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________________General Description
The MAX1673 charge-pump inverter provides a low-
cost, compact means of generating a regulated nega-
tive output from a positive input at up to 125mA. It
requires only three small capacitors, and only two resis-
tors to set its output voltage. The input range is 2V to
5.5V. The regulated output can be set from 0V to -VIN in
Skip regulation mode or -1.5V to -VIN in 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 quies-
cent 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 constant-
frequency ripple, which is easily filtered for low-noise
applications.
This device also features a 1µA logic-controlled shut-
down 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
8
7
IN
GNDCAP+
CAP-
LIN/SKIP
SO
TOP VIEW
3
4
6
5
MAX1673
MAX1673
IN
INPUT 2V TO 5.5V
REGULATED
NEGATIVE
OUTPUT
(UP TO -1 x VIN,
UP TO 125mA)
LIN/SKIP
FB
OUT
GND
CAP+
ON OFF SHDN
CAP-
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.
MAX1673
Regulated, 125mA-Output,
Charge-Pump DC-DC Inverter
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VIN = VSHDN = +5V, CIN = 10µF, COUT = 22µF, CFLY = 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 (VIN + 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 (TA= +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 ∆VLDR
0.01 %/mA
0.005
LIN/SKIP = IN
(LIN mode)
LIN/SKIP = GND
(Skip mode)
IOUT = 25mA to
125mA, Figure 1
LIN/SKIP = GND
(Skip mode)
LIN/SKIP = IN
(LIN mode)
SHDN = GND
VFB = -25mV, VOUT = -3V,
LIN/SKIP = GND (Skip mode)
VFB = -100mV, VOUT = -3V,
LIN/SKIP = IN (LIN mode)
LIN/SKIP = GND
(Skip mode)
LIN/SKIP = IN
(LIN mode)
R1 =100kΩ, ±1%,
R2 = 60.4kΩ, ±1%,
IOUT = 0mA to
125mA, Figure 1
PARAMETER SYMBOL MIN TYP MAX UNITS
Output Voltage VOUT
-2.90 -3.02 -3.15
Maximum Output Current IOUT(MAX) 125 mA
Minimum Output Voltage -1.5
-2.92 -3.02 -3.12
V
Input Voltage Range VIN 2.0 5.5 V
2.7 5.5
VOUT 0V
Quiescent Current (IIN Current) IQ
816 mA
0.035 0.2
Shutdown Current (IIN Current) ISHDN 0.1 1 µA
Line Regulation ∆VLNR
0.01 %/V
1
Open-Loop Output Resistance
(Dropout) RO3.5 10 Ω
CONDITIONS
LIN/SKIP = IN
VIN = 4.5V to 5.5V,
Figure 4,
VREF ≠VIN
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 = VSHDN = +5V, CIN = 10µF, COUT = 22µF, CFLY = 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)VIL 0.3 x VIN V2V ≤VIN ≤5.5V
Logic High Input
(SHDN, LIN/SKIP)VIH 0.7 x VIN V2V ≤VIN ≤5.5V
FB Input Bias Current IFB
150 600 nA
LIN/SKIP = IN
(LIN mode)
PARAMETER SYMBOL MIN TYP MAX UNITS
FB Threshold VFBT -25 0 25 mV
Switching Frequency
(LIN Mode) ƒOSC 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, CFLY = 2.2µF, COUT = 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)
COUT = 10µF
CFLY = COUT
10
COUT = 22µF
COUT = 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)
COUT = 10µF
COUT = 22µF
COUT = 47µF
CFLY = COUT
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)
VOUT (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 = 3.5VVIN = 4V
VIN = 5V
CIRCUIT OF FIGURE 4
VREF ≠ VIN
0
4
2
8
6
10
12
TA = +25°C
2 43 5 6
DROPOUT OUTPUT RESISTANCE
vs. INPUT VOLTAGE
MAX1673 TOC07
VIN (V)
RDROPOUT (Ω)
TA = +85°C
TA = -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
VREF ≠ VIN
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
VOUT = -3V
CIRCUIT OF FIGURE 4
VREF ≠ VIN
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
VREF ≠ VIN
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
VOUT
50mV/div
25mA
125mA
IOUT
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
VIN
2V/div
LINE-TRANSIENT RESPONSE (LIN MODE)
MAX1673 TOC12
50µs/div
IOUT = 100mA
CIRCUIT OF FIGURE 4
VOUT
50mV/div
4.5V
5.5V
VIN
2V/div
LINE-TRANSIENT RESPONSE (SKIP MODE)
MAX1673 TOC13
50µs/div
IOUT = 100mA
CIRCUIT OF FIGURE 4
Typical Operating Characteristics (continued)
(Circuit of Figure 1, VIN = +5V, CFLY = 2.2µF, COUT = 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 applica-
tions, 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 out-
put 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
(CFLY) 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 CFLY 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
CIN
10µF
COUT
22µF
CFLY
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
COUT
CFLY
S1 CAP+
CAP-
IN
S4
S3
350kHz
Figure 2. Charging CFLY
S2 OUT
COUT
CFLY
S1
IN
S4
S3
350kHz
CAP+
CAP-
Figure 3. Transferring Charge on CFLY to COUT
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 regula-
tion 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 con-
tinuously at 350kHz. The MAX1673 controls the charge
on CFLY by varying the gate drive on S1 (Figure 2).
