Rainbow Electronics MAX1673 User Manual

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For small orders, phone [phone] ext. 3468.

________________General Description

The MAX1673 charge-pump inverter provides a low­cost, compact means of generating a regulated nega­tive output from a positive input at up to 125mA. It
requires only three small capacitors, and only two resis­tors to set its output voltage. The input range is 2V to

5.5V. The regulated output can be set from 0V to -VINin
Skip regulation mode or -1.5V to -VINin Linear (LIN)
regulation mode.

In Skip mode, the MAX1673 regulates by varying its
switching frequency as a function of load current. This
On-Demand™ switching gives the MAX1673 two
advantages: very small capacitors and very low quies­cent supply current. At heavy loads, it transfers energy
from the input to the output by switching at up to
350kHz. It switches more slowly at light loads, using
only 35µA quiescent supply current.

In Linear mode, the MAX1673 switches at a constant
350kHz at all loads and regulates by controlling
the current-path resistance. This provides constant­frequency ripple, which is easily filtered for low-noise
applications.

This device also features a 1µA logic-controlled shut­down mode and is available in a standard 8-pin SO
package. For a device that delivers about 10mA and
fits in a smaller package, refer to the MAX868.

________________________Applications

Hard Disk Drives Measurement Instruments
Camcorders Modems
Analog Signal-Processing Digital Cameras

Applications

____________________________Features

♦ Regulated Negative Output Voltage

(up to -1 x VIN)

♦ 125mA Output Current
♦ 35µA Quiescent Supply Current

(Skip-mode regulation)

♦ 350kHz Fixed-Frequency, Low-Noise Output

(Linear-mode regulation)

♦ 2V to 5.5V Input Range
♦ 1µA Logic-Controlled Shutdown

MAX1673

Regulated, 125mA-Output,

Charge-Pump DC-DC Inverter

________________________________________________________________

Maxim Integrated Products

1

FB

OUTSHDN

1
2

87IN

GNDCAP+

CAP-

LIN/SKIP

SO

TOP VIEW

3

4

6

5

MAX1673

Typical Operating Circuit

___________________Pin Configuration

19-1334; Rev 0; 1/98

PART

MAX1673ESA -40°C to +85°C

TEMP. RANGE PIN-PACKAGE

8 SO

_______________Ordering Information

On-Demand™ is a trademark of Maxim Integrated Products.

INPUT 2V TO 5.5V

ON

OFF

IN

SHDN

MAX1673

CAP+

CAP-

LIN/SKIP

FB

OUT

GND

REGULATED

NEGATIVE

OUTPUT

(UP TO -1 x V

UP TO 125mA)

,

IN

MAX1673

Regulated, 125mA-Output,
Charge-Pump DC-DC Inverter

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(VIN= V

SHDN

= +5V, CIN= 10µF, C

OUT

= 22µF, C

FLY

= 2.2µF, TA= -40°C to +85°C, unless otherwise noted. Typical values are at

TA= +25°C.) (Note 2)

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..............................................................................-0.3V to +6V

CAP+, FB, LIN/SKIP.....................................-0.3V to (V

IN

+ 0.3V)

SHDN........................................................................-0.3V to +6V

OUT, CAP-................................................................-6V to +0.3V

Continuous Output Current...............................................135mA

Output Short-Circuit Duration to GND (Note 1)....................1sec

Continuous Power Dissipation (T

A

= +70°C)

(derate 5.88mW/°C above +70°C)...............................450mW

Operating Temperature Range ...........................-40°C to +85°C

Junction Temperature......................................................+150°C

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

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

Note 1: Shorting OUT to IN may damage the device and should be avoided.

Output Resistance to Ground
in Shutdown Mode

1 5 Ω

SHDN = GND

Load Regulation ∆V

LDR

0.01
%/mA

0.005

LIN/SKIP = IN
(LIN mode)

LIN/SKIP = GND
(Skip mode)

I

OUT

= 25mA to

125mA, Figure 1

LIN/SKIP = GND
(Skip mode)

LIN/SKIP = IN
(LIN mode)

SHDN = GND

VFB= -25mV, V

OUT

= -3V,

LIN/SKIP = GND (Skip mode)

VFB= -100mV, V

OUT

= -3V,

LIN/SKIP = IN (LIN mode)

LIN/SKIP = GND
(Skip mode)

