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19-0374; Rev 1; 5/96
KIT ATION EVALU LE VAILAB A
3.3V/5V or Adjustable-Output, Single-Cell DC-DC Converters
____________________________Features
o 0.8V to 6.0V Input Supply Voltage o 0.9V Guaranteed Start-Up Supply Voltage o >80% Efficiency Over Wide Load Range o 100A No-Load Battery Current (VOUT = 3.3V) o 1A Shutdown Mode o Up to 250kHz Switching Frequency o 1.5% Reference Tolerance o Low-Battery Detector (LBI/LBO) o Available in Ultra-Small 8-Pin MAX Package (1.11mm high) o Circuit Fits in 0.2in2
_______________General Description
The MAX866 and MAX867 are ultra-small, high-efficiency, CMOS, step-up, DC-DC switching regulators for 1-cell battery-powered systems. The MAX866 accepts a positive input voltage between 0.8V and VOUT and converts it to a higher, pin-selectable output voltage of 3.3V or 5V. The MAX867 adjustable version accepts 0.8V to 6.0V input voltages and generates a higher adjustable output voltage in the 2.7V to 6.0V range. Typical efficiencies are greater than 80%. Typical no-load supply current is 100A (1A in shutdown). The MAX866/MAX867 combine ultra-low quiescent supply current and high efficiency to give maximum battery life. Its high switching frequency permits the use of small, low-cost inductors and capacitors. Additionally, internal peak-current limiting protects the IC.
MAX866/MAX867
______________Ordering Information ________________________Applications
Pagers Remote Controls Detectors 1-Cell Battery-Operated Equipment Backup Supplies
PART MAX866C/D MAX866ESA MAX866EUA MAX867C/D MAX867ESA MAX867EUA TEMP. RANGE 0C to +70C -40C to +85C -40C to +85C 0C to +70C -40C to +85C -40C to +85C PIN-PACKAGE Dice* 8 SO 8 MAX Dice* 8 SO 8 MAX
* Dice are tested at TA = +25C only.
__________Typical Operating Circuit
INPUT 0.8V TO VOUT
_________________Pin Configurations
TOP VIEW
SHDN 3/5 1 2 8 7 LX GND OUT LBI
330H OUTPUT 5V OR 3.3V ON/OFF SHDN LX MBRS0520LTI OR 1N5817 47F
REF 3 LBO 4
MAX866
6 5
SO/MAX
MAX866
3V/5V SELECT LOW-BATTERY DETECTOR INPUT 3/5 LBI REF 0.22F LBO LOW-BATTERY DETECTOR OUTPUT OUT
SHDN FB 1 2 8 7 LX GND OUT LBI
REF 3 LBO 4
MAX867
6 5
GND
SO/MAX
________________________________________________________________ Maxim Integrated Products
1
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3.3V/5V or Adjustable-Output, Single-Cell DC-DC Converters MAX866/MAX867
ABSOLUTE MAXIMUM RATINGS
Supply Voltage (OUT to GND) ...................................-0.3V, +7V Switch Voltage (LX to GND) .......................................-0.3V, +7V ---- --- SHDN , LBO to GND ....................................................-0.3V, +7V - - LBI, REF, 3/ 5, FB to GND ............................-0.3V, (VOUT + 0.3V) Reference Current (IREF) ..................................................2.5mA Continuous Power Dissipation (TA = +70C) SO (derate 5.88mW/C above +70C) .........................471mW MAX (derate 4.1mW/C above +70C) ......................330mW Reverse Battery Current (TA +45C) (Note 1)................750mA Operating Temperature Ranges MAX86_C/D .......................................................0C to +70C MAX86_E_A ....................................................-40C to +85C Junction Temperature .....................................................+150C Storage Temperature Range ............................-65C to +160C Lead Temperature (soldering, 10sec) ............................+300C
Note 1: Reverse battery current is measured from the Typical Operating Circuit's battery input terminal to GND when the battery is connected backwards. A reverse current of 750mA will not exceed the package dissipation limits but, if left for an extended time (more than ten minutes), may degrade performance.
