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MC34280 Power Supply & Management IC for Handheld Electronic Products
The MC34280 is a power supply integrated circuit which provides two boost regulated outputs and some power management supervisory functions. Both regulators apply Pulse-Frequency-Modulation (PFM). The main step-up regulator output can be externally adjusted from 2.7V to 5V. An internal synchronous rectifier is used to ensure high efficiency (achieve 87%). The auxiliary regulator with a built-in power transistor can be configured to produce a wide range of positive voltage (can be used for LCD contrast voltage). This voltage can be adjusted from +5V to +25V by an external potentiometer; or by a microprocessor, digitally through a 6-bit internal DAC. The MC34280 has been designed for battery powered hand-held products. With the low start-up voltage from 1V and the low quiescent current (typical 35 A); the MC34280 is best suited to operate from 1 to 2 AA/ AAA cell. Moreover, supervisory functions such as low battery detection, CPU power-on reset, and back-up battery control, are also included in the chip. It makes the MC34280 the best one-chip power management solution for applications such as electronic organizers and PDAs.
32 1
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32-LEAD LQFP FTB SUFFIX CASE 873A
MARKING DIAGRAM
MC34280F TB AWLYYWW
A WL YY WW
= Assembly Location = Wafer Lot = Year = Work Week
FEATURES:
VMAIN VMAINSW VMAINGND NC LIBAOUT LIBATIN VAUXEMR VAUXSW 32 1 VMAINFB VBAT ENABLE VDD PDELAY VREF AGND IREF LOWBATSEN NC VAUXBASE VAUXCHG VAUXBDV VAUXFBN VAUXREF VAUXFBP VAUXEN MC34280
* Low Input Voltage, 1V up * Low Quiescent Current in Standby Mode: 35A typical * PFM and Synchronous Rectification to ensure high efficiency * * * * * * * * * * * *
(87% @200mA Load) Adjustable Main Output: nominal 3.3V @ 200mA max, with 1.8V input Auxiliary Output Voltage can be digitally controlled by microprocessor Auxiliary Output Voltage: +5V @ 25mA max, with 1.8V input +25V @ 15mA max, with 1.8V input Current Limit Protection Power-ON Reset Signal with Programmable Delay Battery Low Detection Lithium Battery Back-up 32-Pin LQFP Package
PIN CONNECTIONS
APPLICATIONS:
Digital Organizer and Dictionary Personal Digital Assistance (PDA) Dual Output Power Supply (For MPU, Logic, Memory, LCD) Handheld Battery Powered Device (1-2 AA/AAA cell)
ORDERING INFORMATION
Device MC34280FTB MC34280FTBR2 Package LQFP LQFP Shipping 250 Units/Tray 1800 Tape & Reel
(c) Semiconductor Components Industries, LLC, 1999
1
February, 2000 - Rev. 2
DGND PROB LOWBATB LIBATON LIBATCL VAUXADJ VAUXCON Publication Order Number: MC34280/D
MC34280
Figure 1. Typical Application Block Diagram
Battery Lock Switch
CVDD c = 20u Riref r = 480 k GND IREF AGND 8 7 VREF 6 5 GND GND VREF Cpor c = 80n GND PDELAY VDD
VBAT Ren r = 1000 k
CMAINb c = 100p RMAINb r = 1000 k
VBAT
Optional CMAINbp c = 100u 10 V SMT tantalum GND
GND
VDD 4
ENABLE 3
VBAT 2
VMAINFB 1 R123 r=5
VBAT RLBa r = 300 k RLBb r = 900 k GND GND PORB 11 LOWBATB LIBATON LIBATCL 12 13 14 VAUXADJ 15 VAUXCON PORB LOWBAT LIBATON LIBATCL VAUXADJ VAUXCON VAUXEN VAUXFBP VAUXREF (1.1 V to 2.2 V) LAUX L = 22u (Rs < 60 mOhm) VBAT CAUXbp c = 100u 10 V SMT tantalum Optional GND 30 V SMT tantalum VAUXEN Auxiliary Regulator 17 18 19 VAUXFBN 20 VBAT 21 VAUXBDV 22 23 16 Level Control Current Limit Control and Base Drive Q1 Lithium Battery Backup Power ON Reset Current Bias Voltage Reference Low Battery Detect
