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19-1334; Rev 0; 1/98
Regulated, 125mA-Output, Charge-Pump DC-DC Inverter
________________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 -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-DemandTM 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 35A 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 1A 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.
____________________________Features
o Regulated Negative Output Voltage (up to -1 x VIN) o 125mA Output Current o 35A Quiescent Supply Current (Skip-mode regulation) o 350kHz Fixed-Frequency, Low-Noise Output (Linear-mode regulation) o 2V to 5.5V Input Range o 1A Logic-Controlled Shutdown
MAX1673
_______________Ordering Information
PART MAX1673ESA TEMP. RANGE -40C to +85C PIN-PACKAGE 8 SO
________________________Applications
Hard Disk Drives Camcorders Analog Signal-Processing Applications Measurement Instruments Modems Digital Cameras
Typical Operating Circuit
INPUT 2V TO 5.5V
___________________Pin Configuration
TOP VIEW
LIN/SKIP CAP+ CAP1 2 8 7 IN CAP+ GND FB OUT CAPLIN/SKIP GND ON OFF SHDN IN FB REGULATED NEGATIVE OUTPUT (UP TO -1 x VIN, UP TO 125mA)
MAX1673
OUT
MAX1673
3 6 5 SHDN 4
SO
On-DemandTM is a trademark of Maxim Integrated Products.
________________________________________________________________ Maxim Integrated Products 1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800. For small orders, phone 408-737-7600 ext. 3468.
Regulated, 125mA-Output, Charge-Pump DC-DC Inverter MAX1673
ABSOLUTE MAXIMUM RATINGS
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 = +70C) (derate 5.88mW/C above +70C) ...............................450mW Operating Temperature Range ...........................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +160C Lead Temperature (soldering, 10sec) .............................+300C
Note 1: Shorting OUT to IN may damage the device and should be avoided.
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.
ELECTRICAL CHARACTERISTICS
(VIN = V SHDN = +5V, CIN = 10F, COUT = 22F, CFLY = 2.2F, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 2) PARAMETER Input Voltage Range Minimum Output Voltage Maximum Output Current SYMBOL VIN VOUT IOUT(MAX) LIN/SKIP = IN R1 =100k, 1%, (LIN mode) R2 = 60.4k, 1%, IOUT = 0mA to 125mA, Figure 1 LIN/SKIP = GND (Skip mode) VFB = -100mV, VOUT = -3V, LIN/SKIP = IN (LIN mode) Quiescent Current (IIN Current) IQ ISHDN VFB = -25mV, VOUT = -3V, LIN/SKIP = GND (Skip mode) SHDN = GND VIN = 4.5V to 5.5V, Figure 4, VREF VIN LIN/SKIP = IN (LIN mode) LIN/SKIP = GND (Skip mode) LIN/SKIP = IN (LIN mode) LIN/SKIP = GND (Skip mode) LIN/SKIP = GND (Skip mode) SHDN = GND CONDITIONS LIN/SKIP = GND (Skip mode) LIN/SKIP = IN (LIN mode) LIN/SKIP = GND LIN/SKIP = IN -1.5 125 -2.90 -3.02 -3.15 V -2.92 -3.02 -3.12 MIN 2.0 2.7 0 TYP MAX 5.5 5.5 UNITS V V mA
Output Voltage
VOUT
8 0.035 0.1 0.01
16 mA 0.2 1 A
Shutdown Current (IIN Current)
Line Regulation
VLNR
%/V 1 0.01 %/mA 0.005 3.5 1 10 5
Load Regulation
VLDR
IOUT = 25mA to 125mA, Figure 1
Open-Loop Output Resistance (Dropout) Output Resistance to Ground in Shutdown Mode
RO
2
_______________________________________________________________________________________
Regulated, 125mA-Output, Charge-Pump DC-DC Inverter
ELECTRICAL CHARACTERISTICS (continued)
(VIN = V SHDN = +5V, CIN = 10F, COUT = 22F, CFLY = 2.2F, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 2) PARAMETER Switching Frequency (LIN Mode) FB Threshold SYMBOL OSC VFBT TA = +25C TA = -40C to +85C LIN/SKIP = GND (Skip mode) LIN/SKIP = IN (LIN mode) LIN/SKIP = GND (Skip mode) CONDITIONS MIN 250 205 -25 0 150 VFB = -25mV VFB = -25mV 1 100 1 VIH VIL 2V VIN 5.5V 2V VIN 5.5V 0.7 x VIN 0.3 x VIN A V V TYP 350 MAX 460 515 25 600 nA UNITS kHz mV
MAX1673
FB Input Bias Current
IFB
Input Bias Current (SHDN, LIN/SKIP) Logic High Input (SHDN, LIN/SKIP) Logic Low Input (SHDN, LIN/SKIP)
Note 2: Specifications to -40C are guaranteed by design, not production tested.