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
(Circuit of Figure 2, VIN = 1.2V, ILOAD = 0mA, TA = +25C, unless otherwise noted.) PARAMETER Minimum Start-Up Supply Voltage 0.9V VIN 3V - - MAX866, 3/ 5 = 0V, 0mA ILOAD 6mA - - MAX866, 3/ 5 = 3V, 0mA ILOAD 8mA 4.80 3.17 4.80 4.75 3.13 4.75 4.80 3.17 4.80 6 8 6 10 15 10 CONDITIONS MIN TYP 0.8 5.0 3.3 5.0 5.0 3.3 5.0 5.0 3.3 5.0 9 13 9 15 23 15 27 100 1 500 No REF load - - 3/ 5 = 3V, -20A REF load 250A, CREF = 0.22F With falling edge 1.22 1.25 0.8 1.22 1.25 1.28 2.0 1.28 60 A A A mA V % V mA MAX 0.9 5.20 3.43 5.20 5.25 3.47 5.25 5.20 3.43 5.20 V UNITS V
Output Voltage (Note 2)
MAX867, VOUT = 5V, 0mA ILOAD 6mA - - MAX866, 3/ 5 = 0V, 0mA ILOAD 6mA 0.9V VIN 3V, - - TA =TMIN TO TMAX MAX866, 3/ 5 = 3V, 0mA ILOAD 8mA (Note 3) MAX867, V = 5V, 0mA I 6mA
OUT LOAD
1.2V VIN 3V
- - MAX866, 3/ 5 = 0V, 0mA ILOAD 10mA - - MAX866, 3/ 5 = 3V, 0mA ILOAD 15mA MAX867, VOUT = 5V, 0mA ILOAD 10mA - - MAX866, 3/ 5 = 0V, 4.8V VLOAD 5.2V - - MAX866, 3/ 5 = 3V, 3.17V VLOAD 3.43V MAX867, VOUT = 5V, 4.8V VLOAD 5.2V - - MAX866, 3/ 5 = 0V, 4.8V VLOAD 5.2V - - MAX866, 3/ 5 = 3V, 3.17V VLOAD 3.43V MAX867, VOUT = 5V, 4.8V VLOAD 5.2V
0.9V VIN 3V Maximum Load Current (Note 2) 1.2V VIN 3V
Quiescent Supply Current in 3.3V mode (Note 4) No-Load Battery Current Shutdown Quiescent Current (Note 4) Peak Inductor Current Limit Reference Voltage Reference Load Regulation LBI Input Threshold 2
- - ILOAD = 0mA, 3/ 5 = 3V, LBI = 1.5V, VOUT = 3.47V, FB = 1.5V Output set for 3.3V, measured at VIN in Figure 2, VIN = 1.5V ---- --- - - SHDN = 0V, 3/ 5 = 3V, LBI = 1.5V, VOUT = 3.47V, FB = 1.5V
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3.3V/5V or Adjustable-Output, Single-Cell DC-DC Converters
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 2, VIN = 1.2V, ILOAD = 0mA, TA = +25C, unless otherwise noted.) PARAMETER LBI Input Hysteresis LBO Output Voltage Low LBO Output Leakage Current --- - - ---- - SHDN , 3/ 5 Input Voltage Low ---- --- - - SHDN , 3/ 5 Input Voltage High ---- --- - - SHDN , 3/ 5, FB, LBI Input Current FB Voltage Output Voltage Range ISINK = 2mA, open-drain output LBO = 5V 0.32 x VOUT --- - ---- - - LBI = 1.5V, FB = 1.5V, SHDN = 0V or 3V, 3/ 5 = 0V or 3V MAX867, output in regulation MAX867 1.22 2.7 40 1.25 100 1.28 6.0 CONDITIONS MIN TYP 25 0.4 1 0.08 x VOUT MAX UNITS mV V A V V nA V V
MAX866/MAX867
Note 2: Output current specified with circuit of Figure 2 and CoilCraft D01608-334 inductor for test purposes only. More (or less) output current can be supplied with other coil types depending on inductance value and coil resistance. See Typical Operating Characteristics for other coil types. Output voltage and output current are guaranteed over this VIN operating range once the device has started up. Actual VIN start-up voltage depends on load current. Note 3: Output voltage specifications over temperature are guaranteed by design to limits that are 6 sigma from either side of the mean. Note 4: Current measured into OUT. VOUT is forced to 3.47V to maintain LX off when measuring device current.