LMAIN L = 33u (Rs < 60 mOhm) VMAIN
LOWBATSEN DGND 9 10
Control and Gate Drive Startup d
s M2 M1
d 32
VMAIN 1N5817 CMAIN c = 100u 10 V SMT tantalum GND
Current Limit
s
31 VMAINSW VMAINGND 30 29 d M3 s 27 VAUXEMR 26 VAUXSW 25 GND GND LIBATIN N/C GND
Main Regulator with Synchronous Rectifier
28 LIBATOUT
24 N/C
VAUXBASE VAUXCHG
1N5818 Caux c = 30u
VAUX Optional Rauxb r = 2.2 M GND CAUXb c = 2n
Rauxa r = 200 k
CAUXa c = 33n
GND
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MC34280
TIMING DIAGRAMS
VBAT
ENABLE VMAINreg - 0.15 V VMAINreg
VMAIN
T
POR
+
1.22 0.5
C por
RIref
PORB
tPORC
VAUXEN
Figure 2. Startup Timing
VBAT
LOWBAT Threshold
LOWBATB
VMAIN VMAINreg - 0.5 V ENABLE
PORB
Figure 3. Power Down Timing
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MC34280
TIMING DIAGRAMS (Con't)
VAUXCON
Total N Pulses
Total M Pulses
VAUXADJ
DV +
N 64
@ 1.1 V
"Countup" Flag is HIGH "Countup" Flag is LOW
DV +
M 1.1 V 64
@
2.2 V
1.65 V Reset VAUXREF
VAUXREF 1.1 V
Figure 4. Auxiliary Regulator Voltage Control
tCW tCL
tCC tDL tRJL
VAUXCON tJC tJL
VAUXADJ
tDW tJW
tRW
Figure 5. Auxiliary Regulator Voltage Control Timing
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Pin No. 32 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 10 11 9 8 7 6 5 4 3 2 1
LOWBATSEN VMAINGND VAUXBASE VAUXEMR VAUXCHG VAUXCON LOWBATB LIBATOUT VMAINSW
Function
VAUXBDV
VAUXFBN
VAUXREF
VAUXFBP
VAUXADJ
VMAINFB
VAUXSW
LIBATON
VAUXEN
LIBATCL
ENABLE
PDELAY
LIBATIN
VMAIN
DGND
AGND
PORB
VREF
VBAT
IREF
VDD
NC
NC
Type/Direction
Analog / Output
Analog / Output
Analog / Output
Analog / Output
Analog / Output
Analog / Output
Analog / Output
Analog / Output
Analog / Output
CMOS / Output
CMOS / Output
Analog Ground
Power Ground
Digital Ground
Analog / Input
Analog / Input
Analog / Input
Analog / Input
Analog / Input
Analog / Input
Analog / Input
Analog / Input
CMOS / Input
CMOS / Input
CMOS / Input
CMOS / Input
CMOS / Input
CMOS / Input
Power
Power
PIN FUNCTION DESCRIPTION
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VMAIN output VMAIN inductor connection Ground for VMAIN low side switch no connection Lithium battery output Lithium battery input for backup purposes Emitter output of the VAUX power BJT Collector output of the VAUX power BJT no connection test pin test pin VAUX BJT base drive circuit power supply Feedback pin for VAUX Reference Voltage for VAUX voltage level Feedback pin for VAUX VAUX enable, Active high microprocessor control signal for VAUX voltage control microprocessor control signal for VAUX voltage control microprocessor control signal for Lithium battery backup switch, if it is HIGH, the switch is controlled by LIBATON, otherwise, controlled by internal logic microprocessor control signal for Lithium battery backup switch, the switch is ON when LIBATON=HIGH and LIBATCL=HIGH Active LOW low battery detect output Active LOW Power-On reset signal Resistive network connection for defining low battery detect threshold Resistor connection for defining internal current bias and PDELAY current Bandgap Reference output voltage. Nominal voltage is 1.25V Capacitor connection for defining Power-On signal delay Connect to decoupling capacitor for internal logic supply Chip enable, Active high, ENABLE activates VMAIN after battery plug in, ENABLE is inactive after VMAIN is on Main battery supply Feedback pin for VMAIN
MC34280
5
Description
MC34280
ABSOLUTE MAXIMUM RATINGS (TA = 25C, unless otherwise noted.)
