Datasheet LT1610 (Analog Devices) - 10

LT1610
U U W U APPLICATIONS INFORMATION
output capacitor because it introduces a zero in the regulator’s loop gain. This zero may not be effective because the ceramic capacitor’s ESR is very low. Most VOUT current mode switching regulators (including the LT1610) 100mV/DIV can easily be compensated without this zero. Any design LOAD should be tested for stability at the extremes of operating CURRENT temperatures; this is particularly so of circuits that use 105mA 5mA ceramic output capacitors. 500µs/DIV 1610 F10 Figure 9 details a 2.5V to 5V boost converter. Transient
Figure 10. Tantalum Output Capacitor and Internal RC Compensation
response to a 5mA to 105mA load step is pictured in Figure 10. The “double trace” of VOUT at 105mA load is due to the ESR of C2. This ESR aids stability. In Figure 11, C2 is replaced by a 10µF ceramic capacitor. Note the low phase margin; at higher input voltage, the converter may oscil- VOUT 100mV/DIV late. After replacing the internal compensation network with an external 220pF/220k series RC, the transient LOAD response is shown in Figure 12. This is acceptable tran- CURRENT 105mA sient response. 5mA 500µs/DIV 1610 F11
Table 1 Figure 11. 10
µ
F X5R-Type Ceramic Output Capacitor FIGURE C2 COMPENSATION and Internal RC Compensation has Low Phase Margin
10 AVX TAJA226M006 Tantalum Internal 11 Taiyo Yuden JMK316BJ106 Internal 12 Taiyo Yuden JMK316BJ106 220pF/220k VOUT L1 100mV/DIV 10µH D1 VOUT VIN 5V 2.5V 100mA LOAD 6 5 CURRENT 1M V 105mA IN SW 5mA 3 2 SHDN FB 500µs/DIV + 1610 F12 + C1 LT1610 R2 C2 22µF 324k 22µF
Figure 12. Ceramic Output Capacitor with 220pF/220k
1 7 V GND
External Compensation has Adequate Phase Margin
C COMP PGND RC 8 4 CC C1: AVX TAJA226M006 1610 F09 C2: SEE TABLE D1: MOTOROLA MBR0520 L1: MURATA LQH30100
Figure 9. 2.5V to 5V Boost Converter Can Operate with a Ceramic Output Capacitor as Long as Proper RC and CC are Used. Disconnect COMP Pin if External Compensation Components Are Used
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