__________________________________________Typical Operating Characteristics
(Circuits of Figure 2, TA = +25C, unless otherwise noted.)
EFFICIENCY vs. LOAD CURRENT (VOUT = 3.3V)
MAX866/667-01
EFFICIENCY vs. LOAD CURRENT (VOUT = 3.3V)
MAX866/67-02
EFFICIENCY vs. LOAD CURRENT (VOUT = 5.0V)
90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 TOP TO BOTTOM: VIN = 2.0V VIN = 1.5V VIN = 1.25V VIN = 1.0V VIN = 0.75V VIN = 0.5V 0.01 0.1 1 10 100 1000 L = SUMIDA CD73-331 (330H, 1.5)
MAX866/667-03 MAX866/67-06
100 90 80 EFFICIENCY (%) L = SUMIDA CD73-331 (330H, 1.5)
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 TOP TO BOTTOM: VIN = 2.0V VIN = 1.5V VIN = 1.25V VIN = 1.0V VIN = 0.75V L = COILCRAFT D01608-334 (330H, 2.9)
100
70 60 50 40 30 20 10 0 0.01 0.1 1 10 100 1000 LOAD CURRENT (mA) TOP TO BOTTOM: VIN = 2.0V VIN = 1.5V VIN = 1.25V VIN = 1.0V VIN = 0.75V VIN = 0.5V
0.01
0.1
1
10
100
LOAD CURRENT (mA)
LOAD CURRENT (mA)
EFFICIENCY vs. LOAD CURRENT (VOUT = 5.0V)
MAX866/67-04
NO-LOAD BATTERY CURRENT vs. BATTERY VOLTAGE (VOUT = 3.3V)
DECREASING BATTERY VOLTAGE
MAX866/67-05
NO-LOAD BATTERY CURRENT vs. BATTERY VOLTAGE (VOUT = 5V)
4000 3500 BATTERY CURRENT (A) 3000 2500 2000 1500 1000 500 0 INCREASING BATTERY VOLTAGE DECREASING BATTERY VOLTAGE
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 0.01 0.1 1 10 TOP TO BOTTOM: VIN = 2.0V VIN = 1.5V VIN = 1.25V VIN = 1.0V VIN = 0.75V L = COILCRAFT D01608-334 (330H, 2.9)
1200 1000 800 600 400 200 0 INCREASING BATTERY VOLTAGE
100
BATTERY CURRENT (A)
0
0.2
0.4
0.6
0.8 1.0 1.2
1.4 1.6
0
0.2
0.4
0.6
0.8 1.0 1.2
1.4 1.6
LOAD CURRENT (mA)
BATTERY VOLTAGE (V)
BATTERY VOLTAGE (V)
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3.3V/5V or Adjustable-Output, Single-Cell DC-DC Converters MAX866/MAX867
____________________________Typical Operating Characteristics (continued)
(Circuits of Figure 2, TA = +25C, unless otherwise noted.)