_______________________________________________________________________________________
3
Regulated, 125mA-Output, Charge-Pump DC-DC Inverter MAX1673
Typical Operating Characteristics
(Circuit of Figure 1, VIN = +5V, CFLY = 2.2F, COUT = 22F, TA = +25C, unless otherwise noted.)
OUTPUT RIPPLE vs. LOAD CURRENT (LIN MODE)
MAX1673 RTOC01
OUTPUT RIPPLE vs. LOAD CURRENT (SKIP MODE)
MAX1673 TOC02
OUTPUT VOLTAGE vs. LOAD CURRENT
-3.07 -3.06 -3.05 VOUT (V) SKIP MODE
MAX1673 TOC03
140 120 PEAK-TO-PEAK RIPPLE (mV) 100 COUT = 22F 80 60 40 20 0 0 25 50 75 100 125 COUT = 47F C CFLY = OUT 10 COUT = 10F
250 COUT = 10F PEAK-TO-PEAK RIPPLE (mV) 200
-3.08
150 COUT = 22F 100 COUT = 47F C CFLY = OUT 10 0 25 50 75 100 125 150 LOAD CURRENT (mA)
-3.04 -3.03 -3.02 -3.01
50
-3.00 -2.99 -2.98 0 25 50 75 100
LIN MODE
0 150 LOAD CURRENT (mA)
125
150
LOAD CURRENT (mA)
EFFICIENCY vs. LOAD CURRENT (SKIP MODE)
MAX1673 TOC04
EFFICIENCY vs. LOAD CURRENT (LIN MODE)
MAX1673 TOC05
EFFICIENCY vs. INPUT VOLTAGE
MAX1673 TOC06
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 0 VREF VIN CIRCUIT OF FIGURE 4 20 40 60 80 100 120 VIN = 3.5V VIN = 4V VIN = 5V
90 80 70 EFFICIENCY (%) 60 50 40 30 20 10 0 VREF VIN CIRCUIT OF FIGURE 4 0 20 40 60 80 100 120 VIN = 5V VIN = 4V VIN = 4.5V
90 80 EFFICIENCY (%) 70 60 LIN MODE 50 40 30 VREF VIN 100mA LOAD VOUT = -3V CIRCUIT OF FIGURE 4 3.5 4.0 4.5 VIN (V) 5.0 5.5
SKIP MODE
140
140
6.0
LOAD CURRENT (mA)
LOAD CURRENT (mA)
DROPOUT OUTPUT RESISTANCE vs. INPUT VOLTAGE
MAX1673 TOC07
QUIESCENT CURRENT vs. INPUT VOLTAGE (LIN MODE)
MAX1673 TOC08
QUIESCENT CURRENT vs. INPUT VOLTAGE (SKIP MODE)
40 QUIESCENT CURRENT (A) 35 30 25 20 15 10 DOES NOT INCLUDE BIAS CURRENT FOR RESISTOR DIVIDER
MAX1673 TOC09
12 10 8 6 4 2 0 2 3 4 VIN (V) 5 6
12 10 8 6 4 2 0 2 3 4 VIN (V) DOES NOT INCLUDE BIAS CURRENT FOR RESISTOR DIVIDER
45
TA = +25C TA = +85C
TA = -40C
QUIESCENT CURRENT (mA)
RDROPOUT ()
VREF VIN CIRCUIT OF FIGURE 4 5 6
5 0 2 3 4 VIN (V) 5 6
4
_______________________________________________________________________________________
Regulated, 125mA-Output, Charge-Pump DC-DC Inverter
Typical Operating Characteristics (continued)
(Circuit of Figure 1, VIN = +5V, CFLY = 2.2F, COUT = 22F, TA = +25C, unless otherwise noted.)
