Datasheet ML4869ES-3, ML4869ES-5, ML4869CS-3, ML4869CS-5 Datasheet (Micro Linear Corporation)
Page 1
July 2000
PRELIMINARY
ML4869
Medium Current Boost Regulator
with Load Disconnect
GENERAL DESCRIPTION
The ML4869 is a continuous conduction boost regulator
designed for DC to DC conversion in multiple cell battery
power systems. Continuous conduction allows the
regulator to maximize output current for a given inductor.
The maximum switching frequency can exceed 200kHz,
allowing the use of small, low cost inductors. The ML4869
is capable of start-up with input voltages as low as 1.8V,
and is available in 5V and 3.3V output versions with an
output voltage accuracy of ±3%.
An integrated synchronous rectifier eliminates the need
for an external Schottky diode and provides a lower
forward voltage drop, resulting in higher conversion
efficiency. In addition, low quiescent current and variable
frequency operation result in high efficiency even at light
loads. The ML4869 requires only a few external
components to build a very small regulator capable of
achieving conversion efficiencies approaching 85%.
The SHDN input allows the user to stop the regulator from
switching, and provides complete isolation of the load
from the battery.
FEATURES
■ Guaranteed full load start-up and operation at
1.8V input
■ Continuous conduction mode for high output current
■ Pulse Frequency Modulation and internal synchronous
rectification for high efficiency
■ Isolates the load from the input during shutdown
■ Minimum external components
■ Low ON resistance internal switching FETs
■ Low supply current
■ 5V and 3.3V output versions
■ Shutdown current = 1µA MAX
BLOCK DIAGRAM
V
IN
2
+
–
V
L1
SHDN
1
START-UP
CONTROL
BOOST
PWR GND
6
V
L2
SYNCHRONOUS
RECTIFIER
CONTROL
+
–
2.4V
8
GND
SHUTDOWN
CONTROL
+
–
3
SHDN
V
OUT
4
5
1
Page 2
ML4869
PIN CONFIGURATION
ML4869
8-Pin SOIC (S08)
V
L1
V
IN
GND
SHDN
PIN DESCRIPTION
PIN NAME FUNCTION
1V
2V
L1
IN
3 GND Ground
4 SHDN Pulling this pin to VIN shuts down the
Boost inductor connection
Battery input voltage
regulator, isolating the load from the
input
1
2
3
4
TOP VIEW
8
7
6
5
PIN NAME FUNCTION
5V
6V
PWR GND
NC
V
L2
V
OUT
OUT
L2
Boost regulator output
Boost inductor connection
7 NC No connection
8 PWR GND Return for the NMOS output transistor
2
Page 3
ML4869
ABSOLUTE MAXIMUM RATINGS
Absolute maximum ratings are those values beyond which
the device could be permanently damaged. Absolute
maximum ratings are stress ratings only and functional
device operation is not implied.
V
............................................................................................... 7V
OUT
Voltage on any other pin ..... GND - 0.3V to V
Peak Switch Current (I
Average Switch Current (I
) ......................................... 2A
PEAK
)..................................... 1A
AVG
OUT
+ 0.3V
OPERATING CONDITIONS
Temperature Range
ML4869CS-X .............................................. 0°C to 70°C
ML4869ES-X ........................................... -20°C to 70°C
VIN Operating Range .......................1.8V to V
OUT
- 0.2V
Junction Temperature ..............................................150°C
Storage Temperature Range ..................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec) .....................260°C
Thermal Resistance (qJA).................................... 160°C/W
ELECTRICAL CHARACTERISTICS
Unless otherwise specified, VIN = Operating Voltage Range, TA = Operating Temperature Range (Note 1)
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
SUPPLY
I
IN(Q)
I
OUT(Q)VOUT
PFM REGULATOR
I
PEAKIL
V
OUT
SHUTDOWN
V
V
Note 1:
VIN Quiescent Current VIN = V
Peak Current VIN = 2.4V –3 Suffix 700 800 900 mA
Output Voltage I
Load Regulation -3 Suffix, VIN = 2.4V, I
Input Low Voltage 0.5 V
IL
Input High Voltage VIN - 0.5 V
IH
Input Bias Current -100 100 nA
Limits are guaranteed by 100% testing, sampling, or correlation with worst case test conditions.
