View MAX1612_29479.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

19-4785; Rev 0; 11/98
UAL IT MAN TION K T VALUA A SHEE E S DAT OLLOW F
Bridge-Battery Backup Controllers for Notebooks
Features
o Reduce Battery Size and Cost o Four Key Circuit Blocks Adjustable Boost DC-DC Converter NiCd/NiMH Trickle Charger Always-On Linear Regulator (+28V Input) Low-Battery Detector o Low 18A Quiescent Current o Selectable Charging/Discharging Rates o Preset Linear-Regulator Voltage 5V (MAX1612) 3.3V (MAX1613) o 4V to 28V Main Input Voltage Range o Internal Switch Boost Converter o Small 16-Pin QSOP Package
General Description
The MAX1612/MAX1613 manage the bridge battery (sometimes called a hot-swap or auxiliary battery) in portable systems such as notebook computers. They feature a step-up DC-DC converter that boosts 2-cell or 3-cell bridge-battery voltages up to the same level as the main battery. This voltage boosting technique reduces the number of cells otherwise required for a 6cell plus diode-OR bridging scheme, reducing overall size and cost. Another key feature is a trickle-charge timer that minimizes battery damage caused by constant charging and eliminates trickle-charge current drain on the main battery once the bridge battery is topped off. These devices contain a highly flexible collection of independent circuit blocks that can be wired together in an autonomous stand-alone configuration or used in conjunction with a microcontroller. In addition to the boost converter and charge timer, there is a micropower linear regulator (useful for RTC/CMOS backup as well as for powering a microcontroller) and a high-precision low-battery detection comparator. The two devices differ only in the preset linear-regulator output voltage: +5.0V for the MAX1612 and +3.3V for the MAX1613. Both devices come in a space-saving 16-pin QSOP package.
MAX1612/MAX1613
Ordering Information
PART MAX1612EEE MAX1613EEE TEMP. RANGE -40C to +85C -40C to +85C PIN-PACKAGE 16 QSOP 16 QSOP
Applications
Notebook Computers Portable Equipment Backup Battery Applications
Typical Operating Circuit
TOP VIEW
MAIN BATTERY OR WALL ADAPTER
Pin Configuration
ISET 1 BBATT 2
LRI DC-DC OUTPUT V+
16 LRI 15 LRO 14 PGND
LX 3 LBO 4
BBATT AUXILIARY BRIDGE BATTERY
MAX1612 MAX1613
APPLICATION CIRCUIT
MAX1630
+3.3V +5V
BBON 5 DCMD 6
MAX1612 MAX1613
13 CD 12 CC 11 GND 10 LBI 9 FB
DC-DC CONVERTER
CCMD 7 FULL 8
VCPU
QSOP ________________________________________________________________ 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 1-800-835-8769.
Bridge-Battery Backup Controllers for Notebooks MAX1612/MAX1613
ABSOLUTE MAXIMUM RATINGS
LRI, ISET to GND....................................................-0.3V to +30V LX to GND ..............................................................-0.3V to +14V PGND to GND .......................................................-0.3V to +0.3V BBATT, LRO, CCMD, DCMD, FULL, BBON, LBO to GND ..........................................................-0.3V to +6V CC, CD, LBI, FB to GND...........................-0.3V to (VLRO + 0.3V) FB, LBI, ISET, and BBATT Current......................................50mA LRO Output Current ...........................................................50mA Continuous Power Dissipation (TA = +70C) QSOP (derate 8.30mW/C above +70C) .................... 667mW Operating Temperature Range MAX1612/MAX1613EEE ...................................-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
