Rainbow Electronics MAX868 User Manual

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General Description

The MAX868 inverting charge pump provides a low-cost
and compact means of generating a regulated negative
voltage up to -2 x VINfrom a positive input voltage
between 1.8V and 5.5V. It uses a pulse-frequency­modulation (PFM) control scheme to generate the regulat­ed negative output voltage. PFM operation is obtained
by gating the internal 450kHz oscillator on and off as
needed to maintain output voltage regulation. This
unique on-demand switching scheme gives the MAX868
excellent light-load efficiency without degrading its full­load operation (up to 30mA), permitting smaller capaci­tors to take advantage of the oscillator’s high switching
frequency.

The MAX868 requires no inductors; only four capacitors
are required to build a complete DC-DC converter.
Output voltage regulation is achieved by adding just two
resistors. The MAX868 comes in a 10-pin µMAX pack­age, which is only 1.11mm high and occupies just half
the board area of a standard 8-pin SO.

________________________Applications

Small LCD Panels
Cell Phones
Cordless Phones
Camcorders
Handy-Terminals, PDAs
Medical Instruments
Battery-Operated Equipment

____________________________Features

♦ Regulated Negative Output Voltage

(up to -2 x VIN)

♦ Ultra-Small, 10-Pin µMAX Package
♦ On-Demand Switching at up to 450kHz
♦ 30µA Quiescent Supply Current
♦ Requires Only Four Small External Capacitors
♦ 1.8V to 5.5V Input Voltage Range
♦ 0.1µA Logic-Controlled Shutdown
♦ Up to 30mA Output Current

MAX868

Regulated, Adjustable -2x

Inverting Charge Pump

________________________________________________________________

Maxim Integrated Products

1

1
2
3
4
5

10

9
8
7
6

FB
SHDN
C2+
INPGND

C1-

OUT

GND

MAX868

µMAX

TOP VIEW

C2-C1+

Configuration

MAX868

C1+

IN

PGND

SHDN

GND

FB

OUT

0.1µF

1µF

2.2µF

V

OUT

= 0V TO -2 x V

IN

V

IN

= 1.8V TO 5.5V

0.1µF

C1-

C2+

C2-

Typical Operating Circuit

19-1290; Rev 1; 2/98

PART

MAX868C/D
MAX868EUB -40°C to +85°C

0°C to +70°C

TEMP. RANGE PIN-PACKAGE

Dice*
10 µMAX

Ordering Information

*

Dice are tested at TA= +25°C.

MAX868

Regulated, Adjustable -2x
Inverting Charge Pump

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(VIN= +3.3V, SHDN = IN, C1 = C2 = 0.22µF, CIN= 1µF, C

OUT

= 10µF, TA= 0°C to +85°C, unless otherwise noted. Typical values

are at T

A

= +25°C.)

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.

IN to GND.................................................................-0.3V to +6V

OUT to GND...........................................................+0.3V to -12V

IN to OUT.................................................................-0.3V to -17V

C1+ to GND........................................(V

IN

- 12V) to (VIN+ 0.3V)

C1- to GND.............................................................+0.3V to -12V

C2+ to GND....................................................(V

IN

+ 0.3V) to -6V

C2- to GND...............................................................+0.3V to -6V

SHDN, FB to GND .......................................-0.3V to (V

IN

+ 0.3V)

PGND to GND .......................................................-0.3V to +0.3V

Output Current....................................................................35mA

Short-Circuit Duration.................................................Continuous

Continuous Power Dissipation (T

A

= +70°C)

10-pin µMAX (derate 5.6mW/°C above +70°C)...........444mW

Operating Temperature Range

MAX868EUB....................................................-40°C to +85°C

Storage Temperature Range.............................-65°C to +160°C

Lead Temperature (soldering, 10sec).............................+300°C

FB = IN

No load, VFB= -50mV

RL= 3kΩ to GND

VIN= 5.5V, SHDN = IN or GND

VIN= 1.8V to 5.5V

SHDN = GND (OUT pulls to GND)

VIN= 1.8V to 5.5V, TA= +25°C

I

OUT

= 5mA, FB = IN

No load, SHDN = GND
VFB= 50mV

Closed loop

V

OUT

= -5V

CONDITIONS

nA-100 1 100

SHDN Input Bias Current

V

0.7V

IN

V

IH

SHDN Input Threshold

0.3V

IN

V

IL

nA-50 1 50FB Input Bias Current

mA

30

I

OUT

Output Current

12

mA5

I

IN

Supply Current

µA30 50

V1.8 5.5V

IN

Supply-Voltage Range

mV-30 30

15 50

R

OUT

Open-Loop Output
Resistance

Ω

125

70 100

µA0.1 1IIN,

SHDN

Shutdown Current

kHz

293 450 607

Oscillator Frequency

270 630

f

OSC

Ω0.2R

OUT,CL

Closed-Loop Output
Resistance

UNITSMIN TYP MAXSYMBOLPARAMETER

TA= +25°C
TA= 0°C to +85°C

TA= +25°C
TA= 0°C to +85°C

VIN= 3.3V, V

OUT

= -5V

VIN= 5V, V

OUT

= -3.3V

VIN= 1.8V to 5.5V

mV-40 40

FB Trip Point

TA= 0°C to +85°C

TA= +25°C

MAX868

Regulated, Adjustable -2x

Inverting Charge Pump

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS

(VIN= +3.3V, C1 = C2 = 0.22µF, CIN= 1µF, C

OUT

= 10µF, TA= -40°C to +85°C, unless otherwise noted. (Note 1)

Note 1: Specifications to -40°C are guaranteed by design, not production tested.