Parameter Power Supply Voltage Digital Pin Voltage General Analog Pin Voltage Pin VAUXSW to Pin VAUXEMR Voltage (Continuous) Pin VMAINSW to Pin VMAIN Voltage (Continuous) Operating Junction Temperature Ambient Operating Temperature Storage Temperature Symbol VBAT Vdigital Vanalog VAUXCE Vsyn Min -0.3 -0.3 -0.3 -0.3 Max 7.0 7.0 7.0 30 0.3 Unit Vdc Vdc Vdc Vdc Vdc C C C
AAAA A A AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAA A AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAA A AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAA A AAAA A A AAA A AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAA A AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAA AA A AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AA A AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAA A AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAA A
Tj (max) Ta 150 70 0 Tstg - 50 150
STATIC ELECTRICAL CHARACTERISTICS (Circuit of Figure 1, VP = 1.8V, Iload = 0 mA, TA = 0 to 70C unless
otherwise noted.) Rating Symbol VBAT Vmain Vmain_range I3.3_1.8 Freqmax_VM ILIM_VM VAUX_range VAUXREF_L VAUXREF_H VAUXREF_S Freqmax_VL ILIM_VL Iqstandby Vrefno_load VLOBAT_L VLOBAT_H IchgPDELAY VthPDELAY 1.19 0.8 1.05 0.8 1.19 1.0 35 1.22 0.85 1.1 1.0 1.22 0.85 5.0 1.0 2.0 1.1 2.2 17 1.0 Min 1.0 3.13 2.7 3.3 Typ
Max
Unit V
Operating Supply Voltage1 VMAIN output voltage VMAIN output voltage range2 VMAIN output current3 VMAIN maximum switching frequency4 VMAIN peak coil static current limit VAUX output voltage range VAUXREF lower level voltage VAUXREF upper level voltage VAUXREF step size VAUX maximum switching frequency VAUX peak coil static current limit Quiescent Supply Current at Standby Mode5 Reference Voltage @ no load Battery Low Detect lower hysteresis threshold6 Battery Low Detect upper hysteresis threshold PDELAY Pin output charging current PDELAY Pin voltage threshold
3.47 5.0 200 100 1.15 25 1.2 2.4
V V mA kHz A V V V mV
120
kHz A
60 1.25 0.9 1.15 1.2 1.25
A V V V A V
NOTE: 1. Output current capability is reduced with supply voltage due to decreased energy transfer. The supply voltage must not be higher than VMAIN+0.6V to ensure boost operation. Max Start-up loading is typically 1V at 400 A, 1.8V at 4.4 mA, and 2.2V at 88 mA. NOTE: 2. Output voltage can be adjusted by external resistor to the VMAINFB pin. NOTE: 3. At VBAT = 1.8V, output current capability increases with VBAT. NOTE: 4. Only when current limit is not reached. NOTE: 5. This is average current consumed by the IC from VDD, which is low-pass filtered from VMAIN, when only VMAIN is enabled and at no loading. NOTE: 6. This is the minimum of "LOWBATB" threshold for battery voltage, the threshold can be increased by external resistor divider from "VBAT" to "LOWBATSEN".
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MC34280
DYNAMIC ELECTRICAL CHARACTERISTICS (Refer to TIMING DIAGRAMS, TA = 0 to 70C unless otherwise noted.)
Rating Minimum PORB to Control delay Minimum VAUXCON pulse HIGH width Minimum VAUXCON pulse LOW width Minimum VAUXADJ to VAUXCON delay Minimum VAUXADJ pulse HIGH width Minimum VAUXADJ pulse LOW width Minimum VAUXCON LOW to VAUXADJ pulse delay1 Minimum hold time of VAUXADJ for Reset VAUXREF Minimum VAUXADJ pulse HIGH width for Reset VAUXREF Minimum hold time of VAUXADJ for Decrement VAUXREF Minimum VAUXADJ pulse HIGH width for Decrement VAUXREF
NOTE: 1. For not resetting VAUXREF.
Symbol tPORC tCW tCC tCL tJW tJC tJL tRJL tRW tDL tDW
Min
Typ
Max 500 5.0 8.0 1.0 1.0 1.0 1.0 500 1.0 500 1.0
Unit nS S S S S S S nS S nS S
TYPICAL ELECTRICAL CHARACTERISTICS
Figure 6. Efficiency of VMAIN versus Output Current (VMAIN = 3.3 V, L = 33 uH, Various VIN)
Eff VMAIN , EFFICIENCY OF VMAIN (%)
Figure 7. Efficiency of VMAIN versus Input Voltage (VMAIN = 3.3 V, L1 = 33 uH, Various IOUT)
90% X 85% X
90% Eff VMAIN , EFFICIENCY OF VMAIN (%)
85%
80%
Vin = 3V Vin = 1.8V Vin = 1.5V Vin = 1V
80% X 75% X 70% 1 1.5 2 VIN, INPUT VOLTAGE (V) Iout = 10mA Iout = 60mA Iout = 100mA Iout = 150mA Iout = 200mA 2.5 3
75%
70% 0 50 100 150 200 250 300 IOUT_MAIN, MAIN OUTPUT CURRENT (mA)
Figure 8. Efficiency of VAUX versus Output Current (VAUX = 25 V, L2 = 33 uH, Various VIN)