(VLRI = VISET = 20V, CCMD = DCMD = BBON = LRO, VBBATT = 3V, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) (Note 1) PARAMETER Linear-Regulator Input Voltage Range Linear-Regulator Quiescent Current SYMBOL VLRI MAX1612 MAX1613 V BBON 2V ILRI V DCMD = 0, R BBON = 1M to GND (boost converter on) 5.7V VLRI 28V (MAX1612) 4V VLRI 28V (MAX1613) 4.7 3.1 CONDITIONS MIN 5.7 4 18 42 5.0 3.3 TYP MAX 28 28 28 58 5.3 A UNIT V
Linear-Regulator Output Voltage
VLRO
0 ILRO 10mA
V
3.5
Linear-Regulator Output Undervoltage Lockout Threshold BATTERY CHARGER ISET Leakage Current BBATT Leakage Current Charge-Switch On Voltage Charge-Switch Loss Current LOW-BATTERY COMPARATOR LBI Falling Trip Voltage LBI Rising Trip Voltage LBI Input Current LBO, FULL Output Leakage Current LBO, FULL Output Voltage Low LBI Comparator Response Time
VUVLO
LRO rising hysteresis = 200mV
2.65
2.97
V
IISET(LEAK)
VISET = 28V, VBBATT = 0 -5 0.5
0.3 1 0.1
5 5 1.3 5
A A V %
IBBATT(LEAK) VISET = 0 or 28V, VBBATT = 6V IISET = 10mA, V CCMD = 0, VBBATT = 2V CCMD = GND, IISET = 10mA, VBBATT = 2V, %loss = [(IISET - IBBATT) / IISET) * 100% VLBTL VLBTH ILBI ILBO, IFULL VLBI = 1.9V V LBO = VFULL = 5.5V ISINK = 1mA tPD Overdrive = 100mV
1.76 1.955
1.8 2 0.2
1.84 2.045 10 1 0.4
V V nA A V s
20
2
_______________________________________________________________________________________
Bridge-Battery Backup Controllers for Notebooks
ELECTRICAL CHARACTERISTICS (continued)
(VLRI = VISET = 20V, CCMD = DCMD = BBON = LRO, VBBATT = 3V, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) (Note 1) PARAMETER DC-DC CONVERTER FB Trip Point FB Input Current LX Switch Current Limit LX Off-Leakage LX On-Resistance LX Zero Crossing Trip Threshold BBON Logic Input Low Voltage TIMER BLOCK CC Output Current CD Oscillator Frequency CC Oscillator Frequency ISET Logic Input Low Voltage CD to CC Current Matching Logic Input Low Level Logic Input High Level Logic Input Leakage Current V CCMD = 0, CC = GND CCD = 3.3nF CCC = 33nF Resets the counter V DCMD = 0, CD = GND CCMD, DCMD CCMD, DCMD V CCMD, V DCMD = 0 to VLRO 2.2 1 4.35 600 60 0.4 -1 5.00 758 75.8 RDSON VFB IFB IPEAK VFB = 2.1V R BBON = 100k to GND VLX = 12V ILX = 200mA Voltage that allows a new cycle, defined as (VBBATT - VLX) (see DC-DC Converter section) -0.2 0.580 1.95 0.15 0.835 0.01 0.5 -0.1 2.05 10 1.100 10 1.5 0.2 2.1 5.65 950 95 1 0.8 V nA A A V V A Hz Hz V % V V A SYMBOL CONDITIONS MIN TYP MAX UNIT
MAX1612/MAX1613
CDOSC CCOSC
VIL VIH I(CCMD), I(DCMD)
Note 1: Specifications from 0C to -40C are guaranteed by design, not production tested.
Typical Operating Characteristics
(Circuit of Figure 3, TA = +25C, unless otherwise noted.)
DISCHARGE TIME vs. OUTPUT CURRENT
MAX612-01
OSCILLATOR FREQUENCY vs. CAPACITANCE
MAX1612-02
EFFICIENCY vs. OUTPUT CURRENT (BBATT = 3.6V)
80 70 EFFICIENCY (%) 60 50 40 30 BBATT = 3.6V RBBON = 240k NOTE: DC-DC CONVERTER SUPPLIES VLRI 1 10 100 1m 10m 100m 1
MAX612-03
120 2 CELLS (SANYO N-50AAA) DISCHARGE TIME (MINUTES) 100 80 VOUT = 5V 60 40 20 0 0 5 10 15 20 25 30 35 40 VOUT = 7V
100k
90 VOUT = 5V VOUT = 7V VOUT = 6V
OSCILLATOR FREQUENCY (Hz)
10k
1k
100 CC
CD
10
20 10
45
1 0.1
0 1 10 CAPACITANCE (nF) 100 1000 OUTPUT CURRENT (A)
OUTPUT CURRENT (mA)
_______________________________________________________________________________________
3
Bridge-Battery Backup Controllers for Notebooks MAX1612/MAX1613
Typical Operating Characteristics (continued)
(Circuit of Figure 3, TA = +25C, unless otherwise noted.)