- 0.2V, SHDN = 0V 3 6 µA
OUT
VIN = SHDN = 2.4V, V
Quiescent Current SHDN = 0V 25 35 µA
VIN = SHDN = 2.4V 14 20 µA
V
= V
OUT
OUT
See Figure 1 -5 Suffix 4.95 5.05 5.15 V
-5 Suffix, VIN = 2.4V, I
OUT(NOM)
= 0 -3 Suffix 3.30 3.35 3.40 V
= 0V 0.3 1 µA
OUT
–5 Suffix 750 850 950 mA
= 310mA 3.20 3.25 3.40 V
OUT
= 185mA 4.85 4.95 5.15 V
OUT
3
Page 4
ML4869
V
IN
100µF
27µH
(SUMIDA CD75)
ML4869
V
PWR GND
L1
V
IN
GND
SHDN
V
NC
V
OUT
L2
100µF
Figure 1. Application Test Circuit
I
L
I
OUT
Q1
PWR GND
6
V
L2
SYNCHRONOUS
RECTIFIER
CONTROL
I
SET
8
A3
Q3
Q2
A2
+
–
2.4V
GND
+
–
3
SHUTDOWN
CONTROL
SHDN
V
OUT
4
V
OUT
5
1
V
L1
V
2
R
IN
SENSE
+
–
A1
SHDN
START-UP
CONTROL
BOOST
Figure 2. PFM Regulator Block Diagram
I
L(MAX)
I
I
SET
L
0
V
OUT
V
L2
0
Q1 ON
Q2 OFF
Q1 OFF
Q2 ON
Figure 3. Inductor Current and Voltage Waveforms
4
Page 5
ML4869
FUNCTIONAL DESCRIPTION
The ML4869 combines a unique form of current mode
control with a synchronous rectifier to create a boost
converter that can deliver high currents while maintaining
high efficiency. Current mode control allows the use of a
very small high frequency inductor and output capacitor.
Synchronous rectification replaces the conventional
external Schottky diode with an on-chip P-channel
MOSFET to reduce losses, eliminate an external
component, and provide the means for load disconnect.
Also included on-chip are an N-channel MOSFET main
switch and a current sense resistor.
REGULATOR OPERATION
The ML4869 is a variable frequency, current mode
switching regulator. Its unique control scheme converts
efficiently over more than three decades of load current.
A block diagram of the boost converter including the key
external components is shown in Figure 2.
Error amp A3 converts deviations in the desired output
voltage to a small current, I
measured through a current sense resistor (R
is amplified by A1. The boost control block matches the
average inductor current to a multiple of the I
by switching Q1 on and off. The peak inductor current is
limited by the controller to about 650mA.
At light loads, I
inductor discharge cycle , causing Q1 to stop switching.
Depending on the load, this idle time can extend to
tenths of seconds. When the circuit is not switching, only
25µA of supply current is drawn from the output. This
allows the part to remain efficient even when the load
current drops below 250µA.
Amplifier A2 and the PMOS transistor Q2 work together
to form a low forward drop diode. When transistor Q1
turns off, the current flowing in the inductor causes VL2 to
go high. As the voltage on VL2 rises above V
amplifier A2 allows the PMOS transistor Q2 to turn on. In
discontinuous operation, (where IL always returns to zero),
A2 uses the resistive drop across the PMOS switch Q2 to
sense zero inductor current and turns the PMOS switch
off. In continuous operation, the PMOS turn off point is
independent of A2 and is determined by the boost
control circuitry.
Typical continuous mode inductor current and voltage
waveforms are shown in Figure 3.
SHUTDOWN
will momentarily reach zero after an
SET
. The inductor current is
SET
SENSE
SET
OUT
) which
current
,
DESIGN CONSIDERATIONS
OUTPUT CURRENT CAPABILITY
The maximum current available at the output of the
regulator is related to the maximum inductor current by
the ratio of the input to output voltage and the conversion
efficiency. The maximum inductor current is limited by
the boost converter to about 650mA. The conversion
efficiency is determined mainly by the internal switches
as well as the external components, but can be estimated
at about 80%. The maximum average output current can
be estimated by using the typical performance curves
shown in Figures 4 and 5, or by calculation using the
following equations:
V
I
OUT V
I
OUT V
Since the maximum output current is based on when the
inductor current goes into current limit, it is not
recommended to operate the ML4869 at the maximum
output current continuously. Applications that have high
transient load currents should be evaluated under worst
case conditions to determine suitability.
INDUCTOR SELECTION
The ML4869 is able to operate over a wide range of
inductor values. A value of 10µH is a good choice, but
any value between 5µH and 33µH is acceptable. As the
inductor value changes, the control circuitry will
automatically adjust to keep the inductor current under
control. Choosing an inductance value of less than 10µH
will reduce the component’s footprint, but the efficiency
and maximum output current may drop.