RL= 3kΩ to GND

VFB= 50mV

No load, VFB= -50mV
No load, SHDN = GND

CONDITIONS

kHz270 630f

OSC

Oscillator Frequency

µA1I

IN,SHDN

Shutdown Current

V1.8 5.5V

IN

Supply-Voltage Range

µA55I

IN

Supply Current

UNITSMIN TYP MAXSYMBOLPARAMETER

I

OUT

= 5mA, FB = IN

VIN= 1.8V to 5.5V

SHDN = GND (OUT pulls to GND)
VIN= 1.8V to 5.5V

nA-100 100FB Input Bias Current

mV-40 40FB Trip Point

125

Open-Loop Output
Resistance

Ω

50

R

OUT

VIN= 5.5V, SHDN = IN or GND

VIN= 1.8V to 5.5V

nA-100 100

SHDN Input Bias Current

V

0.7V

IN

V

IH

SHDN Input Threshold

0.3V

IN

V

IL

__________________________________________Typical Operating Characteristics

(Circuit of Figure 5, TA= +25°C, unless otherwise noted.)

-35

-25

-30

-20

-5

0

-10

-15

5

0 10 15 20 255 30 35 40 45 50

LOAD-REGULATION ERROR

vs. LOAD CURRENT

(V

IN

= 5V)

MAX868-01

LOAD CURRENT (mA)

LOAD-REGULATION ERROR (mV)

V

OUT

= -7.5V

V

OUT

= -3.3V

V

OUT

= -5V

-15

-9

-12

0

-3

-6

3

0 5 10 15 20 25

LOAD-REGULATION ERROR

vs. LOAD CURRENT

(V

IN

= 3.3V)

MAX868-02

LOAD CURRENT (mA)

LOAD-REGULATION ERROR (mV)

V

OUT

= -3.3V

V

OUT

= -5V

400

410

430

440

420

480
470
460
450

500
490

-40 -20 0 20 40 60 80 100

MAXIMUM SWITCHING FREQUENCY

vs. TEMPERATURE

MAX868-03

TEMPERATURE (°C)

MAXIMUM SWITCHING FREQUENCY (kHz)

FB = IN

VIN = 3.3V

VIN = 2V

VIN = 5V

MAX868

Regulated, Adjustable -2x
Inverting Charge Pump

4 _______________________________________________________________________________________

____________________________Typical Operating Characteristics (continued)

(Circuit of Figure 5, TA= +25°C, unless otherwise noted.)

0

0.01 10.1 10 100

EFFICIENCY vs. LOAD CURRENT

(V

IN

= 5V)

10

MAX868-04

LOAD CURRENT (mA)

EFFICIENCY (%)

50
40
30

20

60

70

80

V

OUT

= -5V

V

OUT

= -7.5V

V

OUT

= -3.3V

0

0.01 10.1 10 100

EFFICIENCY vs. LOAD CURRENT

(V

IN

= 3.3V)

10

MAX868-05

LOAD CURRENT (mA)

EFFICIENCY (%)

50
40
30

20

60

70

80

V

OUT

= -5V

V

OUT

= -3.3V

0

0.01 10.1 10 100

EFFICIENCY vs. LOAD CURRENT

(V

IN

= 5V)

10

MAX868-06

LOAD CURRENT (mA)

EFFICIENCY (%)

50
40
30

20

60

70

80

CIRCUIT OF FIGURE 6

V

OUT

= -2.5V

V

OUT

= -3.3V

0

60
40
20

100

80

180
160
140
120

200

-40 -20 0 20 40 60 80 100

OPEN-LOOP OUTPUT IMPEDANCE

vs. TEMPERATURE

(FB = IN, V

OUT

= -2 x VIN)

MAX868-07

TEMPERATURE (°C)

OUTPUT IMPEDANCE (Ω)

VIN = 2V

VIN = 3.3V

VIN = 5V

20µs/div

20mV/div

V

IN

= 3.3V, V

OUT

= -3.3V, I

LOAD

= 5mA,

V

OUT

AC COUPLED (20mV/div), C

OUT

= 10µF CERAMIC

OUTPUT VOLTAGE RIPPLE

(C

OUT

= 10µF CERAMIC)

MAX868-10

0

60
40
20

100

80

180
160
140
120

200

-40 -20 0 20 40 60 80 100

OPEN-LOOP OUTPUT IMPEDANCE

vs. TEMPERATURE

(FB = IN, V

OUT

= -VIN)

MAX868-08

TEMPERATURE (°C)

OUTPUT IMPEDANCE (Ω)

VIN = 2V

CIRCUIT OF FIGURE 6

VIN = 3.3V

VIN = 5V

20µs/div

20mV/div

V

IN

= 3.3V, V

OUT

= -3.3V, I

LOAD

= 5mA,

V

OUT

AC COUPLED (20mV/div), C

OUT

= 10µF (AVX TPS)

OUTPUT VOLTAGE RIPPLE
(C

OUT

= 10µF TANTALUM)

MAX868-09

20µs/div

20mV/div

V

IN

= 3.3V, V

OUT

= -3.3V, I

LOAD

= 5mA,

V

OUT

AC COUPLED (20mV/div), C

OUT

= 2.2µF CERAMIC

OUTPUT VOLTAGE RIPPLE

MAX868-11

200µs/div

10mA/div

20mV/div

V

IN

= 5V, V

OUT

= -5V, I

OUT

= 1mA TO 11mA STEP

LOAD-TRANSIENT RESPONSE

MAX868-12