View MAX865_150808.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

19-0472; Rev 1; 7/97
Compact, Dual-Output Charge Pump
_______________General Description
The MAX865 is a CMOS charge-pump DC-DC converter in an ultra-small MAX package. It produces positive and negative outputs from a single positive input, and requires only four capacitors. The charge pump first doubles the input voltage, then inverts the doubled voltage. The input voltage ranges from +1.5V to +6.0V. The internal oscillator is guaranteed to be between 20kHz and 38kHz, keeping noise above the audio range while consuming minimal supply current. A 75 output impedance permits useful output currents up to 20mA. The MAX865 comes in a 1.11mm-high, 8-pin MAX package that occupies half the board area of a standard 8-pin SOIC. For a device with selectable frequencies and logic-controlled shutdown, refer to the MAX864 data sheet.
____________________________Features
o 1.11mm-High MAX Package o Compact: Circuit Fits in 0.08in2 o Requires Only Four Capacitors o Dual Outputs (positive and negative) o +1.5V to +6.0V Input Voltage o 20kHz (min) Frequency (above the audio range)
MAX865
______________Ordering Information
PART MAX865C/D MAX865EUA TEMP. RANGE 0C to +70C -40C to +85C PIN-PACKAGE Dice 8 MAX
________________________Applications
Low-Voltage GaAsFET Bias in Wireless Handsets VCO and GaAsFET Supplies Split Supply from 3 Ni Cells or 1 Li+ Cell Low-Cost Split Supply for Low-Voltage Data-Acquisition Systems Split Supply for Analog Circuitry LCD Panels
__________Typical Operating Circuit
VIN (+1.5V to +6.0V)
__________________Pin Configuration
IN C1+
MAX865
V+ +2*VIN
TOP VIEW
C1C2+
C1C2+ C2-
1 2 3
8
C1+ V+ IN GND
MAX865
7 6 5
VC2GND
-2*VIN
V- 4
MAX
GND
GND
+VIN to 2VIN CONVERTER
________________________________________________________________ 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.
Compact, Dual-Output Charge Pump MAX865
ABSOLUTE MAXIMUM RATINGS
V+ to GND .................................................................+12V, -0.3V IN to GND .................................................................+6.2V, -0.3V V- to GND ..................................................................-12V, +0.3V V- Output Current .............................................................100mA V- Short-Circuit to GND ................................................Indefinite Continuous Power Dissipation (TA = +70C) MAX (derate 4.1mW/C above +70C) .......................330mW Operating Temperature Range MAX865EUA .....................................................-40C to +85C Storage Temperature Range .............................-65C to +160C Lead Temperature (soldering, 10sec) .............................+300C
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 = 5V, C1 = C2 = C3 = C4 = 3.3F, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER Minimum Supply Voltage Maximum Supply Voltage Supply Current Oscillator Frequency RLOAD = 10k RLOAD = 10k TA = +25C TA = -40C to +85C (Note 1) TA = +25C TA = -40C to +85C (Note 1) IV+ = 1mA, IV- = 0mA V+ = 10V (forced), IV- = 1mA Power Efficiency Voltage Conversion Efficiency IL = 5mA V+, RL = V-, RL = 95 90 TA = +25C TA = TMIN to TMAX TA = +25C TA = TMIN to TMAX 85 99 98 75 19.5 18 150 24 0.6 CONDITIONS MIN 2.0 TYP 1.5 6.0 1.05 1.15 32.5 34 200 280 100 140 % % MAX UNITS V V mA kHz
Output Resistance
Note 1: These specifications are guaranteed by design and are not production tested.
__________________________________________Typical Operating Characteristics
(Circuit of Figure 1, VIN = 5V, TA = +25C, unless otherwise noted.)