When the output voltage falls, CFLY charges faster due
to increased gate drive. Since the device switches con-
tinuously, the regulation scheme minimizes output ripple,
the output noise contains well-defined frequency compo-
nents, 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 VOUT 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 VOUT depends on the accuracy of the
voltage biasing the voltage-divider network (R1, R2).
Use a separate reference voltage if VIN is an unregulat-
ed voltage or if greater accuracy is desired (Figure 4).
Adjust the output voltage from -1.5V to -VIN in LIN
mode or 0V to -VIN in Skip mode with external resistors
R1 and R2 as shown in Figures 1 and 4. In either regu-
lating mode (LIN or Skip), FB servos to 0V. Use the
following equations to select R1 and R2 for the desired
output voltage:
where VREF can be either VIN or some other positive
reference source.
Typically, choose a voltage-divider current of 50µA to
minimize the effect of FB input current:
R1 = VREF / 50µA
R2 = -VOUT / 50µA
Capacitor Selection
A CFLY 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
CFLY, due to their small size, low cost, and low equiva-
lent series resistance (ESR). To ensure proper opera-
tion over the entire temperature range, choose ceramic
capacitors with X7R (or equivalent) low-temperature-
coefficient (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 capaci-
tance values of CFLY and COUT, and the ESR of COUT.
The ESR ripple contribution occurs as COUT charges.
The charging current creates a negative voltage pulse
across the capacitor’s ESR that recedes as COUT
charges. At equilibrium, when the voltage on CFLY
approaches that on COUT, no charging current flows.
Secondly, the ripple contribution due to charge transfer
between capacitors creates a pulse as charge flows to
COUT. Adding the two terms does not determine peak-
to-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 COUT 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
CIN
10µF
COUT
22µF
CFLY
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
VREF
5V
VOUT = -VREF x
R2
R1
Figure 4. Separate VREF 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 CFLY and COUT are their respective capacitance
values, ESRCOUT is the equivalent series resistance of
COUT, ROUT is the MAX1673 open-loop output imped-
ance (typically 3.5Ω, and fOSC is the MAX1673 switch-
ing frequency (typically 350kHz). If ESRCOUT is very
small, as is likely when ceramic capacitors are used,
VRIPPLE (TRANSFER) dominates. If ESR is relatively
large, as with low-cost tantalum capacitors, then VRIP-
PLE (ESR) dominates.
When operating in LIN mode, use the following equa-
tion to approximate peak-to-peak output voltage ripple:
where COUT is the output capacitor value, ESRCOUT is
the output capacitor’s ESR, and fOSC 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 COUT is the output capacitor value, and fMIN 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.
COUT = 75 x 10-6 R1
R1 + R2 OUT
I
V = I
2 f C 2I ESR
RIPPLE OUT
OSC OUT OUT COUT
+
Vf R (C C )
RIPPLE(ESR) = 2 VIN – VOUT
OSC
1
OUT FLY OUT
+
V 8 fRC
RIPPLE(ESR) = VIN – VOUT
OSC
ESRCOUT
2
OUT FLY
PRODUCTION METHOD MANUFACTURER SERIES PHONE FAX
Surface-Mount Tantalum AVX TPS (803) 946-0690 (803) 448-2170
Matsuo 267 (714) 969-2491 (714) 960-6492
Sprague 593D, 595D (603) 224-1961 (603) 224-1430
Surface-Mount Ceramic AVX X7R (803) 946-0590 (803) 626-3123
Matsuo X7R (714) 969-2491 (714) 960-6492
Table 1. Partial Listing of Capacitor Vendors
___________________Chip Information
TRANSISTOR COUNT: 386
SUBSTRATE CONNECTED TO: IN