EFFICIENCY vs. OUTPUT CURRENT (BBATT = 2.4V)
MAX612-04
EFFICIENCY vs. OUTPUT CURRENT (BBATT = 6V)
MAX612-05
QUIESCENT CURRENT vs. LRI VOLTAGE
MAX1612 QUIESCENT CURRENT (A) 40 MAX1613 RBBON = 100k TO GND 30 MAX1612 20 MAX1613 10 VBBON = VLRO
MAX612-06
90 80 70 EFFICIENCY (%) 60 50 40 30 20 10 0 1 10 100 1m 10m 100m 1 OUTPUT CURRENT (A) BBATT = 2.4V RBBON = 240k NOTE: DC-DC CONVERTER SUPPLIES VLRI VOUT = 5V VOUT = 7V VOUT = 6V
90 80 70 EFFICIENCY (%) 60 50 40 30 20 10 0 1 10
BBATT = 3.6V
50
BBATT = 2.4V
VOUT = 6V RBBON = 240k NOTE: DC-DC CONVERTER SUPPLIES VLRI 100 1m 10m 100m 1
0 0 5 10 15 VLRI (V) 20 25 30
OUTPUT CURRENT (A)
PEAK CURRENT vs. BBON CURRENT
MAX612-07
BBATT LEAKAGE CURRENT vs. BBATT INPUT VOLTAGE
MAX612-08
MAX1613 LRO VOLTAGE vs. LRI VOLTAGE
ILOAD = 5mA 3.33
MAX612-09
1200 1000 PEAK CURRENT (mA) 800 600 400 200 0 5 7 9
2.0 1.5 BBATT LEAKAGE CURRENT (A) 1.0 0.5 0 -0.5 -1.0
3.35
VLRO (V)
3.31
3.29
3.27 -1.5 -2.0 3.25 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 0 5 10 15 VLRI (V) 20 25 30 BBATT INPUT VOLTAGE (V)
11 13 15 17 19 21 23 25 BBON CURRENT (A)
MAX1613 LRO VOLTAGE vs. LOAD CURRENT
VLRI = 20V 3.34 3.32 VLRO (V) 3.30 3.28 3.26 3.24 3.22 3.20 0 2 4 6 8 10 12 14 16 18 20 LOAD CURRENT (mA) 100 120
MAX612-10
SWITCHING FREQUENCY vs. RBBON
MAX612-11
3.36
350 SWITCHING FREQUENCY (kHz)
300
250
200
150
160
200
240 RBBON (k)
280
320
360
4
_______________________________________________________________________________________
Bridge-Battery Backup Controllers for Notebooks
Pin Description
PIN 1 2 3 4 NAME ISET BBATT LX LBO FUNCTION Bridge-Battery Charge-Current Input. Connect a current-setting resistor from this input to a voltage higher than the bridge battery. Maximum current rating is 10mA. Pulling ISET below 0.4V resets the internal counter. Bridge-Battery Connection. Bridge-battery charger output. Step-Up DC-DC Converter N-Channel MOSFET Drain. The maximum operating range is 12V. Open-Drain Low-Battery Detector Output. When VLBI falls below 1.8V, LBO sinks current. When VLBI rises above 2.0V, LBO becomes high impedance. Bridge-Battery On Input. When high, the DC-DC converter turns off. When pulled low through an external resistor, the resistor sets the peak inductor current. The inductor current is approximately 42,000 times the current in the external resistor (RBBON). Discharge Command Input. When low with CCMD high, the internal timer counts down at a frequency set by the CD capacitor. When both DCMD and CCMD are low, discharge takes precedence. Charge Command Input. When low with DCMD high, the internal switch from ISET to BBATT is closed, charging the bridge