LIN/SKIP = IN
(LIN mode)

R1 =100kΩ, ±1%,
R2 = 60.4kΩ, ±1%,
I

OUT

= 0mA to

125mA, Figure 1

PARAMETER SYMBOL MIN TYP MAX UNITS

Output Voltage V

OUT

-2.90 -3.02 -3.15

Maximum Output Current I

OUT(MAX)

125 mA

Minimum Output Voltage

-1.5

-2.92 -3.02 -3.12

V

Input Voltage Range V

IN

2.0 5.5
V

2.7 5.5

V

OUT

0

V

Quiescent Current (IINCurrent)

I

Q

8 16

mA

0.035 0.2

Shutdown Current (IINCurrent) I

SHDN

0.1 1 µA

Line Regulation ∆V

LNR

0.01
%/V

1

Open-Loop Output Resistance
(Dropout)

R

O

3.5 10 Ω

CONDITIONS

LIN/SKIP = IN

VIN= 4.5V to 5.5V,
Figure 4,
V

REF

≠ V

IN

LIN/SKIP = GND (Skip mode)
LIN/SKIP = IN (LIN mode)
LIN/SKIP = GND

LIN/SKIP = GND (Skip mode)

VFB= -25mV

MAX1673

Regulated, 125mA-Output,

Charge-Pump DC-DC Inverter

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(VIN= V

SHDN

= +5V, CIN= 10µF, C

OUT

= 22µF, C

FLY

= 2.2µF, TA= -40°C to +85°C, unless otherwise noted. Typical values are at

TA= +25°C.) (Note 2)

Note 2: Specifications to -40°C are guaranteed by design, not production tested.

Logic Low Input
(SHDN, LIN/SKIP)

V

IL

0.3 x V

IN

V2V ≤ VIN≤ 5.5V

Logic High Input
(SHDN, LIN/SKIP)

V

IH

0.7 x V

IN

V2V ≤ VIN≤ 5.5V

FB Input Bias Current I

FB

150 600

nA

LIN/SKIP = IN
(LIN mode)

PARAMETER SYMBOL MIN TYP MAX UNITS

FB Threshold V

FBT

-25 0 25 mV

Switching Frequency
(LIN Mode)

ƒ

OSC

250 350 460

kHz

CONDITIONS

Input Bias Current
(SHDN, LIN/SKIP)

LIN/SKIP = GND (Skip mode)

TA= +25°C

1 µA

1 100

LIN/SKIP = GND
(Skip mode)

VFB= -25mV

TA= -40°C to +85°C 205 515

MAX1673

Regulated, 125mA-Output,
Charge-Pump DC-DC Inverter

4 _______________________________________________________________________________________

Typical Operating Characteristics

(Circuit of Figure 1, VIN= +5V, C

FLY

= 2.2µF, C

OUT

= 22µF, TA= +25°C, unless otherwise noted.)

0

40

20

80

60

120

100

140

0 50 7525 100 125 150

OUTPUT RIPPLE

vs. LOAD CURRENT (LIN MODE)

MAX1673 RTOC01

LOAD CURRENT (mA)

PEAK-TO-PEAK RIPPLE (mV)

C

OUT

= 10µF

C

FLY

=

C

OUT

10

C

OUT

= 22µF

C

OUT

= 47µF

0

50

150

100

200

250

0 5025 75 100 125 150

OUTPUT RIPPLE

vs. LOAD CURRENT (SKIP MODE)

MAX1673 TOC02

LOAD CURRENT (mA)

PEAK-TO-PEAK RIPPLE (mV)

C

OUT

= 10µF

C

OUT

= 22µF

C

OUT

= 47µF

C

FLY

=

C

OUT

10

-2.98

-3.01

-3.00

-2.99

-3.02

-3.03

-3.04

-3.05

-3.06

-3.07

-3.08

0 5025 75 100 125 150

OUTPUT VOLTAGE

vs. LOAD CURRENT

MAX1673 TOC03

LOAD CURRENT (mA)

V

OUT

(V)

LIN MODE

SKIP MODE

0

30
20
10

50
40

90
80
70
60

100

0 20 40 60 80 100 120 140

EFFICIENCY vs. LOAD CURRENT

(SKIP MODE)

MAX1673 TOC04

LOAD CURRENT (mA)

EFFICIENCY (%)

