FAN5354 Datasheet, PDF (6/14 Pages) Fairchild Semiconductor – 3MHz, 3A Synchronous Buck Regulator

Typical Characteristics
Unless otherwise specified, VIN=5V, VOUT=1.2V, circuit of Figure 1, and components per Table 1.
1000
900
1.2VOUT boundary
1.2VOUT boundary
800
3.3VOUT boundary
700
3.3VOUT boundary
Always PWM
600
500
Hysteresis
400
300
200
Always PFM
100
0
2.7
3.2
3.7
4.2
4.7
5.2
Input Voltage(V)
Figure 9. PFM/PWM Mode-Change Boundaries
3.5
3.0
2.5
2.0
1.5
VIN = 4.1V
VIN = 4.0V
1.0
VIN = 3.9V
VIN = 3.8V
0.5
-
0
0.5
1
1.5
2
2.5
3
Load Current (A)
Figure 10. Effect of tOFF Minimum on Reducing Switching
Frequency at Large Duty Cycles, VOUT=3.3V
PFM
PWM
16
14
12
10
8
6
5VIN, 1.2VOUT
4
3.3VIN, 1.2VOUT
2
5VIN,3.3VOUT
0
0.1
1
10
100
1000
10000
Load Current(mA)
Figure 11. Output Voltage Ripple vs. Load Current
(See explanation on page 12)
90
80
70
60
50
1.2VOUT,1.5A load
40
3.3VOUT, 0.5A load in PFM
3.3VOUT, 1.5A load
30
20
0.01
0.1
1
10
100
Frequency (KHz)
Figure 12. Power Supply Rejection Ratio (PSRR)
V_OUT
I_L
Figure 13. PFM-to-PWM Mode Transition, Slowly
Increasing Load Current, 2µs/div.
Figure 14 PWM-to-PFM Mode Transition, Slowly
Decreasing Load Current, 2µs/div.
© 2009 Fairchild Semiconductor Corporation
FAN5354 • Rev. 1.0.4
6
www.fairchildsemi.com