80% Eff VAUX , EFFICIENCY OF VAUX (%) 75% 70% 65% 60% 55% 50% 1 3 5 7 9 11 13 15 IOUT_AUX, AUX OUTPUT CURRENT (mA) Vin = 3V Vin = 1.8V Vin = 1.5V Vin = 1V Eff VAUX , EFFICIENCY OF VAUX (%) 80% 75% 70% 65% 60% 55% 50%
Figure 9. Efficiency of VAUX versus Input Voltage (VAUX = 25 V, L2 = 33 uH, Various IOUT)
Iout = 1mA Iout = 5mA Iout = 10mA Iout = 15mA 1 1.5 2 VIN, INPUT VOLTAGE (V) 2.5 3
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MC34280
TYPICAL ELECTRICAL CHARACTERISTICS (Cont'd)
Figure 10. Efficiency of VAUX versus Output Current (VAUX = 20 V, L2 = 33 uH, Various VIN)
80% Eff VAUX, EFFICIENCY OF VAUX (%) 75% 70% 65% 60% 55% 50% 1 3 5 7 9 11 13 15 IOUT_AUX, AUX OUTPUT CURRENT (mA) Vin = 3V Vin = 1.8V Vin = 1.5V Vin = 1V Eff VAUX, EFFICIENCY OF VAUX (%) 80% 75% 70% 65% 60% 55% 50% 1 1.5 2 VIN, INPUT VOLTAGE (V) 2.5 3 Iout = 1mA Iout = 5mA Iout = 10mA Iout = 15mA
Figure 11. Efficiency of VAUX versus Input Voltage (VAUX = 20 V, L2 = 33 uH, Various IOUT)
Figure 12. Efficiency of VAUX versus Output Current (VAUX = 5 V, L2 = 82 uH, Various VIN)
85% Eff VAUX, EFFICIENCY OF VAUX (%) 80% 75% 70% 65% 60% 55% 50% 45% 40% 1 5 10 15 20 Vin = 3V Vin = 2.4V Vin = 1.8V Vin = 1.5V Vin = 1V 25 30 35 Eff VAUX, EFFICIENCY OF VAUX (%)
Figure 13. Efficiency of VAUX versus Input Voltage (VAUX = 5 V, L2 = 82 uH, Various IOUT)
85% 80% 75% 70% 65% 50% 1 1.5 2 VIN, INPUT VOLTAGE (V) 2.5 3 Iout = 1V Iout = 5V Iout = 10V Iout = 15V Iout = 25V
IOUT_AUX, AUX OUTPUT CURRENT (mA)
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MC34280
Figure 14. VMAIN Output Ripple (Medium Load) Figure 15. VMAIN Output Ripple (Heavy Load)
20 uS / div 1: VMAIN = 3.3 V (50 mV/div, AC COUPLED) 2: Voltage at VMAINSW (1 V/div)
10 uS / div 1: VMAIN = 3.3 V (50 mV/div, AC COUPLED) 2: Voltage at VMAINSW (1 V/div)
Figure 16. VAUX Output Ripple (Medium Load)
Figure 17. VAUX Output Ripple (Heavy Load)
20 uS / div 1: VAUX = 20 V (50 mV/div, AC COUPLED) 2: Voltage at VAUXSW (10 V/div)
10 uS / div 1: VAUX = 20 V (50 mV/div, AC COUPLED) 2: Voltage at VAUXSW (10 V/div)
Figure 18. VMAIN Startup and Power-On Reset
Figure 19. VAUX Startup
50 mS / div 1: VMAIN from 1 V to 3.3 V (1 V/div) 2: Voltage of PORB (2 V/div) 3: Voltage of ENABLE (2 V/div)
5 mS / div 1: VAUX from 1.8 V to 20 V (5 V/div) 2: VAUXEN (2 V/div)
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MC34280
DETAILED OPERATING DESCRIPTION
General
The MC34280 is a power supply integrated circuit which provides two boost regulated outputs and some power management supervisory functions. Both regulators apply Pulse-Frequency-Modulation (PFM). The main boost regulator output can be externally adjusted from 2.7V to 5V. An internal synchronous rectifier is used to ensure high efficiency (achieve 87%). The auxiliary regulator with a built-in power transistor can be configured to produce a wide range of positive voltage (can be used to supply a LCD contrast voltage). This voltage can be adjusted from +5V to +25V by an external potentiometer; or by a microprocessor, digitally through a 6-bit internal DAC. The MC34280 has been designed for battery powered hand-held products. With the low start-up voltage from 1V and the low quiescent current (typical 35 A); the MC34280 is best suited to operate from 1 to 2 AA/ AAA cell. Moreover, supervisory functions such as low battery detection, CPU power-on reset, and back-up battery control, are also included in the chip. It makes the MC34280 the best one-chip power management solution for applications such as electronic organizers and PDAs.
Pulse Frequency Modulation (PFM)
Iref
0.5 + RIref
(A)
This bias current is used for all internal current bias as well as setting VMAIN value. For the latter application, Iref is doubled and fed as current sink at Pin 1. With external resistor RMAINb tied from Pin1 to Pin32, a constant level shift is generated in between the two pins. In close-loop operation, voltage at Pin 1 (i.e. Output feedback voltage) is needed to be regulated at the internal reference voltage level, 1.22V. Therefore, the delta voltage across Pin 1 and Pin 32 which can be adjusted by RMAINb determines the Main Output voltage. If the feedback voltage drops below 1.22V, internal comparator sets switching cycle to start. So, VMAIN can be calculated as follows.