VIN = 3.5V

VIN = 4V

VIN = 5V

CIRCUIT OF FIGURE 4

V

REF

≠ V

IN

0

4

2

8

6

10

12

T

A

= +25°C

2 43 5 6

DROPOUT OUTPUT RESISTANCE

vs. INPUT VOLTAGE

MAX1673 TOC07

VIN (V)

R

DROPOUT

(Ω)

TA = +85°C

T

A

= -40°C

0

20
10

50
40
30

80
70
60

90

0 40 6020 80 100 120 140

EFFICIENCY vs. LOAD CURRENT

(LIN MODE)

MAX1673 TOC05

LOAD CURRENT (mA)

EFFICIENCY (%)

VIN = 4V

VIN = 4.5V

VIN = 5V

CIRCUIT OF FIGURE 4

V

REF

≠ V

IN

30

50

40

70

60

80

90

3.5 4.54.0 5.0 5.5 6.0

EFFICIENCY vs. INPUT VOLTAGE

MAX1673 TOC06

VIN (V)

EFFICIENCY (%)

SKIP MODE

LIN MODE

100mA LOAD
V

OUT

= -3V

CIRCUIT OF FIGURE 4

V

REF

≠ V

IN

0

4

2

8

6

10

12

2 43 5 6

QUIESCENT CURRENT vs. INPUT VOLTAGE

(LIN MODE)

MAX1673 TOC08

VIN (V)

QUIESCENT CURRENT (mA)

DOES NOT INCLUDE BIAS CURRENT
FOR RESISTOR DIVIDER

V

REF

≠ V

IN

CIRCUIT OF FIGURE 4

0

20
15
10

5

35
30
25

40

45

2 43 5 6

QUIESCENT CURRENT vs. INPUT VOLTAGE

(SKIP MODE)

MAX1673 TOC09

VIN (V)

QUIESCENT CURRENT (µA)

DOES NOT INCLUDE BIAS CURRENT
FOR RESISTOR DIVIDER

MAX1673

Regulated, 125mA-Output,

Charge-Pump DC-DC Inverter

_______________________________________________________________________________________ 5

V

OUT

50mV/div

25mA

125mA

I

OUT

100mA/div

LOAD-TRANSIENT RESPONSE (LIN MODE)

MAX1673 TOC10

250µs/div

CIRCUIT OF FIGURE 4

V

OUT

50mV/div

25mA

125mA

LOAD-TRANSIENT RESPONSE (SKIP MODE)

MAX1673 TOC11

250µs/div

CIRCUIT OF FIGURE 4

I

OUT

100mA/div

V

OUT

50mV/div

4.5V

5.5V

V

IN

2V/div

LINE-TRANSIENT RESPONSE (LIN MODE)

MAX1673 TOC12

50µs/div

I

OUT

= 100mA

CIRCUIT OF FIGURE 4

V

OUT

50mV/div

4.5V

5.5V

V

IN

2V/div

LINE-TRANSIENT RESPONSE (SKIP MODE)

MAX1673 TOC13

50µs/div

I

OUT

= 100mA

CIRCUIT OF FIGURE 4

Typical Operating Characteristics (continued)

(Circuit of Figure 1, VIN= +5V, C

FLY

= 2.2µF, C

OUT

= 22µF, TA= +25°C, unless otherwise noted.)

MAX1673

Detailed Description

The MAX1673 new-generation, high-output-current,
regulated charge-pump DC-DC inverter provides up to
125mA. Designed specifically for compact applica­tions, a complete regulating circuit requires only three
small capacitors and two resistors. The MAX1673
employs On-Demand™ regulation circuitry, providing
output regulation modes optimized for either lowest out­put noise or lowest supply current. In addition, the
MAX1673 includes shutdown control.

In Linear (LIN) mode or when heavily loaded in Skip
mode, the charge pump runs continuously at 350kHz.
During one-half of the oscillator period, switches S1 and
S2 close (Figure 2), charging the transfer capacitor
(C

FLY

) to the input voltage (CAP- = GND, and CAP+ =
IN). During the other half cycle, switches S3 and S4
close (Figure 3), transferring the charge on C

FLY

to the

output capacitor (CAP+ = GND, CAP- = OUT).

