LTC1558-3.3/LTC1558-5 Backup Battery Controller with Programmable Output U DESCRIPTION FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Complete Battery Backup System in an SO-8, 16-Pin GN or SO Package Generates Adjustable Backup Voltage from a Single 1.2V NiCd Button Cell Automatic Main Supply to Backup Switching Minimum 100mW Output Power Automatic Fast Recharge of NiCd Battery Programmable NiCd Trickle Charge Current Smart NiCd Charger Minimizes Recharge Time and Maximizes System Efficiency After Backup On-Chip Power-On Reset Pushbutton Reset Input Reset Assertion Guaranteed at VCC = 1V Short-Circuit Protection Thermal Limiting U APPLICATIONS ■ ■ ■ ■ Notebook Computers Palmtop Computers/PDAs Portable Instruments Battery-Powered Systems The LTC®1558 is a backup battery controller that provides all the functions necessary to implement a backup power supply using a single NiCd cell. It includes a 1.2V boost converter, an intelligent 2-stage battery charger, automatic backup switching and a microprocessor reset generator. The boost converter uses a synchronous switching architecture to achieve a typical efficiency of 70%, ensuring maximum backup lifetime from a small NiCd cell. The on-chip NiCd charger uses an internal gas gauge to minimize fast recharge time and prevent overcharging of the backup cell. The LTC1558 also provides a user programmable trickle charge current to compensate for self discharge losses in the backup cell. The LTC1558’s automatic backup switching architecture requires minimum intervention from the host system and provides feedback to the host to minimize system loading in the backup state. Its internal VCC fault detector and reset generator eliminate the need for a separate microprocessor supervisory chip in most applications. The LTC1558 is available in an SO-8, 16-lead GN or SO package. , LTC and LT are registered trademarks of Linear Technology Corporation. U TYPICAL APPLICATION L1 22µH* + C1 1µF LTC1558-3.3 R1 14k 1 2 3 4 RESET S1 SW VBAK GND VCC CTL BACKUP FB RESET 8 + C2 0.1µF R2 100k 450 7 6 SYSTEM µP 5 R3 220k MAIN BATTERY 4.5V TO 10V Q1 Si4431DY R4 221k 1% R5 100k 1% + CIN 100µF 16V ×2 LTC1435† SYNCHRONOUS BUCK REGULATOR VCC 3.3V LOAD CURRENT 3A AT NORMAL MODE 30mA AT BACKUP MODE 1558 TA01 *SUMIDA CD54-22µH **SANYO CADNICA N-110AA † CONSULT LTC1435 DATA SHEET FOR CIRCUIT APPLICATION INFORMATION VCC = 3.3V VBAK = 3.78V NiCd CELL CAPACITY = 110mAHrs 400 BACKUP TIME (MINUTES) 1.2V NiCd BACKUP **BATTERY Backup Time vs 3.3V Output Load Current 350 300 250 200 150 100 50 0 0 5 15 20 10 LOAD CURRENT (mA) 25 30 1558 TA02 1 LTC1558-3.3/LTC1558-5 W W U W ABSOLUTE MAXIMUM RATINGS (Note 1) Terminal Voltages VCC .......................................................................................... 6V VBAK, BACKUP ..................................................... 12V SW ...................................................................... 14V All Other Pins .................................. – 0.3V to VCC + 0.3V Input Currents (SW) ........................................... 500mA VBAK Output Current ................... Short-Circuit Protected Operating Ambient Temperature Range ....... 0°C to 70°C Junction Temperature .......................................... 125°C Storage Temperature Range .................. – 65°C to 150°C Lead Temperature (Soldering, 10 sec)................... 300°C U W U PACKAGE/ORDER INFORMATION ORDER PART NUMBER TOP VIEW SW 1 8 VBAK GND 2 7 VCC CTL 3 FB 4 LTC1558CS8-3.3 LTC1558CS8-5 6 BACKUP 5 RESET S8 PART MARKING S8 PACKAGE 8-LEAD PLASTIC SO TJMAX = 125°C, θJA = 130°C/ W 155833 15585 TOP VIEW SW 1 16 VBAK SW 2 15 VBAK PGND 3 ORDER PART NUMBER LTC1558CGN-3.3 LTC1558CGN-5 LTC1558CS-3.3 LTC1558CS-5 14 VCC GND 4 13 BACKUP CTL 5 12 RESET SHDN 6 11 RESET FB 7 10 NC NC 8 9 LOBAT GN PACKAGE S PACKAGE 16-LEAD PLASTIC SSOP 16-LEAD PLASTIC SO TJMAX = 125°C, θJA = 110°C/ W (GN) TJMAX = 125°C, θJA = 110°C/ W (S) Consult factory for Industrial and Military grade parts. ELECTRICAL CHARACTERISTICS SYMBOL PARAMETER VBAT = 1.2V, TA = 0°C to 70°C unless otherwise noted. CONDITIONS MIN TYP MAX UNITS 3.465 5.250 V V Battery Backup Switching VCC Operating Voltage Range VBAT Backup Battery Cell Voltage ● 1.0 1.2 1.5 V VREF Internal Reference Voltage ● 1.247 1.272 1.297 V IVCC Quiescent Supply Current (Note 2) ● 155 250 µA IBAT Peak Inductor Current (Backup Mode) 165 330 225 445 mA mA IBAT(SHDN) Battery Standby Current LTC1558-3.3 LTC1558-5 ● ● Boost Converter in Low Current Mode (Note 7) Boost Converter in High Current Mode (Note 7) ● ● VCC = 0V ● IVCC(SHDN) Supply Current During Shutdown (Note 3) 2.90 4.40 80 225 0.1 ● 15 µA 50 µA VBAK(ON) Backup Request Trip Point Voltage at VFB Relative to VREF ● – 10.5 – 7.5 – 5.5 % VBST(ON) Boost Converter Assertion Trip Point Voltage at VFB Relative to VREF ● – 10.5 – 7.5 – 5.5 % VBAK(OFF) Backup Deassertion Trip Point Voltage at VFB Relative to VREF ● –9 –6 –4 % VBST(OFF) Boost Converter Deassertion Trip Point Voltage at VFB Relative to VREF ● – 10.5 – 7.5 – 5.5 % VLOBAT Low VBAT Detect (Note 3) ● 0.95 1 1.05 V 2 LTC1558-3.3/LTC1558-5 ELECTRICAL CHARACTERISTICS VBAT = 1.2V, TA = 0°C to 70°C unless otherwise noted. SYMBOL PARAMETER CONDITIONS VUVLO(ON) VCC UVLO Trip Voltage (Note 4) LTC1558-3.3 LTC1558-5 VUVLO(OFF) VCC UVLO Recovery Trip Voltage (Note 4) LTC1558-3.3 LTC1558-5 VLOBAT VBAT UVLO Trip Voltage (Note 5) MIN TYP MAX UNITS ● ● 2.90 4.40 3.00 4.55 3.10 4.70 V V ● ● 3.00 4.55 3.10 4.70 3.20 4.85 V V ● 0.85 0.9 0.95 V ● 11 16 21 mA 2 mA Backup Battery Charger ICHGF Battery Charge Current Fast Recharge ICHGT Programmable Trickle Charge Current Range QRECH Fast Recharge Factor (Note 6) QTRK Nominal Trickle Charge Multiplier Factor ICHGT = 1mA VCTL(CLAMP) Trickle Charge Clamp Voltage ICHGT = 1mA 0.05 ● 1.35 1.6 1.85 C/C 8 10 12 A/A 0.45 0.5 0.55 V 250 mV Pushbutton Reset VCTL CTL Input Threshold tCTL CTL Input Low Time (Debounce Time) 20 ms Reset Timer tHRESET Pushbutton Duration for Hard Reset tRST RESET Pulse Width VCTL Low for < tHRESET (Soft Reset) VCTL Low for > tHRESET (Hard Reset) ● ● 1.10 1.8 3.4 s 50 115 80 185 150 345 µs ms VRST1 RESET Output Voltage VCC = 1V, ISINK = 10µA ● 5 200 mV VRST RESET Output Voltage VCC = 4.25V, ISINK = 1.6mA ● 0.1 0.4 V ISC RESET Output Current Output Source Current, VCC = 3.3V Output Source Current, VCC = 5V 10 20 mA mA Short-Circuit Current Output Sink Current, VCC = 3.3V Output Sink Current, VCC = 5V 20 40 mA mA ∆VCC = – (9% VCC + 300mV), VOD = 300mV 9 µs Internal VCC Monitor Comparator tPLH VUVLO(ON) Comparator Propagation Delay (Rising) Shutdown Pin (Note 3) VSHDN ISHDN SHDN Input Threshold SHDN Pin Bias Current Logic Low, VIL Logic High, VIH ● ● VCC = 5V, VSHDN = 0V ● 0.8 V V 8 15 µA 1 10 nA 2 Feedback Pin IFB FB Pin Bias Current The ● denotes specifications which apply over the full operating temperature range. Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: Quiescent current is measured during pushbutton reset. Note 3: Only applies to 16-pin version. Note 4: Thresholds will track each other and are guaranteed not to overlap. Note 5: Low cell voltage reset is only triggered when 0.25V < VCTL < 0.9V for at least 20µs while in backup mode. Note 6: Fast recharge factor is defined as the ratio of charge replenished to the NiCd battery during fast recharge to the charge drawn from the NiCd battery during backup. Note 7: The LTC1558 switches automatically between the low and high operating current levels. See Applications Information for more details. 3 LTC1558-3.3/LTC1558-5 U W TYPICAL PERFORMANCE CHARACTERISTICS Output Power vs Battery Voltage 100 75 50 25 125 VBATT = 1.2V VBAK = 6V POUT = 100mW 2.5 BACKUP TIME (HOURS) 125 OUTPUT POWER (mW) 3.0 VCC = 5V (LTC1558-5) VBAK = 6V SWITCHING FREQUENCY (kHz) 150 Boost Converter Switching Frequency Backup Time vs Battery Capacity 2.0 1.5 1.0 0.5 0 0 1.0 1.1 1.2 1.3 NiCd TERMINAL VOLTAGE (V) 0 1.4 125 250 375 NiCd CELL CAPACITY (mAHr) 1558 G01 60 40 VBATT = 1.2V VCC = 3.3V (LTC1558-3.3) IPK = 330mA 0.995 9.5 9.0 8.5 0.990 0.985 0.980 0.975 0.970 0.965 0.960 8.0 0.955 0.950 0.1 1 NiCd BATTERY TRICKLE CURRENT (mA) 0 2 RESET Output Voltage vs Supply Voltage 3.5 6 VCC = 5V (LTC1558-5) 10 4 3 2 1 64 128 256 BATTERY CAPACITY (mAHr) 512 1558 G07 4 RESET VOLTAGE (V) 20 0 VCC = 3.3V (LTC1558-3.3) 3.0 5 RESET VOLTAGE (V) TIME (HOURS) 50 0 75 1558 G06 RESET Output Voltage vs Supply Voltage Fast Recharge Time (Assume Fully Exhausted NiCd Battery) 30 25 50 TEMPERATURE (°C) 1558 G05 1558 G04 60 10 1.000 10.0 7.5 0.05 10 40 6 4 8 OUTPUT VOLTAGE, VBAK (V) 1.005 CURRENT RATIO (mA/mA) TRICKLE CHARGE FACTOR (mA/mA) DUTY CYCLE (%) 80 2 Normalized Fast Recharge Current vs Temperature VBATT = 1.2V 6 4 8 OUTPUT VOLTAGE, VBAK (V) 25 1558 G03 10.5 2 50 Trickle Charge Multiplier Factor 100 0 75 1558 G02 Boost Converter Switching Duty Cycle 20 100 0 500 VBATT = 1.2V VCC = 3.3V (LTC1558-3.3) IPK = 330mA 4.7V 4.55V 0 1 2 3 4 SUPPLY VOLTAGE (V) 2.5 2.0 1.5 1.0 3.10V 0.5 5 6 1558 G08 0 3V 0 2 3 1 SUPPLY VOLTAGE (V) 4 1558 G09 LTC1558-3.3/LTC1558-5 U U U PIN FUNCTIONS Pin Numbers are Shown First for the SO-8 Package Then the GN16 and S16 Packages SW (Pins 1/1, 2): Boost Converter Switching Node. Connect a 22µH inductor from SW to the positive terminal of the backup cell. In backup mode, this node is alternately switched between ground and VBAK, generating the backup output voltage. In fast or trickle charge mode, an internal regulator outputs a constant DC current from this pin through the 22µH inductor and into the NiCd battery. During power-up or undervoltage lockout (UVLO), the SW pin enters a high impedance state. GND (Pins 2/4): System Ground. The low power internal circuitry returns to this pin in the 16-pin packages. GND and PGND are bonded together to this pin in the SO-8. CTL (Pins 3/5): Control. This pin provides three functions. In backup mode this pin enters a high impedance state and monitors the backup battery cell voltage (VBAT). If VBAT drops below 0.9V, the LTC1558 enters into UVLO. During trickle charge mode, an external resistor REXT sets the trickle charge current. In all modes, pulling the CTL pin below 250mV will generate either a “soft” or “hard” reset pulse. See the Applications Information section for more information. FB (Pins 4/7): Output Voltage Feedback. This pin is fed to the LTC1558’s internal comparators. The boost converter’s output voltage is set with an external resistor divider connected from VBAK to FB. The LTC1558 enters backup mode when FB drops 7.5% below the internal reference voltage (VREF). During backup, the boost converter runs whenever FB drops below this (VREF – 7.5%) threshold. The LTC1558 exits backup mode when FB rises above (VREF – 6%). RESET (Pins 5/11): System Reset, Active Low. This is an open-drain output. This pin provides a low going reset signal to the system processor. A 200ms pulse is generated if the CTL pin is pulled low for more than two seconds (“hard” reset) or when the LTC1558 comes out of UVLO. The “hard reset” stops the internal boost converter if it is running. This pin is held low whenever the LTC1558 is in UVLO and is guaranteed to be valid when VCC is greater than or equal to 1V. RESET also provides a low going 100µs signal if the CTL pin is pulled low for less than two seconds (“soft” reset). Unlike hard reset, soft reset does not affect the LTC1558’s current operating mode. BACKUP (Pins 6/13): Backup Active. This is an open-drain output that pulls low unless the LTC1558 is in backup mode. BACKUP signals the system controller that the system is in backup mode so that it can reduce system loading. BACKUP can also be used to drive the gate of a P-channel MOSFET in series with the main system regulator’s input. A 12V Zener diode is connected internally to this pin to act as a voltage clamp. See the Applications Information section for more details. VCC (Pins 7/14): Power Supply Input. All internal circuits except the boost converter are powered from this pin. A 0.1µF bypass capacitor is required from VCC to ground. The UVLO detector inside the LTC1558 monitors VCC.If VCC drops below the rated output voltage by greater than 9%, the LTC1558 enters UVLO mode and RESET is asserted. The LTC1558 will only exit from UVLO if VCC rises to greater than – 6% of the rated output voltage. See the Applications Information section for more details. VBAK (Pins 8/15,16): Backup Supply Output. The LTC1558’s boost converter provides regulated output voltage to the system