START-UP INPUT VOLTAGE vs. LOAD CURRENT (VOUT = 3.3V)
MAX186-14AMAX866/67-07
START-UP INPUT VOLTAGE vs. LOAD CURRENT (VOUT = 5V)
MAX866/67-08 MAX186-14A
INPUT VOLTAGE vs. LOAD CURRENT (VOUT = 3.3V)
100H 2.5 INPUT VOLTAGE (V) 2.0 1.5 22H 1.0 0.5 0 1mH 330H 47H
MAX186-14AMAX866/67-09
1.5 1.4 START-UP INPUT VOLTAGE (V) 1.3 1.2 1.1 1.0 0.9 0.8 0.7 0.6 0.5 0.1 1 10 1mH 220H 330H 100H 47H
1.5 1.4 START-UP INPUT VOLTAGE (V) 1.3 1.2 1.1 1.0 0.9 0.8 0.7 0.6 0.5 330H 100H 220H 47H
3.0
100
0.1
1
10
100
1
10
100
1000
LOAD CURRENT (mA)
LOAD CURRENT (mA)
LOAD CURRENT (mA)
INPUT VOLTAGE vs. LOAD CURRENT (VOUT = 5V)
MAX186-14AMAX866/67-10
REFERENCE VOLTAGE vs. REFERENCE CURRENT
9 VREF LOAD REGULATION (mV) 8 7 6 5 4 3 2 1
MAX866/67-11
3.0 2.5 INPUT VOLTAGE (V) 2.0 1.5 1.0 0.5 0 1 10 100 22H 100H
10
330H 47H
0 1000 0 LOAD CURRENT (mA) 100 200 50 150 REFERENCE LOAD CURRENT (A) 250
MAX866 LINE-TRANSIENT RESPONSE (3.3V MODE)
MAX866 LINE-TRANSIENT RESPONSE (5V MODE)
A
A
B
B
1ms/div A: 3.3V OUTPUT VOLTAGE, AC COUPLED 20mV/div B: INPUT VOLTAGE (0.9V AND 1.4V) 500mV/div ILOAD = 10mA, COUT = 47F
1ms/div A: 5.0V OUTPUT VOLTAGE, AC COUPLED 20mV/div B: INPUT VOLTAGE (0.9V AND 1.4V) 500mV/div ILOAD = 10mA, COUT = 47F
4
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3.3V/5V or Adjustable-Output, Single-Cell DC-DC Converters
____________________________Typical Operating Characteristics (continued)
(Circuits of Figure 2, TA = +25C, unless otherwise noted.) MAX866 LOAD-TRANSIENT RESPONSE (3.3V MODE) MAX866 LOAD-TRANSIENT RESPONSE (5V MODE)
MAX866/MAX867
A
A
B
B
1ms/div A: 3.3V OUTPUT VOLTAGE, AC COUPLED 20mV/div B: OUTPUT CURRENT (0mA AND 10mA) 5mV/div (TEKTRONIX P6042 CURRENT PROBE) ILOAD = 5mA, COUT = 47F, VIN = 1.25V
1ms/div A: 5.0V OUTPUT VOLTAGE, AC COUPLED 20mV/div B: OUTPUT CURRENT (0mA AND 10mA) 5mV/div (TEKTRONIX P6042 CURRENT PROBE) ILOAD = 5mA, COUT = 47F, VIN = 1.25V
MAX866 SHUTDOWN RESPONSE (3.3V MODE)
MAX866 SHUTDOWN RESPONSE (5V MODE)
A A
B
B
10ms/div A: 3.3V OUTPUT VOLTAGE, 2V/div B: SHDN INPUT VOLTAGE (0V AND 5V) 2V/div ILOAD = 10mA
10ms/div A: 5.0V OUTPUT VOLTAGE, 2V/div B: SHDN INPUT VOLTAGE (0V AND 5V) 5V/div ILOAD = 10mA
MAX867 LBI AND FB THRESHOLD vs. TEMPERATURE
MAX866/67-24
MAX866 OUTPUT VOLTAGE ERROR vs. TEMPERATURE
MAX866/67-25
START-UP VOLTAGE vs. TEMPERATURE
ILOAD = 0A START-UP VOLTAGE (V) 0.9
MAX866/67-26
1.260
0.5 OUTPUT VOLTAGE ERROR (%) 3.3V MODE
1.0
LBI, FB VOLTAGE (V)
LBI
0.8
1.250
0 5V MODE
0.7
0.6 ILOAD= OA -0.5 -60 -40 -20 0 20 40 60 TEMPERATURE (C) 80 100 0.5 -60 -40 -20 0 20 40 60 TEMPERATURE (C) 80 100
VFB (MAX867) 1.240 -60 -40 -20 0 20 40 60 TEMPERATURE (C) 80 100
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3.3V/5V or Adjustable-Output, Single-Cell DC-DC Converters MAX866/MAX867
____________________________Typical Operating Characteristics (continued)
(Circuits of Figure 2, TA = +25C, unless otherwise noted.)