Regulated, 125mA-Output,
Charge-Pump DC-DC Inverter

6 _______________________________________________________________________________________

______________________________________________________________Pin Description

MAX1673

IN

INPUT

5.0V

OUTPUT

-3V

C

IN

10µF

C

OUT

22µF

C

FLY

2.2µF

LIN/SKIP

FB

R1
100k

R1

60.4k

OUT

GND

CAP+

ON

OFF

4

2

3

SHDN

CAP-

LIN

SKIP

1

7

5

6

8

Figure 1. Standard Application Circuit

S2

OUT

C

OUT

C

FLY

S1

CAP+

CAP-

IN

S4

S3

350kHz

Figure 2. Charging C

FLY

S2

OUT

C

OUT

C

FLY

S1

IN

S4

S3

350kHz

CAP+

CAP-

Figure 3. Transferring Charge on C

FLY

to C

OUT

Inverting Charge-Pump OutputOUT5
Feedback Input. Connect FB to a resistor-divider from IN (or other reference source) to OUT for regulated

output voltages (Figures 1 and 4).

FB6

GroundGND7
Power-Supply Positive Voltage InputIN8

Shutdown Control Input. Drive SHDN low to shut down the MAX1673. Connect SHDN to IN for normal
operation. OUT connects to GND through a 1Ω (typical) resistor in shutdown mode.

SHDN

4

Negative Terminal of Flying CapacitorCAP-3

PIN

Positive Terminal of Flying CapacitorCAP+2

Regulation-Mode Select Input. Driving LIN/SKIP high or connecting it to IN selects LIN mode, with regula­tion accomplished by modulating switch resistance. Driving LIN/SKIP low or connecting it to GND selects
Skip mode, where the device regulates by skipping charge-pump pulses.

LIN/SKIP

1

FUNCTIONNAME

Linear Mode (Constant-Frequency Mode)

In LIN mode (LIN/SKIP = IN), the charge pump runs con­tinuously at 350kHz. The MAX1673 controls the charge
on C

FLY

by varying the gate drive on S1 (Figure 2).

When the output voltage falls, C

FLY

charges faster due
to increased gate drive. Since the device switches con­tinuously, the regulation scheme minimizes output ripple,
the output noise contains well-defined frequency compo­nents, and the circuit requires much smaller external
capacitors than in Skip mode for a given output ripple.*
However, LIN mode is less efficient than Skip mode due
to higher operating current (8mA typical).

Skip Mode

In Skip mode (LIN/SKIP = GND), the device switches
only as needed to maintain regulation on FB. Switching
cycles are skipped until the voltage on FB rises above
GND. Skip mode has higher output noise than LIN
mode, but minimizes operating current.

Shutdown Mode

When SHDN (a CMOS-compatible input) is driven low,
the MAX1673 enters low-power shutdown mode.
Charge-pump switching action halts and an internal 1Ω
switch pulls V

OUT

to ground. Connect SHDN to IN or

drive high for normal operation.

*See Output Ripple vs. Load Current in

Typical Operating Characteristics

.

Applications Information

Resistor Selection

(Output Voltage Selection)

The accuracy of V

OUT

depends on the accuracy of the
voltage biasing the voltage-divider network (R1, R2).
Use a separate reference voltage if VINis an unregulat­ed voltage or if greater accuracy is desired (Figure 4).

Adjust the output voltage from -1.5V to -VINin LIN
mode or 0V to -VINin Skip mode with external resistors
R1 and R2 as shown in Figures 1 and 4. In either regu­lating mode (LIN or Skip), FB servos to 0V. Use the
following equations to select R1 and R2 for the desired
output voltage:

where V

REF

can be either VINor some other positive

reference source.
Typically, choose a voltage-divider current of 50µA to

minimize the effect of FB input current:

R1 = V

REF

/ 50µA

R2 = -V

OUT

/ 50µA

Capacitor Selection

A C

FLY

value of 1µF or more is sufficient to supply the
specified load current. However, for minimum ripple in
Skip mode, this value may need to be increased.
Maxim recommends 2.2µF.

Surface-mount ceramic capacitors are preferred for
C

FLY

, due to their small size, low cost, and low equiva­lent series resistance (ESR). To ensure proper opera­tion over the entire temperature range, choose ceramic
capacitors with X7R (or equivalent) low-temperature­coefficient (tempco) dielectrics. See Table 1 for a list of
suggested capacitor suppliers.