battery. CCMD is inhibited if DCMD is low. The internal timer counts up at a frequency set by the CC capacitor. Open-Drain Bridge-Battery Full Indicator Output. When the internal timer reaches all 1sec, FULL goes high impedance. Feedback Input of Step-Up DC-DC Converter. Regulates to 2V. Connect feedback resistors to set output voltage (Figure 2). Low-Battery-Detector Input. When LBI falls below 1.8V, LBO goes low and sinks current. When LBI goes above 2.0V, LBO goes high impedance. Hysteresis is typically 200mV. Ground Charge Oscillator Capacitor Input. This capacitor programs the charging oscillator frequency, which sets the time for the internal counter to reach all 1s. Determine the capacitor value by: CC (in nF) = 4.3 * charge time (in hours). Discharge Oscillator Capacitor Input. This capacitor sets the discharging oscillator frequency, which determines the maximum time to decrement the counter from all 1s to all 0s. Calculate the capacitor value as follows: CD (in nF) = 4.3 * discharge time (in hours). Power Ground and Step-Up DC-DC Converter N-Channel MOSFET Source 5V (MAX1612) or 3.3V (MAX1613) Linear-Regulator Output. Bypass to GND with a 1F capacitor. Maximum external load current is 10mA. Linear-Regulator Supply Input
MAX1612/MAX1613
5
BBON
6
DCMD
7
CCMD
8 9 10 11 12
FULL FB LBI GND CC
13 14 15 16
CD PGND LRO LRI
_______________________________________________________________________________________
5
Bridge-Battery Backup Controllers for Notebooks MAX1612/MAX1613
VMAIN VCHARGE RISET L1 VBBATT TO MAIN DC-DC COUT
D1 LRI ISET BBATT
LRO TO EXTERNAL LOADS
+3.3/+5V LINEAR REGULATOR
MAX1612 MAX1613
2.0V REFERENCE
LX PULSEFREQUENCY MODULATION CONTROL BLOCK N-CHANNEL PGND FB R1
GND
CC CCC CD CCD
CHARGE OSCILLATOR
TIMER BLOCK CHARGE/DISCHARGE COUNTER
R2 LBI
DISCHARGE OSCILLATOR
R3
1.8V/2.0V FULL CCMD DCMD BBON LBO
RBBON
Figure 1. Functional Diagram
_______________Detailed Description
The MAX1612/MAX1613 manage the bridge battery (auxiliary battery) in portable systems. These devices consist of a timer block that monitors the charging process, a linear regulator for supplying IC power and external circuitry to the MAX1612/MAX1613, and a DCDC step-up converter that powers the system when the main battery is removed (Figure 1). The boost DC-DC converter reduces the number of bridge-battery cells required to supply the system's DC-DC converter. When the main supply is present, the DC-DC converter is inactive, reducing the drain on the main battery to only 18A. However, if the main battery voltage falls (as detected by the low-battery comparator), the bridge battery becomes the input source.