OUTPUT CURRENT CAPABILITY vs. TEMPERATURE
MAX866/67-27
QUIESCENT SUPPLY CURRENT vs. TEMPERATURE
QUIESCENT SUPPLY CURRENT (A) VOUT = 3.47V 28
MAX866/67-28
REFERENCE VOLTAGE vs. TEMPERATURE
MAX866/67-29
30 VIN = 1.2V OUTPUT CURRENT (mA) 25
30
1.255
26 IOUT 24
REFERENCE VOLTAGE (V)
20 VIN = 0.9V 15 3.3V MODE 10 -60 -40 -20 0 20 40 60 TEMPERATURE (C)
1.250
IREF = 0A
22
80 100
20 -60 -40 -20 0 20 40 60 TEMPERATURE (C)
80 100
1.245 -60 -40 -20 0 20 40 60 TEMPERATURE (C)
80 100
______________________________________________________________Pin Description
PIN MAX866 1 2 -- 3 4 5 6 7 8 MAX867 1 -- 2 3 4 5 6 7 8 NAME --- - ---- SHDN - - 3/ 5 FB REF LBO LBI OUT GND LX FUNCTION Shutdown Input. When low, the entire circuit is off and VOUT = VIN - VD, where VD is the forward voltage drop of the external Schottky rectifier. Selects the output voltage; connect to GND for 5V output, and to OUT for 3.3V output. Feedback Input for adjustable-output operation. Connect to an external resistor voltage divider between OUT and GND. 1.25V Reference Voltage Output. Bypass with 0.22F to GND (0.1F if there is no external reference load). Maximum load capability is 250A source, 20A sink. Low-Battery Output. An open-drain N-channel MOSFET sinks current when the voltage at LBI drops below 1.25V. Low-Battery Input. When the voltage on LBI drops below 1.25V, LBO sinks current. If not used, connect to VIN. Connect OUT to the regulator output. OUT provides bootstrap power to the IC. Power Ground. Must be low impedance; solder directly to ground plane. N-Channel Power-MOSFET Drain
6
_______________________________________________________________________________________
3.3V/5V or Adjustable-Output, Single-Cell DC-DC Converters MAX866/MAX867
MINIMUM OFF-TIME ONE-SHOT
VBATT Q ONE-SHOT TRIG LX F/F S R Q N VOUT
SHDN
3/5* GND TRIG ONE-SHOT CURRENT-LIMIT COMPARATOR OUT Q
MAXIMUM ON-TIME ONE-SHOT
MAX866/MAX867
*
FB**
**
*
ERROR COMPARATOR
**
LBO N LBI COMPARATOR LBI REF
REFERENCE
*MAX866 ONLY **MAX867 ONLY
Figure 1. Block Diagram
_______________Detailed Description
Operating Principle
The MAX866/MAX867 combine a switch-mode regulator, N-channel power MOSFET, precision voltage reference, and power-fail detector in a single monolithic device. The MOSFET is a "sense-FET" type for best efficiency, and has a very low gate threshold voltage to ensure start-up with low battery voltages (0.8V typ).
PFM Control Scheme
The MAX866/MAX867 control scheme (Figure 1) combines low-voltage efficiency (80% typ) with low battery
drain (100A typ). There is no oscillator; switching is accomplished by a pair of one shots that set a maximum LX on-time (4.5s typ) and a minimum LX off-time (1s). LX on-time will be terminated early if the inductor current reaches 0.5A before 4.5s elapses. With the standard application circuit (Figure 2a), LX current is typically less than 50mA, so LX on-time is normally not terminated by the 0.5A limit and lasts the complete 4.5s. The LX on-resistance is typically 1 to minimize switch losses. The MAX866/MAX867 switching frequency depends on load, input voltage, and inductor value, and it can range up to 250kHz with typical component values.
