 3.3V
VStart up v s. output current
VStart up vs . out put cur rent
1600
1600
1500
1500
1400
1400
1300
1300
VStart up (mV)
VStart up (mV)
Vout =5V
1200
1100
1000
Vout =3.3V
1200
1100
1000
900
900
800
800
700
700
600
600
0.1
1
10
Output cu rrent (mA)
6/16
1000
100
1000
0.1
1
10
Output current (mA)
100
1000
L6920DC
5
Detailed description
Detailed description
The L6920DC 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.
These performances are achieved via a strong reduction of quiescent current (10µA only)
and adopting a synchronous 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.
A simplified block diagram is shown here below.
Figure 5.
Simplified block diagram
VOUT
OUT
ZERO CROSSING
-
VREF
+
+
-+
VBG
SHDN
A
FB
Y
VOUT
GND
R1,R2
A
B
C
Y
B
-
VOUT
LX
OPAMP
(CR)
+
C
VBG
-
Q
Toff min
1µsec
S
+
FB
Ton max
5µsec
VBG
LBI
5.1
GND
+
R
CURRENT LIMIT
LBO
VIN
D99IN1041
Principle of operation
In L6920DC 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 L6920DC
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 N-channel power switch. The switch is turned off if the current
flowing in the inductor reaches the current limit or after a maximum on time set to 5µs.
●
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 1µs. 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.
7/16
Detailed description
L6920DC
So, in case of light load, the device works in PFM mode, as shown in Figure 8:
Figure 6.
PFM mode condition: Vout = 5V; Vbatt =1.5V ; C2 = Vout ; C3 = Inductor
Current
Figure 7 shows how the device works in case of heavy load.
Figure 7.
8/16
Heavy load conditions C2 = Vout; C3 = Inductor Current; Vout = 5V;
Vbatt=1.5V
L6920DC
Detailed description
The maximum load current is defined by the following relationship:
Equation 1
V in
V out – V in
I LOAD_LIM = ----------- ⋅ ⎛ I LIM – T OFF_MIN ⋅ -------------------------⎞ ⋅ η
⎝
2⋅ L ⎠
V out
Where ηis the efficiency and ILIM is the current limit.
Of course, if ILOAD is greater than ILOAD_LIM the regulation is lost (Figure 8).
Figure 8.
5.2
No regulation C2 = Vout ; C3 = Inductor Current
Start-up
One of the key features of L6920DC is the startup at supply voltage down to 0.8V (please
see the diagram in Figure 4).
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 RDS(on) 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.
9/16
Detailed description
5.3
L6920DC
Shutdown
In shutdown mode (SHDN pulled low) all internal circuitries are turned off, minimizing the
current provided by the battery (ISHDN < 100 nA, in typical case).
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.
5.4
Low battery detection
The L6920DC includes a low battery detector comparator.
Threshold is VREF voltage and a hysteresis is added to avoid oscillations when input crosses
the threshold slowly. The LBO is an open drain output so a pull up resistor is required for a
proper use.
5.5
Low battery input
It is possible to fix, using an external resistor divider, the LBO threshold, in order to adapt
the LBO detection at the correct input source, by the following equation:
Equation 2
V batt-th = 1.23V ⋅ ⎛⎝ 1 + R1
--------⎞⎠
R2
Where Vbatt-th is the battery voltage at which the internal comparetor is triggered.
5.6
Reverse polarity
A protection circuit has been implemented to avoid that L6920DC 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.
If a battery can be inserted in reverse direction, a non polarized capacitor should be
installed in location of C2.
5.7
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.
10/16
L6920DC
Detailed description
Table 5. Output voltage connection
Vout = 3.3V
FB pin connected to OUT (see application circuit)
Vout = 5V
FB pin connected to GND
1.8V < Vout < 5.5V
Figure 9.
FB pin connected to a resistive divider V out = 1.23V ⋅ ⎛ 1 + R4
--------⎞
⎝
R5⎠
Test circuit
R2
R1
LBI
VBATT=1.5V
VBATT
_____
2
SHDN
5
7
L1 10µH
VOUT
C2
VOUT=2.5V
8
47µF
C1
L6920DB
L6920DC
VREF
R3
47µF
___
4
C4
LBO
100nF
3
1
R4
200KΩ
FB
6
GND
R5
200KΩ
11/16
Package mechanical data
6
L6920DC
Package mechanical data
In order to meet environmental requirements, ST offers these devices in ECOPACK®
packages. These packages have a Lead-free second level interconnect . The category of
second level interconnect is marked on the package and on the inner box label, in
compliance with JEDEC Standard JESD97. The maximum ratings related to soldering
conditions are also marked on the inner box label. ECOPACK is an ST trademark.
ECOPACK specifications are available at: www.st.com
12/16
L6920DC
Package mechanical data
Table 6. MSOP8 Mechanical data
mm.
inch
Dim.
Min
Typ
A
Max
Min
Typ
1.10
A1
0.050
A2
0.750
b
Max
0.043
0.150
0.002
0.950
0.03
0.250
0.400
0.010
0.016
c
0.130
0.230
0.005
0.009
D (1)
2.900
3.000
3.100
0.114
0.118
0.122
E
4.650
4.900
5.150
0.183
0.193
0.20
E1 (1)
2.900
3.000
3.100
0.114
0.118
0.122
e
L
L1
0.850
0.650
0.400
0.550
aaa
0.033
0.037
0.026
0.700
0.016
0.950
k
0.006
0.022
0.028
0.037
0° (min.) 6° (max.)
0.100
0.004
1. D and F does not include mold flash or protrusions. Mold flash or potrusions shall not exceed 0.15mm
(.006inch) per side.
Figure 10. Package dimensions
13/16
Order code
7
L6920DC
Order code
Table 7. Order code
14/16
Part number
Package
Packaging
L6920DC
MSOP8
Tube
L6920DCTR
MSOP8
Tape and reel
L6920DC
8
Revision history
Revision history
Table 8. Revision history
Date
Revision
29-Jun-2006
1
Changes
First issue
15/16
L6920DC
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