VMAIN
+ 1.22 ) RMAINb RIref
(V)
From the above equation, although VMAIN can be adjusted by RMAINb and RIref ratio, for setting VMAIN, it is suggested, by changing RMAINb value with RIref kept at 480K. Since changing RIref will alter internal bias current which will affect timing functions of Max ON time (TON1 ) and Min OFF time (TOFF1 ). Their relationships are as follows;
Both regulators apply PFM. With this switching scheme, every cycle is started as the feedback voltage is lower than the internal reference. This is normally performed by internal comparator. As cycle starts, Low-Side switch (i.e. M1 in Figure 1) is turned ON for a fixed ON time duration (namely, Ton) unless current limit comparator senses coil current reaches its preset limit. In the latter case, M1 is OFF instantly. So Ton is defined as the maximum ON time of M1. When M1 is ON, coil current ramps up so energy is being stored inside the coil. At the moment just after M1 is OFF, the Synchronous Rectifier (i.e. M2 in Figure 1) or any rectification device (such as Schottky Diode of Auxiliary Regulator) is turned ON to direct coil current to charge up the output bulk capacitor. Provided that coil current is not reached, every switching cycle delivers fixed amount of energy to the bulk capacitor. So for higher loading, larger amount of energy (Charge) is withdrawn from the bulk capacitor, and as output voltage is needed to regulated, larger amount of Charge is needed to be supplied to the bulk capacitor, that means switching frequency is needed to be increased; and vice-versa.
Main Regulator
+ 1.7 T + 6.4 OFF 1
T ON 1
10 -11 10 -12
RIref (S) RIref (S)
Continuous Conduction Mode and Discontinuous Conduction Mode
Figure 20 shows the simplified block diagram of Main Regulator. Notice that precise bias current Iref is generated by a VI converter and external resistor RIref, where
In Figure 21, regulator is operating at Continuous Conduction Mode. A switching cycle is started as the output feedback voltage drops below internal voltage reference VREF. At that instant, the coil current does not drop to zero yet, and it starts to ramp up for the next cycle. As the coil current ramps up, loading makes the output voltage to decrease as the energy supply path to the output bulk capacitor is disconnected. And after Ton elapsed, M1 is OFF, M2 becomes ON, energy is dumped to the bulk capacitor. Output voltage is increased as excessive charge is pumped in, then it is decreased after the coil current drops below the loading. Notice the abrupt spike of output voltage is due to ESR of the bulk capacitor. Feedback voltage can be resistor-divided down or level-shift down from the output voltage. As this feedback voltage drops below VREF, next switching cycle starts.
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MC34280
DETAILED OPERATING DESCRIPTION (Cont'd)
VBAT CMAINb 100 pF 2 x Iref RMAINb 1000 kOhm 31 ZLC COMP3 M2 x2 0.5 V Iref IREF 8 RIref 480 kOhm Voltage Reference 1.22 V VCOMP COMP1 VDD 1-SHOT for Min. OFF Time R S AGND Voltage Reference & Current Bias Main Regulator with Synchronous Rectifier Q ILIM DGND COMP2 S Qb DGND VMAINGND 30 R Q M1 +ve Edge Delay for Max. ON Time VDD senseFET 32 CMAIN 100 uF + VMAIN VMAINSW L1 33uH
1
VMAINFB
AGND
Figure 20. Simplified Block Diagram of Main Regulator
In Figure 22, regulator is operating at Discontinuous Conduction Mode, waveforms are similar to those of Figure 21. However, coil current drops to zero before next switching cycle starts. To estimate conduction mode, below equation can be used.
