19-0653; Rev 0; 11/06 KIT ATION EVALU E L B A AVAIL Complete Backup Management IC for NiMH Batteries The MAX8672 complete power manager for backup batteries in smart devices offers feature-programmable battery charging and main-system backup. The device includes a charger for 1- or 2-cell NiMH backup batteries. A low-quiescent current synchronous-rectified boost converter and LDO supply up to 20mA during system backup. The BST output is internally set to regulate at 3.05V. The MAX8672 LDO is powered from the boost converter output and is adjustable from 1.5V to 3.05V. The MAX8672 features programmable charge current, undervoltage lockout (UVLO), and maximum cell voltage. Charging is controlled by both a timer and thermistor monitor. Battery UVLO prevents excessive battery discharge and keeps inactive-battery drain current below 50nA. In addition, both LDO and boost converter outputs block reverse current so that diodes are not needed when connecting these outputs directly to system supplies. The MAX8672 requires that a valid system supply be present before system backup operation can occur. The MAX8672 is available in a 14-pin, 3mm x 3mm TDFN package and is rated for -40°C to +85°C operation. Features o o o o o o o o o o Charges 1- or 2-Cell NiMH Backup Batteries Programmable Charge Current DC Trickle Charge Mode for Maximum Cell Life Deep-Recovery Charge Restores Cells < 1V Programmable Charge Timer Programmable Charge-Voltage Limit and Battery UVLO Reverse Current Blocking on BATT, LDO, and Boost—No Diodes Needed No Battery Drain When Off (< 50nA) Thermistor Sensing Disables Standard Charge Battery Restart Charge Threshold Prevents Overcharge Ordering Information PART PIN-PACKAGE MAX8672ETD+T PKG CODE 14 TDFN-14 (3mm x 3mm) T14334+2 The MAX8672 operates in the -40°C to +85°C extended operating temperature range. +Denotes lead-free package. Typical Operating Circuit Applications PDA, Palmtop, and Wireless Handhelds THRM CT Smart Cell Phones MAX8672 Pin Configuration 2.7V TO 5.5V INPUT IN CHGV CHGV FBL LDO BST LX GND TOP VIEW THRM DR 14 13 12 11 10 9 8 CHGI TRKI FBL BATT BACKUP BATTERY CONNECTION MAX8672 LDO 1.75V BST 3.05V 5 6 7 IN UV 4 DR CHGI 3 BATT 2 TRKI 1 CT UV TDFN (3mm x 3mm) GND LX ________________________________________________________________ Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. 1 MAX8672 General Description MAX8672 Complete Backup Management IC for NiMH Batteries ABSOLUTE MAXIMUM RATINGS IN, BATT, BST, LDO, UV to GND ..........................-0.3V to +6.0V FBL to GND ...............................................-0.3V to (VBST + 0.3V) CT, CHGI, TRKI, CHGV, THRM, DR to GND ...............................................-0.3V to (VIN + 0.3V) ILX ..................................................................................0.9ARMS Continuous Power Dissipation (TA = +70°C) 14-Pin, 3mm x 3mm TDFN (derate 18.2 mW/°C above +70°C) .........................1454.5mW Operating Temperature Range ...........................-40°C to +85°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10s) .................................+300°C Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS (VIN = 3.6V, TA = -40°C to +85°C, CCT = 0.1µF, unless otherwise noted.) (Note 1) PARAMETER IN Voltage Range IN Undervoltage Lockout Threshold IN Supply Current Internal Load Current on BST (Note 2) CONDITIONS MIN TYP MAX UNITS 2.45 40 117 5.5 2.60 100 170 V V µA TA = -40°C to +50°C 91 125 µA TA = -40°C to +85°C 91 150 2.7 2.20 VIN rising, hysteresis = 100mV (typ) VBATT > VBATT(CHG) VIN = 3.3V VBST = 3.3V, no BST or LDO load, boost and LDO on VIN = 0V BATT Quiescent Supply Current—Backup Mode VBATT = 1.55V, VBST = 3.3V, VIN = 0V, VBATT(CHG) = 1.5V BATT Quiescent Supply Current—Charging VBATT = 1.55V, VBST = 3.3V, VIN = 3.6V BATT Leakage Current to IN VBATT = 3.0V, VIN = 0V Total BATT Battery Leakage Current During UVLO (BATT, LX, and DR Leakage) VBATT = 0 to 3.0V 3 µA 3 µA TA = +25oC 0.01 0.1 TA = +85oC TA = -40°C to +50°C 0.07 5 50 TA = +85oC 50 µA nA CHARGER AND BATTERY 1mA ≤ IBATT(CHG) ≤ 20mA, VIN - VBATT > 400mV CHGI Current-Limit Accuracy IBATT(CHG) = 1mA, VIN VBATT > 400mV 0.1mA ≤ IBATT(CHG) ≤ 1mA, VIN - VBATT > 400mV TA = -40oC to +85oC -10 +10 TA = 0oC to +85oC -10 +10 o TA = -40 C to +85 C -15 +15 TA = -40oC to +85oC -20 +20 o CHGI Bias Voltage CHGI Resistor Range 600 IBATT(TRK) = 1mA TRKI Current-Limit Accuracy IBATT(TRK) = 0.1mA 5 1000 TA = -40oC to +85oC -10 +10 TA = 0oC to +85oC -10 +10 o -15 +15 o TA = -40 C to +85 C % mV kΩ % DC Trickle-Current Programming Range IBATT(TRK) 0.1 1 mA Charge-Current Programming Range IBATT(CHG) 0.1 20 mA TRKI Bias Voltage 600 TRKI Resistor Range Charger Dropout Voltage 2 100 VIN - VBATT where IBATT(CHG) falls by 10% of initial value; VIN = 3.6V, IBATT(CHG) = 20mA mV 1000 250 _______________________________________________________________________________________ kΩ mV Complete Backup Management IC for NiMH Batteries (VIN = 3.6V, TA = -40°C to +85°C, CCT = 0.1µF, unless otherwise noted.) (Note 1) PARAMETER CHGV