EFFICIENCY vs. OUTPUT CURRENT (VIN = 5V)
MAX865-01
EFFICIENCY vs. OUTPUT CURRENT (VIN = 3.3V)
MAX865-02
EFFICIENCY vs. OUTPUT CURRENT (VIN = 2V)
90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 VV+
MAX865-03
100 90 80 EFFICIENCY (%) VV+
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 VV+
100
70 60 50 40 30 20 10 0 0 2 4 6 8
10 12
14 16 18
0
1
2
3
4
5
6
7
8
0
0.5
1.0
1.5
2.0
2.5
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
2
_______________________________________________________________________________________
Compact, Dual-Output Charge Pump
____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 1, VIN = 5V, TA = +25C, unless otherwise noted.)
OUTPUT VOLTAGE vs. OUTPUT CURRENT
MAX865-04
MAX865
OUTPUT VOLTAGE RIPPLE vs. PUMP CAPACITANCE
MAX865-05
OUTPUT CURRENT vs. PUMP CAPACITANCE
OUTPUT CURRENT, V+ TO V- (mA) VIN = 4.75V, V+ + |V-| = 16V
MAX865-06
10 8 OUTPUT VOLTAGE, V+, V- (V) 6 4 2 0 -2 -4 -6 -8 -10 0 2 4 6 8 10 OUTPUT CURRENT (mA) V+ 12 BOTH V+ AND V- LOADED EQUALLY C1 = C2 = C3 = C4 = 3.3F VIN = 4.75V
V+
400 OUTPUT VOLTAGE RIPPLE (mVp-p) 350 300 250 200 150 100 50 0 0 5 F D C1 = C2 = C3 = C4 A: V+, IN = 4.75V, V+ + |V-| = 16V B: V+, IN = 3.15V, V+ + |V-| = 10V C: V+, IN = 1.90V, V+ + |V-| = 6V D: V-, IN = 4.75V, V+ + |V-| = 16V E: V-, IN = 3.15V, V+ + |V-| = 10V F: V-, IN = 1.90V, V+ + |V-| = 6V AE BC
7 6 5 4 3
V-
VIN = 3.15V, V+ + |V-| = 10V
VIN = 1.90V, V+ + |V-| = 6V 2 1 C1 = C2 = C3 = C4 0
V-
14
10 15 20 25 30 35 40 45 50 PUMP CAPACITANCE (F)
0
5
10 15 20 25 30 35 40 45 50 PUMP CAPACITANCE (F)
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX865-07
OUTPUT RESISTANCE vs. TEMPERATURE
C1 = C2 = C3 = C4 = 3.3F V-, VIN = 3.3V V-, VIN = 5.0V
MAX865-08
1000 900 SUPPLY CURRENT (A) 800 700 600 500 400 300 200 100 0 2.0 2.5 3.0 3.5 4.0 4.5 C1 = C2 = C3 = C4 = 3.3F
300 250 200 150 100 50 0 V+, VIN = 5.0V
OUTPUT RESISTANCE ()
V+, VIN = 3.3V
5.0 5.5 6.0
-55 -35 -15
5
25
45
65
85 105 125
SUPPLY VOLTAGE (V)
TEMPERATURE (C)
PUMP FREQUENCY vs. TEMPERATURE
MAX865-09
OUTPUT RESISTANCE vs. SUPPLY VOLTAGE
MAX865-10
27 VIN = 5.0V 25 PUMP FREQUENCY (kHz) 23 21 VIN = 2.0V 19 17 15 -40 -20 0 20 40 60 80 C1 = C2 = C3 = C4 = 3.3F VIN = 3.3V
250
OUTPUT RESISTANCE ()
200
V-
150 V+ 100
50
C1 = C2 = C3 = C4 = 3.3F
0 100 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 TEMPERATURE (C) SUPPLY VOLTAGE (V)
