HT7167

Synchronous Boost Converter

1.

Typical Application

2.

Feature Description

2.1.

Functional Modes (Mode pin)

Operation

The synchronous boost converter HT7167 operates at a quasi-constant frequency pulse width modulation

off-time of the switching cycle. At the beginning of each switching cycle, the low-side N-MOSFET switch is

turned on, and the inductor current ramps up to a peak current that is determined by the output of the

internal error amplifier. After the peak current is reached, the current comparator trips, and it turns off the

low-side N-MOSFET switch and the inductor current goes through the body diode of the high-side N-

MOSFET in a dead-time duration. After the dead-time duration, the high-side N-MOSFET switch is turned

on. Because the output voltage is higher than the input voltage, the inductor current decreases. The high-

side switch is not turned off until the fixed off-time is reached. After a short dead-time duration, the low-side

switch turns on again and the switching cycle is repeated.

In light load condition, the HT7167 implements two operation modes, PFM mode and forced PWM mode, to

meet different application requirements. The operation mode is set by the status of the MODE pin. When

PWM Mode

In the forced PWM mode, the HT7167 keeps the switching frequency unchanged in light load condition.

When the load current decreases, the output of the internal error amplifier decreases as well to keep the

inductor peak current down, delivering less power from input to output. When the output current further

reduces, the current through the inductor will decrease to zero during the off-time. The high-side N-

MOSFET is not turned off even if the current through the MOSFET is zero. Thus, the inductor current

changes its direction after it runs to zero. The power flow is from output side to input side. The efficiency

will be low in this mode. But with the fixed switching frequency, there is no audible noise and other

problems which might be caused by low switching frequency in light load condition.

PFM Mode

The HT7167 improves the efficiency at light load with the PFM mode. When the converter operates in light

load condition, the output of the internal error amplifier decreases to make the inductor peak current down,

delivering less power to the load. When the output current further reduces, the current through the inductor

L1

2 . 2 u F

C2

0 . 1 u F

C3

R1

R freq

V IN

R3

R4

1 0 0 k

R6

R5

C4

4 7 n F

1 u F

4 7 0 u F

1 0 u F

1 u F

ILIM

C OM P

FB

1 u F

1 0 u F1 0 u F

1 0 u F

1 0 u F 4 7 0 u F

1 0 u F

R7

C 1 8

Q1

A ON 6 4 0 5

C 2 1

2 2 n F

R 2 1

1 5 0 k

D IS DR V

B OO ST

8

SW

7

SW

6

SW

5

SW

4

FS W

3

EN

2

V IN

9

NC

12

M O DE

13

V OU T

14

V OU T

15

V OU T

16

FB

17

C OM P

18

ILIM

19

H T7 1 6 7

R9

1 0 0 R