2a pwm dc-dc step-down converters, Typical operating characteristics (continued) – Rainbow Electronics MAX1557 User Manual
Page 5
MAX1556/MAX1557
16µA I
Q
, 1.2A PWM DC-DC
Step-Down Converters
_______________________________________________________________________________________
5
LIGHT-LOAD SWITCHING WAVEFORMS
MAX1556/7 toc10
20mV/div
AC-COUPLED
V
LX
V
OUT
I
LX
2V/div
0
4
µs/div
0
200mA/div
SOFT-START/SHUTDOWN WAVEFORMS
MAX1556/7 toc11
5V/div
I
LX
V
SHDN
V
OUT
I
IN
500mA/div
0
0
100
µs/div
0
1V/div
0
500mA/div
C
SS
= 470pF
R
LOAD
= 4
Ω
SOFT-START RAMP TIME vs. C
SS
MAX1556/7 toc12
C
SS
(pF)
SOFT-START RAMP TIME (ms)
500
1000
1500
2000
1
10
0.1
0
2500
LOAD TRANSIENT
MAX1556/7 toc13
50mV/div
AC-COUPLED
500mA/div
V
OUT
I
OUT
20
µs/div
0
I
OUTMIN
= 20mA
LOAD TRANSIENT
MAX1556/7 toc14
50mV/div
AC-COUPLED
500mA/div
V
OUT
I
OUT
20
µs/div
0
I
OUTMIN
= 180mA
LINE TRANSIENT
MAX1556/7 toc15
10mV/div
AC-COUPLED
V
IN
V
OUT
I
LX
3.5V
4V
40
µs/div
0
200mA/div
BODE PLOT
MAX1556/7 toc16
FREQUENCY (kHz)
GAIN (dB)
PHASE (DEGREES)
100
10
1
-50
-40
-30
-20
-10
0
10
20
30
40
-60
-30
0
30
60
90
120
150
180
210
240
-60
0.1
1000
0dB
PHASE MARGIN = 53
°
C
OUT
= 22
µF, R
LOAD
= 4
Ω
Typical Operating Characteristics (continued)
(V
IN
= V
INP
= 3.6V, D1 = D2 = SHDN = IN, Circuits of Figures 2 and 3, T
A
= +25°C, unless otherwise noted.)