6
The MAX1612/MAX1613 have an internal linear regulator set at +5V (MAX1612) or +3.3V (MAX1613). The linear regulator can deliver a load up to 10mA, making it capable of powering external components such as a microcontroller (Figure 4). An undervoltage lockout feature disables the device when the input voltage falls below the operating range, preventing the DC-DC converter from inadvertently powering up. The MAX1612/MAX1613 feature an internal counter intended to track the charging and discharging process. The counter tracks the charge on the bridge battery, allowing trickle charge to terminate when the maximum charge is achieved. The charging rate is determined by current through the ISET switch, and limited by the switch's maximum current specification as well as by the bridge cell's charging capability. As
_______________________________________________________________________________________
Bridge-Battery Backup Controllers for Notebooks
Timer Block
LRO
MAX1612/MAX1613
1M MICROCONTROLLER 250k GND BBON
MAX1612 MAX1613
I/O
2N7002
Figure 2. Reducing BBON Noise Sensitivity
The MAX1612/MAX1613 have an internal charge/discharge counter that keeps track of the bridge-battery charging/discharging process. When CCMD is low and DCMD is high, the internal counter increments until the FULL pin goes high, indicating that the counter has reached all 1s. The maximum counter value is 221. Additional pulses from the CC oscillator will not cause the counter to wrap around. In the stand-alone application (Figure 3), terminate the charging process automatically by connecting FULL to CCMD. In a microcontroller application, pull CCMD high. The counter only specifies the maximum time for full charging; it does not control the actual rate of charging. CCMD controls the charging switch, and the resistor at ISET sets the charging rate. During the discharging process, drive DCMD low in order to begin decrementing the counter. When the counter is full, FULL is high. As soon as the counter decrements just two counts, the FULL pin sinks current, indicating that the battery is no longer full. The counter only indicates the relative portion of the charge remaining. The incrementing and decrementing rate depends on the maximum charge and discharge times set forth by charging and discharging rates (see the following equations for CC and CD). Note that the actual discharging is caused by the input current of the step-up DC-DC converter loading down the bridge battery, which is controlled via BBON rather than by DCMD. The CC and CD capacitor values determine the upcount and downcount rates by controlling the discharging oscillator frequency. Determine the maximum charge and discharge times as follows: CCC (nF) = 4.3 * tHRS CCD (nF) = 4.3 * tHRS where CCC is the charging capacitor, CCD is the discharging capacitor and tHRS is the maximum time in hours for the process. Choose values that allow for losses in the battery charging and discharging process, such as battery charging inefficiencies, errors in charging current value caused by variable main battery voltages, leakage currents, and losses in the device's internal switch. For charging, use the standard charge rate recommended by the battery manufacturer. The maximum charging current is restricted to the battery specifications. Consult the battery manufacturer's specifications. Do not set the charging current above 10mA.
specifications vary, the counter frequency can be adjusted to accommodate these variances by adjusting CCC. Similarly, the discharging oscillator frequency can be adjusted with the CCD capacitor. However, the rate of bridge battery discharge depends on the DC-DC converter's load. Decrementing the charge/discharge counter is used only to estimate the remaining charge on the bridge battery. The counter increments (or decrements) based on CCMD and DCMD logic states. Note that the net charge must exceed the net discharge to compensate for charging efficiency losses. Figure 3 shows a typical stand-alone application (see Design Procedure for details). It reduces the need for an external microcontroller to manage these functions. However, if the design requires greater flexibility, a microcontroller can be used as shown in Figure 4.
DC-DC Converter
The DC-DC step-up converter is a pulse-frequency modulated (PFM) type. The on-time is determined by the time it takes for the inductor current to ramp up to the peak current limit (set via RBBON), which in turn is determined by the bridge battery voltage and the inductor value. With light load or no load, the converter is forced to operate in discontinuous-conduction mode (where the inductor current decays to zero with each cycle) by a comparator that monitors the LX voltage waveform. The converter will not start a new cycle until the voltage at LX goes below the battery voltage. At full load, the converter operates at the crossover point between continuous and discontinuous mode. This "edge of continuous" algorithm results in the minimum possible physical size for the inductor. At light loads, the devices pulse infrequently to maintain output regulation (VFB 2V). Note that the LX comparator requires the DC-DC output voltage to be set at least 0.6V above the maximum bridge battery voltage.
_______________________________________________________________________________________
7
Bridge-Battery Backup Controllers for Notebooks MAX1612/MAX1613
BRIDGE BATTERY 100F 22H MBR0530 LX 22F PGND 470k 470k FULL CCMD LBO FB 160k DCMD 20k BBON CC 4.7nF CD 68nF LBI GND 200k SYSTEM DC-DC (MAX1630) MAIN BATTERY
BBATT ALWAYS-ON OUTPUT +5V/3.3V
LRO 1F
MAX1612 MAX1613
2.2k ISET 0.33F 442k
Figure 3. Stand-Alone Application
The counter block can be used to estimate the charge remaining in the battery. For example, if the maximum expected charge time is 14 hours (CCC = 60nF) and the maximum expected discharge time is about 2 hours (CCD = 8.6nF), the battery reaches full charge in 14 hours with the FULL pin going high. If the bridge battery must supply the load for 1 hour, the counter will decrement down to about half full. Recharging the battery will now require only 7 hours to reach all 1s in the counter, signaling with FULL going high. If both DCMD and CCMD are pulled low simultaneously, the counter defaults to the discharge mode. When the bridge battery is supplying the circuit, it is considered to be in discharge mode (Table 1).