Iroom
T SW
+
1
*
I
T ON h Vin Vout
(S);
Ipk
+
1
LOAD T ON T SW
+ h2
TON L
Vin 2 Vout
* ILOAD
*
) Vin2
T ON L
(A)
where, is efficiency, refer to Figure 6
For Discontinuous Conduction mode, provided that current limit is not reached,
T SW
if Iroom > 0, the regulator is at Discontinuous Conduction mode if Iroom = 0, the regulator is at Critical Conduction mode where coil current just drops to zero and next cycle starts. if Iroom < 0, the regulator is at Continuous Conduction mode For Continuous Conduction mode, provided that current limit is not reached,
+
2 @T ON Vout 2@L@I @ h@Vin * 1 LOAD
Vin
(S);
Ipk
+ Vin @ TON L
(A)
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MC34280
Cycle Starts VREF Feedback Voltage tdl M1 ON tdh M2 OFF Ipk M2 ON M2 OFF TON M2 ON M2 OFF M2 ON M1 OFF M1 ON M1 OFF M1 ON M1 OFF
Loading Current, ILOAD Coil Current VMAIN + 1 V VMAIN TSW
V@SW VMAIN Zoom-In
0V
Figure 21. Waveforms of Continuous Conduction Mode
Cycle Starts Feedback Voltage VREF tdl M1 ON tdh M2 OFF M2 OFF M2 OFF M1 OFF M1 ON M1 OFF M1 ON M1 OFF
Ipk
TON
Loading Current, ILOAD Coil Current VMAIN + 1 V VMAIN VIN V@SW VMAIN Zoom-In 0V TSW
Figure 22. Waveforms of Discontinuous Conduction Mode
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MC34280
DETAILED OPERATING DESCRIPTION (Cont'd)
Synchronous Rectification
A Synchronous Rectifier is used in the main regulator to enhance efficiency. Synchronous rectifier is normally realized by powerFET with gate control circuitry which, however, involved relative complicated timing concerns. In Figure 20, as main switch M1 is being turned OFF, if the synchronous switch M2 is just turned ON with M1 not being completed turned OFF, current will be shunt from the output bulk capacitor through M2 and M1 to ground. This power loss lowers overall efficiency. So a certain amount of dead time is introduced to make sure M1 is completely OFF before M2 is being turned ON, this timing is indicated as tdh in Figure 21. When the main regulator is operating in continuous mode, as M2 is being turned OFF, and M1 is just turned ON with M2 not being completed OFF, the above mentioned situation will occur. So dead time is introduced to make sure M2 is completed OFF before M1 is being turned ON, this is indicated as tdl in Figure 21. When the main regulator is operating in discontinuous mode, as coil current is dropped to zero, M2 is supposed to be OFF. Fail to do so, reverse current will flow from the output bulk capacitor through M2 and then the inductor to the battery input. It causes damage to the battery. So M2-voltage-drop sensing comparator (COMP3 of Figure 20) comes with fixed offset voltage to switch M2 OFF before any reverse current builds up. However, if M2 is
switch OFF too early, large residue coil current flows through the body diode of M2 and increases conduction loss. Therefore, determination on the offset voltage is essential for optimum performance.
Auxiliary Regulator
The Auxiliary Regulator is a boost regulator, applies PFM scheme to enhance high efficiency and reduce quiescent current. An internal voltage comparator (COMP1 of Figure 23) detects when the voltage of Pin VAUXFBN drops below that of Pin VAUXFBP. The internal power BJT is then switched ON for a fixed-ON-time (or until the internal current limit is reached), and coil current is allowed to build up. As the BJT is switched OFF, coil current will flow through the external Schottky diode to charge up the bulk capacitor. After a fixed-mimimum-OFF time elapses, next switching cycle will start if the output of the voltage comparator is HIGH. Refer to Figure 23, the VAUX regulation level is determined by the equation as follows,
V AUX
+
VAUXFBP
R @ 1 ) RAUXb
(V)
AUXa
Where Max ON Time, TON2, and Min OFF Time, TOFF2 can be determined by the following equations.
T ON 2 T OFF 2
+ 1.7 + 2.1
10 -11 10 -12
RIref (S) RIref (S)
VBAT L2 33uH
RAUXa 200 kOhm
RAUXb 2200 kOhm VBAT
VAUXREF 19
VAUXFBP 18
VAUXFBN 20 +ve Edge Delay for Max. ON Time
VAUXBDV 21
VAUXSW 25 senseBJT + CAUX 33 uF Q1 VAUXEMR
2.2 V 6-Bit Counter 6-Bit 6 1.1 V 15 16 17 Input Logic VCOMP COMP1
R
Q
S
Qb
26
VAUXADJ VAUXCON VAUXEN
1-SHOT for Min. OFF Time ILIM COMP2
Auxiliary Level Control
Auxiliary Regulator
AGND
Figure 23. Simplified Block Diagram of Auxiliary Regulator
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MC34280
DETAILED OPERATING DESCRIPTION (Cont'd)
Auxiliary Regulator (Cont'd) Current Limit for Both regulators
As the Auxiliary Regulator control scheme is the same as the Main Regulator, equations for conduction mode, Tsw and Ipk can also be applied, However, h to be used for caculation is refered to Figure 8, 10, or 12. If external potentiometer is used for voltage level adjustment, internal 1.22V reference voltage can be used as shown in the application diagram of Figure 24.
From Figure 20 and Figure 23, sense devices (senseFET or senseBJT) are applied to sample coil current as the low-side switch is ON. With that sample current flowing through a sense resistor, sense-voltage is developed. Threshold detector (COMP2 in both figures) detects whether the sense-voltage is higher than preset level. If it happens, detector output reset the flip-flop to switch OFF low-side switch, and the switch can only be ON as next cycle starts.
