LTC1559-3.3/LTC1559-5 Backup Battery Controller with Fixed Output U DESCRIPTION FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Complete Battery Backup System in an SO-8, 16-Pin GN or SO Package Generates Fixed Backup Voltage (3.07V/4.63V) 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 Onboard Power-Up and Push-Button Reset Generator Performs VCC Supervisory Functions Reset Assertion Guaranteed at VCC = 1V Short-Circuit Protection Thermal Limiting ■ ■ ■ The on-chip NiCd charger uses an internal gas gauge to minimize fast recharge time and prevent overcharging of the backup cell, thereby improving system efficiency and extending the life of the backup cell. The LTC1559 also provides a user programmable trickle charge current to compensate for self-discharge losses in the backup cell. The LTC1559’s automatic backup switching scheme 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. U APPLICATIONS ■ The LTC®1559 is a backup battery controller that provides all the functions necessary to implement a backup 3.3V or 5V power supply using a single NiCd cell. It includes a 1.2V to 3.07V/4.63V 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. Notebook Computers Palmtop Computers/PDAs Portable Instruments Battery-Powered Systems The LTC1559 is available in an SO-8, 16-pin GN or SO package. , LTC and LT are registered trademarks of Linear Technology Corporation. U TYPICAL APPLICATION Backup Time vs VBAK Output Load Current *L1 22µH + C1 1µF S1 RESET R1 68k 1 8 SW VBAK 7 2 VCC GND 3 CTL LTC1559-3.3 6 BACKUP 4 5 PS RESET 800 + R2 100k SYSTEM µP † MAIN BATTERY 4.5V TO 28V LTC1435 SYNCHRONOUS BUCK REGULATOR VBAK = 3.07V NiCd CELL = P-11AAH (110mA Hrs) 700 C2 1µF Q1 + C3 P-MOSFET 100µF Si9424DY VOUT 10V 3.3V AT NORMAL MODE * SUMIDA CD54-22µH 3A VBAK ** PANASONIC P-11AAH 33mA (3.07V) AT BACKUP MODE † CONSULT LTC1435 DATA SHEET FOR >33mA (3.3V) AT NORMAL MODE 1559 TA01 APPLICATION CIRCUIT INFORMATION BACKUP TIME (MINUTES) **BACKUP BATTERY 1.2V NiCd 600 500 400 300 200 100 0 0 5 20 30 15 25 10 VBAK LOAD CURRENT (mA) 35 1559 TA02 1 LTC1559-3.3/LTC1559-5 W W U W ABSOLUTE MAXIMUM RATINGS (Note 1) Terminal Voltages VCC ........................................................................ 6V VBAK .................................................................... 12V SW ...................................................................... 14V All Other Pins .............................. – 0.3V to VCC + 0.3V SW Input Currents ............................................. 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 PS 4 LTC1559CS8-3.3 LTC1559CS8-5 6 BACKUP 5 RESET S8 PACKAGE 8-LEAD PLASTIC SO S8 PART MARKING TJMAX = 125°C, θJA = 130°C/ W 155933 15595 TOP VIEW SW 1 16 VBAK SW 2 15 VBAK PGND 3 ORDER PART NUMBER LTC1559CGN-3.3 LTC1559CGN-5 LTC1559CS-3.3 LTC1559CS-5 14 VCC GND 4 13 BACKUP CTL 5 12 RESET SHDN 6 11 RESET PS 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 Battery Backup Switching VCC Operating Voltage Range VBAT Backup Battery Cell Voltage IVCC Quiescent Supply Current (Note 2) IBAT Peak Inductor Current (Backup) IBAT(SHDN) Battery Standby Current LTC1559-3.3 LTC1559-5 ● ● 2.900 4.400 ● 1.0 ● Boost Converter in Low Current Mode (Note 7) Boost Converter in High Current Mode (Note 7) ● ● VCC = 0V ● 80 225 3.5 5.5 V V 1.2 1.5 V 155 250 µA 165 330 225 445 mA mA 0.1 15 µA 50 µA VBAK(ON) VCC Backup Request/Booster Assertion Trip Point (Note 4) LTC1559-3.3 LTC1559-5 ● ● 3.011 4.475 3.070 4.625 3.127 4.775 V V VBAK(OFF) VCC Backup Deassertion Trip Point (Note 4) LTC1559-3.3 LTC1559-5 ● ● 3.061 4.550 3.119 4.700 3.176 4.850 V V VLOBAT1 Low VBAT Detect (Note 3) ● 0.95 1.00 1.05 V VUVLO(ON) VCC UVLO Trip Voltage (Note 4) LTC1559-3.3 LTC1559-5 ● ● 2.904 4.400 3.003 4.550 3.102 4.700 V V VUVLO(OFF) VCC UVLO Trip Voltage (Note 4) LTC1559-3.3 LTC1559-5 ● ● 3.061 4.550 3.119 4.700 3.176 4.850 V V IVCC(SHDN) Supply Current During Shutdown (Note 3) 2 ● LTC1559-3.3/LTC1559-5 ELECTRICAL CHARACTERISTICS SYMBOL PARAMETER VBAT = 1.2V, TA = 0°C to 70°C unless otherwise noted. CONDITIONS MIN TYP MAX UNITS 0.85 0.9 0.95 V 16 21 mA 2 mA UVLO Reset Monitor VLOBAT2 VBAT UVLO Trip Voltage (Note 5) ● Backup Battery Charger ICHGF Battery Charge Current During Fast Recharge ● 11 ICHGT User-Programmable Trickle Charge Current Range ● 0.05 QRECH Fast Recharge Factor (Note 6) QTRK Nominal Trickle Charge Multiplier Factor VCTL(CLAMP) CTL Clamp Voltage in Trickle Mode 1.35 1.6 1.85 C/C A/A ICHGT = 1mA ● 8 10 12 ICHGT = 1mA ● 0.45 0.5 0.55 V 250 mV 20 26 1.10 1.8 3.4 sec 50 115 80 185 150 345 µs ms mV Push-Button Reset VCTL CTL Input Threshold t CTL CTL Input Low Time (Debounce Time) ms Reset Timer t HRESET Push-Button Duration for Hard Reset