Datasheet
MAX1714
+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-
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.
High-Speed Step-Down Controller
for Notebook Computers
10 ______________________________________________________________________________________
Table 1. Component Selection for Standard Applications
Table 2. Component Suppliers
4.5V to 5.5V7V to 20V7V to 20V
Input Range
100µF, 10V
Sanyo POSCAP 10TPA100M
(2) 470µF 6V
Kemet T510X477108M006AS
470µF, 6V
Kemet T510X477108M006AS
C2 Output Capacitor
100µF, 10V
Sanyo POSCAP 10TPA100M
(2) 10µF, 25V
Taiyo Yuden TMK432BJ106KM
10µF, 25V
Taiyo Yuden TMK432BJ106KM
C1 Input Capacitor
3.3µH
Coiltronics UP1B-3R3
1.5µH
Sumida CEP1251R5MC
6.8µH
Coilcraft DO3316P-682
L1 Inductor
Motorola MBR0520LT1Motorola MBRS340T3Nihon EP10QY03D2 Rectifier
International Rectifier
1/2 IRF7301
Fairchild Semiconductor
FDS6670A
Fairchild Semiconductor
1/2 FDS6982A
Q2 Low-Side
MOSFET
International Rectifier
1/2 IRF7301
International Rectifier
IRF7811
Fairchild Semiconductor
1/2 FDS6982A
Q1 High-Side
MOSFET
600kHz300kHz300kHz
Frequency
2.5V AT 1.5A1.6V AT 8A2.5V AT 4ACOMPONENT
[1] 602-994-6430602-303-5454Motorola
[1] 408-986-1442408-986-0424Kemet
[1] 408-721-1635408-822-2181Fairchild
[1] 561-241-9339561-241-7876Coiltronics
[1] 847-639-1469847-639-6400Coilcraft
[1] 516-435-1824516-435-1110Central Semiconductor
[1] 803-626-3123803-946-0690AVX
FACTORY FAX
[Country Code]
USA PHONEMANUFACTURER
[1] 714-960-6492714-969-2491Matsuo
[1] 310-322-3332310-322-3331International Rectifier
[1] 408-573-4159408-573-4150Taiyo Yuden
[1] 603-224-1430603-224-1961Sprague
[1] 408-970-3950
408-988-8000
800-554-5565
Siliconix
[81] 7-2070-1174619-661-6835Sanyo
[81] 3-3494-7414805-867-2555*NIEC (Nihon)
[1] 814-238-0490
814-237-1431
800-831-9172
Murata
[81] 3-3607-5144847-956-0666Sumida
[1] 847-390-4405847-390-4461TDK
*Distributor