Datasheet

MAX1761
Small, Dual, High-Efficiency
Buck Controller for Notebooks
10 ______________________________________________________________________________________
comparator has 40mV hysteresis to prevent startup
oscillations on slowly rising input voltages.
If VL is not driven externally, then V+ should be at least
5V to ensure proper operation. If V+ is running from a
5V (±10%) supply, V+ should be externally connected
to VL. Overdriving the VL regulator with an external 5V
supply also increases the MAX1761’s efficiency.
Voltage Reference (REF)
The internal 2V reference is accurate to ±1% (max)
over temperature and can supply a 50µA load current.
Bypass REF to GND with a 0.1µF capacitor when REF
is unloaded. Use a 0.22µF capacitor when applying an
external load.
Free-Running Constant-On-Time PWM
Controller with Input Feed-Forward
The Quick-PWM control architecture is a constant-on-
time, current-mode type with voltage feed-forward
(Figure 3). This architecture relies on the output ripple
voltage to provide the PWM ramp signal. Thus, the out-
put filter capacitor’s ESR acts as a feedback resistor.
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 directly pro-
portional to output voltage (see the On-Time One-Shot
section). 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 minimum off-
time one-shot has timed out.
Table 1. Component Selection for Standard Applications
COMPONENT 2.5V AT 2.0A 2.5V AT 3.5A 1.8V AT 2.0A 3.3V AT 2A
Input Range 5V to 18V 5V to 18V 5V to 18V 5V to 18V
Frequency 350kHz 350kHz 250kHz 350kHz
Complementary
P- and N-Channel
MOSFETs
Fairchild FDS8958A Siliconix IRF7319 Fairchild FDS8958A Fairchild FDS8958A
Inductor
7µH
Sumida CDRH104-
7R0NC
3.5µH
Sumida CDRH127-
3R5NC
7µH
Sumida CDRH104-
7R0NC
10µH
Sumida CDRH104-
100NC
Input Capacitor
10µF, 25V
Taiyo Yuden
TMK432BJ106KM
2 x 10µF, 25V
Taiyo Yuden
TMK432BJ106KM
10µF, 25V
Taiyo Yuden
TMK432BJ106KM
10µF, 25V
Taiyo Yuden
TMK432BJ106KM
Output Capacitor
330µF, 10V
Kemet
T510X 337K101
2 x 330µF, 10V
Kemet
T510X 337K010
330µF, 10V
Kemet
T510X 337K010
330µF, 10V
Kemet
T510X 337K010
R
1
= Short R
1
= 1k R
3
= Short R
1
= Short
C urr ent- S ense
Feed b ack Resi stor s
R
2
= Open R
2
= 1k R
4
= Open R
2
= Open
Table 2. Component Suppliers
SUPPLIER PHONE WEB
Fairchild
Semiconductor
408-822-2181 www.fairchildsemi.com
Kemet 408-986-0424 www.kemet.com
Panasonic 847-468-5624 ww w.p anasonic. com
Rohm 760-929-2100
www.rohmelectronics.
com
Sanyo 619-661-6835 www.secc.co.jp
Siliconix 408-988-8000 www.vishay.com
Sumida 847-956-0666 www.sumida.com
Taiyo Yuden 408-573-4150 www.t-yuden.com