_______________________________________________________________________________________
3
Compact, Dual-Output Charge Pump MAX865
____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 1, VIN = 5V, TA = +25C, unless otherwise noted.)
OUTPUT RIPPLE (C1 = C2 = C3 = C4 = 1F)
OUTPUT RIPPLE (C1 = C2 = C3 = C4 = 3.3F)
V- OUTPUT 20mV/div
V- OUTPUT 10mV/div
V+ OUTPUT 50mV/div
V+ OUTPUT 10mV/div
10s/div VIN = 4.75V, 1mA LOAD VIN = 4.75V, 1mA LOAD
10s/div
_____________________Pin Description
PIN NAME C1C2+ C2VGND IN V+ C1+ FUNCTION Negative Terminal of the Flying Boost Capacitor Positive Terminal of the Flying Inverting Capacitor Negative Terminal of the Flying Inverting Capacitor Output of the Inverting Charge Pump Ground Positive Power-Supply Input
3.3F 3.3F C2VIN GND VIN
1
2 3 4 5 6 7 8
3.3F C1C2+ MAX865 C1+ IV+ V+ 3.3F RL+ OUT+
IVRL-
Output of the Boost Charge Pump Positive Terminal of the Flying Boost Capacitor
OUT-
Figure 1. Test Circuit
4 _______________________________________________________________________________________
Compact, Dual-Output Charge Pump
_______________Detailed Description
The MAX865 contains all the circuitry needed to implement a voltage doubler/inverter. Only four external capacitors are needed. These may be polarized electrolytic or ceramic capacitors with values ranging from 1F to 100F. Figure 2a shows the ideal operation of the positive voltage doubler. The on-chip oscillator generates a 50% duty-cycle clock signal. During the first half cycle, switches S2 and S4 open, switches S1 and S3 close, and capacitor C1 charges to the input voltage (V IN). During the second half cycle, switches S1 and S3 open, switches S2 and S4 close, and capacitor C1 is level shifted upward by VIN. Assuming ideal switches and no load on C3, charge transfers into C3 from C1 such that the voltage on C3 will be 2VIN, generating the positive supply output (V+). Figure 2b illustrates the ideal operation of the negative converter. The switches of the negative converter are out of phase with the positive converter. During the second half cycle, switches S6 and S8 open and switches S5 and S7 close, charging C2 from V+ (pumped up to 2VIN by the positive charge pump) to GND. In the first half of the clock cycle, switches S5 and S7 open, switches S6 and S8 close, and the charge on capacitor C2 transfers to C4, generating the negative supply. The eight switches are CMOS power MOSFETs. Switches S1, S2, S4, and S5 are P-channel devices, while switches S3, S6, S7, and S8 are N-channel devices.
MAX865
Charge-Pump Output
The MAX865 is not a voltage regulator: the output source resistance of either charge pump is approximately 150 at room temperature with VIN = +5V, and V+ and V- will approach +10V and -10V, respectively, when lightly loaded. Both V+ and V- will droop toward GND as the current draw from either V+ or V- increases, since V- is derived from V+. Treating each converter separately, the droop of the negative supply (VDROOP-) is the product of the current draw from V(IV-) and the source resistance of the negative converter (RS-): VDROOP- = I V - x RS The droop of the positive supply (V DROOP+ ) is the product of the current draw from the positive supply (I LOAD+ ) and the source resistance of the positive
a)
V+ S1 IN C1 C3 C1+ S2
b)
V+ S5 C2+ S6 GND IV+ RL+ C2 IVC4 S3 GND C1S4 IN GND C2S7 S8 VRL-
Figure 2. Idealized Voltage Quadrupler: a) Positive Charge Pump; b) Negative Charge Pump
_______________________________________________________________________________________
5
Compact, Dual-Output Charge Pump MAX865
converter (RS+), where ILOAD+ is the combination of IVand the external load on V+ (IV+): VDROOP+ = ILOAD+ x RS+ = I V+ + I V - x RS+ Determine V+ and V- as follows: V+ = 2VIN - VDROOP+ V - = (V+ - VDROOP ) = -(2VIN - VDROOP+ - VDROOP- ) The output resistance for the positive and negative charge pumps are tested and specified separately. The positive charge pump is tested with V- unloaded. The negative charge pump is tested with V+ supplied from an external source, isolating the negative charge pump. Current draw from either V+ or V- is supplied by the reservoir capacitor alone during one half cycle of the clock. Calculate the resulting ripple voltage on either output as follows: VRIPPLE =
1 2
Efficiency Considerations
Theoretically, a charge-pump voltage multiplier can approach 100% power efficiency under the following conditions: * The charge-pump switches have virtually no offset and extremely low on-resistance. * The drive circuitry consumes minimal power. * The impedances of the reservoir and pump capacitors are negligible. For the MAX865, the energy loss per clock cycle is the sum of the energy loss in the positive and negative converters, as follows:
LOSSCYCLE = LOSSPOS + LOSSNEG =
2 C1 ( V + ) - 2( V + ) ( VIN ) 2 2 C2 ( V + ) - ( V - ) + 2 1 2 1
(
)
ILOAD (1 / fPUMP ) (1 / CRESERVOIR )
The average power loss is simply: PLOSS = LOSSCYCLE x fPUMP Resulting in an efficiency of: = Total Output Power / Total Output Power - PLOSS
where ILOAD is the load on either V+ or V-. For the typical fPUMP of 30kHz with 3.3F reservoir capacitors, the ripple is 25mV when ILOAD is 5mA. Remember that, in most applications, the total load on V+ is the V+ load current (I V+) and the current taken by the negative charge pump (IV-).