It is important to use an inductor that is rated to handle
1.0A peak currents without saturating. Also choose an
inductor with low winding resistance. A good rule of
thumb is to allow 5 to 10mW of resistance for each 1µH of
inductance.
The final selection of the inductor will be based on tradeoffs between size, cost and efficiency. Inductor tolerance,
core and copper loss will vary with the type of inductor
selected and should be evaluated with a ML4869 under
worst case conditions to determine its suitability.
Several manufacturers supply standard inductance values
in surface mount packages:
0686
()
5
0619
(. )
33
..
V
.
IN MIN
()
V
5
IN MIN
()
V
.
33
−
−
0144=×
.
0144=×
A
A
(1)
(2)
The ML4869 output can be shut down by pulling the
SHDN pin high (to VIN). When SHDN is high, the
regulator stops switching, the control circuitry is powered
down, and the body diode of the PMOS synchronous
rectifier is disconnected from the output. By switching
Q1, Q2, and Q3 off, the load is isolated from the input.
This allows the output voltage to be independent of the
input while in shutdown.
Coilcraft (847) 639-6400
Coiltronics (561) 241-7876
Dale (605) 665-9301
Sumida (847) 956-0666
5
Page 6
ML4869
DESIGN CONSIDERATIONS
(Continued)
OUTPUT CAPACITOR
The output capacitor filters the pulses of current from the
switching regulator. Since the switching frequency will
vary with inductance, the minimum output capacitance
required to reduce the output ripple to an acceptable
level will be a function of the inductor used. Therefore, to
maintain an output voltage with less than 100mV of ripple
at full load current, use the following equation:
L
C
OUT
×44
=
V
OUT
(3)
The output capacitor’s Equivalent Series Resistance (ESR)
and Equivalent Series Inductance (ESL), also contribute to
the ripple. Just after the Q1 turns off, the current in the
output capacitor ramps quickly to between 0.3A and
600
500
V
= 3.3V
OUT
400
V
= 5V
(mA)
300
OUT
I
200
100
OUT
0.9A. This fast change in current through the capacitor’s
ESL causes a high frequency (5ns) spike to appear on the
output. After the ESL spike settles, the output still has a
ripple component equal to the product of inductor
discharge current and the ESR. To minimize these effects,
choose an output capacitor with less than 10nH of ESL
and less than 100mW of ESR.
Suitable tantalum capacitors can be obtained from the
following vendors:
AVX (207) 282-5111
Kemet (846) 963-6300
Sprague (207) 324-4140
95.0
90.0
85.0
EFFICIENCY (%)
80.0
V
OUT
V
= 5V
OUT
= 3.3V
0.0
2.00 3.00 4.503.50
1.50 2.50 5.004.00
Figure 4. I
250
200
150
(nA)
IN
I
100
50
0
VIN (V)
vs. VIN Using the Circuit of Figure 8 Figure 5. Efficiency vs. I
OUT
V
= 5V
OUT
V
= 3.3V
OUT
012345 86
VIN (V)
7
75.0
0.1 1 10 1000100
I
OUT
Using the Circuit of Figure 8
OUT
80
70
V
= 5V
V
OUT
OUT
= 3.3V
35
VIN (V)
(µA)
IN
I
60
50
40
30
20
(mA)
Figure 6. Input Leakage vs. VIN in Shutdown Figure 7. No Load Input Current vs. V
412
IN
6
Page 7
ML4869
µ
DEISGN CONSIDERATIONS
(Continued)
In applications where the ML4869 is operated at or near
the maximum output current, it is recommended to add a
10nF to 100nF ceramic or film capacitor from V
OUT
to
GND. The optimum value of the high frequency bypass
capacitor is dependent on the layout and the value of the
bulk output capacitor selected.
INPUT CAPACITOR
Due to the high input current drawn at startup and
possibly during operation, it is recommended to decouple
the input with a capacitor with a value of 47µF to 100µF.
This filtering prevents the input ripple from affecting the
ML4869 control circuitry, and also improves the
efficiency by reducing the I2R losses during the charge
cycle of the inductor. Again, a low ESR capacitor (such as
tantalum) is recommended.
It is also recommended that low source impedance
batteries be used. Otherwise, the voltage drop across the
source impedance during high input current situations will
cause the ML4869 to fail to startup or to operate
unreliably. In general, for two cell applications the source
impedance should be less than 400mW, which means that
small alkaline cells should be avoided.
10µH
(SUMIDA CD5A)
ML4869
V
PWR GND
V
IN
100µF
L1
V
IN
GND
SHDN
V
OUT
0.01µF
V
NC
L2
100µF
V
OUT
Figure 8. Design Example Schematic Diagram
DESIGN EXAMPLE
In order to design a boost converter using the ML4869,
it is necessary to define the values of a few parameters.