7
_______________________________________________________________________________________
3.3V/5V or Adjustable-Output, Single-Cell DC-DC Converters MAX866/MAX867
Voltage Reference
The precision voltage reference is suitable for driving external loads, such as an analog-to-digital converter. The voltage-reference output changes less than 2% when sourcing up to 250A and sinking up to 20A. If the reference drives an external load, bypass it with 0.22F to GND. If the reference is unloaded, bypass it with at least 0.1F.
__________________Design Procedure
Output Voltage Selection
For the MAX866, you can select a 3.3V or 5V output voltage under logic control, or by tying 3/5 to GND or OUT. The MAX867's output voltage is set by two resistors, R1 and R2 (Figure 2b), which form a voltage divider between the output and FB. Use the following equation to determine the output voltage: R1 + R2 VOUT = VREF ( ________ ) R2 where VREF = 1.25V. To simplify resistor selection: VOUT R1 = R2 ( _____ - 1) VREF
Logic Inputs and Outputs
The 3/5 input is internally diode clamped to GND and OUT, and should not be connected to signals outside this range. The SHDN input and LBO output (opendrain) are not clamped to V+ and can be pulled as high as 7V regardless of the voltage at OUT. Do not leave control inputs (3/5, LBI, or SHDN) floating.
VIN C1 47F L1 330H 8 D1 VOUT C2 47F 1 3 C3 0.1F 5
VIN C1 47F L1 330F 8 D1 VOUT C2 47F
5
LBI
LX
LBI
LX
MAX866
OUT 1 3 C3 0.1F SHDN REF GND 7 3/5 LBO
6 2 4
R1
MAX867
OUT SHDN REF GND 7 FB LBO
6 2 4
R1
OUTPUT SELECT
R2
L1 = COILCRAFT DO1608-334 D1 = MOTOROLA MBR0520LTI
L1 = COILCRAFT DO1608-334 D1 = MOTOROLA MBR0520LTI
Figure 2a. Standard Application Circuit--Preset Output Voltage
Figure 2b. Standard Application Circuit--Adjustable Output Voltage
8
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3.3V/5V or Adjustable-Output, Single-Cell DC-DC Converters MAX866/MAX867
FOR VTH > 1.25V
VIN
FOR VTH < 1.25V
VIN R5
OUT
6 R9 1M
Q1 MMDFZP02E VOUT (3.3V/5V) R11 1M
MAX866
R3 LBI 5
MAX866
LBI
5
MAX866
LBO R6
4 R7 5 R10 1M Q2 2N3904 R8 1M
R4
OUT
6
LBI
(1.25V)
VTH -1 VREF WHERE VTH = THE VIN TRIP THRESHOLD R3 = R4
(
)
VREF - VTH VOUT - VREF WHERE VTH = THE VIN TRIP THRESHOLD R5 = R6
(
)
LOAD
Figure 3. Low-Battery Detector Circuits
Figure 4. Low-Voltage Start-Up Circuit
Since the input bias current at FB has a maximum value of 100nA, large values (10k to 300k) can be used for R1 and R2 with no significant accuracy loss. For 1% error, the current through R1 should be at least 100 times FB's bias current.
Low-Battery Detection, VTH > 1.25V
The MAX866 series contains an on-chip comparator for low-battery detection. If the voltage at LBI falls below the regulator's internal reference voltage (1.25V), LBO (an open-drain output) sinks current to GND. The lowbattery monitor's threshold is set by two resistors, R3 and R4 (Figure 3). Set the threshold voltage using the following equation: VTH R3 = R4 (____ - 1) VREF where VTH is the desired threshold of the low-battery detector and VREF is the internal 1.25V reference. Since the LBI current is less than 100nA, large resistor values (typically 10k to 300k) can be used for R3 and R4 to minimize loading of the input supply. When the voltage at LBI is below the internal threshold, LBO sinks current to GND. Connect a pull-up resistor of 100k or more from LBO to OUT when driving CMOS circuits. When LBI is above the threshold, the LBO output is off. If the low-battery comparator is not used, connect LBI to VIN and leave LBO open.