typical on-state voltage drop of 1V (Figure 1). Therefore, the charge current equals: IISET = [ (VCHARGE - VBBATT ) - 1V] / RISET
Linear-Regulator Output (LRO)
The linear-regulator output, LRO, is set at +5.0V for the MAX1612 and at +3.3V for the MAX1613, with a tolerance of 6%. For powering external circuitry such as the microcontroller shown in Figure 4, LRO is guaranteed to deliver up to 10mA while maintaining regulation. If the voltage at the linear-regulator input falls below the operating range, an undervoltage-lockout feature shuts down the entire device.
Charge Current Selection (ISET)
A resistor between ISET and a voltage higher than the bridge battery sets the charging rate. The switch is open when CCMD is high and is turned on when CCMD is pulled low (assuming DCMD is high). If the voltage at ISET falls below 0.4V, the internal counter resets to all 0s. The internal high-voltage switch has a
Table 1. CCMD, DCMD Truth Table
DCMD 0 0 1 1 CCMD 0 1 0 1 COUNTER Count Down Count Down Count Up No Count ISET SWITCH Off Off On Off
8
_______________________________________________________________________________________
Bridge-Battery Backup Controllers for Notebooks MAX1612/MAX1613
BRIDGE BATTERY 47F MAIN BATTERY 15H MBR0530 LX 20F PGND SYSTEM DC-DC (MAX1630)
BBATT
LRO 1F VCC MICROCONTROLLER I/O I/O I/O 250k I/O I/O I/O 2N7002* 0.01F DCMD CCMD CC CD 0.1F LBI GND LBO FULL FB BBON 470k 470k
MAX1612 MAX1613
2.4k ISET 0.33F 750k
35.2k
479.1k
*OPTIONAL, TO RESET COUNTER
Figure 4. Microcontroller-Based Application
Low-Battery Comparator (LBI, LBO)
The MAX1612/MAX1613 feature a low-battery comparator with a factory-preset 1.8V threshold. This comparator is intended to monitor the main high-voltage battery. As the voltage falls below 1.8V, the open-drain LBO output sinks current. With 200mV of hysteresis, the output will not go high until VLBI exceeds 2.0V. LBO can easily be connected to BBON to start the DC-DC converter when VLBI < 1.8V (stand-alone application, Figure 3). Figure 4 shows an application using a microcontroller, where LBO alerts the microcontroller to the falling voltage and pulls BBON low through an external resistor to start the DC-DC converter while also pulling DCMD low to start the counter.
to 2V, so that when the control input is forced low, the voltage across RBBON is 2V. When driving BBON from external logic, ensure the low state has minimal noise. Otherwise, drive RBBON with an N-channel FET whose source is returned directly to GND (Figure 2).
