2A, Low-Voltage, Step-Down Regulator with
Synchronous Rectification and Internal Switches
MAX1644
Typical Operating Characteristics
(Circuit of Figure 1, T
A
= +25°C, unless otherwise noted.)
DC LOAD-REGULATION ERROR
vs. OUTPUT CURRENT
MAX1644-02
EFFICIENCY vs. OUTPUT CURRENT
MAX1644-01
EFFICIENCY vs. OUTPUT CURRENT
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
V
IN
= 5V, V
OUT
= 1.5V,
L = 6.0μH, R
TOFF
= 270kΩ
V
IN
= 3.3V, V
OUT
= 1.5V,
L = 4.7μH, R
TOFF
= 200kΩ
0
DC LOAD-REGULATION ERROR (%)
-0.1
-0.2
-0.3
-0.4
-0.5
-0.6
-0.7
-0.8
-0.9
0.01
0.1
1
10
-1.0
0.0001
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0.001
0.01
0.1
1
V
IN
= 5V, V
OUT
= 3.3V,
L = 6.0μH, R
TOFF
= 120kΩ
A
B
D
E
C
10
0
0.001
0.001
0.01
0.1
1
10
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
A: V
IN
= 3.3V, V
OUT
= 1.5V, L = 4.7μH,
R
TOFF
= 200kΩ, FBSEL = GND
B: V
IN
= 3.3V, V
OUT
= 1.5V, L = 4.7μH,
R
TOFF
= 200kΩ, FBSEL = REF
C: V
IN
= 5V, V
OUT
= 3.3V, L = 6.0μH,
R
TOFF
= 120kΩ, FBSEL = OPEN
D: V
IN
= 5V, V
OUT
= 1.5V, L = 6.0μH,
R
TOFF
= 270kΩ, FBSEL = GND
E: V
IN
= 5V, V
OUT
= 1.5V, L = 6.0μH,
R
TOFF
= 270kΩ, FBSEL = REF
SWITCHING FREQUENCY
vs. OUTPUT CURRENT
MAX1644-04
OFF-TIME vs. R
TOFF
4.0
3.5
MAX1644-06
350
300
SWITCHING FREQUENCY (kHz)
250
200
150
100
50
0
0
0.5
1.0
1.5
V
IN
= 5V,
V
OUT
= 3.3V,
L = 6.0μH,
R
TOFF
= 120kΩ
V
IN
= 5V,
V
OUT
= 1.5V,
L = 6.0μH,
R
TOFF
= 270kΩ
4.5
V
IN
= 3.3V,
V
OUT
= 1.5V,
L = 4.7μH,
R
TOFF
= 200kΩ
3.0
t
OFF
(μs)
2.5
2.0
1.5
1.0
0.5
0
2.0
0
100
200
300
R
TOFF
(kΩ)
400
500
600
OUTPUT CURRENT (A)
SUPPLY CURRENT vs. SUPPLY VOLTAGE
500
450
SUPPLY CURRENT I
CC
(μA)
400
350
300
250
200
150
100
50
0
0
1
2
3
4
5
6
SUPPLY VOLTAGE
UNDERVOLTAGE
LOCKOUT
SHDN = GND
SHDN = V
IN
= V
CC
I
OUT
= 0
MAX1644-07
STARTUP AND
SHUTDOWN TRANSIENTS
0.09
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
SHUTDOWN SUPPLY CURRENT I
IN
+ I
CC
(μA)
0
MAX1644-09
0.10
V
SHDN
5V/div
I
IN
1A/div
V
OUT
2V/div
0
0
V
SS
1V/div
0
V
IN
= 5.0V, V
OUT
= 3.3V, I
OUT
= 2A
2ms/div
4
_______________________________________________________________________________________
MAX1644-03
100
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