through VBAK during backup mode. 16-Pin GN and SO Package PGND (Pin 3): Power Ground. The internal driver circuitry returns to this pin. PGND should be connected to a low impedance ground plane in close proximity to the NiCd battery cell. SHDN (Pin 6): Chip Shutdown. A TTL-compatible active low voltage at SHDN puts the LTC1558 into low power shutdown mode. In shutdown, all internal circuits power down and are held in a reset state. The SW, CTL and VBAK pins enter into high impedance states. In shutdown mode, supply current drops to below 50µA and current drawn from the backup cell drops to below 15µA. 5 LTC1558-3.3/LTC1558-5 U U U PIN FUNCTIONS LOBAT (Pin 9): Low-Battery Detector Output. This is an open-drain output that pulls low when the backup cell drops below 1V. It gives early warning to the system controller that the backup cell is getting weak. This pin is disabled when the LTC1558 is in trickle charge mode. RESET (Pin 12): System Reset, Active High. This is a TTLcompatible output driver. It can be used to connect to systems that require active high logic. The RESET output will go high whenever RESET is pulled low. If RESET is externally pulled low, RESET will go high. W BLOCK DIAGRAM P1 SW VBAK VCC/VBAK CHARGER CTL N1 BOOST/BACKUP LOGIC + FB RESET – LEVEL SENSE AND DEBOUNCE VREF VCC BACKUP VREF GAS GAUGE – RESET GENERATOR RESET + LOBAT – + UVLO DETECTOR THERMAL LIMIT SHUTDOWN LOGIC SHDN BANDGAP VREF = 1.272V 1558 BD U W SWITCHING WAVEFORMS Simplified LTC1558 Connections in a Battery Backup System 1.2V NiCd Cold Power Boot-Up (Main Battery Replaced/Turned On) TO SYSTEM CONTROL SW BACKUP RESET LTC1558 VBAK FB RATED BATTERY TERMINAL VOLTAGE 1 VBAT 2 3 4 – 6% RATED VCC VOLTAGE VCC VBAK QEXT VBAT MAIN BATTERY R1 VIN + CIN MAIN SYSTEM REGULATOR MULTIPLE POWER OUTPUTS VCC 200ms RESET R2 FOR MORE DETAILED APPLICATION SCHEMATICS PLEASE REFER TO THE TYPICAL APPLICATIONS SECTION 1558 SW01 BACKUP 1558 SW02 6 LTC1558-3.3/LTC1558-5 U W SWITCHING WAVEFORMS Cold Power Boot-Up Description 3. The LTC1558’s internal bandgap wakes up. The LTC1558’s internal boost converter does not turn on as RESET remains asserted. Once VFB is greater than (VREF – 6%), BACKUP is deasserted after the tPHL delay time. QEXT turns on and VBAK = VBAT. 1. The VBAT voltage increases and turns on the QEXT body diode. VBAK follows VBAT by one body diode drop. 2. VBAK increases above the system regulator’s minimum input voltage. The system regulator wakes up and starts ramping up the system power supply. RESET remains asserted from VCC = 1V. 4. RESET is asserted for a further 200ms after VCC exceeds – 6% of its rated value. Backup Mode (Main Battery Discharged) 1V 1.2V 0.9V VNICD BOOST CONVERTER OUTPUT – 7.5% –6% – 7.5% – 7.5% VFB tRISE tFALL BACKUP INDUCTOR CURRENT tRISE tRISE RESET tRISE LOBAT 1 2 3 4 1558 SW03 Backup Mode Description 1. Trigger into Backup Mode. The main battery fails and VFB drops 7.5% below the LTC1558’s internal VREF. The BACKUP pin is asserted after a tRISE delay time and the LTC1558’s boost converter is turned on. 2. Backup Mode. The LTC1558’s boost converter charges and discharges the inductor with 165mA peak current. If VFB doesn’t recover above (VREF – 7.5%) (due to a heavy load), the boost converter increases peak charging current to 330mA. When V FB rises above (VREF – 7.5%), the boost converter stops but the BACKUP pin remains asserted. 3. Recovery from Backup Mode. While the boost converter is running, the main battery is restored. This causes the external MOSFET’s body diode to conduct and VFB is pulled higher than (VREF – 6%). BACKUP deasserts and the boost converter finishes its last cycle. 4. Trigger into UVLO. During backup, the 1.2V NiCd cell grows weak and its terminal voltage falls. The LOBAT pin is asserted to give an early warning when the cell voltage drops below 1V. RESET is asserted when the cell voltage drops below 0.9V and the LTC1558 enters UVLO mode. 7 LTC1558-3.3/LTC1558-5 U W U U APPLICATIONS INFORMATION Overview The LTC1558 is a versatile backup battery control system designed to provide all the functions necessary to implement a complete, highly integrated backup system within a single chip. It allows the system to maintain its rated supply voltage during backup, offering maximum system design flexibility. The LTC1558 allows the use of a low cost rechargeable NiCd cell for backup, eliminating the need for expensive, replaceable 4.5V lithium backup cells. The LTC1558 includes an onboard boost converter designed to generate an adjustable voltage (3V to 10V) from a single 1.2V NiCd cell. This voltage is connected to the system’s DC/DC converter input, enabling the system to continue operation when the main battery fails. A “smart” recharging circuit uses an accumulating gas gauge to measure the charge extracted from the backup battery during a backup cycle. This measured charge is then replaced in a fast recharge cycle, without wasting excess power or overcharging the backup cell. An externally adjustable trickle charge circuit maintains the cell charge after the fast charge cycle has completed, minimizing drain from the main battery during standby. Included in the LTC1558 is a complete backup circuit that monitors the main system power and automatically switches in the backup circuit as the primary power supply falls away (due to a weak or disconnected main battery). The LTC1558 also performs VCC supervisory functions during normal system operations. An LTC1558-3.3 monitors a 3.3V supply voltage at its VCC pin whereas an LTC1558-5 monitors a 5V supply at its VCC pin. In both cases, the LTC1558 derives power for the majority of the internal circuitry (except for the boost converter) from the VCC pin. Table 1 shows the signal conditions for the LTC1558’s various operating modes. Note that VCC in Table 1 refers to the rated VCC voltage, 3.3V or 5V. Boost Converter Operation The LTC1558 uses an onboard synchronous boost converter with a fixed peak current architecture that provides a simple and flexible system solution while eliminating the need for conventional frequency compensation. The boost converter’s output, set by the external divider connected to the FB pin, supports the main system regulator during 8 Table 1 