Rainbow Electronics MAX1844 - Manual (Page 9)

Standard Application Circuit
The standard application circuit (Figure 1) generates a
2.5V rail for general-purpose use in a notebook computer.
See Table 1 for component selections. Table 2 lists com-
ponent manufacturers.
MAX1844
High-Speed Step-Down Controller with
Accurate Current Limit for Notebook Computers
_______________________________________________________________________________________ 9
PIN
QSOP QFN
NAME FUNCTION
14 11 V CC
Analog Supply Input. Connect to the system supply voltage, 4.5V to 5.5V, with a series 20 Ω resistor.
Bypass to GND with a 1µF (min) ceramic capacitor.
15 12 TON
On-Time Selection-Control Input. This four-level logic input sets the nominal DH on-time. Connect to
GND, REF, V
CC , or leave TON unconnected to select the following nominal switching frequencies:
GND = 600kHz, REF = 450kHz, floating = 300kHz, and V CC = 200kHz.
16 13 V+
Battery Voltage Sense Connection. Connect to input power source. V+ is used only to set the PWM
one-shot timing.
17 14 SKIP
Pulse-Skipping Control Input. Connect to V CC for low-noise, forced-PWM mode. Connect to GND to
enable pulse-skipping operation.
18 15 BST
Boost Flying-Capacitor Connection. Connect to an external capacitor and diode according to the
Standard Application Circuit (Figure 1). See the MOSFET Gate Drivers (DH, DL) section.
19 16 LX
External Inductor Connection. Connect LX to the switched side of the inductor. LX serves as the
lower supply rail for the DH high-side gate driver.
20 17 DH High-Side Gate-Driver Output. Swings from LX to BST.
Pin Description (continued)
Table 1. Component Selection for
Standard Applications
COMPONENT 2.5V AT 4A
C1 Input Capacitor
10 µ F, 25V
Taiyo Yuden TMK432BJ106KM or
TDK C4532X5R1E106M
C2 Output Capacitor
330
µ
F, 6V
Kemet T510X477108M006AS or
Sanyo 6TPB330M
D1 Schottky Nihon EP10QY03
L1 Inductor
4.7
µ
H
Coilcraft DO33116P-682 or
Sumida CDRH124-4R7MC
Q1 High-Side MOSFET
Fairchild Semiconductor
1/2 FDS6982A
Q2 Low-Side MOSFET
Fairchild Semiconductor
1/2 FDS6982A
R SENSE
0.015
Ω ±
1%, 0.5W resistor
IRC LR2010-01-R015F or
Dale WSL-2010-R015F
Table 2. Component Suppliers
*Distributor
SUPPLIER USA PHONE FACTORY FAX
Coilcraft 847-639-6400 1-847-639-1469
Dale-Vishay 203-452-5664 1-203-452-5670
Fairchild 408-822-2181 1-408-721-1635
IRC 800-752-8708 1-828-264-7204
Kemet 408-986-0424 1-408-986-1442
NIEC (Nihon) 805-867-2555* 81-3-3494-7414
Sanyo 619-661-6835 81-7-2070-1174
Sumida 847-956-0666 81-3-3607-5144
Taiyo Yuden 408-573-4150 1-408-573-4159
TDK 847-390-4461 1-847-390-4405