Output Current CONDITIONS MIN VCHGV = 1V Measured at BATT o TA = +25 C VBATT(CHG) Voltage-Limit Accuracy VBATT(TRK) to VBATT(CHG) Ratio RCHGV = 28.7kΩ MAX 13 CHGV Resistor Range VBATT(CHG) Voltage-Limit Adjust Range TYP UNITS µA 28.7 57.4 kΩ 1.50 3.00 V -1 +1 TA = 0oC to +50oC -1.25 +1.25 TA = -30oC to +85oC -2.25 +2.25 % Sets 1.41V when VCHGV = 1.5V, measured at BATT 0.926 0.940 0.954 — VBATT(RSTRT) to VBATT(CHG) Ratio Sets 1.225V when VCHGV = 1.5V, measured at BATT 0.799 0.816 0.832 — VBATT(DR) to VBATT(CHG) Ratio Sets 1.00V when VCHGV = 1.5V, measured at BATT; this is the VBATT above which deep recovery (DR) turns off; the falling threshold is typically 50mV below this 0.653 0.667 0.680 — 0.775 0.816 0.861 — 10 20 % VDR Output Voltage to VBATT(CHG) Ratio Measured at BATT; no load on DR DR Load Regulation IDR = 0 to 10mA o TA = +25 C 20 TA = -40oC to +85oC 25 Charge-Timer Accuracy Does not include capacitor error Timer Adjust Range CHGI timer period, CCT = 0.047µF = 8h (480min) Thermistor Hot-Trip Point Thermistor Cold-Trip Point 2 Cold-Trip Thermistor Resistance UV Output Current min o 44 45 46 o C o -2 -1 0 o C o C RTHERM = 100kΩ at TA = +25 C, TA rising RTHERM = 100kΩ at TA = +25 C, TA falling Thermistor Temperature Hysteresis Hot-Trip Thermistor Resistance 2000 % 2 TA rising 42.00 TA falling 43.71 45.42 48.15 TA falling 325.5 342.0 TA rising 302.0 VUV = 1V 4 358.6 kΩ µA UV Resistor Range 49.9 215 kΩ UV Battery-Cutoff Programmable Range 0.8 3.5 V -2 +2 -3.25 +3.25 1.5 3.05 UV Battery-Cutoff Accuracy RUV = 49.9kΩ TA = 0oC to +50oC TA = -30oC to +85oC % LDO LDO Output-Voltage Range Using external resistors, no load FBL Regulation Voltage VBST = 3.3V, VLDO = 3.05V LDO Output Current (Note 3) LDO Load Regulation VBST = 3.3V, VLDO = 3.05V, ILDO = 1mA to 20mA LDO Dropout Voltage LDO Dropout Resistance FBL Input Bias Current 1.275 V 20 mA 0.08 0.2 %/mA VLDO = 2.5V, ILDO = 10mA 50 100 mV VLDO = 2.5V 5 VFBL = 1.25V 1.225 1.25 V TA = +25oC 3 TA = +85oC 15 Ω 50 nA _______________________________________________________________________________________ 3 MAX8672 ELECTRICAL CHARACTERISTICS (continued) ELECTRICAL CHARACTERISTICS (continued) (VIN = 3.6V, TA = -40°C to +85°C, CCT = 0.1µF, unless otherwise noted.) (Note 1) PARAMETER CONDITIONS MIN TYP MAX UNITS 2.989 3.05 3.111 V 20 mA 600 mA Ω BOOST CONVERTER BST Output Voltage Boost Output Current 1-cell input (Note 3) LX Current Limit 400 500 n-Channel On-Resistance ILX = 200mA 0.4 1 p-Channel On-Resistance ILX = -200mA 0.7 2 Ω 3.5 5 6.5 µs 5 20 35 mA n-Channel Maximum On-Time p-Channel Off-Current Threshold Note 1: Parameters are 100% production tested at TA = +25°C. Limits over the operating temperature range are guaranteed by design. Note 2: BATT current is higher due to boost ratio and efficiency. Note 3: Total load from both BST and LDO cannot exceed 20mA. Typical Operating Characteristics (VIN = 3.6V, Circuit of Figure 6, TA = +25°C, unless otherwise noted.) 10 ICHG = 3mA 5 VBST = 3.3V, VBATT(CHG) = 3V, RDR = 549Ω, VBATT RISING 10 ICHG = 3mA 5 ICHG = 200μA 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 0 0 0.5 1.0 2.5 3.0 0 3.5 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 BATTERY-CHARGE PROFILE (2 NiMH CELLS) ICHG = 3mA 5 ICHG = 200μA 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 INPUT VOLTAGE (V) 3.5 MAX8672 toc06 2.15 3.0 2.10 VBATT (V) 2.5 2.05 CHARGE TERMINATION AT VBATT(CHG) 2.0 1.5 1.0 2.00 VBATT = 2.4V, VBST = 3.3V, RCHGI = 49.9kΩ 0 4 2.0 CHARGE CURRENT (ICHG) vs. TEMPERATURE VBATT = 2.4V, RCHGV = 57.6kΩ, VBST = 3.3V 0 1.5 ICHG = 200μA -5 2-CELL CHARGE CURRENT (ICHG) vs. INPUT VOLTAGE (VIN) 20 -5 ICHG = 3mA 5 INPUT VOLTAGE (V) ICHG = 20mA 10 10 BATTERY VOLTAGE (V) 25 15 VBATT = 1.2V, RCHGV = 28.7kΩ, VBST = 3.3V 15 BATTERY VOLTAGE (V) CHARGE CURRENT (mA) 0 ICHG = 20mA 20 ICHG = 200μA 0 MAX8672 toc04 0 MAX8672 toc02 20 15 25 CHARGE CURRENT (mA) VBST = 3.3V, VBATT(CHG) = 1.5V, RDR = 274Ω, VBATT RISING 15 ICHG = 20mA MAX8672 toc05 CHARGE CURRENT (mA) 20 25 CHARGE CURRENT (mA) ICHG = 20mA MAX8672 toc01 25 1-CELL CHARGE CURRENT (ICHG) vs. INPUT VOLTAGE (VIN) 2-CELL CHARGE CURRENT (ICHG) vs. BATTERY VOLTAGE (VBATT) MAX8672 toc03 1-CELL CHARGE CURRENT (ICHG) vs. BATTERY VOLTAGE (VBATT) CHARGE CURRENT (mA) MAX8672 Complete Backup Management IC for NiMH Batteries 1.95 -40 -15 35 10 TEMPERATURE (°C) 60 85 TRICKLE CHARGE STARTS AT VBATT(TRK) VIN = 4V, VBST = 3.3V, R1 = 402kΩ, R2 = 24.9kΩ, R3 = 165kΩ, R4 = R5 = 124kΩ, R6 = 56kΩ, R7 = OPEN, R8 = SHORT, R9 = 110kΩ, C1 = 0.047μF 0.5 0 0 60 120 180 240 300 360 420 TIME (min) _______________________________________________________________________________________ 480 Complete Backup Management IC for NiMH Batteries VBATT = 1.2V 60 50 40 30 20 10 300 250 200 150 50 VIN = NOT CONNECTED 0 0.01 0.1 1 0 100 10 0.8 1.6 2.4 2.8 VBATT(CHG) = 1.5V 17.5 15 2.0 2.5 60 90 120 150 180 CT FREQUENCY vs. TEMPERATURE 18.0 17.5 CT FREQUENCY (Hz) 12.5 10.0 7.5 17.0 16.5 16.0 5.0 VIN = VBST = VLDO = 0V VBATT = 0.9V RCHGV = 28.7kΩ 2.5 0.0 1.0 30 15.0 RDR = 100Ω 3.0 -40 -15 BATTERY VOLTAGE (V) 10 35 60 15.5 CCT = 0.047μF, X7R, 10% 15.0 85 -40 -15 10 35 60 85 TEMPERATURE (°C) TEMPERATURE (°C) MAX BATT CHARGE VOLTAGE vs. TEMPERATURE (1-CELL NiMH) LIGHT-LOAD SWITCHING WAVEFORMS MAX8672 toc14 MAX8672 toc13 1.55 MAX BATT CHARGE VOLTAGE (V) 0.5 2.9 0 MAX8672 toc11 BATT INPUT LEAKAGE CURRENT (nA) MAX8672 toc10 5 VBATT = 2.4V VBATT = 1.2V BST LOAD CURRENT (mA) 20.0 VBATT(CHG) = 3.0V 3.0 3.2 BATT INPUT LEAKAGE CURRENT DURING UVLO vs. TEMPERATURE 10 3.1 2.8 2.0 DR CURRENT (IDR) vs. BATTERY VOLTAGE (VBATT) 15 0 1.2 BATT VOLTAGE (V) 20 0 ILDO ,IBST = 0A, VIN = NOT CONNECTED, BACKUP MODE BST LOAD CURRENT (mA) 25 DR CURRENT (mA) 350 100 VIN = NOT CONNECTED BST OUTPUT VOLTAGE (V) 400 MAX8672 toc09 450 BATT CURRENT (μA) VBATT = 2.4V 70 3.2 MAX8672 toc08 90 EFFICIENCY (%) 500 MAX8672 toc07 100 80 BST OUTPUT VOLTAGE vs. BST LOAD CURRENT BATT INPUT CURRENT (WHILE BOOSTING) vs. BATT VOLTAGE MAX8672 toc12 BST EFFICIENCY vs. BST LOAD CURRENT 1.53 3.05V VBST 50mV/div VLX 1V/div 1.51 1.49 0V 1.47 RCHGV = 28.7kΩ 1.45 -40 -15 10 35 60 85 ILX 200mA/div IBST = 2mA 0A 10μs/div TEMPERATURE (°C) _______________________________________________________________________________________ 5 MAX8672 Typical Operating Characteristics (continued) (VIN = 3.6V, Circuit of Figure 6, TA = +25°C, unless otherwise noted.) Typical Operating Characteristics (continued) (VIN = 3.6V, Circuit of Figure 6, TA = +25°C, unless otherwise noted.) HEAVY-LOAD SWITCHING WAVEFORMS BST LOAD TRANSIENT MAX8672 toc15 MAX8672 toc16 3.05V VBST 50mV/div IBST 20mA/div VLX 1V/div 0A 0V 0V ILX 200mA/div VBST 20mV/div AC-COUPLED IBST = 20mA VBATT = 2.4V 0A 10μs/div 200μs/div BST OUTPUT VOLTAGE vs. LDO LOAD CURRENT LDO LOAD TRANSIENT VIN = NOT CONNECTED MAX8672 toc17 MAX8672 toc18 3.2 BST OUTPUT VOLTAGE (V) 3.1 ILDO 20mA/div 0A 3.0 VLDO 10mV/div AC-COUPLED VBATT = 2.4V VBATT = 1.2V 2.9 0V VBATT = 2.4V 2.8 0 30 60 90 120 150 200μs/div 180 LDO LOAD CURRENT (mA) BATTERY RIPPLE (VBATT_P-P) vs. TEMPERATURE BST RESPONSE TO LDO LOAD TRANSIENT MAX8672 toc19 MAX8672 toc20 300 250 CBATT = 10μF ILDO 0A 20mA/div VBATT_P-P (mV) MAX8672 Complete Backup Management IC for NiMH Batteries 200 150 100 VBST 20mV/div AC-COUPLED 0V CBATT = 47μF 50 VBATT = 2.4V 200μs/div 0 -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 45 TEMPERATURE (°C) 6 _______________________________________________________________________________________ Complete Backup Management IC for NiMH Batteries PIN NAME 1 CT 2 CHGI Programming Input for the Standard Charge-Current Rate. Connect a resistor (RCHGI) from CHGI to GND to program the standard charge current from 100µA to 20mA. 3 TRKI Programming Input for the DC Trickle-Charge Rate. Connect a resistor from TRKI to GND to program the trickle-charge current. 4 BATT Backup-Battery Connection. The backup battery charges from IN but does not allow reverse current to IN when VIN < VBATT. BATT input current is less than 0.1µA when VBATT is below the UV threshold. 5 IN Power Input. Range is 2.7V to 5.5V. DR Programming Input for Deep-Recovery Threshold. The DR output adds charge current when VBATT is below the VBATT(DR) threshold (and THRM is valid) by biasing an external resistor connected from DR to BATT. The DR output voltage, VDR, is 0.816 times the VBATT(CHG) limit set by VCHGV (VDR = 1.224V for a 1.5V VBATT(CHG)). The DR current is sourced in addition to the standard charge current set by RCHGI. 7 UV Programming Input for the BATT Undervoltage Lockout (UVLO), VBATT(UV). The UVLO threshold is programmed by connecting a resistor from UV to GND. The backup LDO and boost converter cannot start after UVLO occurs, or on power-up, until a valid VIN and VBST are applied. VBATT(UV) is programmable from VBATT = 0.8V to 3.5V. An open circuit at UV disables the boost and LDO and interrupts battery drain. UVLO also latches off backup circuitry to minimize battery drain. 8 GND 9 LX 10 BST 11 LDO LDO Output. Programmable from 1.5V to 3.05V. LDO has reverse current blocking. FBL Programming Input for the LDO Output Voltage. Connect FBL to the center of a resistor-divider connected between LDO and GND. The FBL threshold is 1.25V. 6 12 13 CHGV FUNCTION Programming Input for Charge Timer. Connect a capacitor from CT to GND to program the charge timer (range: 2min to 2000min, nominally programmed to 8h = 480min with CCT = 0.047µF). Ground Boost Converter Switch Node. Connect the boost inductor from LX to BATT. Boost Converter Output. BST has reverse current blocking when VBST is higher than VIN or VBATT. The MAX8672 operates with VBST down to 2.35V. The BST output is factory preset for 3.05V for use with 3.3V systems. Other voltages are available on request. Programming Input for the Charge Voltage Limit (VBATT(CHG)). Also programs the trickle threshold (VBATT(TRK)), standard charge-restart voltage (VBATT(RSTRT)), DR threshold (VBATT(DR)), and the DR output voltage (VDR). For NiMH, program 1.5V VBATT(CHG) per cell, so that the max possible voltage is 1.55V per cell with tolerances. VBATT(CHG) is programmable from 1.5V to 3.0V by connecting a resistor from CHGV to GND. When the battery voltage rises to VBATT(CHG), standard charging stops. When the battery voltage falls to VBATT(TRK), trickle charge begins. Standard charge does not resume until the battery voltage falls to VBATT(RSTRT). 