MAX1673
LOAD-TRANSIENT RESPONSE (LIN MODE)
MAX1673 TOC10
LOAD-TRANSIENT RESPONSE (SKIP MODE)
MAX1673 TOC11
IOUT 100mA/div
125mA 25mA
IOUT 100mA/div CIRCUIT OF FIGURE 4
125mA 25mA
VOUT 50mV/div CIRCUIT OF FIGURE 4 250s/div
VOUT 50mV/div
250s/div
LINE-TRANSIENT RESPONSE (LIN MODE)
MAX1673 TOC12
LINE-TRANSIENT RESPONSE (SKIP MODE)
MAX1673 TOC13
VIN 2V/div
5.5V 4.5V
VIN 2V/div
IOUT = 100mA CIRCUIT OF FIGURE 4
5.5V 4.5V
VOUT 50mV/div
VOUT 50mV/div IOUT = 100mA CIRCUIT OF FIGURE 4 50s/div 50s/div
_______________________________________________________________________________________
5
Regulated, 125mA-Output, Charge-Pump DC-DC Inverter MAX1673
______________________________________________________________Pin Description
PIN 1 2 3 4 5 6 7 8 NAME LIN/SKIP CAP+ CAPSHDN OUT FB GND IN FUNCTION 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. Positive Terminal of Flying Capacitor Negative Terminal of Flying Capacitor Shutdown Control Input. Drive SHDN low to shut down the MAX1673. Connect SHDN to IN for normal operation. OUT connects to GND through a 1 (typical) resistor in shutdown mode. Inverting Charge-Pump Output Feedback Input. Connect FB to a resistor-divider from IN (or other reference source) to OUT for regulated output voltages (Figures 1 and 4). Ground Power-Supply Positive Voltage Input
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-DemandTM 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 (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).
S1 IN S2 CFLY
CAP+
S3 COUT OUT
S4 CAP-
350kHz
INPUT 5.0V CIN 10F OFF 4 2 CFLY 2.2F LIN SKIP SHDN IN
8 FB 6
R1 100k
Figure 2. Charging CFLY
ON
CAP+ MAX1673 OUT CAPLIN/SKIP GND 7
R1 60.4k 5 COUT 22F OUTPUT -3V
S1 IN S2 CFLY
CAP+
S3 COUT OUT
3 1
S4 CAP-
350kHz
Figure 1. Standard Application Circuit
6
Figure 3. Transferring Charge on CFLY to COUT
_______________________________________________________________________________________
Regulated, 125mA-Output, Charge-Pump DC-DC Inverter
Linear Mode (Constant-Frequency Mode)
In LIN mode (LIN/SKIP = IN), the charge pump runs continuously 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 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).
INPUT 5.0V VREF 5V CIN 10F OFF 4 2 CFLY 2.2F LIN SKIP SHDN IN R1 100k FB 6 R2 60.4k OUT CAPLIN/SKIP GND 7 5 COUT 22F OUTPUT -3V VOUT = -VREF x R2 R1
MAX1673
8
ON
CAP+ MAX1673
3 1
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.
Figure 4. Separate VREF for Voltage Divider
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 1 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.
Capacitor Selection
A CFLY value of 1F 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 2.2F. Surface-mount ceramic capacitors are preferred for CFLY, 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 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 C OUT charges. At equilibrium, when the voltage on C FLY 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 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 COUT ESR is:
7
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 unregulated voltage or if greater accuracy is desired (Figure 4). Adjust the output voltage from -1.5V to -V IN 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 regulating mode (LIN or Skip), FB servos to 0V. Use the following equations to select R1 and R2 for the desired output voltage: R2 VOUT = - VREF R1 where VREF can be either VIN or some other positive reference source. Typically, choose a voltage-divider current of 50A to minimize the effect of FB input current: R1 = VREF / 50A R2 = -VOUT / 50A
_______________________________________________________________________________________
Regulated, 125mA-Output, Charge-Pump DC-DC Inverter MAX1673
V -V ESR VRIPPLE(ESR) = 8 IN OUT 2 COUT R fOSC OUT CFLY
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 expression for the ripple component predominantly due to charge transfer is:
V -V 1 VRIPPLE(ESR) = 2 IN OUT R fOSC OUT (CFLY + C OUT )
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.
where CFLY and COUT are their respective capacitance values, ESRCOUT is the equivalent series resistance of COUT, ROUT is the MAX1673 open-loop output impedance (typically 3.5, and fOSC is the MAX1673 switching frequency (typically 350kHz). If ESRCOUT 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 VRIPPLE (ESR) dominates. When operating in LIN mode, use the following equation to approximate peak-to-peak output voltage ripple:
VRIPPLE = I 2f
OUT
___________________Chip Information
TRANSISTOR COUNT: 386 SUBSTRATE CONNECTED TO: IN
OSC
C
OUT
+ 2IOUT ESRCOUT
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 temperature range, choose a low-ESR (no more than 100m) output capacitance using the following equation:
COUT = 75 x 10 - 6 R1 + R2
R1 IOUT
Table 1. Partial Listing of Capacitor Vendors
PRODUCTION METHOD Surface-Mount Tantalum MANUFACTURER AVX Matsuo Sprague Surface-Mount Ceramic AVX Matsuo SERIES TPS 267 593D, 595D X7R X7R PHONE (803) 946-0690 (714) 969-2491 (603) 224-1961 (803) 946-0590 (714) 969-2491 FAX (803) 448-2170 (714) 960-6492 (603) 224-1430 (803) 626-3123 (714) 960-6492
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 (c) 1998 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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