Datasheet LT1513, LT1513-2 (Analog Devices) - 10
| Manufacturer | Analog Devices |
| Description | SEPIC Constant- or Programmable-Current/Constant-Voltage Battery Charger |
| Pages / Page | 16 / 10 — APPLICATIONS INFORMATION. Programmed Charging Current. Voltage Mode Loop … |
| File Format / Size | PDF / 220 Kb |
| Document Language | English |
APPLICATIONS INFORMATION. Programmed Charging Current. Voltage Mode Loop Stability. Figure 5
Model Line for this Datasheet
Text Version of Document
LT1513/LT1513-2
U U W U APPLICATIONS INFORMATION Programmed Charging Current
exceed 60µA to maintain a sharp constant voltage to LT1513-2 charging current can be programmed with a DC constant current crossover characteristic. ICHARGE can voltage source or equivalent PWM signal, as shown in also be controlled by a PWM input. Assuming the signal is Figure 5. In constant-current mode, I a CMOS rail-to-rail output with a source impedance of less FB acts as a virtual ground. The I than a few hundred ohms, effective I SET voltage across R5 is balanced by the SET is VCC multiplied voltage across R4 in the ratio R4/R5. by the PWM ratio. ICHARGE has good linearity over the entire 0% to 100% range. Charging current is given by:
Voltage Mode Loop Stability
V R4 R5 I I ISET FBVOS CHARGE = ( )( / )– The LT1513 operates in constant-voltage mode during the R3 final phase of charging lithium-ion and lead-acid batteries. IFB input current is small and can normally be ignored, but This feedback loop is stabilized with a series resistor and IFB offset voltage must be considered if operating over a capacitor on the VC pin of the chip. Figure 6 shows the wide range of program currents. The voltage across R3 at simplified model for the voltage loop. The error amplifier is maximum charge current can be increased to reduce modeled as a transconductance stage with gm = 1500µmho offset errors at lower charge currents. In Figure 5, ISET from 0V to 5V corresponds to an ICHARGE of 0A to 1A +37/– 62mA. C4 and R4 smooth the switch current wave- LT1513-2 IFB form. During constant-current operation, the voltage feed- L1B R5 R4 back network loads the FB pin, which is held at V 249k 10k REF by the ISET IFB amplifier. It is recommended that this load does not C4 R3 0.1µF 0.2Ω 1513 F05
Figure 5
MODULATOR SECTION IP I 4(V V1 g P IN) m = = V1 VIN + VBAT CP** VIN = DC INPUT VOLTAGE R1* 3pF VBAT = DC BATTERY VOLTAGE 71.5k C1 C1 RP** RCAP RBAT 1M – FB ≈0.15Ω 0.1Ω V EACH C + + C1 EA BATTERY + 22µF R5 R2 EACH R g 330Ω G m 12.5k 330k 1500µmho 1.245V C5 0.1µF 1513 F06 * FOR 8.4V BATTERY. ADJUST VALUE OF R1 FOR ACTUAL BATTERY VOLTAGE ** RP AND CP MODEL PHASE DELAY IN THE MODULATOR THIS IS A SIMPLIFIED AC MODEL FOR THE LT1513 IN CONSTANT- AS SHOWN, THIS LOOP HAS A UNITY-GAIN FREQUENCY OF VOLTAGE MODE. RESISTOR AND CAPACITOR NUMBERS ABOUT 250Hz. UNITY-GAIN WILL MOVE OUT TO SEVERAL CORRESPOND TO THOSE USED IN FIGURE 1. RP AND CP MODEL KILOHERTZ IF BATTERY RESISTANCE INCREASES TO SEVERAL THE PHASE DELAY IN THE MODULATOR. C3 IS 3pF FOR A 10µH OHMS. R5 IS NOT USED IN ALL APPLICATIONS, BUT IT GIVES INDUCTOR. IT SHOULD BE SCALED PROPORTIONALLY FOR OTHER BETTER PHASE MARGIN IN CONSTANT-VOLTAGE MODE WITH INDUCTOR VALUES (6pF FOR 20µH). THE MODULATOR IS A HIGH BATTERY RESISTANCE. TRANSCONDUCTANCE WHOSE GAIN IS A FUNCTION OF INPUT AND BATTERY VOLTAGE AS SHOWN.
