TPS61000, TPS61001, TPS61002, TPS61003, TPS61004, TPS61005, TPS61006, TPS61007

SINGLE- AND DUAL-CELL BOOST CONVERTER WITH START-UP INTO FULL LOAD

SLVS279C – MARCH 2000 – REVISED APRIL 2003

4

POST OFFICE BOX 655303

functional block diagram (continued)

adjustable output-voltage option (TPS61007 only)

VREF

VBAT

Control Logic

Oscillator

Gate Drive

UVLO

Current Sense

Current Limit

Slope Compensation

Bandgap

Reference

EN

LBI

LBO

GND

COMP

L1

D1

VOUT

CO

CI

SW

Comparator

LBI/LBO

Comparator

Error

Amplifier

Antiringing

Comparator

and Switch

FB

FBGND

detailed description

controller circuit

The device is based on a current-mode control topology using a constant-frequency pulse-width modulator to

regulate the output voltage. It runs at an oscillator frequency of 500 kHz. The current sense is implemented by

measuring the voltage across the switch. The controller also limits the current through the power switch on a

pulse-by-pulse basis. Care must be taken that the inductor saturation current is higher than the current limit of

the TPS6100x. This prevents the inductor from going into saturation and therefore protects both device and

inductor. The current limit should not become active during normal operating conditions.

The TPS6100x is designed for high efficiency over a wide output current range. Even at light loads the efficiency

stays high because the controller enters a power-save mode, minimizing switching losses of the converter. In

this mode, the controller only switches if the output voltage trips below a set threshold voltage. It ramps up the

output voltage with one or several pulses, and again goes into the power-save mode once the output voltage

exceeds the threshold voltage. The controller enters the power-save mode when the output current drops to

levels that force the discontinuous current mode. It calculates a minimum duty cycle based on input and output

voltage and uses the calculation for the transition out of the power-save mode into continuous current mode.

The control loop must be externally compensated with an R/C/C network connected to the COMP pin. See the

application section for more details on the design of the compensation network.

device enable

The device is put into operation when EN is set high. During start-up of the converter the input current from the

battery is limited until the voltage on COMP reaches its operating point. The device is put into a shutdown mode

when EN is set to GND. In this mode, the regulator stops switching and all internal control circuitry including

the low-battery comparator is switched off. The output voltage drops to one diode drop below the input voltage

in shutdown.