Datasheet LM828M5X, LM828M5 Datasheet (NSC)

LM828
Switched Capacitor Voltage Converter

LM828 Switched Capacitor Voltage Converter

March 1999

General Description

The LM828 CMOS charge-pump voltage converter inverts a
positive voltage in the range of +1.8V to +5.5V to the corre­sponding negative voltage of −1.8V to −5.5V. The LM828
uses two low cost capacitors to provide up to 25 mA of out­put current.

The LM828 operates at 12 kHz switching frequency to re­duce output resistance and voltageripple.With an operating
current of only 40 µA (operating efficiency greater than 96
with most loads), the LM828 provides ideal performance for
battery powered systems. The device is in a tiny SOT-23-5
package.

Basic Application Circuits

Voltage Inverter

+5V to −10V Converter

Features

n Inverts Input Supply Voltage
n SOT-23-5 Package
n 20Ω Typical Output Impedance
n 97%Typical Conversion Efficiency at 5 mA

Applications

n Cellular Phones

%

n Pagers
n PDAs
n Operational Amplifier Power Supplies
n Interface Power Supplies
n Handheld Instruments

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DS100137-2

© 1999 National Semiconductor Corporation DS100137 www.national.com

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.

Supply Voltage (V+ to
GND, or GND to OUT)

V+ and OUT Continuous
Output Current

Output Short-Circuit

5.8V

50 mA

1 sec.

T

(Note 3) 150˚C

JMax

θ

(Note 3) 300˚C/W

JA

Operating Junction

−40˚C to 85˚C

Temperature Range
Storage Temperature

−65˚C to +150˚C

Range
Lead Temp. (Soldering, 10

300˚C

seconds)
ESD Rating (Note 7) 2kV

Duration to GND (Note 2)
Continuous Power

Dissipation (T
25˚C)(Note 3)

=

A

240 mW

Electrical Characteristics

Limits in standard typeface are for T
less otherwise specified: V+=5V, C

Symbol Parameter Condition Min Typ Max Units

V+ Supply Voltage R
I

Q

R

OUT

f

OSC

f

SW

P

EFF

V

OEFF

Note 1: Absolute maximum ratings indicate limits beyond which damage to the device may occur. Electrical specifications do not apply when operating the device
beyond its rated operating conditions.

Note 2: OUT may be shorted to GND for one second without damage. However, shorting OUT to V+ may damage the device and should be avoided. Also, for tem­peratures above 85˚C, OUT must not be shorted to GND or V+, or the device may be damaged.

Note 3: The maximum allowable power dissipation is calculated by using P
ambient temperature, and θ

Note 4: In the test circuit, capacitors C
voltage and efficiency.

Note 5: Specified output resistance includes internal switch resistance and capacitor ESR. See the details in the application information.
Note 6: The output switches operate at one half of the oscillator frequency, f
Note 7: The human body model is a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin.

Supply Current No Load 40 75 µA

Output Resistance (Note 5) I
Oscillator Frequency (Note 6) Internal 12 24 56 kHz
Switching Frequency (Note 6) Measured at CAP+ 6 12 28 kHz
Power Efficiency I
Voltage Conversion Efficiency No Load 95 99.96

is the junction-to-ambient thermal resistance of the package.

JA

=

25˚C, and limits in boldface type apply over the full operating temperature range. Un-

J

=

=

C

10 µF. (Note 4)

1

2

=

10kΩ 1.8 5.5 V

L

115

=

5mA 20 65 Ω

L

=

5mA 97

L

=

DMax

and C2are 10 µF,0.3ΩmaximumESRcapacitors.Capacitors with higher ESR will increase output resistance, reduce output

1

=

OSC

(T

JMax−TA

2f

SW

.

)/θJA, where T

is the maximum junction temperature, TAis the

JMax

%
%

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Test Circuit

*

C1and C2are 10 µF capacitors.

FIGURE 1. LM828 Test Circuit

Typical Performance Characteristics

Supply Current vs
Supply Voltage

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Output Source Resistance
vs Supply Voltage

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(Circuit of Figure 1, V+=5V unless otherwise specified)

Supply Current vs
Temperature

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Output Source Resistance
vs Temperature

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DS100137-32

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Typical Performance Characteristics (Circuit of Figure 1, V+

specified) (Continued)

=

5V unless otherwise

Output Voltage
vs Load Current

Switching Frequency vs
Supply Voltage

Connection Diagram

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Efficiency vs
Load Current

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Switching Frequency vs
Temperature

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5-Lead Small Outline Package (M5)

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Actual Size

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Top View With Package Marking

Ordering Information

Order Number Package

Number

LM828M5 MA05B S08A (Note 8) Tape and Reel (250 units/rail)

LM828M5X MA05B S08A (Note 8) Tape and Reel (3000 units/rail)

Note 8: The first letter ″S″ identifies the part as a switched capacitor converter. The next two numbers are the device number.Larger quantity reels are available upon
request.

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Package Marking Supplied as

Pin Description

Pin Name Function

1 OUT Negative voltage output.
2 V+ Power supply positive input.
3 CAP− Connect this pin to the negative terminal of the charge-pump capacitor.
4 GND Power supply ground input.
5 CAP+ Connect this pin to the positive terminal of the charge-pump capacitor.

Circuit Description

The LM828 contains four large CMOS switches which are
switched in a sequence to invert the input supply voltage.
Energy transfer and storage are provided by external capaci­tors.

Figure 2

When S
age V+. During this time interval, switches S
open. In the second time interval, S
same time, S
number of cycles, the voltage across C
V+. Since the anode of C
at the cathode of C
rent. The output voltage drop when a load is added is deter­mined by the parasitic resistance (R
switches and the ESR of the capacitors) and the charge

illustrates the voltage conversion scheme.

and S3are closed, C1charges to the supply volt-

1

and S3are open; at the

and S4are closed, C1is charging C2. After a

2

2

equals −(V+) when there is no load cur-

2

1

is connected to ground, the output

ds(on)

and S4are

2

will be pumped to

2

of the MOSFET

transfer loss between capacitors.

DS100137-26

FIGURE 2. Voltage Inverting Principle

Application Information

a function of the ON resistance of the internal MOSFET
switches, the oscillator frequency, the capacitance and the
ESR of both C
and discharging C
rent, the effect of the ESR of the pumping capacitor C
be multiplied by four in the output resistance. The output ca­pacitor C
mately equal to the output current, therefore, this ESR term

and C2. Since the switching current charging

1

is approximately twice as the output cur-

1

is charging and discharging at a current approxi-

2

will

1

only counts once in the output resistance. A good approxi­mation of R

is:

out

where RSWis the sum of the ON resistance of the internal
MOSFET switches shown in

Figure 2

.

High capacitance, low ESR capacitors will reduce the output
resistance.

The peak-to-peak output voltage ripple is determined by the
oscillator frequency, the capacitance and ESR of the output
capacitor C

:

2

Again, using a low ESR capacitor will result in lower ripple.

Capacitor Selection

The output resistance and ripple voltage are dependent on
the capacitance and ESR values of the external capacitors.
The output voltage drop is the load current times the output
resistance, and the power efficiency is

Simple Negative Voltage Converter

The main application of LM828 is to generate a negative
supply voltage. The voltage inverter circuit uses only two ex­ternal capacitors as shown in the Basic Application Circuits.
The range of the input supply voltage is 1.8V to 5.5V.

The output characteristics of this circuit can be approximated
by an ideal voltage source in series with a resistance. The
voltage source equals −(V+). The output resistance, R

,is

out

Where IQ(V+) is the quiescent power loss of the IC device,

2

and I

R

is the conversion loss associated with the switch

L

out

on-resistance, the two external capacitors and their ESRs.
The selection of capacitors is based on the specifications of

the dropout voltage (which equals I
age ripple, and the converter efficiency.Low ESR capacitors
(following table) are recommended to maximize efficiency,
reduce the output voltage drop and voltage ripple.

Low ESR Capacitor Manufacturers

Manufacturer Phone Capacitor Type

Nichicon Corp. (708)-843-7500 PL & PF series, through-hole aluminum electrolytic
AVX Corp. (803)-448-9411 TPS series, surface-mount tantalum
Sprague (207)-324-4140 593D, 594D, 595D series, surface-mount tantalum
Sanyo (619)-661-6835 OS-CON series, through-hole aluminum electrolytic

), the output volt-

outRout

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Application Information (Continued)
Low ESR Capacitor Manufacturers (Continued)

Manufacturer Phone Capacitor Type

Murata (800)-831-9172 Ceramic chip capacitors
Taiyo Yuden (800)-348-2496 Ceramic chip capacitors
Tokin (408)-432-8020 Ceramic chip capacitors

Other Applications

Paralleling Devices

Any number of LM828s can be paralleled to reduce the out­put resistance. Each device must have its own pumping ca­pacitor C
shown in Figure 3. The composite output resistance is:

, while only one output capacitor C

1

FIGURE 3. Lowering Output Resistance by Paralleling Devices

is needed as

out

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Cascading Devices

Cascading the LM828s is an easy way to produce a greater
negative voltage (e.g. A two-stage cascade circuit is shown
in Figure 4).

If n is the integer representing the number of devices cas­caded, the unloaded output voltage V
tive output resistance is equal to the weighted sum of each

is (-nVin). The effec-

out

individual device:

=

R

out

nR

out_1

+ n/2 R

out_2

+...+R

out_n

FIGURE 4. Increasing Output Voltage by Cascading Devices

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This can be seen by first assuming that each device is 100
percent efficient. Since the output voltage is different on
each device the output current is as well. Each cascaded de­vice sees less current at the output than the previous so the
R

voltage drop is lower in each device added. Note that,

OUT

the number of n is practically limited since the increasing of
n significantly reduces the efficiency, and increases the out­put resistance and output voltage ripple.

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Other Applications (Continued)

Combined Doubler and Inverter

In Figure 5, the LM828 is used to provide a positive voltage
doubler and a negative voltage converter. Note that the total
current drawn from the two outputs should not exceed 40
mA.

FIGURE 5. Combined Voltage Doubler and Inverter

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Regulating V

OUT

It is possible to regulate the negative output of the LM828 by
use of a low dropout regulator (such as the LP2980). The
whole converter is depicted in Figure 6. This converter can
give a regulated output from −1.8V to −5.5V by choosing the
proper resistor ratio:

=

V

where, V

(1+R1/R2)

V

out

ref

=

1.23V

ref

FIGURE 6. Combining LM828 with LP2980 to Make a Negative Adjustable Regulator

Note that the following conditions must be satisfied simulta­neously for worst case design:

>

V

V

in_min

+I

in_max

+I

V

out_min+Vdrop_max

out_maxxRout_max

<

V

out_max+Vdrop_min

out_minxRout_min

(LP2980)

(LM828)

(LP2980)

(LM828)

DS100137-12

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Physical Dimensions inches (millimeters) unless otherwise noted

LM828 Switched Capacitor Voltage Converter

5-Lead Small Outline Package (M5)

NS Package Number MA05B

For Order Numbers, refer to the table in the ″Ordering Information″ section of this document.

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