The output capacitor stores the charge transferred from
the flying capacitor and services the load between
oscillator cycles. A good general rule is to make the
output capacitance at least ten times greater than that
of the flying capacitor.

When in Skip mode, output ripple depends mostly on
two parameters: charge transfer between the capaci­tance values of C

FLY

and C

OUT

, and the ESR of C

OUT

.

The ESR ripple contribution occurs as C

OUT

charges.
The charging current creates a negative voltage pulse
across the capacitor’s ESR that recedes as C

OUT

charges. At equilibrium, when the voltage on C

FLY

approaches that on C

OUT

, no charging current flows.
Secondly, the ripple contribution due to charge transfer
between capacitors creates a pulse as charge flows to
C

OUT

. Adding the two terms does not determine peak­to-peak ripple because their peaks do not occur at the
same time. It is best to use only the dominant term. The
expression for the ripple component predominantly due
to C

OUT

ESR is:

V = -V

R2

R1

OUT

REF

MAX1673

Regulated, 125mA-Output,

Charge-Pump DC-DC Inverter

_______________________________________________________________________________________ 7

MAX1673

IN

INPUT

5.0V

OUTPUT

-3V

C

IN

10µF

C

OUT

22µF

C

FLY

2.2µF

LIN/SKIP

FB

R1

100k

R2

60.4k

OUT

GND

CAP+

ON

OFF

4

2

3

SHDN

CAP-

LIN

SKIP

1

7

5

6

8

V

REF

5V

V

OUT = -VREF

x

R2
R1

Figure 4. Separate V

REF

for Voltage Divider

MAX1673

Regulated, 125mA-Output,
Charge-Pump DC-DC Inverter

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.

8

_____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600

© 1998 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

The expression for the ripple component predominantly
due to charge transfer is:

where C

FLY

and C

OUT

are their respective capacitance

values, ESR

COUT

is the equivalent series resistance of

C

OUT

, R

OUT

is the MAX1673 open-loop output imped-

ance (typically 3.5Ω, and f

OSC

is the MAX1673 switch-

ing frequency (typically 350kHz). If ESR

COUT

is very
small, as is likely when ceramic capacitors are used,
V

RIPPLE (TRANSFER)

dominates. If ESR is relatively

large, as with low-cost tantalum capacitors, then V

RIP-

PLE (ESR)

dominates.

When operating in LIN mode, use the following equa­tion to approximate peak-to-peak output voltage ripple:

where C

OUT

is the output capacitor value, ESR

COUT

is

the output capacitor’s ESR, and f

OSC

is the MAX1673

oscillator frequency (typically 350kHz).
To ensure LIN mode stability over the entire tempera-

ture range, choose a low-ESR (no more than 100mΩ)
output capacitance using the following equation:

where C

OUT

is the output capacitor value, and f

MIN

is
the minimum oscillator frequency (250kHz). See Table
1 for a list of suggested capacitor suppliers.

Layout Considerations

The MAX1673’s high oscillator frequency requires good
layout technique, which ensures stability and helps
maintain the output voltage under heavy loads. Take
the following steps to ensure good layout:

• Mount all components as close together as possible.

• Place the feedback resistors R1 and R2 close to the

FB pin, and minimize the PC trace length at the FB
circuit node.

• Keep traces short to minimize parasitic inductance

and capacitance.

• Use a ground plane.

C

OUT

=75 x 10

-6

R1

R1 + R2

OUT











I

V =

I

2 f C

2I ESR

RIPPLE

OUT

OSC OUT

OUT COUT

+

V

f R

(C C

)

RIPPLE(ESR)

= 2

VIN – V

OUT

OSC

1

OUT

FLY OUT

 





































+

V 8

f

R

C

RIPPLE(ESR)

=

VIN – V

OUT

OSC

ESR

COUT

2

OUT FLY

 





































PRODUCTION METHOD MANUFACTURER SERIES PHONE FAX

Surface-Mount Tantalum

AVX TPS [phone] [phone]
Matsuo 267 [phone] [phone]
Sprague 593D, 595D [phone] [phone]

Surface-Mount Ceramic

AVX X7R [phone] [phone]
Matsuo X7R [phone] [phone]

Table 1. Partial Listing of Capacitor Vendors

___________________Chip Information

TRANSISTOR COUNT: 386
SUBSTRATE CONNECTED TO: IN