CVDD c = 20u GND VBAT Ren r = 1000 k CMAINb c = 100p RMAINb r = 1000 k
Cpor c = 80n GND
GND GND Vref RLBa r = 300 k
Riref r = 480 k 8 9 10 32 31 30 MC34280 29 28 27 26 25 17 18 19 20 21 22 23 24 GND VBAT GND 7 6 5 4 3 2 1
RLBb r = 900 k
1N5817 VBAT LMAIN L = 33uH CMAIN c = 100u GND
GND GND PORB LOWBAT LIBATON LIBATCL
11 12 13 14 15 16 GND GND
GND 1N5818 Caux c = 30u LAUX L = 33uH GND
VAUX
VAUXEN VBAT GND
Rauxb r = 2.2 M
Rauxa r = 200 k GND
Figure 24. Application Diagram with External Potentiometer for VAUX Adjustment
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MC34280
DETAILED OPERATING DESCRIPTION (Cont'd)
Auxiliary voltage adjustment
The VAUX voltage can be adjusted by the microprocessor control signals, namely, VAUXCON and VAUXADJ. The control signal pattern is shown in Figure 4. The input truth table is shown in Figure 25. When VAUXEN is LOW, the Auxiliary Regulator is shut down, only the counter content is retained. The initial counter content is mid-range of 6-bit. At the rising edge of VAUXCON, if VAUXADJ is LOW (/ HIGH), each following VAUXADJ pulse enclosed by the VAUXCON pulse packet increments (/ decrements) the 6-bit counter. At the falling edge of VAUXCON, the counter content is then latched to a 6-bit DAC and is converted to a voltage level of VAUXREF between 1.1V and 2.2V. At the falling edge of VAUXCON, if VAUXADJ is HIGH, the counter content will be reset to mid-range (1.65V). This is also the default setting just after power-ON reset is removed. The 6-bit DAC converts the counter content to voltage level ranging from 1.1 to 2.2V, so there are altogether 64 levels, and each voltage step is 17mV. When the counter content reaches its maximum or minimum, further pulse of VAUXADJ will be disregarded, until counting direction is changed.
Power-ON Reset
auxiliary regulator. Meanwhile, the startup circuitry will be shut down. The Power-ON Reset block also starts to charge up the external capacitor tied from Pin PDELAY to ground with precise constant current. As the Pin PDELAY's voltage reaches an internal set threshold, Pin PORB will go HIGH to awake the microprocessor. And,
T POR
+
1.22 0.5
C por
RIref (S)
From Figure 3, if, by any chance, VMAIN is dropped below the user-defined VMAIN output level minus 0.5V, PORB will go LOW to indicate the OUTPUT LOW situation. And, the IC will continue to function until the VMAIN is dropped below 2V.
Low-Battery-Detect
The Low-Battery-Detect block is actually a voltage comparator. Pin LOWBAT is LOW, if the voltage of external Pin LOWBATSEN is lower than 0.85V internal reference. The IC will neglect this warning signal. Pin LOWBAT will become HIGH, if the voltage of external Pin LOWBATSEN is recovered to more than 1.1V. From Figure 1, with external resistors RLBa and RLBb, thresholds of Low-Battery-Detect can be adjusted based on the equations below.
V LOBAThigh
The Power-ON Reset block accepts external active HIGH ENABLE signal to activate the IC after battery is plugged in. During the startup period (see Figure 2), the internal startup circuitry is enabled to pump up VMAIN to a certain voltage level, which is the user-defined VMAIN output level minus an offset of 0.15V. The internal power-on reset signal is then disabled to activate the main regulator and conditionally the
VAUXEN
0 1 1 1 1 1 1
+ 1.1
1
R ) RLBa
(V)
LBb
(V)
V LOBATlow
+ 0.85
1
R ) RLBa
LBb
VAUXCON
X 0
VAUXADJ
X X 0 1 Hold the counter content Hold the counter content Set "countup" flag HIGH Set "countup" flag LOW
RESULT
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1 Increment (/ Decrement) the counter if "countup" flag is HIGH (/ LOW) DAC the counter content to VAUXREF voltage level (1.1 - 2.2 V) 0 1 Reset the counter to mid-range, then convert the counter content to VAUXREF voltage level (1.65V)
Figure 25. Auxiliary Voltage Control Input Truth Table
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MC34280
DETAILED OPERATING DESCRIPTION (Cont'd)
Lithium-Battery backup
The backup conduction path which is provided by an internal power switch (typ. 13 Ohm) can be controlled by internal logic or microprocessor. If LIBATCL is LOW, the switch, which is then controlled by internal logic, is ON when the battery is removed and VMAIN is dropped below LIBATIN by more than 100mV, and returns OFF when the battery is plugged back in. If LIBATCL is HIGH, the switch is controlled by microprocessor through LIBATON. The truth table is shown in Figure 26.
Efficiency and Output Ripple
feedback response, destabilizing the regulator and creating a larger ripple at the output. From Figure 1, ripple of Main and AUX regulator can be reduced by CMAINb, CAUXa and CAUXb ranging from 100pF to 100nF respectively. Reducing the ripple is also with improving efficiency, system designers are recommended to do experiments on capacitance values based on the PCB design.