For this example, we have assumed that VIN = 3.0V to
3.6V, V
= 5.0V, and I
OUT
OUT(MAX)
= 250mA
SHUTDOWN
To guarantee proper operation, SHDN must be pulled to
within 0.5V of GND or VIN to prevent excessive power
dissipation and possible oscillations. A graph of input
leakage current while in shutdown is shown in Figure 6.
LAYOUT
Good layout practices will ensure the proper operation of
the ML4869. Some layout guidelines follow:
• Use adequate ground and power traces or planes
• Keep components as close as possible to the ML4869
• Use short trace lengths from the inductor to the V
VL2 pins and from the output capacitor to the V
• Use a single point ground for the ML4869 PWR GND
pin and the input and output capacitors, and connect
the GND pin to PWR GND using a separate trace
• Separate the ground for the converter circuitry from the
ground of the load circuitry and connect at a single
point
L1
OUT
and
pin
First, it must be determined whether the ML4869 is
capable of delivering the output current. This is done
using Equation 1:
I
OUT V
()
5
V
..
0686
IN M IN
()
5
−
V
0 267=×
A
Next, select an inductor:
As previously mentioned, it is the recommended
inductance is 10µH. Make sure that the peak current
rating of the inductor is at least 1.0A, and that the DC
resistance of the inductor is in the range of 50 to 100mW.
Finally, the value of the output capacitor is determined
using Equation 3:
OUT
44 10
=
50
.
F
=
88
V
µ
C
H
×
The closest standard value would be a 100µF capacitor
with an ESR rating of 100mW. If such a low ESR value
cannot be found, two 47µF capacitors in parallel could
also be used.
The complete circuit is shown in Figure 8. As mentioned
previously, the use of an input supply bypass capacitor is
strongly recommended.
7
Page 8
ML4869
PHYSICAL DIMENSIONS
0.017 - 0.027
(0.43 - 0.69)
(4 PLACES)
0.055 - 0.061
(1.40 - 1.55)
0.012 - 0.020
inches (millimeters)
Package: S08
0.189 - 0.199
(4.80 - 5.06)
8
PIN 1 ID
1
0.050 BSC
(1.27 BSC)
(0.30 - 0.51)
SEATING PLANE
0.148 - 0.158
(3.76 - 4.01)
0.059 - 0.069
(1.49 - 1.75)
0.004 - 0.010
(0.10 - 0.26)
8-Pin SOIC
0.228 - 0.244
(5.79 - 6.20)
0º - 8º
0.015 - 0.035
(0.38 - 0.89)
0.006 - 0.010
(0.15 - 0.26)
ORDERING INFORMATION
PART NUMBER OUTPUT VOLTAGE TEMPERATURE RANGE PACKAGE
ML4869CS-3 3.3V 0°C to 70°C 8-Pin SOIC (S08)
ML4869CS-5 5V 0°C to 70°C 8-Pin SOIC (S08)
ML4869ES-3 3.3V -20°C to 70°C 8-Pin SOIC (S08)
ML4869ES-5 5V -20°C to 70°C 8-Pin SOIC (S08)
© Micro Linear 1998. is a registered trademark of Micro Linear Corporation. All other trademarks are the property of their respective owners.
Products described herein may be covered by one or more of the following U.S. patents: 4,897,611; 4,964,026; 5,027,116; 5,281,862; 5,283,483; 5,418,502;
5,508,570; 5,510,727; 5,523,940; 5,546,017; 5,559,470; 5,565,761; 5,592,128; 5,594,376; 5,652,479; 5,661,427; 5,663,874; 5,672,959; 5,689,167; 5,714,897;
5,717,798; 5,742,151; 5,747,977; 5,754,012; 5,757,174; 5,767,653;. Japan: 2,598,946; 2,619,299; 2,704,176. Other patents are pending.
Micro Linear reserves the right to make changes to any product herein to improve reliability, function or design. Micro Linear does not assume any liability
arising out of the application or use of any product described herein, neither does it convey any license under its patent right nor the rights of others. The circuits
contained in this data sheet are offered as possible applications only. Micro Linear makes no warranties or representations as to whether the illustrated circuits
infringe any intellectual property rights of others, and will accept no responsibility or liability for use of any application herein. The customer is urged to consult
with appropriate legal counsel before deciding on a particular application.
8
DS4869-01
2092 Concourse Drive
San Jose, CA 95131
Tel: (408) 433-5200
Fax: (408) 432-0295
www.microlinear.com
04/1/99 Printed in U.S.A.
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