MAX1761 Maxim, MAX1761 Datasheet - Page 19

• Manufacturer Part Number: MAX1761
• Description: Small / Dual / High-Efficiency Buck Controller for Notebooks
• Manufacturer: Maxim

Figure 9. Two Single N-Channel MOSFETs and a Dual P-Channel
MOSFET Design
Figure 10. Two Single N-Channel MOSFETs and Two Single P-Channel MOSFETs Design
Figure 8. Dual N- and P-Channel MOSFET Design
DH1
DH2
DH1
V+
V+
1
1
G
S
S
S
S
G
S
G
P-CHANNEL
P-CHANNEL
P-CHANNEL
______________________________________________________________________________________
D
D
D
D
D
D
D
D
LX1
LX2
LX1
DH1
DH2
D
D
D
D
D
D
D
D
V+
D
D
D
D
N-CHANNEL
N-CHANNEL
1
N-CHANNEL
S
G
S
G
P-CHANNEL
P-CHANNEL
Buck Controller for Notebooks
G
S
S
S
G
S
S
S
1
1
G
S
S
S
1
Small, Dual, High-Efficiency
D
D
D
D
DL1
DL2
DL1
LX1
LX2
where I
allowed by the current-limit circuit, including threshold
tolerance and on-resistance variation. This means that
the MOSFETs must be very well heatsinked. If short-cir-
cuit protection without overload protection is enough, a
normal I
nent stresses.
Choose a Schottky diode (D1, Figure 2) having a for-
ward voltage low enough to prevent the Q2 MOSFET
body diode from turning on during the dead time. As a
general rule, a diode having a DC current rating equal
to 1/3 of the load current is sufficient. This diode is
optional and can be removed if efficiency isn’t critical.
The output voltage adjust range for continuous-conduc-
tion operation is restricted by the nonadjustable 500ns
(max) minimum off-time one-shot. For best dropout per-
formance, use the side with the lower switching fre-
quency, FB2 (250kHz). When working with low input
voltages, the duty-factor limit must be calculated using
worst-case values for on- and off-times. Manufacturing
DH2
D
D
D
D
V+
N-CHANNEL
N-CHANNEL
1
LOAD
LIMIT(MAX)
G
S
S
S
P-CHANNEL
value can be used for calculating compo-
G
S
G
S
1
D
D
D
D
is the maximum valley current
DL1
DL2
Applications Issues
LX2
Dropout Performance
D
D
D
D
N-CHANNEL
G
S
S
S
1
DL2
19