MOTOROLA MAX828SNTR, MAX829SNTR Datasheet

MAX828 MAX829

Switched Capacitor
V oltage Converters

The MAX828/829 are CMOS “charge–pump” voltage converters in
ultra–small SOT–23 5 lead packages. They invert and/or double an
input voltage which can range from +1.5V to +5.5V. Conversion
efficiency is typically >95%. Switching frequency is 12kHz for the
MAX828 and 35kHz for the MAX829.

External component requirement is only two capacitors (3.3µF
nominal) for standard voltage inverter applications. With a few
additional components a positive doubler can also be built. All other
circuitry, including control, oscillator , power MOSFETs are integrated
on–chip. Supply current is 50 µA (MAX828) and 115 µA (MAX829).

The MAX828 and MAX829 are available in a SOT–23 5 lead
surface mount package.

Features

• Charge Pump in SOT–23 5 Lead Package

• >95% Voltage Conversion Efficiency

• Voltage Inversion and/or Doubling

• Low 50 µA (MAX828) Quiescent Current

• Operates from +1.5V to +5.5V

• Up to 25 mA Output Current

• Only Two External Capacitors Required

• Tested Operating Temperature Range: –40°C to +85°C

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SOT–23–5

SN SUFFIX

PRELIMINARY INFORMATION

OUT

CASE TBD

PIN CONFIGURATION

(Top View)

1

2

V

in

–

3

C

5

4

+

C

GND

Typical Applications

• LCD Panel Bias

• Cellular Phones

• Pagers

• PDAs, Portable Dataloggers

• Battery–Powered Devices

TYPICAL OPERATING CIRCUIT

Voltage Inverter

+

C

+

C1

–

C

GND

V

MAX828

MAX829

OUT

SOT–23–5*

NOTE: *SOT–23–5 is equivalent to EIAJ–SC74A

ORDERING INFORMATION

Device Package Shipping

MAX828SNTR SOT–23–5 3000 Tape/Reel

C2

INPUT

–

V
OUTPUT

MAX829SNTR SOT–23–5 3000 Tape/Reel

in

+

 Semiconductor Components Industries, LLC, 1999

February , 2000 – Rev. 0

1 Publication Order Number:

MAX828/D

MAX828 MAX829

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PIN DESCRIPTION

Pin No. Symbol Description

1
2
3
4
4

ABSOLUTE MAXIMUM RATINGS*

Symbol Parameter Value Unit

T

A

P

D

T

stg

T

sol

* Maximum Ratings are those values beyond which damage to the device may occur.

OUT

V

IN

–

C

GND

+

C

Inverting charge pump output
Positive power supply input
Commutation capacitor negative terminal
Ground
Commutation capacitor positive terminal

Input Voltage (VIN to GND) +6.0, – 0.3 V
Output Voltage (OUT to GND) –6.0, +0.3 V
Current at OUT Pin 50 mA
Short–Circuit Duration – OUT to GND Indefinite
Operating Temperature Range –40 to +85 °C
Power Dissipation (TA ≤ 70°C) SOT–23–5

240 mW

Derate by 4mW/°C for TA > 70°C
Storage Temperature Range –65 to +150 °C
Lead Temperature (Soldering, 10 Seconds) +300 °C

ELECTRICAL CHARACTERISTICS (TA = 0°C to +85°C, V

otherwise noted

. Typical values are at TA = 25°C.)

= +5V , C1 = C2 = 10 µF (MAX828), C1 = C2 = 3.3µF (MAX829), unless

IN

Symbol Characteristic Min Typ Max Unit

I

V
F

P

V
R

DD

+

OSC

EFF

EFF

OUT

Supply Current (TA = 25°C)

MAX828
MAX829

Supply Voltage Range (R

LOAD

Oscillator Frequency (TA = 25°C)

MAX828
MAX829

Power Efficiency

I

= 3mA, TA = 25°C

LOAD

Voltage Conversion Efficiency (R
Output Resistance (Note 1.)

I

= 5mA, TA = 25°C

OUT

TA = 0°C to +85°C

= 10k

W)

—
—

— — 5.5 V

8.4

24.5

50

115

12
35

— 96 —

= R) 95 99.9 %

LOAD

—
—

25
—

90

µA

260

kHz

15.6

45.5
%

W

50
65

1. Capacitors C1 and C2 contribution is approximately 20% of the output impedance. For additional information, refer to Equation 1 in the
Applications Information section.

ELECTRICAL CHARACTERISTICS (TA = –40°C to +85°C, V

unless otherwise noted

Symbol

I

V
F

R

DD

in
OSC

OUT

Supply Current

Supply Voltage Range (R
Oscillator Frequency

Output Resistance (I

. Typical values are at TA = 25°C.) (Note 2.)

Characteristic Min Typ Max Unit

MAX828
MAX829

= 10k

W)

MAX828
MAX829

LOAD

= 5mA) — — 65

OUT

= +5V, C1 = C2 = 10µF (MAX828), C1 = C2 = 3.3µF (MAX829),

IN

—
—

—
—

115
325

1.5 — 5.5 V

6.0
19

—
—

20

54.3

µA

kHz

W

2. All –40°C to +85°C specifications are guaranteed by design.

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2

MAX828 MAX829

DET AILED OPERATING DESCRIPTION

The MAX828/829 charge pump converters invert the

voltage applied to the V

pin. Conversion consists of a

IN

two–phase operation (Figure 1). During the first phase,
switches S2 and S4 are open and S1 and S3 are closed.
During this time, C1 charges to the voltage on VIN and load
current is supplied from C2. During the second phase, S2
and S4 are closed, and S1 and S3 are open. This action
connects C1 across C2, restoring charge to C2.