14 — THRM External Thermistor Monitor Connection. Connect an NTC (100kΩ at TA = +25°C) thermistor for -1°C and +45°C charging cutoff. Only trickle charging is allowed outside the temperature limits. These temperature thresholds are programmable by adding series and parallel resistors to the external thermistor. See Table 1. EP Exposed Pad. Connect to GND but do not rely on EP for ground functions. This pad is internally connected to ground through a soft connect, meaning there is no internal metal or bond wire physically connecting the exposed pad to the GND pin. Connecting the exposed pad to ground does not remove the requirement for a good ground connection to the appropriate pins. For good thermal dissipation, the exposed pad must be soldered to the power ground plane. _______________________________________________________________________________________ 7 MAX8672 Pin Description MAX8672 Complete Backup Management IC for NiMH Batteries Detailed Description 100kΩ THRM REF OK HOT OK COLD CT CHGV 2X VCHG COMP TIMER + LOGIC VTRK COMP IN VRSTRT COMP DR A=2 CHGI VDR COMP TRKI VBATT / 2 A=1 R BATT R LDO FBL OFF UV MAX8672 3.05V HYST* AND LDO AND LO BST LOW IQ BOOST CONVERTER The MAX8672 has three states: • System Active/Charging. With a valid VIN (greater than 2.7V and also greater than VBATT), and a valid V BST (greater than 2.35V), the battery charges. LDO and BST are active and available for system backup. Charging and system backup are independent functions. • Backup. When the system supply voltages have fallen below the programmed output voltage, BST and LDO maintain their output voltages and are sourced by the battery. Under these conditions, battery charging has ceased, but this is not a requirement for the backup state. • Off. When the battery voltage has fallen below the UVLO threshold (VBATT(UV)) and VIN is not valid, the IC turns off and all outputs are latched off. If VBATT recovers to above VBATT(UV), charging does not resume until both a valid VIN and VBST are present. Negligible battery current (less than 50nA leakage) is drawn in this state. HYST*: 0.85V HYSTERESIS, COMPARATOR HI AT 3.05V, LO AT 2.2V AND HI LX The MAX8672 is a compact IC for managing backupbattery charging and utilization in PDAs and other smart handheld devices. The IC contains three major blocks: a charger for 1 or 2 NiMH coin cells; a small, very-lowquiescent current step-up DC-DC converter that generates a boosted backup supply; and an LDO that can supply a 2nd backup voltage to an additional system block (typically low-voltage RAM). The MAX8672 does not have a logic control signal for activating backup. The main system supplies are directly connected to the BST and LDO outputs, where LDO and BST are programmed to regulate just below system supply voltages. When system supply voltages exceed the programmed BST and LDO output voltage, BST and LDO are pulled up by the system supplies and do not sink current (BST sinks 80µA for chip operation). When the system supplies fall below the programmed output voltage, BST and LDO operate to maintain system voltages at the programmed values. The LDO and boost converter do not operate any differently in the system’s running (and charging) state than they do in the backup state. The LDO and BST error amplifiers constantly monitor their outputs in both cases. PFM Figure 1. MAX8672 Functional Block Diagram 8 _______________________________________________________________________________________ Complete Backup Management IC for NiMH Batteries CHARGE TIMER EXPIRES limit is achieved. Once standard charge or trickle charge is terminated by the VBATT(CHG) limit, charging ceases. Subsequently, if VBATT falls to the VBATT(TRK) threshold, trickle charge is activated. VBATT then rises and the charging cycle continues. The charger does not enter standard charge again until the battery falls to the VBATT(RSTRT) threshold. When the VBATT(RSTRT) threshold is reached, standard charge begins and the charge timer is reset. Standard charge is also interrupted if the external thermistor temperature sensed at THRM is out of range. When THRM senses a too-hot or too-cold condition during standard charge, the timer pauses and the charger enters trickle charge. NO CHARGE 1.5V VBATT(CHG) 1.41V VBATT(TRK) NO CHARGE TRICKLE STANDARD CHARGE 1.225V VBATT(RSTRT) 1.5V NO CHARGE VBATT(CHG) TRICKLE 1.41V VBATT(TRK) NO CHARGE TRICKLE STANDARD CHARGE 1.225V VBATT(RSTRT) Figure 2. Typical Charge-Current Profiles for 1-Cell Battery _______________________________________________________________________________________ 9 MAX8672 Charger The MAX8672 charger is a comparator-controlled current source with both current and voltage limits programmed by external resistors. Typical charge profiles for