Applications Information
Design Procedure
The following section refers to the Functional Diagram of Figure 1. Step 1: Select the output voltage and maximum output current for the boost DC-DC converter. Generally, choose an output voltage high enough to run the main system's buck DC-DC converters. Assuming the maximum battery capacity is 50mAh (Sanyo 1.2V N-50AAA), the following equations can help the design process: IPEAK = 2 * IOUT * (VOUT + VD) / (VBBATT - VRDSON) IIN = 0.5 * IPEAK
BBON Control Input
The BBON input serves two functions: setting the peak LX switch current, and enabling the DC-DC converter. The control signal is normally applied to RBBON rather than at the pin itself. The peak LX switch current is directly proportional to and 42,000 times greater than the current through R BBON (see Typical Operating Characteristics). The BBON pin is internally regulated
_______________________________________________________________________________________
9
Bridge-Battery Backup Controllers for Notebooks MAX1612/MAX1613
where IPEAK is the peak current, IOUT is the load current, VBBATT is the bridge-battery voltage, VD is the forward drop across D1, VOUT is the output voltage, IIN is average current provided by the bridge battery, and VRDS(ON) is the voltage drop across the internal Nchannel power transistor at LX (typically 0.5V). A larger number of cells reduces the I PEAK and, in effect, reduces the discharge current, thereby extending the discharge time. The same is true for decreasing the output voltage or output current. For example, choose the following values: IOUT = 100mA, VOUT = 5V, and VBBATT = 2V (two cells). Using the minimum voltage of 1V for each cell, Table 2 summarizes some common values. Step 2: To avoid saturation, choose an inductor (L) with a peak current rating above the IPEAK calculated in Step 1. Use low series resistance ( 200m), to optimize efficiency. In this example, a 15H inductor is used. See Table 4 for a list of component suppliers. The "edge-of-continuous" DC-DC algorithm causes the inductor value to fall out of the peak current equation. Therefore, the exact inductor value chosen is not critical to the design. However, the switching frequency is inversely proportional to inductance, so trade-offs of switching losses versus physical inductor size can be made by adjusting the inductor value.
f= (VBBATT - VRDSON ) (VOUT - VBBATT - VD ) L(IPEAK ) (VOUT - VRDSON - VD ) 1
Table 2. Summary of Common Values for Designing with the MAX1612/MAX1613
VOUT VBBATT AVERAGE (V) (V) IPEAK (mA) 6 5 4.5 6 5 4.5 6 5 2 2 2 3 3 3 4 4 600 500 450 400 333 300 300 250 IIN (mA) 300 250 225 200 167 150 150 125 MINIMUM DISCHARGE TIME (MINUTES) 10 12 13.2 15 18 20 20 24
Note: In this table, IOUT = 100mA and battery capacity = 50mAh.
Table 3. Component List
INDUCTORS Sumida CD43 or CD54 series CAPACITORS Sprague 595D series, AVX TPS series RECTIFIERS BATTERY Motorola MBR0530, NIEC EC10QS03L Sanyo N-50AAA
Table 4. Component Suppliers
SUPPLIER AVX Motorola NIEC Sanyo Sumida PHONE USA: 207-287-5111 USA: 408-749-0510 800-521-6274 USA: 805-867-2555 Japan: 81-3-3494-7411 USA: 619-661-6835 Japan: 81-7-2070-6306 USA: 708-956-0666 Japan: 81-3-3607-5111 FAX USA: 207-283-1941
where f is the switching frequency, VOUT is the output voltage, VRDSON is the voltage across the internal MOSFET switch, VD is the forward voltage of D1, IPEAK is the peak current, and VBBATT is the bridge battery voltage. The maximum practical switching frequency is 400kHz. Step 3: Choose the charging (CCC) and discharging (CCD) timing capacitors. These capacitors set the frequency that the counter increments/decrements. CCC (nF) = 4.3 * expected charge time (in hours) CCD (nF) = 4.3 * expected discharge time (in hours) For instance, using a charge time of 16 hours and a discharge time of one hour, CCC = 68nF and CCD = 4.3nF. (Consult battery manufacturers' specifications for standard charging information, which generally compensates for battery inefficiencies.) Step 4: Using the peak current calculated in Step 1, calculate the series resistor (RBBON) as follows: R BBON = (V BBON * 42,000) / IPEAK where V BBON = 2V (internally regulated).
