High-Speed Step-Down Controller
for Notebook Computers
MAX1714
Table 1. Component Selection for Standard Applications
COMPONENT
Input Range
Frequency
Q1 High-Side
MOSFET
Q2 Low-Side
MOSFET
D2 Rectifier
7V to 20V
300kHz
Fairchild Semiconductor
1/2 FDS6982A
Fairchild Semiconductor
1/2 FDS6982A
Nihon EP10QY03
6.8µH
Coilcraft DO3316P-682
10µF, 25V
Taiyo Yuden TMK432BJ106KM
470µF, 6V
Kemet T510X477108M006AS
2.5V AT 4A
7V to 20V
300kHz
1.6V AT 8A
600kHz
2.5V AT 1.5A
4.5V to 5.5V
International Rectifier
IRF7811
Fairchild Semiconductor
FDS6670A
Motorola MBRS340T3
1.5µH
Sumida CEP1251R5MC
(2) 10µF, 25V
Taiyo Yuden TMK432BJ106KM
(2) 470µF 6V
Kemet T510X477108M006AS
International Rectifier
1/2 IRF7301
International Rectifier
1/2 IRF7301
Motorola MBR0520LT1
3.3µH
Coiltronics UP1B-3R3
100µF, 10V
Sanyo POSCAP 10TPA100M
100µF, 10V
Sanyo POSCAP 10TPA100M
L1 Inductor
C1 Input Capacitor
C2 Output Capacitor
Table 2. Component Suppliers
MANUFACTURER
AVX
Central Semiconductor
Coilcraft
Coiltronics
Fairchild
International Rectifier
Kemet
Matsuo
Motorola
Murata
NIEC (Nihon)
Sanyo
Siliconix
Sprague
Sumida
Taiyo Yuden
TDK
*Distributor
USA PHONE
803-946-0690
516-435-1110
847-639-6400
561-241-7876
408-822-2181
310-322-3331
408-986-0424
714-969-2491
602-303-5454
814-237-1431
800-831-9172
805-867-2555*
619-661-6835
408-988-8000
800-554-5565
603-224-1961
847-956-0666
408-573-4150
847-390-4461
FACTORY FAX
[Country Code]
[1] 803-626-3123
[1] 516-435-1824
[1] 847-639-1469
[1] 561-241-9339
[1] 408-721-1635
[1] 310-322-3332
[1] 408-986-1442
[1] 714-960-6492
[1] 602-994-6430
[1] 814-238-0490
[81] 3-3494-7414
[81] 7-2070-1174
[1] 408-970-3950
[1] 603-224-1430
[81] 3-3607-5144
[1] 408-573-4159
[1] 847-390-4405
ply the PWM circuit and gate drivers. If stand-alone
capability is needed, the +5V supply can be generated
with an external linear regulator such as the MAX1615.
The battery and +5V bias inputs can be tied together if
the input source is a fixed +4.5V to +5.5V supply. If the
+5V bias supply is powered up prior to the battery sup-
ply, the enable signal (SHDN) must be delayed until the
battery voltage is present in order to ensure startup. The
+5V bias supply must provide V
CC
and gate-drive
power, so the maximum current drawn is:
I
BIAS
= I
CC
+ f (Q
G1
+ Q
G2
) = 5mA to 30mA (typ)
where I
CC
is 600µA typical, f is the switching frequency,
and Q
G1
and Q
G2
are the MOSFET data sheet total
gate-charge specification limits at V
GS
= 5V.
Free-Running, Constant-On-Time PWM
Controller with Input Feed-Forward
The Quick-PWM control architecture is a pseudo-fixed-fre-
quency, constant-on-time current-mode type with voltage
feed-forward (Figure 2). This architecture relies on the out-
put filter capacitor’s ESR to act as the current-sense resis-
tor, so the output ripple voltage provides the PWM ramp
signal. The control algorithm is simple: the high-side
switch on-time is determined solely by a one-shot whose
period is inversely proportional to input voltage and direct-
ly proportional to output voltage. Another one-shot sets a
minimum off-time (400ns typical). The on-time one-shot is
triggered if the error comparator is low, the low-side switch
current is below the current-limit threshold, and the mini-
mum off-time one-shot has timed out.
+5V Bias Supply (V
CC
and V
DD
)
The MAX1714 requires an external +5V bias supply in
addition to the battery. Typically, this +5V bias supply is
the notebook’s 95% efficient +5V system supply.
Keeping the bias supply external to the IC improves effi-
ciency and eliminates the cost associated with the +5V
linear regulator that would otherwise be needed to sup-
10
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