Datasheet LT1961 (Linear Technology) - 8
| Manufacturer | Linear Technology |
| Description | 1.5A, 1.25MHz Step-Up Switching Regulator |
| Pages / Page | 16 / 8 — APPLICATIONS INFORMATION. INDUCTOR CHOICE AND MAXIMUM OUTPUT. CURRENT. … |
| Revision | A |
| File Format / Size | PDF / 163 Kb |
| Document Language | English |
APPLICATIONS INFORMATION. INDUCTOR CHOICE AND MAXIMUM OUTPUT. CURRENT. Table 2. PART NUMBER. VALUE (uH) ISAT(DC) (Amps) DCR (
Model Line for this Datasheet
Text Version of Document
LT1961
U U W U APPLICATIONS INFORMATION INDUCTOR CHOICE AND MAXIMUM OUTPUT
2
CURRENT
V V V L IN OUT IN MIN = ( ) ( – ) 2 When choosing an inductor, there are 2 conditions that 0.4 V ( ) I ( f OUT OUT )( ) limit the minimum inductance; required output current, The inductor value may need further adjustment for other and avoidance of subharmonic oscillation. The maximum factors such as output voltage ripple and filtering require- output current for the LT1961 in a standard boost con- ments. Remember also, inductance can drop significantly verter configuration with an infinitely large inductor is: with DC current and manufacturing tolerance. V • η The inductor must have a rating greater than its peak I = 1 A IN OUT MAX ( ) .5 V operating current to prevent saturation resulting in effi- OUT ciency loss. Peak inductor current is given by: Where η = converter efficiency (typically 0.87 at high current). V ( ) I ( ) V V ( V ) I OUT OUT IN OUT IN LPEAK = + − As the value of inductance is reduced, ripple current V • η V 2 L ( ) f IN OUT ( ) increases and IOUT(MAX) is reduced. The minimum induc- Also, consideration should be given to the DC resistance tance for a required output current is given by: of the inductor. Inductor resistance contributes directly to the efficiency losses in the overall converter. V V ( – V ) L IN OUT IN MIN = ⎛ Suitable inductors are available from Coilcraft, Coiltronics, V ( ) I ( ⎞ ) V 2 f OUT OUT OUT ( ) . 1 5 – Dale, Sumida, Toko, Murata, Panasonic and other manu- ⎝⎜ VIN • η ⎠⎟ factures. The second condition, avoidance of subharmonic oscilla-
Table 2
tion, must be met if the operating duty cycle is greater than
PART NUMBER VALUE (uH) ISAT(DC) (Amps) DCR (
Ω
) HEIGHT (mm)
50%. The slope compensation circuit within the LT1961
Coiltronics
prevents subharmonic oscillation for inductor ripple cur- TP1-2R2 2.2 1.3 0.188 1.8 rents of up to 0.7A TP2-2R2 2.2 1.5 0.111 2.2 P-P, defining the minimum inductor value to be: TP3-4R7 4.7 1.5 0.181 2.2 TP4- 100 10 1.5 0.146 3.0 V V V
Murata
L IN OUT IN MIN = ( – ) . 0 V 7 f LQH1C1R0M04 1.0 0.51 0.28 1.8 OUT ( ) LQH3C1R0M24 1.0 1.0 0.06 2.0 These conditions define the absolute minimum induc- LQH3C2R2M24 2.2 0.79 0.1 2.0 tance. However, it is generally recommended that to LQH4C1R5M04 1.5 1 0.09 2.6 prevent excessive output noise, and difficulty in obtaining
Sumida
stability, the ripple current is no more than 40% of the CD73- 100 10 1.44 0.080 3.5 average inductor current. Since inductor ripple is: CDRH4D18-2R2 2.2 1.32 0.058 1.8 CDRH5D18-6R2 6.2 1.4 0.071 1.8 V V V I IN OUT IN CDRH5D28-100 10 1.3 0.048 2.8 P−P RIPPLE = ( – ) V L ( ) f OUT ( )
Coilcraft
1008PS-272M 2.7 1.3 0.14 2.7 The recommended minimum inductance is: LPO1704-222M 2.2 1.6 0.12 1.0 LPO1704-332M 3.3 1.3 0.16 1.0 1961fa 8
U U W U APPLICATIONS INFORMATION INDUCTOR CHOICE AND MAXIMUM OUTPUT
2
CURRENT
V V V L IN OUT IN MIN = ( ) ( – ) 2 When choosing an inductor, there are 2 conditions that 0.4 V ( ) I ( f OUT OUT )( ) limit the minimum inductance; required output current, The inductor value may need further adjustment for other and avoidance of subharmonic oscillation. The maximum factors such as output voltage ripple and filtering require- output current for the LT1961 in a standard boost con- ments. Remember also, inductance can drop significantly verter configuration with an infinitely large inductor is: with DC current and manufacturing tolerance. V • η The inductor must have a rating greater than its peak I = 1 A IN OUT MAX ( ) .5 V operating current to prevent saturation resulting in effi- OUT ciency loss. Peak inductor current is given by: Where η = converter efficiency (typically 0.87 at high current). V ( ) I ( ) V V ( V ) I OUT OUT IN OUT IN LPEAK = + − As the value of inductance is reduced, ripple current V • η V 2 L ( ) f IN OUT ( ) increases and IOUT(MAX) is reduced. The minimum induc- Also, consideration should be given to the DC resistance tance for a required output current is given by: of the inductor. Inductor resistance contributes directly to the efficiency losses in the overall converter. V V ( – V ) L IN OUT IN MIN = ⎛ Suitable inductors are available from Coilcraft, Coiltronics, V ( ) I ( ⎞ ) V 2 f OUT OUT OUT ( ) . 1 5 – Dale, Sumida, Toko, Murata, Panasonic and other manu- ⎝⎜ VIN • η ⎠⎟ factures. The second condition, avoidance of subharmonic oscilla-
Table 2
tion, must be met if the operating duty cycle is greater than
PART NUMBER VALUE (uH) ISAT(DC) (Amps) DCR (
Ω
) HEIGHT (mm)
50%. The slope compensation circuit within the LT1961
Coiltronics
prevents subharmonic oscillation for inductor ripple cur- TP1-2R2 2.2 1.3 0.188 1.8 rents of up to 0.7A TP2-2R2 2.2 1.5 0.111 2.2 P-P, defining the minimum inductor value to be: TP3-4R7 4.7 1.5 0.181 2.2 TP4- 100 10 1.5 0.146 3.0 V V V
Murata
L IN OUT IN MIN = ( – ) . 0 V 7 f LQH1C1R0M04 1.0 0.51 0.28 1.8 OUT ( ) LQH3C1R0M24 1.0 1.0 0.06 2.0 These conditions define the absolute minimum induc- LQH3C2R2M24 2.2 0.79 0.1 2.0 tance. However, it is generally recommended that to LQH4C1R5M04 1.5 1 0.09 2.6 prevent excessive output noise, and difficulty in obtaining
Sumida
stability, the ripple current is no more than 40% of the CD73- 100 10 1.44 0.080 3.5 average inductor current. Since inductor ripple is: CDRH4D18-2R2 2.2 1.32 0.058 1.8 CDRH5D18-6R2 6.2 1.4 0.071 1.8 V V V I IN OUT IN CDRH5D28-100 10 1.3 0.048 2.8 P−P RIPPLE = ( – ) V L ( ) f OUT ( )
Coilcraft
1008PS-272M 2.7 1.3 0.14 2.7 The recommended minimum inductance is: LPO1704-222M 2.2 1.6 0.12 1.0 LPO1704-332M 3.3 1.3 0.16 1.0 1961fa 8
