LT1611 Linear Technology, LT1611 Datasheet - Page 7

• Manufacturer Part Number: LT1611
• Description: Constant-Current/ Constant-Voltage 1.4MHz Step-Up DC/DC Converter
• Manufacturer: Linear Technology

OPERATIO
V
LOAD CURRENT
5V
IN
+
C1: AVX TAJB226M010
C2: TAIYO YUDEN LMK212BJ105MG
C3: SEE TEXT
D1: MBR0520
L1A, L1B: SUMIDA CLS62-220
Figure 7. Switching R
Load Step for LT1611 5V to – 5V Converter
AC COUPLED
C1
50mV/DIV
V
SHDN
150mA
Figure 8. Load Step Response of LT1611
with 22 F Tantalum Output Capacitor
IN
50mA
V
OUT
LT1611
22 H
GND
L1A
U
NFB
SW
L2
R1
R2
10k
SWITCH VOLTAGE
1 F
C2
Provides 50mA to 150mA
Figure 10. 22 F “B” Case Tantalum Capacitor (AVX TAJ “B” Series)
Has ESR Resulting in 20mV
10mV/DIV
C
100 s/DIV
PL
5V/DIV
V
OUT
D1
22 H
LOAD = 150mA
L1B
C3
+
–V
OUT
R
100
L1
1611 F07
1611 F08
P–P
R
50
L2
200ns/DIV
Voltage Ripple at Output
Figure 8 shows the output voltage with a 50mA to 150mA
load step, using an AVX TAJ “B” case 22 F tantalum
capacitor at the output. Output perturbation is approxi-
mately 100mV as the load changes from 50mA to 150mA.
Steady-state ripple voltage is 20mV
current and C3’s ESR. Step response can be improved by
adding a 3.3nF capacitor (C
Settling time improves from 150 s to 40 s, although
steady-state ripple voltage does not improve. Figure 10
pictures the output voltage and switch pin voltage at
200ns per division. Note the absence of high frequency
spikes at the output. This is easily repeatable with proper
layout, described in the next section.
LOAD CURRENT
AC COUPLED
20mV/DIV
Figure 9. Addition of C
Improves Load Step Response. C
150mA
50mA
V
OUT
1611 F10
PL
PL
to Figure 7’s Circuit
) as shown in Figure 9.
20 s/DIV
P–P
PL
, due to L1’s ripple
= 3.3nF
LT1611
1611 F09
7