tRST RESET Pulse Width VCTL Low for < tHRESET (Soft Reset) VCTL Low for > tHRESET (Hard Reset) ● ● VRST1 RESET Output Voltage VCC = 1V, ISINK = 10µA ● 5 200 VRST RESET Output Voltage VCC = 4.25V, ISINK = 1.6mA ● 0.1 0.4 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 TA = 25°C 90 mV 7.5 µs V PS Comparator VHYST Comparator Threshold Hysteresis Internal VCC Monitor Comparator tr UVLO, 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 ● 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 push-button reset. Note 3: Only applies to 16-pin version. Note 4: Although the VBAK(ON), VBAK(OFF), VUVLO(ON) and VUVLO(OFF) threshold voltages have a specification tolerance, they are guaranteed by design and tested in production never to overlap. 0.8 V V 15 µA 2 8 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 withdrawn from the NiCd battery during backup. Note 7: The LTC1559 switches automatically between the low and high operating current levels. See Applications Information for more details. 3 LTC1559-3.3/LTC1559-5 U W TYPICAL PERFORMANCE CHARACTERISTICS Output Power vs Battery Voltage 100 80 60 40 20 125 VBAT = 1.2V POUT = 100mW 3.0 BACKUP TIME (HOURS) 120 OUTPUT POWER (mW) 3.5 IPK = 330mA CL = 200µF SWITCHING FREQUENCY (kHz) 140 2.5 2.0 1.5 1.0 LTC1559-3.3 VBAT = 1.2V IPK = 330mA 100 75 50 25 0.5 0 0 1.0 1.1 1.2 1.3 NiCd TERMINAL VOLTAGE (V) 1.4 0 50 125 250 375 NiCd CELL CAPACITY (mA Hr) 500 1559 G01 100 LTC1559-3.3 VBAT = 1.2V IPK = 330mA 20 0 1.005 2 1.000 10.4 0.995 10.3 CURRENT RATIO (mA/mA) TRICKLE CHARGE FACTOR (mA/mA) 40 10.2 10.1 10.0 9.9 9.8 9.7 0.990 0.985 0.980 0.975 0.970 0.965 0.960 9.6 0.955 0.950 9.5 6 4 8 OUTPUT VOLTAGE, VBAK (V) 0 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 NiCd BATTERY TRICKLE CURRENT (mA) 10 1559 G04 25 50 TEMPERATURE (°C) RESET Output Voltage vs Supply Voltage 60 RESET Output Voltage vs Supply Voltage 6 4.0 LTC1559-5 50 75 1559 G06 1559 G05 Fast Recharge Time (Assume NiCd Battery Fully Exhausted) 10 Normalized Fast Recharge Current vs Temperature 10.5 60 6 4 8 OUTPUT VOLTAGE, VBAK (V) 1559 G03 Trickle Charge Multiplier Factor 80 2 1559 G02 Boost Converter Switching Duty Cycle DUTY CYCLE (%) Boost Converter Switching Frequency Backup Time vs Battery Capacity LTC1559-3.3 3.5 5 30 20 RESET VOLTAGE (V) RESET VOLTAGE (V) TIME (HOURS) 3.0 40 4 3 2 2.5 2.0 1.5 1.0 10 1 0 64 128 256 BATTERY CAPACITY (mA Hr) 512 1559 G07 4 0 0.5 4.7V 4.55V 3V 3.12V 0 0 1 2 3 4 SUPPLY VOLTAGE (V) 5 6 1559 G08 0 2 3 1 SUPPLY VOLTAGE (V) 4 1559 G09 LTC1559-3.3/LTC1559-5 U U U PIN FUNCTIONS Pin Numbers Are Shown First for the SO-8 Package Then the GN16 and S16 Packages is guaranteed to be valid when VCC is greater than or equal to 1V. 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. RESET also provides a low going 100µs signal whenever the CTL pin is pulled low for less than two seconds (“soft” reset). Unlike hard reset, soft reset does not affect the LTC1559’s current operating mode. 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 8-pin package. CTL (Pins 3/5): Control. This pin provides three functions. In backup mode this pin is a high impedance input and monitors the backup battery cell voltage (VBAT). If VBAT drops below 0.9V, the LTC1559 enters UVLO. During trickle charge mode, an external resistor REXT sets the trickle charge current. In all modes, pulling the CTL pin below 250mV generates either a “soft” or “hard” reset pulse. See the Applications Information section for more information. BACKUP (Pins 6/13): System Backup Signal. This is a TTL-compatible output driver that pulls low unless the LTC1559 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 output. 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 LTC1559 monitors VCC. If VCC drops below the rated output voltage by 9%, the LTC1559 enters UVLO mode and RESET is asserted. The LTC1559-3.3 exits UVLO if VCC rises to greater than – 5.5% of the rated output voltage. The LTC1559-5 exits UVLO if VCC rises to greater than –6 % of the rated output voltage. See the Applications Information section for more details. PS (Pins 4/7): Power Supply Sense. This pin senses the presence of the main supply and triggers the LTC1559 to terminate backup mode. During backup, VCC is driven externally by the LTC1559’s boost convert’s output (VBAK). When PS > VCC during backup, the LTC1559 pulls down the BACKUP pin, reconnecting the system regulator output to the system VCC. The PS pin is needed in applications that use a P-channel MOSFET (driven by the BACKUP signal) to isolate the system regulator during backup. If not needed, PS can be disabled by tying it to ground. 