LT1613CS5 데이터 시트보기 (PDF) - Linear Technology

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LT1613CS5

1.4MHz, Single Cell DC/DC Converter in 5-Lead SOT-23

Linear Technology 

U

OPERATIO

effect on loop stability, as long as minimum capacitance

requirements are met). The transient response to a load

step of 50mA to 100mA is pictured in Figure 6. Note the

“double trace,” due to the ESR of C2. The loop is stable and

settles in less than 100µs. In Figure 7, C2 is replaced by a

10µF ceramic unit. Phase margin decreases drastically,

L1

10µH

D1

VIN

2.5V

+ C1

15µF

VIN

SW

LT1613

SHDN

SHDN

FB

GND

R1

37.4k

R2

12.1k

VOUT

5V

+ C2

22µF

C1: AVX TAJA156M010R

C2: AVX TAJA226M006R

D1: MOTOROLA MBR0520

L1: MURATA LQH3C100

1613 F05

Figure 5. 2.5V to 5V Boost Converter with “A”

Case Size Tantalum Input and Output Capacitors

VOUT

20mV/DIV

AC COUPLED

LOAD CURRENT 100mA

50mA

200µs/DIV

1613 F06

Figure 6. 2.5V to 5V Boost Converter Transient

Response with 22µF Tantalum Output Capacitor.

Apparent Double Trace on VOUT Is Due to Switching

Frequency Ripple Current Across Capacitor ESR

LT1613

resulting in a severely underdamped response. By adding

R3 and CPL as detailed in Figure 8’s schematic, phase

margin is restored, and transient response to the same

load step is pictured in Figure 9. R3 isolates the device FB

pin from fast edges on the VOUT node due to parasitic PC

trace inductance.

Figure 10’s circuit details a 5V to 12V boost converter,

delivering up to 130mA. The transient response to a load

step of 10mA to 130mA, without CPL, is pictured in

Figure␣ 11. Although the ringing is less than that of the

previous example, the response is still underdamped and

can be improved. After adding R3 and CPL, the improved

transient response is detailed in Figure 12.

Figure 13 shows a SEPIC design, converting a 3V to 10V

input to a 5V output. The transient response to a load step

of 20mA to 120mA, without CPL and R3, is pictured in

Figure␣ 14. After adding these two components, the im-

proved response is shown in Figure 15.

VIN

2.5V

+

C1

15µF

SHUTDOWN

L1

10µH

D1

VIN

SW

LT1613

R3

10k

SHDN

FB

GND

CPL

330pF

R1

37.4k

R2

12.1k

VOUT

5V

C2

10µF

C1: AVX TAJA156M010R

C2: TAIYO YUDEN LMK325BJ106MN

D1: MBR0520

L1: MURATA LQH3C100K04

1613 F08

Figure 8. 2.5V to 5V Boost Converter with Ceramic

Output Capacitor. CPL Added to Increase Phase Margin,

R3 Isolates FB Pin from Fast Edges

VOUT

20mV/DIV

AC COUPLED

VOUT

20mV/DIV

AC COUPLED

LOAD CURRENT

100mA

50mA

200µs/DIV

Figure 7. 2.5V to 5V Boost Converter with

10µF Ceramic Output Capacitor, No CPL

1613 F07

LOAD CURRENT

100mA

50mA

200µs/DIV

1613 F09

Figure 9. 2.5V to 5V Boost Converter with 10µF Ceramic

Output Capacitor, 330pF CPL and 10k in Series with FB Pin

7

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