OPERATING MODES CONDITIONS UVLO Reset 1V < VCC < VCC (Rated Value) – 9% or VBAT < 0.9V Pushbutton Reset VCTL < 250mV UVLO Reset Recovery VCC > VCC (Rated Value) – 6% Backup Mode Activation VFB < (VREF – 7.5%) Backup Mode Exit VFB > (VREF – 6%) Boost Converter Activation VFB < (VREF – 7.5%) Boost Converter Deactivation VFB > (VREF – 7.5%) backup. It can supply a minimum backup power of 100mW. The boost converter operates in a modified pulse skipping mode; each switch cycle transfers a known amount of charge from the backup cell to the regulated output. This prevents uncontrolled discharge of the backup cell and allows the LTC1558 to accurately measure the charge removed from the backup cell by counting the charge pulses. The LTC1558 enters backup mode when the main battery voltage drops. As shown in Figure 1, the main battery voltage is scaled down by an external resistor divider and fed to the LTC1558’s backup comparators. These compare the scaled voltage with an internal trimmed VREF (1.272V), switching the LTC1558 into backup mode when VFB drops 7.5% below VREF. Upon entering backup mode, the BACKUP pin is asserted and the internal boost converter turns on. The BACKUP signal is used to turn off the external P-channel MOSFET, isolating the main battery from the LTC1558 and the system regulator’s input. The LTC1558’s boost converter will charge the input capacitor CIN of the system regulator until VFB rises above (VREF – 7.5%). TO SYSTEM REGULATOR INPUT LTC1588 MAIN BATTERY + CIN BOOST CONVERTER R1 FB BACKUP LOGIC R2 VBAK BACKUP VREF 1558 F01 Figure 1. Typical LTC1558 Connection LTC1558-3.3/LTC1558-5 U U W U APPLICATIONS INFORMATION Once VFB rises above (VREF – 7.5%), the LTC1558’s boost converter deactivates and the freshly charged input capacitor supplies power to the system regulator. The cycle repeats again when the input capacitor’s charge is drained away and VFB again drops below (VREF – 7.5%). The BACKUP pin remains asserted until the main battery is restored. This ensures that the LTC1558 does not switch in and out of backup mode unnecessarily. The LTC1558’s boost converter minimizes output ripple under light load conditions by reducing the charge transferred for the first two consecutive switch cycles. When VFB falls below (VREF – 7.5%), the boost operation starts by connecting the SW pin to ground through an internal 0.5Ω N-channel MOSFET (N1 in the Block Diagram). The current through the external 22µH inductor rises linearly through this switch. VBAK Capacitor ESR 330mA (PEAK) 165mA (PEAK) LIGHT CURRENT MODE HEAVY CURRENT MODE and doubles the internal inductor charging current limit to 330mA for subsequent cycles. This is high current mode. By doubling the peak inductor current, each boost cycle effectively carries four times more energy compared to low current mode (E = 1/2 • LI2), doubling the available output power. When VFB exceeds the (VREF – 7.5%) boost threshold, the LTC1558 stops the boost converter and resets the internal two pulse counter. The next time VFB falls below (VREF – 7.5%), the boost converter restarts in low current mode for at least two boost cycles. Moderate or changing loads will cause the LTC1558 to shift between the two peak inductor current limits, keeping the output in tight regulation. Near its maximum load capability, the LTC1558 will stay in 330mA high current mode and the output voltage VBAK will hover around the user programmed value. 1558 F02 Figure 2. Inductor Current During Switching When the switch current reaches an internally preset level of 165mA, the boost converter connects the SW pin to the VBAK pin through an internal 2Ω P-channel MOSFET (P1 in the Block Diagram). The inductor current discharges through P1, charging up the capacitor connected externally to VBAK (CIN of the system regulator, Figure 1). The inductor current falls at a rate proportional to the difference between the backup cell voltage and the output voltage VBAK. When the inductor current reaches zero, indicating all of its energy has been transferred to the output capacitor, the LTC1558 looks at the FB pin voltage. If VFB has increased above the (VREF – 7.5%) threshold, the boost converter shuts off both switches and waits for VFB to drop below (VREF – 7.5%) again. If VFB is still less than (VREF – 7.5%) after the first boost cycle, the LTC1558 immediately reconnects SW to ground, repeating the boost cycle. If after two consecutive pulses, VFB is still not above the boost threshold (VREF – 7.5%), the LTC1558 decides that the load is not so light after all, The type of output capacitor and the user programmed VBAK value will affect the LTC1558’s output ripple and efficiency. In most applications, the main VBAK capacitor is primarily determined by the requirements of the main power supply. Such a capacitor will generally meet the requirements of the LTC1558. In unusual circumstances or circuits where the main system regulator’s input capacitor is located some distance away from the LTC1558, a local output capacitor may be necessary. 1 BOOST CYCLE VBAK ESR RIPPLE DISCHARGE PERIOD tDISCH CHARGE PERIOD tCH 1588 F03 Figure 3. VBAK Ripple The maximum ripple on the VBAK pin is equal to capacitor ESR voltage drop due to the boost converter’s output current pulses. The ripple frequency and output duty cycle is proportional to the inductor discharge time. Given a fixed inductor value (22µH) and a known peak current limit, the booster’s discharge time in each boost cycle is 9 LTC1558-3.3/LTC1558-5 U W U U APPLICATIONS INFORMATION proportional to the difference between VBAK (3V to 10V) and the battery cell voltage, VBAT (1.2V). Assuming ESR = 0.2Ω, IIND(PEAK) = 330mA, VBAK = 6V, VRIPPLE(P-P) = (IIND(PEAK))(RESR(CAP)) = (330mA)(0.2Ω) = 66mV Since VBAK must be scaled down to VFB, the external resistor ratio = 6V/1.272V = 4.717 Therefore the noise amplitude seen by the FB comparators is: = 66mV/4.717 = 14mV The discharge time period, tDISCH = (L • IIND(PEAK))/(VBAK – VBAT) = (22µH • 330mA)/(6V – 1.2V) = 1.5µs For lowest VBAK = 3V and maximum IIND(PEAK) = 445mA, VRIPPLE(P-P) = 89mV RB resistor ratio = 2.358 Noise amplitude = 37.7mV tDISCH = 5µs The internal VFB comparators are designed to have a slow response time to filter away