Bypass Capacitors
For both regulators, when large values are used for feedback resistors (> 50kOhm), stray capacitance of pin 1 (VMAINFB) and pin 20 (VAUXFBN) can add "lag" to the
LIBATCL
0 1 1
If the metal leads from battery to coils are long, its stray resistance can put additional power loss to the system as AC current is being conducted. In that case, bypass capacitors (CMAINbp and CAUXbp of Figure 1) are recommended to remove AC components of coil currents to minimize that power loss to optimize efficiency.
Action
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X 0 1 The switch is ON when the battery is removed and VMAIN is dropped below LIBATIN by more than 100mV; The switch is OFF when the battery is plugged in. The switch is OFF The switch is ON
LIBATON
Figure 26. Lithium Battery Backup Control Truth Table
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MC34280
PACKAGE DIMENSIONS
32-LEAD LQFP FTB SUFFIX CASE 873A-02
A A1
32 25 4X
0.20 (0.008) AB T-U Z
BASE METAL
1
N
B B1
8
V DETAIL Y
17
F
V1
9
-Z- 9 S1 S
4X
SECTION AE-AE 0.20 (0.008) AC T-U Z
-T-, -U-, -Z-
G -AB-
SEATING PLANE
DETAIL AD
-AC- 0.10 (0.004) AC
8X
M_ R
P AE
CE
DETAIL Y
X DETAIL AD
GAUGE PLANE
0.250 (0.010)
H
W
K
Q_
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EE EE EE
J
-T-
-U-
D
NOTES: 1. DIMENSIONING AND TOLERANCING PER ANSI Y14.5M, 1982. 2. CONTROLLING DIMENSION: MILLIMETER. 3. DATUM PLANE -AB- IS LOCATED AT BOTTOM OF LEAD AND IS COINCIDENT WITH THE LEAD WHERE THE LEAD EXITS THE PLASTIC BODY AT THE BOTTOM OF THE PARTING LINE. 4. DATUMS -T-, -U-, AND -Z- TO BE DETERMINED AT DATUM PLANE -AB-. 5. DIMENSIONS S AND V TO BE DETERMINED AT SEATING PLANE -AC-. 6. DIMENSIONS A AND B DO NOT INCLUDE MOLD PROTRUSION. ALLOWABLE PROTRUSION IS 0.250 (0.010) PER SIDE. DIMENSIONS A AND B DO INCLUDE MOLD MISMATCH AND ARE DETERMINED AT DATUM PLANE -AB-. 7. DIMENSION D DOES NOT INCLUDE DAMBAR PROTRUSION. DAMBAR PROTRUSION SHALL NOT CAUSE THE D DIMENSION TO EXCEED 0.520 (0.020). 8. MINIMUM SOLDER PLATE THICKNESS SHALL BE 0.0076 (0.0003). 9. EXACT SHAPE OF EACH CORNER MAY VARY FROM DEPICTION. MILLIMETERS MIN MAX 7.000 BSC 3.500 BSC 7.000 BSC 3.500 BSC 1.400 1.600 0.300 0.450 1.350 1.450 0.300 0.400 0.800 BSC 0.050 0.150 0.090 0.200 0.500 0.700 12_ REF 0.090 0.160 0.400 BSC 1_ 5_ 0.150 0.250 9.000 BSC 4.500 BSC 9.000 BSC 4.500 BSC 0.200 REF 1.000 REF INCHES MIN MAX 0.276 BSC 0.138 BSC 0.276 BSC 0.138 BSC 0.055 0.063 0.012 0.018 0.053 0.057 0.012 0.016 0.031 BSC 0.002 0.006 0.004 0.008 0.020 0.028 12_ REF 0.004 0.006 0.016 BSC 1_ 5_ 0.006 0.010 0.354 BSC 0.177 BSC 0.354 BSC 0.177 BSC 0.008 REF 0.039 REF
0.20 (0.008)
M
AC T-U Z
AE
DIM A A1 B B1 C D E F G H J K M N P Q R S S1 V V1 W X
MC34280
Notes
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MC34280
Notes
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MC34280
ON Semiconductor and are trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC reserves the right to make changes without further notice to any products herein. SCILLC makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does SCILLC assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidental damages. "Typical" parameters which may be provided in SCILLC data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. All operating parameters, including "Typicals" must be validated for each customer application by customer's technical experts. SCILLC does not convey any license under its patent rights nor the rights of others. SCILLC products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other applications intended to support or sustain life, or for any other application in which the failure of the SCILLC product could create a situation where personal injury or death may occur. Should Buyer purchase or use SCILLC products for any such unintended or unauthorized application, Buyer shall indemnify and hold SCILLC and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that SCILLC was negligent regarding the design or manufacture of the part. SCILLC is an Equal Opportunity/Affirmative Action Employer.
PUBLICATION ORDERING INFORMATION
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MC34280/D

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