a 1-cell NiMH battery are shown in Figure 2 and explained below. When power is applied at IN and BST, the MAX8672 charges the battery at the standard charge current programmed by a resistor connected between CHGI and GND. The MAX8672 remains in standard charge until the charge timer (programmed by CCT) times out, the battery rises to the VBATT(CHG) limit, or the charge is interrupted by a temperature-range violation. If standard charge is terminated by the charge timer, trickle charge mode begins and continues without timing until the VBATT(CHG) MAX8672 Complete Backup Management IC for NiMH Batteries A valid voltage is required on both IN and BST for standard and trickle charging. Once charging begins, if VIN becomes invalid, charging stops, but the timer is paused since the backup circuitry is supplying BST. If VBST falls below 2.2V, the timer resets. If the thermistor hot- or cold-temperature threshold is violated, the charge timer pauses and only trickle charging is allowed. When THRM recovers, the MAX8672 goes to RUN instead of reentering the charge mode. This is done to reevaluate the battery state when the temperature returns to the normal operating range. The charge timer is not reset when returning to the RUN state. Additionally, if VIN is interrupted during standard charge, and the battery voltage is greater than VBATT(RSTRT), the timer pauses until power is reapplied. If the battery voltage falls below VBATT(RSTRT), the timer resets. See the charger state diagram in Figure 3 for more details on charger operation. Trickle charge occurs whenever standard charge is interrupted by timeout, when VBATT falls to VBATT(TRK), or when THRM senses an out-of-temperature-range condition. Trickle charge has the same voltage limit as standard charge and cannot drive the battery above VBATT(CHG). VBST NOT OK VBST NOT OK ANY STATE OFF (RESET TIMER) VBST OK VIN NOT OK AND VBST OK VIN NOT OK AND VBST OK ANY STATE EXCEPT TRICKLE CHARGE AND NO CHARGE STAND BY (TIMER PAUSED) VIN NOT OK AND VBST OK (2-CELL, VCHG > 2.1V) VIN OK VBATT > VBATT(RSTRT) RESET TIMER RUN T > COLD AND T < HOT COLD/HOT TRICKLE (TIMER PAUSED) VBATT < VBATT(DR) - 50mV RESET TIMER COMPLETE VBATT < VBATT(RSTRT) VBATT > VBATT(DR) STANDARD CHARGE DEEPRECOVERY CHARGE VBATT < VBATT(DR) - 50mV TIMER COMPLETE VBATT > VBATT(CHG) VBATT < VBATT(TRK) TRICKLE CHARGE VBATT > VBATT(CHG) T < COLD AND T > HOT T < COLD OR T > HOT VIN NOT OK AND VBST OK (1-CELL, VCHG < 2.1V) VBATT > VBATT(CHG) NO CHARGE AND FORCE TIMER COMPLETE Figure 3. Charger State Diagram 10 ______________________________________________________________________________________ Complete Backup Management IC for NiMH Batteries or when THRM senses an out-of-temperature-range condition. Trickle charge has the same voltage limit as standard charge. The trickle current is programmed from 100µA to 1mA by connecting a resistor (R TRKI) from TRKI to GND (Figure 4). After selecting the battery trickle charge current (IBATT(TRK)) for the application, RTRKI is determined by the following equation: RTRKI (kΩ) = 100 IBATT(TRK)(mA) R8 RCHGV = VBATT(CHG) C1 (CCT) 52265 . × 10−6 (Note that the voltage at CHGV is VBATT(CHG) / 4.) The other voltage thresholds associated with the charging cycle (Figure 2) are dependent upon the selection of VBATT(CHG) as follows: Falling battery threshold to begin trickle charge (VBATT(TRK)): VBATT(TRK) = 0.94 × VBATT(CHG) Rising battery threshold to exit deep-recovery charge (VBATT(DR)): VBATT(DR) = 0.667 × VBATT(CHG) Standard charging of the battery occurs when the MAX8672 is first turned on, or when the battery is discharged below the VBATT(RSTRT) threshold. Standard charge ceases when the VBATT(CHG) limit is reached. The standard charge current (I BATT(CHG) ) is programmed from 0.1mA to 20mA by connecting a resistor (RCHGI) from CHGI to GND (Figure 4). The valid range of RCHGI is 5kΩ to 1MΩ. Once the value of standard charge current (I BATT(CHG) ) has been chosen, the required RCHGI is determined by the following equation: RCHGI (kΩ) = 100 IBATT(CHG)(mA) Trickle Charge Trickle charge occurs whenever standard charge is interrupted by timeout, when VBATT falls to VBATT(TRK), TH1 100kΩ AT +25°C MAX8672 2.7V TO 5.5V INPUT C2 (CIN) IN CHGV R6 (RCHGV) DR C6 (CDR) CHGI TRKI R1 (RDR) R2 (RCHGI) R4 FBL R3 (RTRKI) R5 Falling battery threshold to restart standard charge (VBATT(RSTRT)): VBATT(RSTRT) = 0.816 × VBATT(CHG) THRM CT BATT BACKUP BATTERY LDO C3 (CBATT) C5 (CLDO) UV L1 R9 (RUV) BST GND C4 (CBST) LX Figure 4. External Component Diagram Deep-Recovery Charge The MAX8672 includes a circuit to bring up deep discharged NiMH cells. When power is first applied to IN, if the battery voltage is less than the battery deeprecovery threshold, VBATT(DR), DR connects an internally regulated voltage to an external resistor that sources extra current into the battery. The DR currentlimiting resistor is typically selected for a 0.5C charge rate when the cell voltage is 0V. When DR is on, both the standard charge current and the DR current charge