16-Pin GN and SO Packages 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 if the LTC1559 comes out of UVLO. This “hard reset” stops the internal boost converter if it is running. This pin is held low if the LTC1559 is in UVLO and SHDN (Pin 6): Chip Shutdown. A TTL-compatible active low voltage at SHDN puts the LTC1559 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. VBAK (Pins 8/15,16): Backup Supply Output. The LTC1559’s boost converter provides the regulated output voltage to the system through VBAK during backup mode. 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. 5 LTC1559-3.3/LTC1559-5 U U U PIN FUNCTIONS LOBAT (Pin 9): Low Backup Battery Detector Output. This is an open-drain output with an internal weak pull-up. It is asserted if the NiCd cell terminal voltage drops below 1.0V. This pin is pulled high if the LTC1559 is in trickle charge mode. RESET (Pin 12): System Reset, Active High. This is a TTLcompatible output driver. It can connect to systems that require active high logic. The RESET output will go high if RESET is pulled low. W BLOCK DIAGRAM P1 SW VBAK VCC/VBAK CHARGER N1 CTL BOOST/BACKUP LOGIC + PS RESET – LEVEL SENSE AND DEBOUNCE VREF VCC BACKUP VREF GAS GAUGE – RESET GENERATOR RESET + LOBAT – + UVLO DETECTOR THERMAL LIMIT SHUTDOWN LOGIC SHDN U W SWITCHING WAVEFORMS BANDGAP VREF = 1.272V 1559 BD Cold Power Boot-Up (Main Battery Replaced/Turned On) Simplified LTC1559 Connections in a Battery Backup System 22µH SW 1.2V NiCd LTC1559 PS VCC BACKUP VBAT MAIN BATTERY RESET VIN RATED BATTERY TERMINAL VOLTAGE TO SYSTEM CONTROL 1 VBAT VBAK VOUT MAIN SYSTEM REGULATOR 3 QEXT BACKUP PS SYSTEM VCC VCC RATED VCC VOLTAGE 4 2 –5.5% (LTC1559-3.3) – 6% (LTC1559-5) 200ms COUT RESET 1559 SW01 FOR MORE DETAILED CIRCUIT APPLICATION SCHEMATICS, PLEASE REFER TO THE TYPICAL APPLICATIONS SECTION BACKUP 1559 SW02 6 LTC1559-3.3/LTC1559-5 U W SWITCHING WAVEFORMS Cold Power Boot-Up Description 1. System regulator starts to ramp up the output (PS) once the VBAT voltage increases beyond the minimum input value. 2. VCC starts to increase once PS is high enough to turn on QEXT’s body diode. RESET is asserted when VCC is less than or equal to 1V. 3. The LTC1559’s internal bandgap wakes up. QEXT turns on and VCC = PS. The LTC1559’s internal boost converter does not turn on as RESET remains asserted. 4. RESET is asserted for a further 200ms after VCC reaches – 5.5% of its rated VCC value for the LTC1559-3.3 and – 6% of its rated VCC value for the LTC1559-5. Backup Mode (Main Battery Discharged)— LTC1559-3.3 1V 1.2V 0.9V VNiCd BOOST CONVERTER OUTPUT – 7% –5.5% – 7% – 7% VCC tr tf BACKUP INDUCTOR CURRENT tr tr “1” RESET tr “1” LOBAT (1) (2) (3) (4) 1559 SW03 Backup Mode Description 1. Trigger into Backup Mode. Main battery fails and VCC drops 7% below the rated value. The backup pin is asserted after a tr delay time and the boost converter is turned on. 3. Recovery from Backup Mode. While the boost converter is running, the main battery is restored. This causes the system regulator to increase PS above VCC. When PS > VCC or VCC > VCC(rated value) – 5.5%, the BACKUP pin deasserts and the boost converter finishes its last cycle. 2. Backup Mode. The LTC1559’s boost converter charges and discharges the inductor with 165mA peak current. If VCC doesn’t increase above VCC(rated value) – 7% (due to a heavy load), the boost converter increases peak charging current to 330mA. If VCC rises above VCC(rated value) – 7%, the boost converter stops and the backup pin remains asserted. 4. Trigger into UVLO. During backup, the 1.2V NiCd cell is discharged and its terminal voltage falls. The LOBAT pin is asserted to give an early warning if the cell voltage drops below 1V. RESET is asserted when the cell voltage drops below 0.9V and the LTC1559 enters UVLO mode. 7 LTC1559-3.3/LTC1559-5 U W U U APPLICATIONS INFORMATION Overview The LTC1559 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 LTC1559 allows the use of a low cost rechargeable NiCd cell for backup, eliminating the need for expensive, replaceable 4.5V lithium backup cells. The LTC1559 includes an onboard boost converter designed to generate a fixed voltage (3.07V for 3.3V parts and 4.625V for 5V parts) from a single 1.2V NiCd cell. When connected to the system DC/DC converter’s output, the LTC1559 enables the system connected to the VCC rail to continue operation when the main power supply 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 LTC1559 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 LTC1559 also performs VCC supervisory functions during normal system operations. An LTC1559-3.3 monitors a 3.3V supply voltage at its VCC pin while an LTC1559-5 monitors a 5V supply at its VCC pin. In both cases, the LTC1559 derives power for the majority of the internal