Lo w -Vo lt a g e , P re c is io n S t e p -Do w n
Co n t ro lle r fo r P o rt a b le CP U P o w e r
______________________________________________________________P in De s c rip t io n
PIN
1
NAME
CSH
FUNCTION
Current-Sense Input, High Side
2
CSL
Current-Sense Input, Low Side. Also serves as a feedback input in fixed output modes.
Timed Reset Output. Low for at least 100ms after output voltage is valid, then goes high impedance
(open drain).
3
RESET
MAX136
4
5
6
Shutdown Control Input. Puts chip in shutdown or standby mode, depending on OVP (Table 5).
SHDN
OVP
CC
Overvoltage Protection Enable/Disable. Tie to GND to disable OVP; tie to V to enable OVP.
CC
Compensation pin. Connect a small capacitor to GND to set the integration time constant.
1.100V Reference Output. Capable of sourcing 50µA for external loads; bypass with a 0.22µF
(min) capacitor.
7
REF
Oscillator Frequency Select and Synchronization Input. Tie to V for 300kHz operation; tie to GND for
CC
200kHz operation.
8
SYNC
GND
FB
9, 10
11
Analog Ground
Feedback Input. Tie to GND for fixed 3.3V output; tie to V for fixed 2.5V output; tie to resistor divider for
CC
adjustable mode.
Main Supply Voltage Input. Powers the PWM controller, logic, and reference. Input range is +3.15V to
+5.5V.
12
13
V
CC
5V VL Linear-Regulator Input. The VL linear regulator automatically shuts off if V+ is left open or shorted to
V . Bypass V+ to GND with a 0.1µF capacitor close to the IC.
L
V+
14
15
16
17
18
19
20
VL
DL
5V Linear-Regulator Output. Powers the DL low-side gate driver. Bypass with a 2.2µF (min) capacitor.
Low-Side Gate-Driver Output
PGND
BST
DH
Power Ground
Boost-Capacitor Connection
High-Side Gate-Driver Output
LX
Inductor Connection
Low-Noise Mode Control. Forces fixed-frequency PWM operation when high.
SKIP
first recalculating component values (particularly induc-
______S t a n d a rd Ap p lic a t io n Circ u it
tance value at maximum battery voltage). Adding a
Sc hottky re c tifie r a c ros s the s ync hronous re c tifie r
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.
The basic MAX1636 buck converter (Figure 1) is easily
adapted to meet a wide range of applications with
inp uts up to 30V b y s ub s tituting c omp one nts 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
8
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MAXIM [ MAXIM INTEGRATED PRODUCTS ]
