MAX1687ESA 데이터 시트보기 (PDF) - Maxim Integrated

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MAX1687ESA

Step-Up DC-DC Converters with Precise, Adaptive Current Limit for GSM

Maxim Integrated 

Step-Up DC-DC Converters with

Precise, Adaptive Current Limit for GSM

LX1

LX2

VOUT

VIN

Q1

ZERO

CROSSING

P-SWITCH

Q2

P-SWITCH

CONSTANT

HYSTERETIC

INDUCTOR-CURRENT

CONTROL LOGIC

N-SWITCH

Q3

(LIM)

[CHG]

PEAK/

TROUGH

INDUCTOR-

CURRENT

gm

DETECT

MAX1687

MAX1688

TIMER

gm

REF

FB

VPRECHARGE

VIN

VIN - VDIODE

VOUT

ON

( ) ARE FOR MAX1687

[ ] ARE FOR MAX1688 (ALSO DASHED LINES)

Figure 1. Functional Diagram

When starting up, the MAX1687/MAX1688 employ four

successive phases of operation to reduce the inrush of

current from the battery. These phases are Linear

Regulator Mode, Pseudo Buck Mode, Pseudo Boost

Mode, and Boost Mode. In Linear Mode, the output

connects to the input through a 30Ω precharge PMOS

device (Figure1, Q1). The transition from Linear Mode

to Pseudo Buck Mode occurs when VOUT = VIN - 3V.

The transition from Pseudo Buck Mode to Pseudo

Boost Mode occurs when VOUT = VIN - 0.7V. The tran-

sition from Pseudo Boost Mode to Boost Mode occurs

when VOUT > VIN. Due to these mode changes, the

battery input current remains relatively constant, and

VOUT changes slope as it rises.

Hysteretic Inductor-Current Control

Logic circuits in the MAX1687/MAX1688 control the

inductor ripple current to typically 200mA (Figure 2).

The voltage at LIM (CHG) programs IPEAK. The induc-

tor current oscillates between IPEAK - 200mA and

IPEAK.

Standby/Shutdown

When ON goes low, the device enters Standby Mode,

inductor current ramps to zero, and the output discon-

nects from the input. If ON remains low for greater than

1.2ms (typ), the device shuts down and quiescent cur-

rent drops to 3µA (typ).

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