Rainbow Electronics MAX1636 - Manual (Page 8)

MAX1636
Low-Voltage, Precision Step-Down
Controller for Portable CPU Power
8 _______________________________________________________________________________________
Pin Description
NAME FUNCTION
1 CSH Current-Sense Input, High Side
2 CSL Current-Sense Input, Low Side. Also serves as a feedback input in fixed output modes.
PIN
3 RESET
Timed Reset Output. Low for at least 100ms after output voltage is valid, then goes high impedance
(open drain).
4 SHDN Shutdown Control Input. Puts chip in shutdown or standby mode, depending on OVP (Table 5).
8 SYNC
Oscillator Frequency Select and Synchronization Input. Tie to V CC for 300kHz operation; tie to GND for
200kHz operation.
7 REF
1.100V Reference Output. Capable of sourcing 50µA for external loads; bypass with a 0.22µF
(min) capacitor.
6 CC Compensation pin. Connect a small capacitor to GND to set the integration time constant.
5 OVP Overvoltage Protection Enable/Disable. Tie to GND to disable OVP; tie to V
CC
to enable OVP.
13 V+
5V VL Linear-Regulator Input. The VL linear regulator automatically shuts off if V+ is shorted to V L . Bypass
V+ to GND with a 0.1µF capacitor close to the IC.
12 V
CC
Main Supply Voltage Input. Powers the PWM controller, logic, and reference. Input range is +3.15V to
+5.5V.
11 FB
Feedback Input. Tie to GND for fixed 3.3V output; tie to V CC for fixed 2.5V output; tie to resistor divider for
adjustable mode.
9, 10 GND Analog Ground
15 DL Low-Side Gate-Driver Output
14 VL 5V Linear-Regulator Output. Powers the DL low-side gate driver. Bypass with a 2.2µF (min) capacitor.
20 SKIP Low-Noise Mode Control. Forces fixed-frequency PWM operation when high.
19 LX Inductor Connection
18 DH High-Side Gate-Driver Output
17 BST Boost-Capacitor Connection
16 PGND Power Ground
Standard Application Circuit
The basic MAX1636 buck converter (Figure 1) is easily
adapted to meet a wide range of applications with
inputs up to 30V by substituting components from
Table 1. These circuits represent a good set of trade-
offs between cost, size, and efficiency, while staying
within the worst-case specification limits for stress-
related parameters, such as capacitor ripple current.
Do not change the circuits’ switching frequency without
first recalculating component values (particularly induc-
tance value at maximum battery voltage). Adding a
Schottky rectifier across the synchronous rectifier
improves circuit efficiency by approximately 1%. This
rectifier is otherwise not needed because the MOSFET
required typically incorporates a high-speed silicon
diode from drain to source. Use a Schottky rectifier
rated at a DC current equal to at least one-third of the
load current.