Figure 6. Constant-Voltage Small-Signal Model
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U U W U APPLICATIONS INFORMATION Programmed Charging Current
exceed 60µA to maintain a sharp constant voltage to LT1513-2 charging current can be programmed with a DC constant current crossover characteristic. ICHARGE can voltage source or equivalent PWM signal, as shown in also be controlled by a PWM input. Assuming the signal is Figure 5. In constant-current mode, I a CMOS rail-to-rail output with a source impedance of less FB acts as a virtual ground. The I than a few hundred ohms, effective I SET voltage across R5 is balanced by the SET is VCC multiplied voltage across R4 in the ratio R4/R5. by the PWM ratio. ICHARGE has good linearity over the entire 0% to 100% range. Charging current is given by:
Voltage Mode Loop Stability
V R4 R5 I I ISET FBVOS CHARGE = ( )( / )– The LT1513 operates in constant-voltage mode during the R3 final phase of charging lithium-ion and lead-acid batteries. IFB input current is small and can normally be ignored, but This feedback loop is stabilized with a series resistor and IFB offset voltage must be considered if operating over a capacitor on the VC pin of the chip. Figure 6 shows the wide range of program currents. The voltage across R3 at simplified model for the voltage loop. The error amplifier is maximum charge current can be increased to reduce modeled as a transconductance stage with gm = 1500µmho offset errors at lower charge currents. In Figure 5, ISET from 0V to 5V corresponds to an ICHARGE of 0A to 1A +37/– 62mA. C4 and R4 smooth the switch current wave- LT1513-2 IFB form. During constant-current operation, the voltage feed- L1B R5 R4 back network loads the FB pin, which is held at V 249k 10k REF by the ISET IFB amplifier. It is recommended that this load does not C4 R3 0.1µF 0.2Ω 1513 F05
Figure 5
MODULATOR SECTION IP I 4(V V1 g P IN) m = = V1 VIN + VBAT CP** VIN = DC INPUT VOLTAGE R1* 3pF VBAT = DC BATTERY VOLTAGE 71.5k C1 C1 RP** RCAP RBAT 1M – FB ≈0.15Ω 0.1Ω V EACH C + + C1 EA BATTERY + 22µF R5 R2 EACH R g 330Ω G m 12.5k 330k 1500µmho 1.245V C5 0.1µF 1513 F06 * FOR 8.4V BATTERY. ADJUST VALUE OF R1 FOR ACTUAL BATTERY VOLTAGE ** RP AND CP MODEL PHASE DELAY IN THE MODULATOR THIS IS A SIMPLIFIED AC MODEL FOR THE LT1513 IN CONSTANT- AS SHOWN, THIS LOOP HAS A UNITY-GAIN FREQUENCY OF VOLTAGE MODE. RESISTOR AND CAPACITOR NUMBERS ABOUT 250Hz. UNITY-GAIN WILL MOVE OUT TO SEVERAL CORRESPOND TO THOSE USED IN FIGURE 1. RP AND CP MODEL KILOHERTZ IF BATTERY RESISTANCE INCREASES TO SEVERAL THE PHASE DELAY IN THE MODULATOR. C3 IS 3pF FOR A 10µH OHMS. R5 IS NOT USED IN ALL APPLICATIONS, BUT IT GIVES INDUCTOR. IT SHOULD BE SCALED PROPORTIONALLY FOR OTHER BETTER PHASE MARGIN IN CONSTANT-VOLTAGE MODE WITH INDUCTOR VALUES (6pF FOR 20µH). THE MODULATOR IS A HIGH BATTERY RESISTANCE. TRANSCONDUCTANCE WHOSE GAIN IS A FUNCTION OF INPUT AND BATTERY VOLTAGE AS SHOWN.
Figure 6. Constant-Voltage Small-Signal Model
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