MAX797H Maxim, MAX797H Datasheet - Page 5

• Manufacturer Part Number: MAX797H
• Description: High-Voltage / Step-Down Controller with Synchronous Rectifier for CPU Power
• Manufacturer: Maxim

Dual Mode is a trademark of Maxim Integrated Products.
Rail-to-Rail is a registered trademark of Nippon Motorola Ltd.
______________________________________________________________Pin Description
PIN
10
11
12
13
14
15
16
1
2
3
4
5
6
7
8
9
NAME
SHDN
PGND
SYNC
GND
SKIP
CSH
REF
CSL
BST
DH
FB
V+
DL
SS
VL
LX
High-Voltage, Step-Down Controller with
_______________________________________________________________________________________
Soft-Start Timing Capacitor Connection. Ramp time to full current limit is approximately 1ms/nF.
Disables pulse-skipping mode when high. Connect SKIP to GND for normal use. Do not leave unconnected.
With SKIP grounded, the device automatically changes from pulse-skipping operation to full PWM operation
when the load current exceeds approximately 30% of maximum.
Reference Voltage Output. Bypass REF to GND with 0.33µF minimum.
Low-noise Analog Ground and Feedback Reference Point
Oscillator Synchronization and Frequency Select. Tie SYNC to GND or VL for 150kHz operation; tie to REF for
300kHz operation. A high-to-low transition begins a new cycle. Drive SYNC with 0V to 5V logic levels (see
Electrical Characteristics for V
340kHz.
Shutdown Control Input, Active Low. Logic threshold is set at approximately 1V (V
MOSFET). Tie SHDN to V+ for automatic start-up.
Feedback Input. Regulates at FB = REF (approximately 2.505V) in adjustable mode. FB is a Dual Mode
input that also selects the fixed-output voltage settings as follows:
Current-Sense Input, High Side. Current-limit level is 100mV referred to CSL.
Current-Sense Input, Low Side. CSL also serves as the feedback input in fixed-output modes.
Battery Voltage Input (4.5V to 30V). Bypass V+ to PGND close to the IC with a 0.1µF capacitor. Connects to a
linear regulator that powers VL.
5V Internal Linear-Regulator Output. VL is also the supply-voltage rail for the chip. It is switched to the output
voltage via CSL (V
5mA for external loads.
Power Ground
Low-Side Gate-Drive Output. DL normally drives the synchronous-rectifier MOSFET. Swings 0V to VL.
Boost Capacitor Connection for High-Side Gate Drive (0.1µF)
Switching Node (inductor) Connection. LX can swing 2V below ground without hazard.
High-Side Gate-Drive Output. DH normally drives the main buck switch. It is a floating driver output that
swings from LX to BST, riding on the LX switching-node voltage.
Connect to GND for 3.3V operation.
Connect to VL for 5V operation.
Connect to a resistor divider for adjustable mode. FB can be driven with 5V Rail-to-Rail ® logic to change
the output voltage under system control.
Synchronous Rectifier for CPU Power
CSL
> 4.5V) for automatic bootstrapping. Bypass to GND with 4.7µF. VL can supply up to
IH
and V
IL
specifications). SYNC capture range is guaranteed to be 190kHz to
FUNCTION
TH
of an internal N-channel
TM
5