Figure 3. This circuit uses VOUT (3.3V or 5.0V in the MAX866, adjustable in MAX867) as a reference. The voltage divider formed by R5 and R6 allows the effective trip point of VIN to be set below 1.25V. R6 is usually set to approximately 100k, and R5 is given by the formula: R5 = [R6 x (VREF - VTH)] / (VOUT - VREF) Note that LBI drops below the 1.25V LBI threshold trip point when either VIN or VOUT is low. Since VOUT regulation and the LBI threshold are derived from the same internal voltage reference, they track together over temperature.
Low-Battery Start-Up
The MAX866/MAX867 are bootstrapped circuits; they can start under no-load conditions at much lower battery voltages than under full load. Once started, the output can maintain a moderate load as the battery voltage decreases below the start-up voltage (see Typical Operating Characteristics). The circuit shown in Figure 4 allows the circuit to start with no load, then uses the LBI circuit and an external low-threshold P-channel MOSFET switch to apply the load after the output has started. Resistors R7 and R8 are selected to trip the LBI detector at about 90% of the output voltage. On start-up, LBI and LBO are low, Q2 is off, and transistor Q1's gate is held high by R11. This disconnects the load, allowing the MAX866 to bootstrap itself at the lowest possible voltage. When the output reaches its final output voltage, LBI and LBO go high, turning on Q2, Q1, and the load.
Low-Battery Detection, VTH < 1.25V
When the low-battery detection threshold voltage is below 1.25V, use the circuit shown on the right in
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9
3.3V/5V or Adjustable-Output, Single-Cell DC-DC Converters MAX866/MAX867
Table 1. Component Suppliers
PRODUCTION METHOD INDUCTORS CAPACITORS Matsuo 267 series Sprague 595D series AVX TPS series RECTIFIERS Motorola MBR 0530 Nihon EC15QS02L
Surface Mount
See Table 2
Miniature Through Hole
Sumida RCH654-220
Sanyo OS-CON series low-ESR organic semiconductor PHONE FAX (803) 626-3123 (847) 639-1469 (714) 960-6492 (602) 244-4015 (814) 238-0490 (805) 867-2698 81-3-3494-7414 (619) 661-1055 81-7-2070-1174 (847) 956-0702 81-3-3607-5144 (847) 390-4405 (310) 515-1962
Motorola 1N5017
COMPANY AVX Coilcraft Matsuo Motorola Murata-Erie Nihon Sanyo Sumida TDK J.W. Miller
USA: (803) 946-0690 USA: (847) 639-6400 USA: (714) 969-2491 USA: (602) 244-5303 USA: (800) 831-9172 USA: (805) 867-2555 Japan: 81-3-3494-7411 USA: (619) 661-6835 Japan: 81-7-2070-6306 USA: (847) 956-0666 Japan: 81-3-3607-5111 USA: (847) 390-4461 USA: (310) 515-1720
Inductor Selection
An inductor value of 330H works well in most applications, supplying loads over 10mA and allowing typical start-up voltages of 0.8V. The inductor value is not critical, and the MAX866/MAX867 can operate with values from 22H to 1mH. In general, smaller inductor values supply more output current while larger values start with lower input voltage. Several inductor suppliers and part numbers are listed in Tables 1 and 2. The peak inductor current should not exceed the inductor's current rating. Since the MAX866/MAX867 current limit of 0.5A will not be reached in most applications, the peak coil current (IPK) is: IPK = (VIN(max) x 4.5s) / L For a typical 1-cell alkaline design, VIN(max) is 1.55V, so: IPK = (1.55V x 4.5s) / 330H = 21.14mA
which is well within the ratings of most surface-mount coils. Higher efficiency and output current are achieved with lower inductor resistance, but unfortunately this is inversely related to physical size. Table 2 indicates resistance and height for each coil. Some of the smallest coils have resistances over 10, and will not provide the same output power or efficiency of a 1 coil. At light loads however (below 5mA), the efficiency differences between low- and high-resistance coils may be only a percent or two. The Typical Operating Characteristics graphs show efficiency and output current plots for 1.5 and 2.9, 330H coils.
