Pin description (continued) – Rainbow Electronics MAX1635 User Manual

Page 7

MAX1630–MAX1635

Multi-Output, Low-Noise Power-Supply

Controllers for Notebook Computers

_______________________________________________________________________________________

_________________________________________________Pin Description (continued)

PIN

FUNCTION

NAME

Dual-Purpose Timing Capacitor Pin and ON/OFF Control Input. See

Power-Up Sequencing and

ON/

OFF Controls

section.

TIME/ON5

Oscillator Synchronization and Frequency Select. Tie to VL for 300kHz operation; tie to GND for 200kHz
operation. Can be driven at 240kHz to 350kHz for external synchronization.

SYNC

Active-Low Timed Reset Output. RESET swings GND to VL. Goes high after a fixed 32,000 clock-cycle
delay following power-up.

RESET

Logic-Control Input that disables Idle Mode when high. Connect to GND for normal use.

SKIP

2.5V Reference Voltage Output. Bypass to GND with 1µF minimum.

REF

Low-Noise Analog Ground and Feedback Reference Point

GND

Feedback Input for the 5V SMPS; regulates at FB5 = REF (approx. 2.5V) in adjustable mode. FB5 is a
Dual Mode input that also selects the 5V fixed output voltage setting when tied to GND. Connect FB5 to
a resistor divider for adjustable-output mode.

FB5

Gate-Drive Output for the 5V, high-side N-channel switch. DH5 is a floating driver output that swings
from LX5 to BST5, riding on the LX5 switching node voltage.

DH5

Pin-Strap Input that selects the SMPS power-up sequence:

SEQ = GND: 5V before 3.3V, RESET output determined by both outputs
SEQ = REF: Separate ON3/ON5 controls, RESET output determined by 3.3V output
SEQ = VL: 3.3V before 5V, RESET output determined by both outputs

SEQ

Power Ground

PGND

Gate-Drive Output for the low-side synchronous-rectifier MOSFET. Swings 0V to VL.

DL5

Boost capacitor connection for high-side gate drive (0.1µF)

BST5

Switching Node (inductor) Connection. Can swing 2V below ground without hazard.

LX5

Current-Sense Input for the 5V SMPS. Current-limit level is 100mV referred to CSL5.

CSH5

Current-Sense Input for the 5V SMPS. Also serves as the feedback input in fixed-output mode, and as
the bootstrap supply input when the voltage on CSL5/VL is > 4.5V.

CSL5

Shutdown Control Input, active low. Logic threshold is set at approximately 1V. For automatic start-up,
connect SHDN to V+ through a 220k

Ω

resistor and bypass SHDN to GND with a 0.01µF capacitor.

SHDN

Battery Voltage Input, +4.2V to +30V. Bypass V+ to PGND close to the IC with a 0.22µF capacitor.
Connects to a linear regulator that powers VL.

V+

5V Internal Linear-Regulator Output. VL is also the supply voltage rail for the chip. After the 5V SMPS
output has reached +4.5V (typical), VL automatically switches to the output voltage via CSL5 for boot-
strapping. Bypass to GND with 4.7µF. VL supplies up to 25mA for external loads.

Supply Voltage Input for the 12OUT Linear Regulator. Also connects to an internal resistor divider for
secondary winding feedback, and to an 18V overvoltage shunt regulator clamp.

(MAX1630/

32/33/35)

Secondary Winding Feedback Input. Normally connected to a resistor divider from an auxiliary output.
SECFB regulates at V

SECFB

= 2.5V (see

Secondary Feedback Regulation Loop

section). Tie to VL if not

used.

SECFB

(MAX1631/

MAX1634)

Boost Capacitor Connection for high-side gate drive (0.1µF)

BST3

Gate-Drive Output for the low-side synchronous-rectifier MOSFET. Swings 0V to VL.

DL3

ON/OFF Control Input. See

Power-Up Sequencing and ON/OFF Controls

section

RUN/ON3

Gate-Drive Output for the 3.3V, high-side N-channel switch. DH3 is a floating driver output that swings
from LX3 to BST3, riding on the LX3 switching node voltage.

DH3

Switching Node (inductor) Connection. Can swing 2V below ground without hazard.

LX3