Datasheet

MAX8792
Single Quick-PWM Step-Down
Controller with Dynamic REFIN
12 ______________________________________________________________________________________
Detailed Description
The MAX8792 step-down controller is ideal for the low-
duty-cycle (high-input voltage to low-output voltage)
applications required by notebook computers. Maxim’s
proprietary Quick-PWM pulse-width modulator in the
MAX8792 is specifically designed for handling fast load
steps while maintaining a relatively constant operating
frequency and inductor operating point over a wide
range of input voltages. The Quick-PWM architecture
circumvents the poor load-transient timing problems of
fixed-frequency, current-mode PWMs while also avoid-
ing the problems caused by widely varying switching
frequencies in conventional constant-on-time (regard-
less of input voltage) PFM control schemes.
+5V Bias Supply (V
CC
/V
DD
)
The MAX8792 requires an external 5V bias supply in
addition to the battery. Typically, this 5V bias supply is
the notebook’s main 95% efficient 5V system supply.
Keeping the bias supply external to the IC improves
efficiency and eliminates the cost associated with the
5V linear regulator that would otherwise be needed to
supply 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 5V bias supply powers both the PWM controller
and internal gate-drive power, so the maximum current
drawn is determined by:
I
BIAS
= I
Q
+ f
SW
Q
G
= 2mA to 20mA (typ)
Table 1. Component Selection for Standard Applications
V
OUT
= 1.5V/1.05V AT 10A
(Figure 1)
V
OUT
= 3.3V AT 5A
(Figure 4)
V
OUT
= 1.5V AT 10A/1.05V AT
7A (Figure 7)
COMPONENT
V
IN
= 7V to 20V
R
TON
= 200kΩ (300kHz)
V
IN
= 7V to 20V
R
TON
= 332kΩ (300kHz)
V
IN
= 4V to 12V
R
TON
= 100kΩ (600kHz)
Input Capacitor
(2x) 10μF, 25V
Taiyo Yuden TMK432BJ106KM
(2x) 10μF, 25V
Taiyo Yuden TMK432BJ106KM
(2x) 10μF, 25V
Taiyo Yuden TMK432BJ106KM
Output Capacitor
(2x) 330μF, 6mΩ
Panasonic EEFSX0D331XR
(1x) 330μF, 18mΩ
SANYO 4TPE330MI
(2x) 330μF, 7mΩ
NEC-TOKIN PSGD0E337M7
Inductor
1.0μH, 3.25mΩ
Würth 744 3552 100
3.3μH, 14mΩ
NEC-TOKIN MPLC1040L3R3
0.68μH, 4.6mΩ
Coiltronics FP3-R68
High-Side MOSFET
Fairchild (1x) FDS8690
8.6mΩ/11.4mΩ (typ/max)
Fairchild (1x) FDS8690
8.6mΩ/11.4mΩ (typ/max)
Low-Side MOSFET
Fairchild (1x) FDS8670
4.2mΩ/5.0mΩ (typ/max)
Siliconix (1x) Si4916DY
N
H
= 18mΩ/22mΩ (typ/max)
N
L
= 15mΩ/18mΩ (typ/max)
Fairchild (1x) FDS8670
4.2mΩ/5.0mΩ (typ/max)
Table 2. Component Suppliers
MANUFACTURER
WEBSITE
AVX Corp. www.avxcorp.com
BI Technologies www.bitechnologies.com
Central
Semiconductor Corp.
www.centralsemi.com
Coiltronics www.cooperet.com
Fairchild
Semiconductor
www.fairchildsemi.com
International Rectifier
www.irf.com
KEMET Corp. www.kemet.com
NEC TOKIN America,
Inc.
www.nec-tokin.com
Panasonic Corp. www.panasonic.com
MANUFACTURER
WEBSITE
Pulse Engineering www.pulseeng.com
Renesas Technology
Corp.
www.renesas.com
SANYO Electric Co.,
Ltd.
www.sanyo.com
Siliconix (Vishay) www.vishay.com
Sumida Corp. www.sumida.com
Taiyo Yuden www.t-yuden.com
TDK Corp. www.component.tdk.com
TOKO America, Inc. www.tokoam.com
Würth Electronik
GmbH & Co. KG
www.we-online.com