Capacitor Selection
A 47F, 6V, 0.85, surface-mount tantalum (SMT) output filter capacitor typically provides 15mV output ripple when stepping up from 0.9V to 1.4V at 10mA. Smaller capacitors (down to 10F with higher ESRs) are acceptable for light loads or in applications that can
10
______________________________________________________________________________________
3.3V/5V or Adjustable-Output, Single-Cell DC-DC Converters MAX866/MAX867
Table 2. Surface-Mount Inductor Information
MANUFACTURER /PART Sumida CD73-331 Sumida CD104-331 Murata-Erie LQH4N331K04M00** TDK NLC565050T-331K** Coilcraft D01608-334 Coilcraft DT1608-334 Coilcraft D03316-334 Coilcraft DT3316-334 J.W. Miller PM105-331K * Shielded ** Low cost INDUCTANCE (mH) 330 330 330 330 330 330* 330 330* 330 RESISTANCE (W) 1.5 1.1 8.2 4.9 2.9 2.9 0.7 0.7 1.1 RATED CURRENT (A) 0.28 0.42 0.095 0.14 0.16 0.16 0.6 0.6 0.52 HEIGHT (mm) 3.5 4 2.6 5 3.2 3.2 5.4 5.4 5.4
tolerate higher output ripple. Values in the 10F to 47F range are recommended. The equivalent series resistance (ESR) of both bypass and filter capacitors affects efficiency and output ripple. Use low-ESR capacitors for best performance, or connect two or more filter capacitors in parallel. Low-ESR, SMT tantalum capacitors are currently available from Sprague (595D series) and AVX (TPS series). See Table 1 for a list of suggested capacitor suppliers.
___________________Chip Topography
SHDN LX
3/5 OR FB* GND 0.084" (2.1336mm) REF OUT
Rectifier Diode
For optimum performance, a switching Schottky diode (such as the 1N5817 or MBR0520LTI) is recommended. Refer to Table 1 for a list of component suppliers. For low output power applications, a PN-junction switching diode (such as the 1N4148) will also work well, although its greater forward voltage drop will reduce efficiency and raise the start-up voltage.
LBO 0.058" (1.4732mm) *3/5 FOR MAX866; FB FOR MAX867.
LBI
PC Layout and Grounding
The circuit's high-frequency operation makes PC layout important for minimizing ground bounce and noise. Keep the IC's GND pin and the ground leads of C1 and C2 (Figure 2) less than 0.2in (5mm) apart. Also keep all connections to the FB and LX pins as short as possible. To maximize output power and efficiency and minimize output ripple voltage, use a ground plane and solder the IC's GND (pin 7) directly to the ground plane.
TRANSISTOR COUNT: 357; SUBSTRATE IS CONNECTED TO OUT.
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11
3.3V/5V or Adjustable-Output, Single-Cell DC-DC Converters MAX866/MAX867
________________________________________________________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
E
H
8-PIN MAX MICROMAX SMALL OUTLINE PACKAGE
D
DIM
D A e B
0.101mm 0.004in.
0-8
A1
C
L
A A1 B C E e H L
INCHES MAX MIN 0.069 0.053 0.010 0.004 0.019 0.014 0.010 0.007 0.157 0.150 0.050 0.244 0.228 0.050 0.016
MILLIMETERS MIN MAX 1.35 1.75 0.10 0.25 0.35 0.49 0.19 0.25 3.80 4.00 1.27 5.80 6.20 0.40 1.27
E
H
Narrow SO SMALL-OUTLINE PACKAGE (0.150 in.)
DIM PINS D D D 8 14 16
INCHES MILLIMETERS MIN MAX MIN MAX 0.189 0.197 4.80 5.00 0.337 0.344 8.55 8.75 0.386 0.394 9.80 10.00
21-0041A
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.
12 __________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600 (c) 1996 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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