(
)
VIN
3.3F 1 2 3.3F 3 4 C1C2- MAX865 C2VC1+ V+ IN GND 8 7
3.3F 1 2 3.3F 6 5 3 4 C1C2+ MAX865 C2VC1+ V+ IN GND 8 7 6 5 3.3F IN GND OUT+
3.3F
OUT-
Figure 3. Paralleling MAX865s
6
_______________________________________________________________________________________
Compact, Dual-Output Charge Pump
A substantial voltage difference exists between (V+ VIN) and VIN for the positive pump, and between V+ and V- if the impedances of the pump capacitors (C1 and C2) are large with respect to their output loads. Larger values of reservoir capacitors (C3 and C4) reduce output ripple. Larger values of both pump and reservoir capacitors improve power efficiency.
Paralleling Devices
Paralleling multiple MAX865s (Figure 3) reduces the output resistance of both the positive and negative converters. The effective output resistance is the output resistance of one device divided by the number of devices. Separate C1 and C2 charge-pump capacitors are required for each MAX865, but the reservoir capacitors C3 and C4 can be shared.
MAX865
Charge-Pump Capacitor Selection
To maintain the lowest output resistance, use capacitors with low effective series resistance (ESR). The chargepump output resistance is a function of C1, C2, C3, and C4's ESR. Therefore, minimizing the charge-pump capacitors' ESR minimizes the total output resistance.
Heavy Output Current Loads
When under heavy loads, where V+ is sourcing current into V- (i.e., load current flows from V+ to V-, rather than from supply to ground), do not allow the V- supply to pull above ground. In applications where large currents flow from V+ to V-, use a Schottky diode (1N5817) between GND and V-, with the anode connected to GND (Figure 4).
__________Applications Information
Positive and Negative Converter
The MAX865 is most commonly used as a dual chargepump voltage converter that provides positive and negative outputs of two times a positive input voltage. The Typical Operating Circuit shows that only four external components are needed: capacitors C1 and C3 for the positive pump, C2 and C4 for the negative pump. In most applications, all four capacitors are low-cost, 3.3F polarized electrolytics. For applications where PC board space is at a premium and very low currents are being drawn from the MAX865, 1F capacitors may be used for the pump capacitors C1 and C2, with 1F reservoir capacitors C3 and C4. Capacitors C2 and C4 must be rated at 12V or greater.
Layout and Grounding
Good layout is important, primarily for good noise performance. To ensure good layout: * Mount all components as close together as possible * Keep traces short to minimize parasitic inductance and capacitance * Use a ground plane.
GND
MAX865
V-
Figure 4. A Schottky diode protects the MAX865 when large currents flow from V+ to V-.
_______________________________________________________________________________________
7
Compact, Dual-Output Charge Pump MAX865
___________________Chip Topography
TRANSISTOR COUNT: 80 SUBSTRATE CONNECTED TO V+
C1C1+
C2+
V+
0.084" (2.13mm) IN
C2-
V0.058" (1.47mm)
GND
________________________________________________________Package Information
DIM
C A 0.101mm 0.004 in B A1 L
e
A A1 B C D E e H L
INCHES MAX MIN 0.044 0.036 0.008 0.004 0.014 0.010 0.007 0.005 0.120 0.116 0.120 0.116 0.0256 0.198 0.188 0.026 0.016 6 0
MILLIMETERS MIN MAX 0.91 1.11 0.10 0.20 0.25 0.36 0.13 0.18 2.95 3.05 2.95 3.05 0.65 4.78 5.03 0.41 0.66 0 6
21-0036D
E
H
8-PIN MAX MICROMAX SMALL-OUTLINE PACKAGE
D
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) 1997 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

▲Up To Search▲

Price & Availability of MAX865

	To Download MAX865 Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .