LT1610
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
current mode switching regulators (including the LT1610)
can easily be compensated without this zero. Any design
should be tested for stability at the extremes of operating
temperatures; this is particularly so of circuits that use
ceramic output capacitors.
Figure 9 details a 2.5V to 5V boost converter. Transient
response to a 5mA to 105mA load step is pictured in Figure
10. The “double trace” of V
OUT
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-
late. After replacing the internal compensation network
with an external 220pF/220k series RC, the transient
response is shown in Figure 12. This is acceptable tran-
sient response.
Table 1
FIGURE
10
11
12
C2
AVX TAJA226M006 Tantalum
Taiyo Yuden JMK316BJ106
Taiyo Yuden JMK316BJ106
L1
10µH
V
OUT
100mV/DIV
LOAD
CURRENT
105mA
5mA
500µs/DIV
1610 F10
COMPENSATION
Internal
Internal
220pF/220k
D1
V
IN
2.5V
6
V
IN
3
5
SW
FB
LT1610
2
1M
+
SHDN
C1
22µF
1
V
C
COMP
8
GND
PGND
4
7
R2
324k
+
R
C
C
C
C1: AVX TAJA226M006
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 R
C
and C
C
are Used. Disconnect COMP Pin if External Compensation
Components Are Used
10
U
W
U
U
Figure 10. Tantalum Output Capacitor
and Internal RC Compensation
V
OUT
100mV/DIV
LOAD
CURRENT
105mA
5mA
500µs/DIV
1610 F11
Figure 11. 10µF X5R-Type Ceramic Output Capacitor
and Internal RC Compensation has Low Phase Margin
V
OUT
100mV/DIV
V
OUT
5V
100mA
LOAD
CURRENT
105mA
5mA
500µs/DIV
1610 F12
C2
22µF
Figure 12. Ceramic Output Capacitor with 220pF/220k
External Compensation has Adequate Phase Margin
1610 F09
LINER [ LINEAR TECHNOLOGY ]