the battery. When the cell voltage reaches VBATT(DR), DR current is turned off and standard charging begins. ______________________________________________________________________________________ 11 MAX8672 Charger Voltage and Standard Charge-Current Limits The MAX8672 charger is a comparator-controlled current source with both current and voltage limits programmed by external resistors. The maximum battery charge-voltage limit (VBATT(CHG)) is programmed by connecting a resistor (RCHGV) from CHGV to GND (Figure 4). The range for the charging voltage limit is 1.5V to 3.0V. For NiMH batteries, VBATT(CHG) is typically selected for a 1.5V max charge per cell. After selecting VBATT(CHG) for the intended application, the required RCHGV is determined by the following equation: MAX8672 Complete Backup Management IC for NiMH Batteries DR charging is allowed only when the THRM temperature is within hot and cold limits. The rising battery-voltage threshold for DR (V BATT(DR) ) is given by the following equation: VBATT(DR) = 0.667 × VBATT(CHG) The DR output voltage is: VDR = 0.816 × VBATT(CHG) Thermistor Monitor The thermistor monitor suspends standard charging (and pauses the standard charge timer) when the thermistor temperature moves above +45°C or below -1°C. The thermistor must be an NTC type with a nominal +25°C resistance of 100kΩ. The temperature trip thresholds are adjusted by adding external resistors in series and in parallel with the thermistor. For the specified thermistor, the resistors values are shown in Table 1. Table 1. Series/Parallel Resistors for Different Thermistor Thresholds (β) SERIES R (kΩ) PARALLEL R (MΩ) HOT TEMP (OC) COLD TEMP (OC) 0 None 45 -1 7.5 None 50 -0.6 13.7 None 55 -0.3 18.7 None 60 0 18.8 6.8 59.9 -1 22.7 None 65 0 23 5.6 65 -1 8.6 1.7 50 Note: With 100kΩ thermistors at +25°C, β = 3977. -5 Charge Timer The MAX8672 includes a charge timer that is programmable from 2min to 2000min. Timer duration is programmed by a capacitor, CCT, connected from CT to GND (Figure 4). The charge-timer duration (tCHG) is determined by the equation: t CHG (minutes) = 10195 × CCT (μF) Boost DC-DC Converter The MAX8672 contains a low-current synchronous-rectified boost converter that can supply up to 20mA. The boost converter’s preset output voltage is 3.05V, intended for backing up a 3.3V supply. Preset output voltages can be obtained from the factory on request. Generally, the output voltage is programmed to be just 12 below the minimum tolerance for the main supply. When the main supply voltage drops below its specified level, the step-up converter begins regulating as long as the load is 20mA or less. The MAX8672 blocks reverse current flow if VBST is higher than VBATT. The MAX8672 typical application expects that a valid system voltage is connected to BST and IN before backup operations are required. The boost DC-DC converter is able to supply a system load (up to 20mA) when the main power source falls below the BST preset voltage, but the IC cannot start up the BST output with just the backup battery alone. BST must initially be powered by the external system in order for the boost converter to start. Then, if the system voltage falls below the BST preset voltage, the boost converter can supply the load. If necessary, this limitation can be overcome for some applications by connecting a diode from IN to BST, so that BST is immediately powered from IN. When VBATT is less than VBST, and VBST is not externally pulled above 3.05V by the main system supply, the boost converter runs as needed to maintain VBST at 3.05V. If, during normal active/charging mode operation, VBATT rises above the main system voltage that is connected to BST, current may flow from the battery to the main system supply, even though no backup operation is expected. For example, in a 2-cell system, if VBATT is 3.2V and the system supply is holding BST at 3.1V, then the backup battery drains into the system supply. The boost synchronous rectifier pMOS contains a body diode that is switched to prevent unwanted current flow (see the BATT-BST Current Flow section). Since the normal maximum charge limit (VBATT(CHG)) for 2 NiMH cells is usually set to 3.0V (for a 3.1V max), and a 3.3V system supply less a 5% tolerance is 3.135V, VBATT does not exceed VBST during normal system operation, resulting in no backup current flow. However, for other BATT or BST voltages where unwanted backup current flow may occur, it can be prevented by connecting a diode in series with the boost inductor to reduce the voltage at BST. The diode may be a Schottky or silicon signal diode, depending on how much voltage needs to be dropped. Boost Output Capacitor Selection Choose output capacitors to supply output peak currents with acceptable voltage ripple. Low equivalent series resistance (ESR) capacitors are recommended. Ceramic capacitors have the lowest ESR, but low-ESR tantalum or polymer capacitors offer a good balance between cost and performance. ______________________________________________________________________________________ Complete Backup Management IC for NiMH Batteries VRIPPLE = VRIPPLE(C) + VRIPPLE(ESR) VRIPPLE(ESR) = IPEAK × RESR VRIPPLE(C) = ⎞ 1⎛ L 2 ⎜ ⎟ IPEAK 2 ⎝ (VBST − VBATT ) × CBST ⎠ where IPEAK is the peak inductor current (see the Boost Inductor Selection section). Since ESR is usually very small in ceramic capacitors, the output ripple is typically dominated by VRIPPLE(C). Capacitance and ESR variation with temperature should be considered for best performance in applications with wide operating-temperature ranges. Boost Inductor Selection The control scheme of the MAX8672 permits flexibility in choosing an inductor. A 4.7µH inductor performs well in most applications. For maximum output current, choose the inductor value so that the controller reaches the current limit before the maximum on-time is reached: L< VBATT × t ON(MAX) ILIM where tON(MAX) is typically 5µs, and the current limit (ILIM) is typically 500mA (see the Electrical Characteristics). For larger inductor values, determine the peak inductor current (IPEAK) by: IPEAK = LDO For backup designs that require two different backup voltages, the MAX8672 includes a small LDO, which is powered from BST. This LDO can supply up to 20mA. Generally, the output voltage is programmed to be just below the minimum tolerance for the main supply. When the main supply voltage drops below its specified level, the LDO begins regulating. The LDO output voltage is adjustable from 1.5V to 3.05V using external resistors (R4 and R5 in Figure 4). Since the FBL input bias current is 50nA (max), select feedback resistor R4 in the 100kΩ to 1MΩ range. After choosing R4, calculate R5 as follows: ⎡V ⎤ R5 = R4⎢ LDO − 1⎥ ⎣ VFBL ⎦ where VFBL = 1.25V. Backup-Battery Bypass Capacitor Selection The MAX8672 boost converter draws 500mA short-term inductor-charging current peaks from the battery when the boost converter operates. Small coin cells that are commonly used for backup often exhibit high output impedance that varies over temperature. For this reason, the backup battery must be bypassed with a highquality ceramic capacitor with X7R, X5R, or better dielectric (CBATT, Figure 4). Typical values are between 10µF and 47µF. Note that high battery ripple can prematurely trigger the UVLO comparator and shut down the boost circuit before the battery is fully discharged. If this is a concern with the selected battery, the UV threshold may be lowered, in addition to using a larger battery bypass capacitance, to accommodate the short-term battery-voltage dip due to ripple. See the Battery Ripple vs. Temperature graph in the Typical Operating Characteristics section. VBATT × t ON(MAX) L ______________________________________________________________________________________ 13 MAX8672 Output-voltage ripple has two components: variations in the charge stored in the output capacitor (CBST) with each BST pulse, and the voltage drop across the capacitor’s ESR due to the current flow into and out of the capacitor. The equations for approximating outputvoltage ripple are: MAX8672 Complete Backup Management IC for NiMH Batteries BACKUP READY* (BOOST AND LDO ENABLED) VIN > 2.45V AND VBST > 3.05V AND VBATT > VBATT(UV) VBATT < VBATT(UV) BATT UVLO (BOOST AND LDO OFF) *NOTE: BACKUP READY DOES NOT MEAN THAT THE BOOST AND LDO ARE OPERATING. WHEN THE BST AND LDO OUTPUTS ARE ENABLED; THEY STILL ONLY OPERATE IF NEEDED WHEN THE SYSTEM FAILS TO HOLD UP THE SUPPLIES. Figure 5. Backup and BATT UVLO State Diagram BATT Undervoltage Lockout When the backup battery discharges to a programmed threshold, VBATT(UV), BATT UVLO is engaged. As a result, the MAX8672 backup functions (BST and LDO) shut down, and a small current (less than 50nA) is drawn from BATT. During BATT UVLO, charge functions still remain active to recharge the battery. Once BATT UVLO occurs, the backup boost converter and LDO do not reactivate until VBST rises above 3.05V and VIN rises above 2.45V (typ). Even if BATT recovers, the backup functions do not activate until a valid VIN and VBST have been present. See the Backup and BATT UVLO State Diagram (Figure 5). The BATT UVLO threshold (VBATT(UV)) is programmed by connecting a resistor (RUV) from UV to GND (Figure 4). For NiMH cells, the UVLO threshold is typically programmed to 0.8V per cell. Once the UVLO threshold value is determined, RUV is calculated from the following equation: VBATT(UV) RUV = 16 × 10−6 14 Note: In order for BATT current to remain below 50nA during BATT UVLO, VBST must fall below 0.5V. If VBST is held up by another source during UVLO, or if VBST is higher than 0.5V, BATT input current during BATT UVLO is typically 500nA. Typically, VBST falls to 0V in most situations. If minimum battery drain during BATT UVLO is critical, then an external pulldown resistor connected between BST and GND may be needed to discharge the BST output. The 500nA BATT drain during UVLO is necessary when VBST is > 0.5V because a comparator must be kept active in order to detect the higher of VBATT or VBST. This comparator switches