this ripple. The (VREF – 6%) FB comparator has a 6µs rising edge delay and 2µs falling edge delay. The (VREF – 7.5%) FB comparator has a similar 6µs rising time delay but a much longer falling time delay of 20µs. This enables the comparator to control the booster properly, and avoids turning off the boost converter prematurely due to false triggering by the ESR ripple. Exit from Backup When a new battery is inserted into the system, the higher main battery voltage turns on the external P-channel MOSFET’s body diode and raises VBAK (and VFB) to a higher voltage. The LTC1558 detects the return of the main 10 battery by watching for VFB to exceed (VREF – 6%). The LTC1558 then stops its internal boost converter and begins to recharge the NiCd cell. BACKUP is deasserted to signal to the system controller to restore system loading and resume normal operations. At the same time, the external P-channel MOSFET is driven by the BACKUP signal. The P-channel MOSFET turns on and allows the main battery to bypass its body diode and drive the system regulator directly. Since the user can replace the main battery anytime during the LTC1558’s backup operations, the BACKUP signal may be deasserted while the boost converter is switching. To prevent the potential problem of residual energy in the inductor, the LTC1558 will only stop the boost converter after it has completed the current boost cycle. UVLO Lockout Under Excessive Backup Load Very heavy loads (above the LTC1558’s maximum power output) will pull the boost converter’s output below the boost threshold. Under these conditions, the LTC1558’s boost converter will continue to supply 330mA current pulses to the system regulator while charge on the VBAK capacitor (CIN) drains away. The system regulator will not maintain its output regulation and the system VCC will drop. When VCC drops below – 9% of the rated voltage for more than 9µs, the LTC1558’s VCC supervisory circuit activates UVLO mode, shutting off the boost converter and asserting the RESET pins. The 9µs delay prevents the LTC1558 from being fooled by brief transients or noise spikes on its VCC pin. Upon receipt of the reset signals, the host system should shut down in a orderly manner. The LTC1558’s VCC supervisory circuit will remain alive until VCC is less than 1V to ensure valid reset pin signals. Backup Cell Voltage Monitoring As the boost converter removes charge from the backup NiCd cell, the cell’s terminal voltage falls. Permanent damage to the NiCd cell can occur if it is discharged to below 0.9V. To prevent this, the LTC1558 monitors the cell’s terminal voltage through the CTL pin during backup. If the CTL pin drops below 0.9V for more than 20µs, the UVLO circuit shuts down the boost converter and asserts the RESET pins. Since the CTL pin can also be connected to an external pushbutton reset, the LTC1558 includes LTC1558-3.3/LTC1558-5 U W U U APPLICATIONS INFORMATION internal logic to ensure that the low cell voltage reset is triggered only if the CTL pin is between 0.9V and 0.25V. This will prevent a pushbutton reset (which pulls CTL below 250mV) from being mistaken as a low cell voltage condition. Unusual situations where the NiCd cell voltage drops drastically below 0.25V will also trigger UVLO, since the LTC1558 will treat this as a “hard” reset after 2 seconds. The LTC1558’s boost converter is designed so that no current drains from the battery to the load during output short circuit or VCC = 0V conditions. This assures that the system can be powered down for a long period of time. This eliminates the risk of finding a nonfunctioning backup system upon power-up. An optional LOBAT output, available in the 16-pin GN or SO package, can be used to signal the system when the cell voltage falls below 1V, giving an early warning that the backup cell is heavily discharged. The LOBAT output is disabled when the LTC1558 is in trickle charge mode because the CTL pin is pulled to 0.5V by the LTC1558. The LTC1558 includes an onboard gas gauge circuit, consisting of a 23-bit divider and a 9-bit up/down counter. The gas gauge logic assumes that the boost converter uses a 22µH inductor, allowing it to estimate battery charge by counting switch pulses. The gas gauge counts up from zero as charge is removed from the backup cell in backup mode. It takes roughly 8.4 million 165mA boost pulses (low current mode) to increment the up/down counter by one count. In high current mode, the 330mA pulses skip the first two bits of the divider because each 330mA pulse carries four times as much energy as a 165mA pulse. At maximum load and VCC = 5V, the gas gauge divider will increment by one count every 7.5µs while the boost converter is running. Full count is reached after approximately 2.2 hours, equivalent to about 512mAhr of charge. Fault Protection and Thermal Limit The LTC1558’s boost converter incorporates two internal timers that turn off the switch transistors if the inductor charge or discharge time gets abnormally long. The inductor charge time may get abnormally long if the NiCd cell voltage drops below 0.25V without triggering the 0.25V < VBAT < 0.9V low cell voltage comparator. In this case, the NiCd cell is assumed to be damaged and the LTC1558’s priority is shutting down the system gracefully. In this case, the timer will shut off the N-channel switch transistor after a maximum charging time (14µs). The boost converter continues switching but delivers reduced output power, causing VCC to drop. The LTC1558 will enter UVLO either when V CC drops below (VCC(RATED VOLTAGE) – 9%) or after the LTC1558 detects CTL lower than 0.25V for 2 seconds, in which case “hard” reset occurs. The discharging time can also get abnormally long if a serious overload condition occurs during switching. The timer will shut off the P-channel pass transistor after 10µs, protecting the boost converter. The LTC1558 will end up in UVLO as VCC drops below (VCC(RATED VOLTAGE) – 9%). In addition, the LTC1558 is protected for safe area operation with an internal thermal shutdown circuit. If the device is overloaded for a long period of time, the thermal shutdown circuit forces the LTC1558 into UVLO. The threshold temperature for thermal shutdown is typically 155°C. Backup Cell Fast Recharge Upon entering recharge mode (after the main battery is restored) the LTC1558 connects a 16mA fast recharge current source from VCC to the SW pin. At the same time, an internal free running oscillator counts down the gas gauge counter at a rate designed to replace about 160% of the charge previously removed from the backup cell. When the gas gauge counter reaches zero, the LTC1558 reduces the charging current at the SW pin to the userprogrammed trickle charge current level. Under some circumstances, the LTC1558 can exit the backup mode with invalid gas gauge contents. This can occur under three possible conditions: a) The backup cell was completely exhausted during a backup cycle and the LTC1558 entered UVLO. b) The backup cell was replaced while the main supply was disabled. c) A backup cycle was terminated prematurely by a “hard” reset or an output overload. 11 LTC1558-3.3/LTC1558-5 U W U U APPLICATIONS INFORMATION In these cases, the LTC1558 assumes that the backup cell is exhausted and presets the gas gauge counter to a default capacity of 128mAhr. It then initiates a recharge cycle. Setting the gas gauge to this default value results in a fast recharge cycle long enough to replenish 1.6 times 128mAhr of charge into the backup cell (13.9 hours). If the backup cell is actually exhausted, it will be fully recharged. If the battery is partially or fully charged, or is significantly smaller than 128mAhr capacity, the extra charging time will be wasted. However, the LTC1558’s 15mA fast charge current should not be high enough to damage the cell. Once the full-count recharge has been completed, the backup cell is assumed to be fully charged and subsequent backup/recharge cycles resume normally. Although the LTC1558 will not fully recharge backup cells larger than 128mAhr capacity upon power-up, it can still be used with such cells. Such a cell will be fully replenished by the subsequent trickle charge cycle. Under most conditions, even a partially charged large cell will still be capable of supporting several hours of backup. For example, a small 60mAhr button cell can back up the system for 20 minutes at an output power of 100mW. Note that at lower programmed VBAK values, the boost converter efficiency improves and allows more backup time from the same cell compared to a higher VBAK value. Once it reaches full recharge, a cell bigger than 512mAhr is likely to overrun the gas gauge counter before it runs out of charge during an extended backup cycle. The LTC1558 gas gauge counter will not roll over if this occurs; it will stay at full count until the backup cycle ends and then partially recharge the cell with a full count cycle as above. Very short backup cycles (< 32s) may not extract enough charge from the backup cell to increment the gas gauge counter at all. To ensure that the backup cell is not slowly “nibbled” away, the gas gauge counter is always incremented by 1mAhr each time the controller comes out of backup. This ensures that the backup cell is always replenished with at least a 1mAhr charge every time the LTC1558 enters backup mode. 12 Battery Backup Cell Trickle Charge When the gas gauge counter reaches zero, the LTC1558 terminates fast recharge and reduces the recharge current to the user-programmed trickle current level. The LTC1558 provides a trickle current that the user can program from 50µA to 2mA. The trickle current is set by an external resistor from the positive terminal of the backup cell to the CTL pin. In trickle charge mode, CTL is regulated to 0.5V, resulting in a CTL pin current of (VBAT – 0.5)/REXT. This current is internally multiplied to feed back ten times the REXT current into the backup battery. Since the LTC1558 trickle charges only after the completion of the fast recharge cycle, the backup cell voltage should be very close to 1.2V. This simplifies the calculation of the REXT resistor value. For example, a 47k resistor from VBAT to CTL sets the trickle charge current to approximately 150µA. VCC 10I 1.2V NiCd CELL SW + I 47µF REXT CTL 1× 11× – + + – 0.5V LTC1558 1558 F04 Figure 4. Trickle Current Charger Undervoltage Lockout The LTC1558 includes an undervoltage lockout (UVLO) system that ensures that the system will shutdown gracefully if the backup cell is exhausted or overloaded. As described in the previous section, the LTC1558 will LTC1558-3.3/LTC1558-5 U W U U APPLICATIONS INFORMATION terminate backup operation and remain off until the main power supply returns. It then runs a fast recharge cycle to recharge the backup cell. An onboard low-battery comparator in the 16-pin GN or SO package provides an early warning signal when the backup cell drops below 1V. The UVLO circuit also trips if the LTC1558’s VCC supervisory circuit detects that VCC drops below – 9% of the rated VCC voltage due to overload or output short-circuit conditions. Once the UVLO circuit trips, the LTC1558 asserts the RESET pins until the VCC voltage drops below 1V. It will then remain off until VCC rises to within (VCC – 6%) of the rated output voltage. During power-up from UVLO, the LTC1558 asserts the RESET pins until the (VCC – 6%) threshold. Once VCC exceeds (VCC – 6%), the RESET pins remain asserted for another 200ms (“hard” reset) before being released to inform the system to start operating. Reset Operation The LTC1558 includes an onboard pushbutton reset switch controller. If the CTL pin is pulled to ground (< 250mV) by a pushbutton or an open-drain output, the LTC1558 generates a pulse at the RESETpins after the trailing edge of CTL B > 0.25V A 0V 20ms < tCTL < 2s tCTL < 20ms RESET 20ms DEBOUNCE 100µs 100µs > 0.25V 0V tCTL > 2s RESET 2s 200ms “HARD” PUSHBUTTON RESET AT CTL CTL < 0.25V FOR MORE THAN 2s CTL The RESET pin is an open-drain output that requires an external pull-up resistor. The RESET pin is a TTL-compatible CMOS output. Shutdown The 16-pin LTC1558 has a TTL-compatible input, SHDN, that shuts down the whole chip, asserts the RESET pins and places the CTL, VBAK and SW pins into high impedance states. The SHDN pin has an internal pull-up that ensures the chip will not shut down if the pin is left floating. The SHDN pin typically draws 8µA when pulled low at VCC = 5V. The chip consumes less than 50µA during shutdown while VCC is still alive. Although there is no SHDN pin for the SO-8 package, the user can shut down the part by pulling CTL to ground. The chip enters “hard” reset leaving only the bandgap and comparators alive. The charger and the boost converter shut off completely. Note that the backup cell slowly discharges through REXT in this mode. Inductor Selection “SOFT” PUSHBUTTON RESET AT CTL A. CTL < 0.25V FOR LESS THAN 20ms B. CTL > 0.25V FOR MORE THAN 20ms CTL the CTL signal. A short (less than 2s) low going signal at CTL will generate a “soft” reset (100µs) pulse at the RESET pins. A low CTL signal for more than 2s will generate a “hard” reset pulse at its RESETpins. During “hard” reset, the LTC1558 will disable the boost converter if it is in backup mode. All signals at the CTL pin are debounced for 20ms to prevent multiple resets, allowing the CTL pin to be connected directly to a pushbutton to ground. 0V 20ms RESET 20ms 20ms DEBOUNCE AT FALLING AND RISING RESET EDGE 1558 F05 The LTC1558 is designed to operate with a recommended inductor value of 22µH (±20%) with < 0.2Ω DC resistance. Using inductor values higher than 22µH will deliver more output power but will cause the gas gauge counter to count inaccurately and under recharge the backup cell. At the same time, the N-channel transistor timer will limit the peak current if the charging time becomes overextended due to the higher inductor value. Using inductor values lower than 22µH will degrade the boost converter’s maximum output power and cause the gas gauge counter to overcharge the backup cell. Table 2 lists the recommended surface mount inductor part numbers. Figure 5. Pushbutton Resets 13 LTC1558-3.3/LTC1558-5 U W U U APPLICATIONS INFORMATION Table 2. Recommended Inductors Table 3. Button/Cylindrical NiCd 1.2V Cells MANUFACTURER PART NUMBER TYP INDUCTOR VALUE DCR (Ω) MANUFACTURER Sumida CD54-220 22µH ±20% 0.18 Sumida CDRH73/74 22µH ±20% 0.2/0.11 Capacitor Selection The LTC1558 requires a minimum VBAK capacitor of 44µF to ensure that the boost converter can regulate the output at 20mA load. The capacitor’s ESR should be small (< 0.2Ω) to minimize voltage spikes that might incorrectly trigger the LTC1558’s internal FB comparators. Note that the LTC1558 can usually share the output capacitor with the system regulator. Thus its ratings like VMAX, IRIPPLE(RMS), etc., will all have to meet the system regulator’s specifications as well. Battery Selection A primary application for the LTC1558 is a “bridging” supply, only providing backup current while the main system battery is being replaced. In these applications, the LTC1558 works well with NiCd button cells or small cylindrical cells, reducing system costs and board space. It is optimized for use with up to 512mAhr battery capacities. The LTC1558 can work with standard or memory backup specific NiCd cells. Memory backup cells can operate at higher temperatures and have lower self discharge rates. The LTC1558’s trickle charger is designed to accommodate both memory backup cells (with low self discharge) and standard cells (with higher self discharge). Some recommended manufacturers and part numbers are listed in Table 3. 14 PART NUMBER CAPACITY (mAhr) RSERIES (Ω) SAFT (Memory Backup) GB60 GB170 GB280 60 170 280 1.1 0.4 0.4 SAFT (Standard) VB10E VB22E VB30E VB60E 100 220 300 600 0.038 0.022 0.017 0.014 Sanyo (Standard) N-50AAA N-110AA N-120TA N-150N N-200AAA N-270AA N-500A 55 120 130 170 220 305 500 0.055 0.03 0.034 0.027 0.021 0.015 0.09 Panasonic (Standard) P-11AA 110 0.08 The internal resistance of the backup cell increases power dissipation as the boost converter draws current from it during switching, degrading efficiency. Due to the fixed inductor peak current architecture, the LTC1558’s boost converter output power drops significantly when the NiCd cell’s internal resistance increases at the end of its charge. This is because the inductor charging time will increase due to a larger R/L time constant, decreasing the switching frequency. It is advisable, especially for batteries with high internal resistance, to include a 47µF bypass capacitor across the battery to ensure that the boost converter can deliver the maximum output power regardless of the NiCd internal resistance. LTC1558-3.3/LTC1558-5 U TYPICAL APPLICATIONS LTC1558-3.3 Low Main Battery Voltage (4.5V to 10V) Application L11† 22µH BACKUP BATTERY 1.2V NiCd R14 14k + C11 47µF 6.3V 3 RESET PUSHBUTTON 2 4 1 SW 7 VCC FB + 8 CTL VBAK LTC1558-3.3 GND RESET C12 1µF 5 RESET 6 BACKUP BACKUP R13 100k MAIN BATTERY 4.5V TO 10V Q11 P-CHANNEL Si4431DY R11 221k 1% *SUMIDA CDRH125-10 **IRC LR2D1D-01-RQ33-F † SUMIDA CD54-220 R12 100k 1% + + C2 1µF 13 VIN 9 4 6 3 CC 330pF 2 CSS 0.1µF CC2 51pF RC 10k COSC 68pF 1 EXTVCC 16 SW BOOST LTC1435 VOSENSE INTVCC ITH SENSE + RUN/SS SENSE – BG SGND 5 CIN 22µF 35V ×2 TG SFB COSC Q1 N-CHANNEL Si4412DY PGND 10 14 15 C4 0.1µF L1* 10µH 12 8 RSENSE** 0.033Ω D1 CMDSH-3 7 + CIN 100µF 10V ×2 R1 35.7k 1% R5 20k 1% C6 100pF C5 1000pF 11 + C3 4.7µF 16V C1 100pF Typical “Low Voltage” Application The maximum main battery voltage is less than the maximum VBAK pin voltage (12V). This configuration has the lowest number of external components. The LTC1435’s minimum input voltage is 3.5V. The VBAK voltage, set by R11 and R12, is programmed to 3.8V. Therefore, the main battery’s lowest voltage should be 3.8V + 1 body diode drop = 4.5V. This will enable a fresh Q2 N-CHANNEL Si4412DY D2 MBRS140T3 VOUT 3.3V 3A 1558 TA03 main battery to turn on the external P-channel MOSFET and power up the system out of UVLO during cold power boot or out of backup mode when the LTC1558 is powering up the system. A 100k pull-up resistor enables the open-drain BACKUP pin to turn the external P-channel MOSFET off when VBAK is higher than VCC. 15 LTC1558-3.3/LTC1558-5 U TYPICAL APPLICATIONS LTC1558-5 Medium Main Battery Voltage (7V to 18V) Application L11† 22µH BACKUP BATTERY 1.2V NiCd R14 14k + C11 47µF 6.3V 3 RESET PUSHBUTTON 2 4 1 SW 7 VCC FB + 8 CTL VBAK LTC1558-5 GND RESET 5 RESET 6 BACKUP BACKUP R13 100k MAIN BATTERY 7V TO 18V Q11 P-CHANNEL Si4431DY R11 422k 1% + C2 1µF 13 VIN 9 4 6 3 CC 330pF 2 CSS 0.1µF CC2 51pF RC 10k COSC 68pF 1 EXTVCC 16 SW BOOST LTC1435 VOSENSE INTVCC ITH SENSE + RUN/SS SENSE – BG SGND 5 Q1 N-CHANNEL Si4412DY PGND 10 14 15 C4 0.1µF L1* 10µH 12 8 RSENSE** 0.033Ω D1 CMDSH-3 7 + COUT 100µF 10V ×2 R1 35.7k 1% R6 11k 1% C6 100pF C5 1000pF 11 + C3 4.7µF 16V C1 100pF Typical “Medium Voltage” Application The maximum main battery voltage is more than the maximum VBAK pin voltage (12V). This configuration is needed for most notebook computers that have 3-cell or 4-cell series connected lithium battery packs. The Schottky diode D11 (1N5818) prevents the main battery’s high terminal voltage from overstressing the LTC1558’s VBAK pin during nonbackup conditions. An internal Zener inside the LTC1558 will clamp VBAK to 12V when the 1N5818’s reverse bias leakage current increases at high temperature. 16 CIN 22µF 35V ×2 TG SFB COSC D11 1N5818 *SUMIDA CDRH125-10 **IRC LR2D1D-01-RQ33-F † SUMIDA CD54-220 R12 100k 1% + C12 1µF Q2 N-CHANNEL Si4412DY D2 MBRS140T3 VOUT 5V 3A 1558 TA04 A 100k pull-up resistor enables the LTC1558’s open-drain BACKUP pin to turn the external P-channel MOSFET off during backup mode, even when VBAK is higher than VCC. The main battery pack should have an internal control to shut itself down once its energy is used up. This prevents the lithium cells from deep discharge damage. Once the main battery shuts down, the FB voltage drops and the LTC1558 switches to backup mode. LTC1558-3.3/LTC1558-5 U TYPICAL APPLICATIONS LTC1558-5 High Main Battery Voltage (48V) Application L11† 22µH BACKUP BATTERY 1.2V NiCd R14 14k R15 100k Q12 2N3906 D11 MBR170 + C11 47µF 6.3V 3 RESET PUSHBUTTON Z11 12V 2 R16 100k 1 SW 7 VCC 8 CTL VBAK LTC1558-5 RESET + C12 1µF 5 RESET 6 GND BACKUP BACKUP FB 4 Q11 P-CHANNEL MTD2955E R11 422k 1% MAIN BATTERY 48V R12 100k 1% D1 1N4148 D2 1N4148 C2 0.068µF 1 2 C1 0.047µF 3 PGATE 16 CAP VIN SHUTDOWN 2 VCC RGND 6 C4 470pF 7 RC 1k CC 3300pF 8 CT SGND ITH SHUTDOWN 1 SENSE – C6 0.1µF RSENSE** 0.04Ω 14 13 P-DRIVE NGATE LTC1149-5 5 12 VCC PGND C3 3.3µF CIN 100µF 100V VOUT 5V 2.5A 15 4 + + Q1 P-CHANNEL MTD2955E L1* 68µH + Q2 N-CHANNEL IRFZ34 D3 MBR380 COUT 220µF 10V OS-CON 11 10 SHUTDOWN 9 SENSE + C5 1000pF R3 100Ω R4 100Ω 1558 TA05 *HURRICANE LAB HL-KI168M **IRC LR2512-01-RO40-5 † SUMIDA CD54-220 Typical “High Voltage” Application The maximum main battery voltage is 48V. The Schottky diode D11 (MBR170) prevents the main battery’s high terminal voltage from overstressing the LTC1558’s VBAK pin during nonbackup conditions. An internal Zener inside the LTC1558 will clamp VBAK to 12V when the MBR170’s reverse bias leakage current increases at high temperature. As shown above, the design must ensure that VBAT does not force the external P-channel MOSFET’s VGS above its maximum rating (15V for the MTD2955E) shown during nonbackup mode. During nonbackup mode, the LTC1558’s open-drain BACKUP pin is low. The external 12V Zener and 2N3906 conduct and the MTD2955E’s VGS is clamped at approximately 12V. During backup, the BACKUP pin floats and the 2N3906’s base voltage is pushed nearer to VBAK. The MTD2955E is effectively turned off, isolating the main battery from VBAK during backup. The main battery pack should have an internal control to shut itself down once its energy is used up. This prevents it from deep discharge damage. 17 LTC1558-3.3/LTC1558-5 U PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted. GN Package 16-Lead Plastic SSOP (Narrow 0.150) (LTC DWG # 05-08-1641) 0.189 – 0.196* (4.801 – 4.978) 16 15 14 13 12 11 10 9 0.229 – 0.244 (5.817 – 6.198) 0.150 – 0.157** (3.810 – 3.988) 1 0.015 ± 0.004 × 45° (0.38 ± 0.10) 0.007 – 0.0098 (0.178 – 0.249) 4 5 6 7 8 0.004 – 0.0098 (0.102 – 0.249) 0° – 8° TYP 0.016 – 0.050 (0.406 – 1.270) * DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE ** DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE 18 0.053 – 0.068 (1.351 – 1.727) 2 3 0.008 – 0.012 (0.203 – 0.305) 0.025 (0.635) BSC GN16 (SSOP) 1197 LTC1558-3.3/LTC1558-5 U PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted. S8 Package 8-Lead Plastic Small Outline (Narrow 0.150) (LTC DWG # 05-08-1610) 0.189 – 0.197* (4.801 – 5.004) 7 8 6 5 0.150 – 0.157** (3.810 – 3.988) 0.228 – 0.244 (5.791 – 6.197) 1 0.010 – 0.020 × 45° (0.254 – 0.508) 0.008 – 0.010 (0.203 – 0.254) 3 2 4 0.053 – 0.069 (1.346 – 1.752) 0.004 – 0.010 (0.101 – 0.254) 0°– 8° TYP 0.016 – 0.050 0.406 – 1.270 0.050 (1.270) TYP 0.014 – 0.019 (0.355 – 0.483) *DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE **DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE SO8 0996 S Package 16-Lead Plastic Small Outline (Narrow 0.150) (LTC DWG # 05-08-1610) 0.386 – 0.394* (9.804 – 10.008) 16 15 14 13 12 11 10 9 0.150 – 0.157** (3.810 – 3.988) 0.228 – 0.244 (5.791 – 6.197) 1 0.010 – 0.020 × 45° (0.254 – 0.508) 0.008 – 0.010 (0.203 – 0.254) 2 3 4 5 6 0.053 – 0.069 (1.346 – 1.752) 0.014 – 0.019 (0.355 – 0.483) 8 0.004 – 0.010 (0.101 – 0.254) 0° – 8° TYP 0.016 – 0.050 0.406 – 1.270 7 0.050 (1.270) TYP S16 0695 *DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE **DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 19 LTC1558-3.3/LTC1558-5 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LTC690/LTC691 LTC694/LTC695 Microprocessor Supervisory Circuits Microprocessor Power Supply Monitor and Backup with Power Fail Comparator LT®1020 Micropower Linear Regulator Includes Low-Battery and Dropout Detectors LT1120 Micropower Linear Regulator SO-8 Package, Includes Low-Battery Detector LTC1149 High Efficiency Synchronous Step-Down Switching Regulator VIN up to 48V, Burst ModeTM Operation LTC1235 Microprocessor Supervisory Circuit Includes Pushbutton Reset and Power Fail Comparator LTC1435 High Efficiency, Low Noise Synchronous Step-Down Switching Regulator Ultrahigh Efficiency, Burst Mode Operation LTC1479 PowerPathTM Controller for Dual Battery Systems Complete Power Management Controller for Battery Notebook Computers and Other Portable Equipment LT1521 Micropower Low Dropout Regulator 300mA, SOT-223 Package Burst Mode and PowerPath are trademarks of Linear Technology Corporation. 20 Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 ● (408) 432-1900 FAX: (408) 434-0507● TELEX: 499-3977 ● www.linear-tech.com 1558f LT/TP 0298 4K • PRINTED IN USA LINEAR TECHNOLOGY CORPORATION 1998