circuitry (except for the boost converter) from its VCC pin. Table 1 shows the signal conditions for the various operating modes of the LTC1559-3.3. Table 2 shows the signal conditions for the various operating modes of the LTC1559-5. Table 1. LTC1559-3.3 Operating Modes OPERATING MODES UVLO Reset CONDITIONS 1V < VCC < VCC(rated value) – 9% or VBAT < 0.9V Push-Button Reset UVLO Reset Recovery Backup Mode Activation Backup Mode Exit VCTL < 250mV VCC > VCC(rated value) – 5.5% VCC < VCC(rated value) – 7% VCC > VCC(rated value) – 5.5% or PS > VCC Boost Converter Activation VCC < VCC(rated value) – 7% Boost Converter Deactivation VCC > VCC(rated value) – 7% Table 2. LTC1559-5 Operating Modes OPERATING MODES UVLO Reset Push-Button Reset UVLO Reset Recovery Backup Mode Activation Backup Mode Exit CONDITIONS 1V < VCC < VCC(rated value) – 9% or VBAT < 0.9V VCTL < 250mV VCC > VCC(rated value) – 6% VCC < VCC(rated value) – 7.5% VCC > VCC(rated value) – 6% or PS > VCC Boost Converter Activation VCC < VCC(rated value) – 7.5% Boost Converter Deactivation VCC > VCC(rated value) – 7.5% Boost Converter Operation The LTC1559 uses an onboard 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 to 93% (LTC1559-3.3) or 92.5% (LTC1559-5) of the rated V CC, supports the system VCC during backup. It supplies 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 LTC1559 to accurately measure the charge removed from the backup cell by counting the charge pulses. The LTC1559 enters backup mode when the main battery voltage drops and causes VCC, the system regulator’s output, to fall. As shown in Figure 1, VCC is scaled down by an internal resistor divider and fed to the LTC1559’s backup comparators. These compare the scaled voltage 8 LTC1559-3.3/LTC1559-5 U U W U APPLICATIONS INFORMATION VCC + COUT LTC1559 SYSTEM REGULATOR SYSTEM VCC BOOST CONVERTER VBAK R1 BACKUP LOGIC BACKUP R2 VREF PS 1559 F01 Figure 1. Typical LTC1559 Connection with an internal trimmed VREF (1.272V), switching the LTC1559 into backup mode if V CC drops 7% (LTC1559-3.3) or 7.5% (LTC1559-5) below its rated value. Upon entering backup mode, the BACKUP pin is asserted and the internal boost converter turns on. The BACKUP signal turns off the external P-channel MOSFET (if used), isolating the system regulator from the LTC1559. The boost converter charges the VCC capacitor, COUT, of the system regulator until VCC rises above VCC (rated value) – 7% (LTC1559-3.3) or VCC (rated value) – 7.5% (LTC1559-5). Once VCC rises above VCC (rated value) – 7% (LTC15593.3), the boost converter deactivates and the freshly charged VCC capacitor COUT supplies power to the system. The cycle repeats again when the VCC capacitor’s charge is drained away and VCC again drops below VCC (rated value) – 7% (LTC1559-3.3). The BACKUP pin remains asserted until the main battery is restored. This ensures that the LTC1559 does not switch in and out of backup mode unnecessarily. The LTC1559’s boost converter minimizes output ripple under light load conditions by reducing the charge trans330mA (PEAK) HEAVY CURRENT MODE 1 BOOST CYCLE VBAK ESR RIPPLE 165mA (PEAK) LIGHT CURRENT MODE ferred for the first two consecutive switch cycles. If VCC falls below VCC (rated value) – 7% (LTC1559-3.3), the boost operation starts by connecting the SW pin internally 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. 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. The inductor current discharges through the P-channel (P1 in the Block Diagram) and charges up the system’s VCC capacitor (COUT 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 LTC1559 monitors the VCC voltage. If VCC has increased above the VCC (rated value) – 7% (LTC1559-3.3) threshold, the boost converter shuts off both switches and waits for VCC to drop below VCC (rated value) – 7% (LTC1559-3.3) again. 1559 F02 Figure 2. Inductor Current During Switching DISCHARGE PERIOD tDISCH CHARGE PERIOD tCH 1559 F03 Figure 3. VBAK Ripple 9 LTC1559-3.3/LTC1559-5 U W U U APPLICATIONS INFORMATION If VCC is still less than VCC (rated value) – 7% (LTC15593.3) after the first boost cycle, the LTC1559 immediately reconnects SW to ground, repeating the boost cycle. If after two consecutive pulses, VCC is still not above the boost threshold VCC (rated value) – 7% (LTC1559-3.3), the LTC1559 decides that the load is not so light after all, 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 VCC exceeds the VCC (rated value) – 7% (LTC1559-3.3) boost threshold, the LTC1559 stops the boost converter and resets the internal 2-pulse counter. The next time VCC falls below VCC (rated value) – 7% (LTC1559-3.3), the boost converter restarts in low current mode for at least two boost cycles. Moderate or changing loads cause the LTC1559 to shift between the two peak inductor current limits, keeping the output in tight regulation. Near its maximum load capability, the LTC1559 will stay in 330mA high current mode and the output voltage V BAK will hover around V CC (rated value) – 7% (LTC1559-3.3). VCC Capacitor ESR The type of output capacitor and the rated VCC value will affect the LTC1559’s output ripple and efficiency. In most applications, the VCC capacitor is primarily determined by the requirements of the main power supply. Such a capacitor will generally meet the requirements of the LTC1559. In unusual circumstances or circuits where the main system VCC capacitor is located some distance away from the LTC1559, a local output capacitor may be necessary. The ripple on the VCC pin is equal to the 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 proportional to the difference between VBAK (93% of the rated VCC for the LTC1559-3.3 and 92.5% of the rated VCC for the LTC1559-5) and the battery cell voltage, VBAT (1.2V). 10 Assuming ESR = 0.2Ω, IIND(PEAK) = 330mA, VCC = 5V, VRIPPLE(P-P) = (IIND(PEAK))(RESR(CAP)) = (330mA)(0.2Ω) = 66mV Since VCC must be scaled down internally, the external resistor ratio: = 5V/1.272V = 3.931 Therefore the ripple seen by the VCC comparators is: = 66mV/3.931 = 16.79mV The discharge time period, tDISCH = (L • IIND(PEAK))/(VBAK – VBAT) = (22µH • 330mA)/(4.625 – 1.2V) = 2.12µs For VCC = 3.3V and IIND(PEAK) = 330mA, VRIPPLE(P-P) = 66mV RB resistor ratio = 3.3/1.272 = 2.594 Ripple voltage = 25.4mV tDISCH = 3.9µs The internal VCC comparators are designed to have a slow response time to filter away this ripple. The VCC (rated value) – 5.5% (LTC1559-3.3) and VCC(rated value) – 9% comparators have a 6µs rising edge delay and 2µs falling edge delay. The VCC (rated value) – 7% (LTC1559-3.3) comparator has a similar 6µs rising time delay but a much longer falling time delay of 20µs. This enables the comparator to control the boost converter properly, and avoids turning off the boost converter prematurely due to false triggering by the ESR ripple. Exit from Backup When a main battery is inserted into the system, the LTC1559 follows a specific sequence to exit backup mode and return control to the main supply. The sequence depends on the type of main power supply used. In systems where the main supply’s output impedance is LTC1559-3.3/LTC1559-5 U W U U APPLICATIONS INFORMATION high when inactive (typically a boost regulator with an output catch diode), the LTC1559 detects the return of the main supply by watching for VCC to exceed VCC (rated value) – 5.5% (LTC1559-3.3). The LTC1559 then shuts down its internal boost converter and begins to recharge the NiCd cell. In such applications, the PS pin is not used and can be tied to ground. No external P-channel MOSFET is required to isolate the main supply from the system VCC during backup. In systems where the main supply’s output impedance is low when inactive (typically buck regulators), the main supply must be disconnected from the system VCC during backup to prevent the inactive supply from loading the LTC1559. This is typically accomplished using an external P-channel MOSFET as shown in Figure 1. When the main supply is restored, the P-channel MOSFET’s body diode forward-biases. This allows current to flow into the system VCC, but the forward drop across this diode may prevent V CC from reaching the V CC (rated value) – 5.5% (LTC1559-3.3) threshold that deactivates the LTC1559’s backup mode. In such systems, the PS pin should connect directly to the output of the main system supply. When the system regulator’s voltage rises about 2.5% above the backup VCC, the PS comparator triggers and causes the LTC1559 to deassert the BACKUP pin signal. This signals the system controller to restore system loading and resume normal operation. At the same time, the external P-MOSFET is driven by the BACKUP signal. The P-channel MOSFET turns on and allows the main regulator to bypass its body diode and drive the system VCC directly. Since the user can replace the main battery anytime during the LTC1559’s backup operation, the BACKUP signal may be deasserted while the boost converter is switching. To prevent the potential problem of residual energy in the inductor, the LTC1559 will only stop the boost converter after it completes the current boost converter cycle. UVLO Under Excessive Backup Load Very heavy loads (above the LTC1559’s maximum power output) will pull the boost converter’s output below the boost threshold. Under these conditions, the LTC1559’s boost converter continues to supply 330mA current pulses to the load while charge on the VCC capacitor drains away. If VCC drops below VCC (rated voltage) – 9% for more than 7.5µs, the LTC1559’s VCC supervisory circuit activates UVLO mode, shutting off the boost converter and asserting the Reset pins. The 7.5µs delay prevents the LTC1559 from being fooled by brief transients or noise spikes on its VCC pin. Upon receipt of the reset signal, the host system should shut down in an orderly manner. The LTC1559’s VCC supervisory circuit will remain alive until VCC is less than 1V to ensure a valid RESET pin signal. 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 LTC1559 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 and RESET pins. Since the CTL pin can also be connected to an external push-button reset, the LTC1559 includes 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 push-button 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 LTC1559 will treat this as a “hard” reset after two seconds. An optional LOBAT output, available in the 16-pin GN or SO package, can be used to signal the system if the cell voltage falls below 1V, giving an early warning that the backup cell is heavily discharged. The LOBAT pin is disabled if the LTC1559 is in trickle charge mode, because the CTL pin is regulated to 0.5V by the LTC1559. Fault Protection and Thermal Limit The LTC1559’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 11 LTC1559-3.3/LTC1559-5 U W U U APPLICATIONS INFORMATION case, the NiCd cell is assumed to be damaged and the LTC1559’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 LTC1559 enters UVLO if VCC drops below VCC(rated value) – 9% or if the LTC1559 detects that CTL is lower than 0.25V for two seconds, in which case “hard” reset occurs. The discharge time can also get abnormally long if a serious overload condition occurs during switching. The timer shuts off the P-channel pass transistor after 10µs, protecting the boost converter. The LTC1559 enters UVLO as VCC drops below VCC(rated value) – 9%. In addition, the LTC1559 has safe area operation protection with an internal thermal shutdown circuit. If the device is overloaded for a long period of time, the thermal shutdown circuit forces the LTC1559 into UVLO. The threshold temperature for thermal shutdown is typically 155°C. The LTC1559’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. Backup Cell Fast Recharge The LTC1559 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 accurately measure battery charge by counting pulses. The gas gauge counts up from zero as charge is removed from the backup cell in backup mode. It takes 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 = 4.625V (LTC1559-5), the gas gauge counter will increment by one count every 7.5µs while the boost converter is running. Full count is reached 12 after approximately 2.2 hours, equivalent to about 512mAhr of charge. Upon entering recharge mode (after the main battery is restored) the LTC1559 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 typically replace 160% of the charge previously removed from the backup cell. When the gas gauge counter reaches zero, the LTC1559 reduces the charging current at the SW pin to the userprogrammed trickle charge current level. Under some circumstances, the LTC1559 can exit backup mode with invalid gas gauge contents. This occurs under three possible conditions: 1. The backup cell was completely exhausted during a backup cycle and the LTC1559 entered UVLO. 2. The backup cell was replaced while the main supply was disabled. 3. A backup cycle was terminated prematurely by a “hard” reset or an output overload. In these cases, the LTC1559 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 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 is wasted. However, the LTC1559’s 16mA fast charge current is not high enough to damage the cell. Once the fullcount recharge has been completed, the backup cell is assumed to be fully charged and subsequent backup/ recharge cycles resume normally. Although the LTC1559 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 LTC1559-3.3/LTC1559-5 U U W U APPLICATIONS INFORMATION example, a small 60mAhr SAFT cell can back up the system for 20 minutes at an output power of 100mW. Note that at VCC = 3.07V (LTC1559-3.3), the boost converter efficiency improves and allows more backup time from the same cell compared to VCC = 4.625V (LTC1559-5). Once it reaches full recharge, a cell bigger than 512mAhr will overrun the gas gauge counter before it runs out of charge during an extended backup cycle. The LTC1559 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 exits backup. This ensures that the backup cell is replenished with at least a 1mAhr charge every time the LTC1559 enters backup mode. Battery Backup Cell Trickle Charge When the gas gauge counter reaches zero, the LTC1559 terminates fast recharge and reduces the recharge current to the user-programmed trickle current level. The LTC1559 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 VCC 10I 1.2V NiCd CELL SW + I 1µF REXT Undervoltage Lockout The LTC1559 includes an undervoltage lockout (UVLO) circuit that shuts the system down gracefully if the backup cell is exhausted or overloaded. As described in the previous section, the LTC1559 terminates backup operation and remains 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 if the backup cell drops below 1V. The UVLO circuit trips if the LTC1559’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 LTC1559 asserts the RESET and RESET pins until the VCC voltage drops below 1V. It then remains off until VCC rises to within – 5.5% of the rated output voltage (LTC1559-3.3). During power-up from UVLO, the LTC1559 asserts the RESET and RESET pins until the V C C ( r a t e d v a l u e) – 5.5% (LTC1559-3.3) threshold. Once VCC exceeds V C C ( r a t e d v a l u e ) – 5.5% (LTC1559-3.3), the RESET and RESET pins remain asserted for another 200ms (“hard” reset) before being released to inform the system to start operating. Reset Operation CTL 1× 11× – + + – 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 LTC1559 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 150µA. 0.5V LTC1559 1559 F04 Figure 4. Trickle Current Charger The LTC1559 includes an onboard push-button reset switch controller. If the CTL pin is pulled to ground (< 250mV) by a push-button or an open-drain output, the LTC1559 generates a pulse at the RESET and RESET pins after the trailing edge of the CTL signal. A short (less than two seconds) low going signal at CTL generates a “soft” reset (100µs) pulse at the reset pins. A low CTL signal for more than two seconds generates a “hard” reset pulse at the RESET and RESET pins. During “hard” reset, the 13 LTC1559-3.3/LTC1559-5 U W U U APPLICATIONS INFORMATION (B) > 0.25V (A) 0V CTL 20ms < tCTL < 2s tCTL < 20ms shut off completely. Note that the backup cell slowly discharges through REXT in this mode. Inductor Selection RESET 20ms DEBOUNCE 100µs 100µs “SOFT” PUSH-BUTTON RESET AT CTL (A) CTL < 0.25V FOR LESS THAN 20ms (B) CTL > 0.25V FOR MORE THAN 20ms > 0.25V 0V CTL tCTL > 2s RESET 2s 200ms “HARD” PUSH-BUTTON RESET AT CTL CTL < 0.25V FOR MORE THAN 2s 0V CTL 20ms The LTC1559 is designed to operate with a recommended inductor value of 22µH (±20%) with < 0.2Ω DC resistance. Using inductor values above 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 3 lists a few recommended surface mount inductor part numbers. Table 3. Recommended Inductors RESET 20ms 20ms DEBOUNCE AT FALLING AND RISING RESET EDGE 1559 F05 Figure 5. Push-Button Resets LTC1559 disables 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 push-button to ground. 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 LTC1559 has a TTL compatible input, SHDN that shuts down the whole chip, asserts the RESET and RESET pins and places the CTL, VBAK and SW pins into high impedance states. The SHDN pin has an internal pullup of 8µA that ensures the chip will not shut down if the pin is left floating. The chip consumes less than 50µA during shutdown. 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 14 MANUFACTURER PART NUMBER TYP INDUCTOR VALUE DCR (Ω) Sumida CD54-220 22µH ±20% 0.18 Sumida CDRH73/74 22µH ±20% 0.2/0.11 Capacitor Selection The LTC1559 requires a VCC capacitor of 100µF to ensure that boost converter can regulate the output under maximum load conditions. The capacitor’s ESR should be small (<0.2Ω) to minimize voltage spikes that might incorrectly trigger the LTC1559’s internal VCC comparators. Note that the LTC1559 can usually share the output capacitor with the system regulator. However, a 1µF is recommended directly at the LTC1559’s VCC pin. The VCC capacitor’s ratings like VMAX, IRIPPLE(RMS) all must meet the system regulator’s specifications as well. Battery Selection A primary application for the LTC1559 is a “bridging” supply, only providing backup current while the main system battery is being replaced. In these applications, the LTC1559 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. LTC1559-3.3/LTC1559-5 U W U U APPLICATIONS INFORMATION The LTC1559 works with standard or memory backup specific NiCd cells. Memory backup cells can operate at higher temperatures and have lower self-discharge rates. The LTC1559’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 4. 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 LTC1559’s boost converter output power drops significantly when the NiCd cell’s internal resistance increases at the end of its charge. The inductor charging time increases 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 1µF or larger bypass capacitor across the battery to ensure that the boost converter can deliver the maximum output power regardless of the NiCd internal resistance. Table 4. Button/Cylindrical NiCd 1.2V Cells MANUFACTURER (TYPE) 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 15 LTC1559-3.3/LTC1559-5 U TYPICAL APPLICATION LTC1559-3.3 Backup System with an LTC1435 Main System Regulator (LTC1435 Output Sense at the Drain of Q11) L11† 22µH BACKUP BATTERY 1.2V NiCd R14 14k + 1 SW C11 1µF 6.3V VCC 3 RESET PUSH-BUTTON 2 4 + MAIN BATTERY 4.5 TO 28V CIN 22µF 35V ×2 13 9 4 VIN EXTVCC 16 TG SW BOOST SFB 3 CC 330pF 2 1 CC2 51pF VOSENSE ITH SENSE + RUN/SS SENSE – COSC BG SGND CSS 0.1µF RC 10k INTVCC 5 PGND 10 CTL LTC1559-3.3 GND PS RESET BACKUP 7 + C12 1µF R15 100k 5 RESET 6 BACKUP Q1 N-CHANNEL Si4412DY C2 0.1µF 14 MAIN OUTPUT 3.3V 15 D1 CMDSH-3 LTC1435 6 8 VBAK 12 C4 0.1µF L1* 10µH 8 + C5 1000pF 7 11 + C3 4.7µF 16V COSC 68pF Q11 P-CHANNEL Si9424Y RSENSE** 0.033Ω Q2 N-CHANNEL Si4412DY C6 100pF D2 MBRS140T3 COUT 100µF 10V ×2 + BACKUP OUTPUT 3.3V C15 100µF 10V R1 35.7k 1% R5 20k 1% *SUMIDA CDRH125-10 **IRC LR2010-01-R033-F †SUMIDA CD54-220 1559 TA03 C1 100pF Description The PS pin connects to Q11’s drain and allows the LTC1559 to detect the restoration of the main battery during backup mode. Once the LTC1435’s output is greater than VOUT 16 during backup mode, the LTC1559 deasserts its BACKUP pin and returns control back to the LTC1435. Q11 turns on and allows the LTC1435 to charge C15. Please refer to the Applications Information section for more details. LTC1559-3.3/LTC1559-5 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) 8 7 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) 0.053 – 0.069 (1.346 – 1.752) 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 0.014 – 0.019 (0.355 – 0.483) 2 3 4 0.004 – 0.010 (0.101 – 0.254) 0.050 (1.270) TYP SO8 0996 17 LTC1559-3.3/LTC1559-5 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 LTC1559-3.3/LTC1559-5 U PACKAGE DESCRIPTION Dimensions in inches (millimeters) unless otherwise noted. 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 LTC1559-3.3/LTC1559-5 U TYPICAL APPLICATION LTC1559-3.3 Backup System with an LTC1435 Main System Regulator (LTC1435 Output Sense at the Source of Q11, LTC1559’s PS Pin Is Grounded) L11† 22µH BACKUP BATTERY 1.2V NiCd R14 14k + 1 SW C11 1µF 6.3V VCC 3 RESET PUSH-BUTTON 2 4 + MAIN BATTERY 4.5 TO 28V CIN 22µF 35V ×2 13 9 4 VIN EXTVCC 16 TG SW BOOST SFB 3 CC 330pF 2 1 CC2 51pF VOSENSE ITH SENSE + RUN/SS SENSE – COSC BG SGND CSS 0.1µF RC 10k INTVCC 5 PGND 10 CTL LTC1559-3.3 GND PS RESET BACKUP 7 + C12 1µF R15 100k 5 RESET 6 BACKUP Q1 N-CHANNEL Si4412DY C2 0.1µF 14 15 D1 CMDSH-3 LTC1435 6 8 VBAK 12 C4 0.1µF L1* 10µH Q11 P-CHANNEL RSENSE** 0.033Ω Si9424DY + 8 C5 1000pF 7 Q2 N-CH Si4412DY 11 + C3 4.7µF 16V D2 MBRS140T3 C6 100pF VOUT 3.3V R1 35.7k 1% R5 20k 1% COSC 68pF COUT 100µF 10V ×2 *SUMIDA CDRH125-10 **IRC LR2010-01-R033-F † SUMIDA CD54-220 1559 TA04 C1 100pF Description With its SENSE pin at the source of Q11, the LTC1435 can raise VOUT above VCC(rated voltage) – 5.5% once the main battery is restored. Thus, the LTC1559 does not use the PS pin to sense the LTC1435’s output during backup mode. The PS pin is grounded in this case. Please refer to the Applications Information section for more details. RELATED PARTS PART NUMBER LTC690/LTC691 LTC694/LTC695 LTC699 LTC1232 LTC1235 LTC1149 DESCRIPTION Microprocessor Supervisory Circuits COMMENTS Microprocessor Power Supply Monitor and Backup with Power Fail Comparator Microprocessor Power Supply Monitor and Backup Include Push-Button Reset Include Push-Button Reset and Power Fail Comparator VIN up to 48V, Burst ModeTM Operation Microprocessor Supervisory Circuits Microprocessor Supervisory Circuits Microprocessor Supervisory Circuits High Efficiency Synchronous Step-Down Switching Regulator LTC1435 High Efficiency, Low Noise Synchronous Ultrahigh Efficiency, Burst Mode Operation Step-Down Switching Regulator LTC1479 PowerPathTM Controller for Dual Complete Power Management Controller for Battery Battery Systems Notebook Computers and Other Portable Equipment LTC1558 Battery Backup Controller with Similar to LTC1559 Except That It Backs up the Main System Regulator’s Programmable Output Input, Allowing Backup of Multiple Output Voltages PowerPath and Burst Mode are trademarks of Linear Technology Corporation. 20 Linear Technology Corporation 1559f LT/TP 1098 4K • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408)432-1900 ● FAX: (408) 434-0507 ● www.linear-tech.com LINEAR TECHNOLOGY CORPORATION 1998