IN

Figure 1. Ideal Switched Capacitor Charge Pump

S1 S2

C1

S3 S4

MAX828/829

C2

V

out

= –(Vin)

APPLICATIONS INFORMATION

Output Voltage Considerations

The MAX828/829 perform voltage conversion but do not
provide regulation. The output voltage will drop in a linear
manner with respect to load current. The value of this
equivalent output resistance is approximately 25W nominal
at +25°C and VIN = +5V . V

is approximately - 5V at light

OUT

loads, and droops according to the equation below:

(4) Losses that occur during charge transfer (from the

commutation capacitor to the output capacitor)
when a voltage difference between the two
capacitors exists.

Most of the conversion losses are due to factors (2), (3)

and (4) above. These losses are given by Equation 1.

P

LOSS(2,3,4)

1

ƪ

(f

OSC

The 1/(f

+

)

)C1

)(C1) term in Equation 1 is the effective output

OSC

2

I

OUT

8R

SWITCH

Equation 1.

R

OUT

)

^

4ESRC1)

I

OUT

2

ESR

C2

ƫ

resistance of an ideal switched capacitor circuit (Figures 2a,
2b).

The losses in the circuit due to factor (4) above are also
shown in Equation 2. The output voltage ripple is given by
Equation 3.

P

LOSS(4)

V

RIPPLE

+

V

+ƪ(0.5)(C1)(V

I

OUT

OSC

f

2

Equation 2.

)(C2)

Equation 3.

ƪ

(V

+

RIPPLE

(f

*

)

IN

2V

2

*

OUT

2(I

OUT

V

OUT

V

RIPPLE

)(ESRC2)

C2C1

2

))(0.5)(C2)

)ƫ

f

OSC

V

out

R

L

V
V

Charge Pump Efficiency

= I

DROP

= – (VIN – V

OUT

OUT

x R

OUT

DROP

)

The overall power efficiency of the charge pump is

affected by four factors:

(1) Losses from power consumed by the internal

oscillator, switch drive, etc. (which vary with input
voltage, temperature and oscillator frequency).

2

(2) I

R losses due to the on–resistance of the MOSFET

switches on–board the charge pump.

(3) Charge pump capacitor losses due to effective

series resistance (ESR).

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Figure 2a. Ideal Switched Capacitor Model

R

EQUIV

EQUIV

+

f C1

V

out

1

C2

R

L

+

V

R

Figure 2b. Equivalent Output Resistance

3

MAX828 MAX829

Capacitor Selection

In order to maintain the lowest output resistance and
output ripple voltage, it is recommended that low ESR
capacitors be used. Additionally, larger values of C1 will
lower the output resistance and larger values of C2 will
reduce output ripple. (See Equation 3).

T able 1 shows various values of C1 and the corresponding
output resistance values at +25°C. It assumes a 0.1W ESR
and 0.5W RSW. Table 2 shows the output voltage ripple for
various values of C2. The V
output load current and 0.1W ESR

T able 1. Output Resistance vs. C1 (ESR = 0.1 Ω)

C1(µF)

0.1 1.7k 580

3.3 55 21

100 6.2 5.1

Table 2. Output Voltage Ripple vs. C2 (ESR = 0.1W) I
= 10mA

C2(µF) MAX828 V

3.3 250 87

100 8.3 2.9

MAX828 R

(W) MAX829 R

OUT

1 170 61

10 21 10
47 8.0 5.7

(mV) MAX829 V

RIPPLE

1 830 290

10 83 28
47 17 6.1

values assume 10mA

RIPPLE

.

C2

OUT

RIPPLE

(W)

OUT

(mV)

V

+

C3

3.3 mF*

+

OUT

15

C1

IN

2

–

C1

3

Voltage Inverter

C1

MAX828

MAX829

GND

C2

3.3 mF*

+

C1

3.3 mF*

4

*10 mF (MAX828)

in

V

out

+

R

L

Figure 3. T est Circuit

Cascading Devices

T wo or more MAX828/829’ s can be cascaded to increase
output voltage (Figure 4). If the output is lightly loaded, it
will be close to (- 2 x V

) but will droop at least by R

IN

OUT

of
the first device multiplied by the IQ of the second. It can be
seen that the output resistance rises rapidly for multiple
cascaded devices.

+

V

in

32

C1

+

4

MAX828
MAX829

“1”

32

C1

+

MAX828
MAX829

4

“n”

Input Supply Bypassing

The VIN input should be capacitively bypassed to reduce
AC impedance and minimize noise effects due to the
switching internal to the device. The recommended
capacitor depends on the configuration of the MAX828/829.

If the device is loaded from OUT to GND it is
recommended that a large value capacitor (at least equal to
C1) be connected from the input to GND. If the device is
loaded from IN to OUT a small (0.1µF) capacitor from IN
to OUT is sufficient.

V oltage Inverter

The most common application for charge pump devices is
the inverter (Figure 3). This application uses two external
capacitors - C1 and C2 (plus a power supply bypass
capacitor, if necessary). The output is equal to –V

plus any

IN

voltage drops due to loading. Refer to Table 1 and Table 2
for capacitor selection.

V

out

5

1

C2

5

+

V

= –nV

out

1

C2

+

in

Figure 4. Cascading MAX828s or MAX829s to

Increase Output V oltage

Paralleling Devices

T o reduce the value of R

, multiple MAX828/829s can

OUT

be connected in parallel (Figure 5). The output resistance
will be reduced by a factor of N where N is the number of
MAX828/829’s. Each device will require it’s own pump
capacitor (C1), but all devices may share one reservoir
capacitor (C2). However, to preserve ripple performance the
value of C2 should be scaled according to the number of
paralleled MAX828/829’s.

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