the body diode of the internal FET connecting these outputs to ensure that current flow is blocked. When VBST falls to approximately 0.5V, the comparator is shut off, and the FET body is connected to block current flowing from BATT to BST. BATT-BST Current Flow The MAX8672 synchronous rectifier pMOS contains an internal body diode connected between BATT and BST. This diode switches to prevent undesired current flow between these pins. Upon startup, the body diode points to the greater of VBATT or VBST, until VBST rises above 3.05V (at least once). Then the body diode switches to point to BST. The body diode points from BATT to BST until V BST falls below 2.2V. When this occurs, the body diode switches to point to the greater of VBATT or VBST. If VBATT exceeds VBST by a few hundred millivolts or more, the body diode is forward biased and current flows from BATT to BST. This is the typical case for a boost converter when the input exceeds the output. When backing up, this typically is not a problem since it is expected that battery current powers the system. When not in backup mode (system power is up and is pulling VBST over 3.05V), current can flow from BATT to BST if VBATT exceeds VBST by enough to forward bias the diode. With two NiMH cells, VBATT charges to 3.0V nominal (3.1V max), so with VBST pulled to more than 3.05V by the system, there is not enough voltage difference to cause significant current to flow from BATT to BST. ______________________________________________________________________________________ Complete Backup Management IC for NiMH Batteries R8 7.5kΩ CT Typical Application Circuit Figure 6 displays the MAX8672 typical application circuit for 2-cell NiMH applications. Corresponding to the requirements for 2-cell NiMH batteries, maximum charge voltage is programmed for 3.0V and the UVLO threshold is set to 1.6V. The LDO output voltage is 1.75V. Standard charge provides 2mA of standard charge current, while trickle charge is programmed to provide 500µA of trickle charge current. A 7.5kΩ resistor is connected in series with the thermistor to program a hot temperature threshold of +50°C and a cold temperature threshold of -0.6°C. C1 0.047μF 2.7V TO 5.5V INPUT THRM TH1 100kΩ AT +25°C IN C2 0.1μF DR C6 0.22μF R1 100Ω CHGV CHGI TRKI R2 50kΩ R3 200kΩ R6 57.6kΩ R4 250kΩ MAX8672 Layout Guidelines Careful PCB layout is important for minimizing ground bounce and noise. Ensure that C2 (IN input capacitor), C3 (BATT input capacitor), C4 (BST bypass capacitor), and C5 (LDO output capacitor) are placed as close as possible to the IC. Avoid using vias to connect C3 or C4 to their respective pins or GND. C3 and C4 grounds should be located next to each other, and this connection can then be used as the star ground point. All other grounds should connect to the star ground. Connect EP to the bottom layer ground plane, and then connect the ground plane to the star ground. Vias on the inductor path are acceptable, if necessary. IN, BATT, BST, and LDO traces should be as wide as possible to minimize inductance. Refer to the MAX8672 evaluation kit for a PCB layout example. MAX8672 Applications Information FBL BATT R5 100kΩ C3 47μF 2-CELL NiMH 1.75V LDO UV L1 4.7μH R9 100kΩ C5 0.47μF 3.05V BST GND C4 22μF LX Figure 6. Typical Application Circuit for the MAX8672 Using a 2-Cell NiMH Chip Information PROCESS: BiCMOS ______________________________________________________________________________________ 15 Package Information (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information go to www.maxim-ic.com/packages.) 6, 8, &10L, DFN THIN.EPS MAX8672 Complete Backup Management IC for NiMH Batteries PACKAGE OUTLINE, 6,8,10 & 14L, TDFN, EXPOSED PAD, 3x3x0.80 mm 21-0137 16 ______________________________________________________________________________________ H 1 2 Complete Backup Management IC for NiMH Batteries COMMON DIMENSIONS PACKAGE VARIATIONS SYMBOL MIN. MAX. PKG. CODE N D2 E2 e JEDEC SPEC b A 0.70 0.80 T633-1 6 1.50±0.10 2.30±0.10 0.95 BSC MO229 / WEEA 0.40±0.05 1.90 REF D 2.90 3.10 T633-2 6 1.50±0.10 2.30±0.10 0.95 BSC MO229 / WEEA 0.40±0.05 1.90 REF [(N/2)-1] x e E 2.90 3.10 T833-1 8 1.50±0.10 2.30±0.10 0.65 BSC MO229 / WEEC 0.30±0.05 1.95 REF A1 0.00 0.05 T833-2 8 1.50±0.10 2.30±0.10 0.65 BSC MO229 / WEEC 0.30±0.05 1.95 REF L 0.20 0.40 T833-3 8 1.50±0.10 2.30±0.10 0.65 BSC MO229 / WEEC 0.30±0.05 1.95 REF T1033-1 10 1.50±0.10 2.30±0.10 0.50 BSC MO229 / WEED-3 0.25±0.05 2.00 REF k 0.25 MIN. A2 0.20 REF. T1033-2 10 1.50±0.10 2.30±0.10 0.50 BSC MO229 / WEED-3 0.25±0.05 2.00 REF T1433-1 14 1.70±0.10 2.30±0.10 0.40 BSC ---- 0.20±0.05 2.40 REF T1433-2 14 1.70±0.10 2.30±0.10 0.40 BSC ---- 0.20±0.05 2.40 REF PACKAGE OUTLINE, 6,8,10 & 14L, TDFN, EXPOSED PAD, 3x3x0.80 mm -DRAWING NOT TO SCALE- 21-0137 H 2 2 Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 17 © 2006 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc. MAX8672 Package Information (continued) (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information go to www.maxim-ic.com/packages.)