10
--
USA: 805-867-2556 Japan: 81-3-3494-7414 USA: 619-661-1055 Japan: 81-7-2070-1174 USA: 708-956-0702 Japan: 81-3-3607-5144
Step 5: Resistors R1, R2, and R3 set the DC-DC converter's output voltage and the low-battery comparator trip value. The sum of R1, R2, and R3 must be less than 2M, to minimize leakage errors. Choose resistor R1 = 750k for the example. Calculate R2 and R3 as follows: R2 = [ VOUT (R3) - 2 (R1) - 2 (R3) ] / (2 - VOUT ) R3 = (R1 + R2) / [ (VTRIP / 1.8) - 1]
______________________________________________________________________________________
Bridge-Battery Backup Controllers for Notebooks MAX1612/MAX1613
Table 5. Surface-Mount Inductor Information
MANUFACTURER AND PART Sumida CD43-8R2 Sumida CD43-150 Sumida CD54-100 Sumida CD54-150 Sumida CD54-220 INDUCTANCE (H) 8.2 15 10 15 22 RESISTANCE () 0.132 0.235 0.100 0.140 0.180 RATED CURRENT (A) 1.26 0.92 1.44 1.30 1.11 HEIGHT (mm) 3.2 3.2 4.5 4.5 4.5
where VOUT is the DC-DC converter's output voltage and VTRIP is the voltage level the main battery must fall below to trip the low-battery comparator. For example, for a +5V boost DC-DC output, a 4.75V main battery trip level is feasible. For this case, R1 = 750k, R2 = 26k, and R3 = 474k. Step 6: Select a resistor value to set the charging current. The resistor value at ISET limits the current through the switch for bridge-battery charging. There is a voltage drop across the high-voltage switch (see Electrical Characteristics) with a typical value of 1V. The maximum charge current through the internal highvoltage switch is 10mA. RISET = (VCHARGE - VSWITCH - VBBATT) / ICHARGE where V CHARGE is the charging supply voltage, VSWITCH is the drop across the high-voltage internal switch, V BBATT is the bridge battery voltage, and ICHARGE is the charge current (in amperes).
Microcontroller-Based Application
The MAX1612/MAX1613 are also suited to operate in a microcontroller-based system. A microcontroller-based application provides more flexibility by allowing for separate, independent control of the charging process, the DC-DC converter, and the counter. Independent control can be beneficial in situations where other subsystems are operating, so that automatic switchover of power might create some timing issues. If necessary, a microcontroller can be used to reset the counter by taking ISET low. Another advantage of a microcontrollerbased system is the ability to stop charging the bridge battery during a fault condition. Figure 4 shows an example of how the MAX1612/ MAX1613 can be interfaced to a MAX1630 to deliver the input voltage to the main DC-DC converter. In this example, the microcontroller monitors the main battery's status and switches over to the bridge battery when V MAIN falls below a specified trip level (see Design Procedure). When VMAIN falls below the LBI threshold, LBO goes low. This signals the microcontroller, via an I/O, to switch over to the bridge battery as the input source to the system main DC-DC converter. In this application, the microcontroller also initiates the bridge-battery charging process. When CCMD goes low with DCMD high, the battery is charged through the internal switch. The counter increments until it overflows and FULL goes high, indicating a full charge. The microcontroller I/O can read and write the appropriate states to control the execution and timing of the entire process. If the main DC-DC is supplied by the main source, the MAX1612/MAX1613's step-up converter turns off, minimizing power consumption. The device typically draws only 18A of quiescent current under this condition.
Stand-Alone Application
To reduce cost and save space, the MAX1612/ MAX1613 can be operated in a stand-alone configuration, which eliminates the need for a microcontroller. A stand-alone configuration could also reduce the workload of an existing microcontroller in the system, thus allowing these unused I/Os to be used for other applications. Figure 3 shows the MAX1612/MAX1613 operating without the microcontroller by using the low-battery detector to monitor the main battery. If the main battery is too low, LBO pulls BBON and DCMD low to start the DCDC step-up converter and allow the bridge battery to discharge. If the bridge battery requires charging, FULL pulls CCMD low to start the battery charging process. If both CCMD and DCMD are low, discharging takes precedence and the bridge battery keeps the boost DC-DC converter active.
______________________________________________________________________________________
11
Bridge-Battery Backup Controllers for Notebooks MAX1612/MAX1613
Chip Information
TRANSISTOR COUNT: 3543
Package Information
QSOP.EPS
12
______________________________________________________________________________________

▲Up To Search▲

Price & Availability of MAX1612

	To Download MAX1612 Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .